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Evidence for the Tidal Destruction of Hot Jupiters by Subgiant Stars
Abstract
Tidal transfer of angular momentum is expected to cause hot Jupiters to
spiral into their host stars. Although the timescale for orbital decay is very
uncertain, it should be faster for systems with larger and more evolved stars.
Indeed, it is well established that hot Jupiters are found less frequently
around subgiant stars than around main-sequence stars. However, the
interpretation of this finding has been ambiguous, because the subgiants are
also thought to be more massive than the F- and G-type stars that dominate the
main-sequence sample. Consequently it has been unclear whether the absence of
hot Jupiters is due to tidal destruction, or inhibited formation of those
planets around massive stars. Here we show that the Galactic space motions of
the planet-hosting subgiant stars demand that on average they be similar in
mass to the planet-hosting main-sequence F- and G-type stars. Therefore the two
samples are likely to differ only in age, and provide a glimpse of the same
exoplanet population both before and after tidal evolution. As a result, the
lack of hot Jupiters orbiting subgiants is clear evidence for their tidal
destruction. Questions remain, though, about the interpretation of other
reported differences between the planet populations around subgiants and
main-sequence stars, such as their period and eccentricity distributions and
overall occurrence rates.
... 2010a ; Reffert et al. 2015 ), there was a dearth of short-period planets found, especially hot Jupiters (Bowler et al. 2010 ;Johnson et al. 2010b ;Reffert et al. 2015 ;Ottoni et al. 2022 ). These results hinted at possible differences between the populations of hot Jupiters around main-sequence and evolved hosts, with planetary spiralling and eventual engulfment being suggested as a mechanism for the depletion of these planets around evolved hosts (Villaver & Livio 2009 ;Schlaufman & Winn 2013 ). ...
... 09 per cent (Grunblatt et al. 2019 ;Temmink & Snellen 2023 ), mostly in line with the results from mainsequence stars. More precise estimates of the planet occurrence rate of evolved stars will reveal whether late-stage stellar evolution has a significant impact on planet demographics, as has been predicted by evolutionary theory (Schlaufman & Winn 2013 ;Villaver et al. 2014 ). ...
... Tidal interactions between a planet and its host star can cause planets to spiral inwards and may eventually lead to tidal destruction (Villaver & Livio 2009 ;Schlaufman & Winn 2013 ). One possible observation of this phenomenon is the dearth of close-in giant planets orbiting evolved stars in RV surv e ys (Johnson et al. 2010b ;Jones et al. 2016 ), which hinted at possible differences in the populations of these planets orbiting evolved and main-sequence hosts. ...
In this work we present the discovery and confirmation of two hot Jupiters orbiting red-giant stars, TOI-4377 b and TOI-4551 b, observed by TESS in the southern ecliptic hemisphere and later followed-up with radial-velocity (RV) observations. For TOI-4377 b we report a mass of and a inflated radius of 1.348 ± 0.081 RJ orbiting an evolved intermediate-mass star (1.36 M⊙, 3.52 R⊙; TIC 394918211) on a period of of 4.378 days. For TOI-4551 b we report a mass of 1.49 ± 0.13 MJ and a radius that is not obviously inflated of , also orbiting an evolved intermediate-mass star (1.31 M⊙, 3.55 R⊙; TIC 204650483) on a period of 9.956 days. We place both planets in context of known systems with hot Jupiters orbiting evolved hosts, and note that both planets follow the observed trend of the known stellar incident flux-planetary radius relation observed for these short-period giants. Additionally, we produce planetary interior models to estimate the heating efficiency with which stellar incident flux is deposited in the planet’s interior, estimating values of and for TOI-4377 b and TOI-4551 b respectively. These values are in line with the known population of hot Jupiters, including hot Jupiters orbiting main sequence hosts, which suggests that the radii of our planets have reinflated in step with their parent star’s brightening as they evolved into the post-main-sequence. Finally, we evaluate the potential to observe orbital decay in both systems.
... Indeed, the long-term fates of hot Jupiters are thought to be dictated by tides. As tides rob energy from a hot Jupiter's orbit, it spirals in towards its host star, eventually colliding after a few billion years of evolution (Rasio et al. 1996;Pätzold et al. 2004;Levrard et al. 2009;Matsumura et al. 2010;Schlaufman & Winn 2013;Hamer & Schlaufman 2019). However, these effects are difficult to observe on human timescales, which limits our ability to constrain fundamental tidal parameters that are often uncertain by many orders of magnitude. ...
... Tides depend sensitively on the inverse scaled semi-major axis R /a, so close-in planets around larger stars are natural targets for observing tides in action. Additionally, evolved stars are probably more dissipative than their main sequence counterparts (Villaver & Livio 2009;Schlaufman & Winn 2013;Weinberg et al. 2017;Barker 2020), so inspiral should be more rapid for their planets to the extent that orbital energy is dissipated in the star. We were therefore motivated to monitor transiting planets on close-in orbits (P < 5 days) around subgiant stars. ...
... Finally, many new planets orbiting evolved stars are being discovered with TESS (Grunblatt et al. 2022a,b;Saunders et al. 2022). If the tidal quality factor obtained here is applicable to other evolved planet-hosting stars, then most of their planets are nearing the ends of their lives (Schlaufman & Winn 2013;Hamer & Schlaufman 2019), and we should begin to see hints of orbital decay for these planets within the next decade. The growing population of planets orbiting evolved stars is an exciting new laboratory for many of the ideas we have presented here. ...
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet (1.1, 5.9) orbiting an evolved host star (2.9, 1.5). Using transit timing measurements from Kepler, Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate ~ms~yr, corresponding to an infall timescale ~Myr. We consider other explanations for the data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed period derivative implies a tidal quality factor , in good agreement with theoretical predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle.
... Indeed, the long-term fates of hot Jupiters are thought to be dictated by tides. As tides rob energy from a hot Jupiter's orbit, it spirals in toward its host star, eventually colliding after a few billion years of evolution (Rasio et al. 1996;Pätzold et al. 2004;Levrard et al. 2009;Matsumura et al. 2010;Schlaufman & Winn 2013;Hamer & Schlaufman 2019). However, these effects are difficult to observe on human timescales, which limits our ability to constrain fundamental tidal parameters that are often uncertain by many orders of magnitude. ...
... Tides depend sensitively on the inverse scaled semimajor axis R å /a, so closein planets around larger stars are natural targets for observing tides in action. Additionally, evolved stars are probably more dissipative than their main-sequence counterparts (Villaver & Livio 2009;Schlaufman & Winn 2013;Weinberg et al. 2017;Barker 2020), so inspiral should be more rapid for their planets to the extent that orbital energy is dissipated in the star. We were therefore motivated to monitor transiting planets on closein orbits (P < 5 days) around subgiant stars. ...
... Finally, many new planets orbiting evolved stars are being discovered with TESS (Grunblatt et al. 2022a(Grunblatt et al. , 2022bSaunders et al. 2022). If the tidal quality factor obtained here is applicable to other evolved planet-hosting stars, then most of their planets are nearing the ends of their lives (Schlaufman & Winn 2013;Hamer & Schlaufman 2019), and we should begin to see hints of orbital decay for these planets within the next decade. The growing population of planets orbiting evolved stars is an exciting new laboratory for many of the ideas we have presented here. ...
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet (1.1 R J , 5.9 M J ) orbiting an evolved host star (2.9 R ⊙ , 1.5 M ⊙ ). Using transit timing measurements from Kepler, Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate P ̇ = 131 − 22 + 20 ms yr ⁻¹ , corresponding to an infall timescale P / P ̇ ≈ 2.5 Myr . We consider other explanations for the data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed period derivative implies a tidal quality factor Q ⋆ ′ = 2.50 − 0.62 + 0.85 × 10 4 , in good agreement with theoretical predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle.
... Recently the masses of evolved stars have been brought into question on several grounds (Lloyd 2011;Schlaufman & Winn 2013), with the possibility raised that the masses of evolved hosts have been overestimated when derived from spectroscopic observations. The mass of these stars is typically recovered by interpolating grids of stellar models to the observed T eff , log g, and [Fe/H], and including additional parameters such as luminosity and colours where available (see Johnson et al. 2007a and references therein). ...
... Finally, we find that the use of optimistic uncertainties on input parameters has the potential to significantly bias the recovered stellar masses. The consequence of such an action would be to bias inferred planet occurrence rates, an argument broadly in agreement with the space-motion based argument of Schlaufman & Winn (2013), i.e., that the masses of evolved exoplanet hosts must be overestimated to explain the observed space motions of the same stars. ...
We investigate the masses of "retired A stars" using asteroseismic detections on seven low-luminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 Missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overestimated. Our targets have all previously been subject to long term radial velocity observations to detect orbiting bodies, and satisfy the criteria used by Johnson et al. (2006) to select survey stars that may have had A-type (or early F-type) main-sequence progenitors. The sample actually spans a somewhat wider range in mass, from up to . Whilst for five of the seven stars the reported discovery mass from spectroscopy exceeds the mass estimated using asteroseismology, there is no strong evidence for a significant, systematic bias across the sample. Moreover, comparisons with other masses from the literature show that the absolute scale of any differences is highly sensitive to the chosen reference literature mass, with the scatter between different literature masses significantly larger than reported error bars. We find that any mass difference can be explained through use of differing constraints during the recovery process. We also conclude that underestimated uncertainties on the input parameters can significantly bias the recovered stellar masses, which may have contributed to the controversy on the mass scale for retired A stars.
... M ⊙ . The debate over this claim is ongoing (Johnson et al. 2013;Lloyd 2013;Schlaufman & Winn 2013;Johnson et al. 2014;Ghezzi & Johnson 2015). A resolution to this issue would carry important implications for the way in which masses are estimated for stars in the subgiant and giant branches, especially in the absence of asteroseismic information. ...
... An alternative interpretation, however, has to do with the notion that the uncertainties on the masses of retired A stars found in the literature are being significantly underestimated (as a result of the underestimation of the uncertainties on spectroscopic parameters). Schlaufman & Winn (2013) showed that the large Galactic space motions of subgiant host stars require that on average their masses be similar to those of mainsequence F-and G-type hosts. Therefore, if the masses of retired A stars were to be characterised by a scatter a few times the nominal mass uncertainty (even in the absence of a systematic bias), there could be enough contamination in the sample from low-mass stars to explain the larger-thanexpected space motions of subgiant host stars. ...
Doppler-based planet surveys point to an increasing occurrence rate of giant planets with stellar mass. Such surveys rely on evolved stars for a sample of intermediate-mass stars (so-called retired A stars), which are more amenable to Doppler observations than their main-sequence progenitors. However, it has been hypothesised that the masses of subgiant and low-luminosity red-giant stars targeted by these surveys --- typically derived from a combination of spectroscopy and isochrone fitting --- may be systematically overestimated. Here, we test this hypothesis for the particular case of the exoplanet-host star HD 212771 using K2 asteroseismology. The benchmark asteroseismic mass () is significantly higher than the value reported in the discovery paper (), which has been used to inform the stellar mass-planet occurrence relation. This result, therefore, does not lend support to the above hypothesis. Implications for the fates of planetary systems are sensitively dependent on stellar mass. Based on the derived asteroseismic mass, we predict the post-main-sequence evolution of the Jovian planet orbiting HD 212771 under the effects of tidal forces and stellar mass loss.
... Using data from the Zwicky Transient Facility (ZTF) time domain survey 9 , we searched for slowly evolving outbursts near the Galactic plane ( Supplementary Information 1). We identified a transient optical source, named ZTF 20aazusyv, at celestial J2000 coordinates α = 19:09: 39.783, δ = +05: 35:04.269 ...
... It has long been known that the population of planets in short orbital periods 1,2,30,31 has sufficiently low orbital angular momentum such that they are unstable to tidal dissipation and are bound to merge with their host stars [32][33][34][35] . This is consistent with the lack of old planetary systems with short orbital periods 36,37 , as well as the dearth of close planets around sub-giant stars [38][39][40] . Therefore, to our knowledge, the observations reported here offer the first direct insight into the effect of planetary engulfment on their host stars to interpret common indirect techniques used to infer past planetary engulfment via its effects on long-term stellar luminosity 5,41 , chemical enrichment 42-44 and stellar rotation [45][46][47] . ...
Planets with short orbital periods (roughly under 10 days) are common around stars like the Sun1,2. Stars expand as they evolve and thus we expect their close planetary companions to be engulfed, possibly powering luminous mass ejections from the host star3–5. However, this phase has never been directly observed. Here we report observations of ZTF SLRN-2020, a short-lived optical outburst in the Galactic disk accompanied by bright and long-lived infrared emission. The resulting light curve and spectra share striking similarities with those of red novae6,7—a class of eruptions now confirmed⁸ to arise from mergers of binary stars. Its exceptionally low optical luminosity (approximately 10³⁵ erg s⁻¹) and radiated energy (approximately 6.5 × 10⁴¹ erg) point to the engulfment of a planet of fewer than roughly ten Jupiter masses by its Sun-like host star. We estimate the Galactic rate of such subluminous red novae to be roughly between 0.1 and several per year. Future Galactic plane surveys should routinely identify these, showing the demographics of planetary engulfment and the ultimate fate of planets in the inner Solar System.
... Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. or log g < 3.8). Until recently, though over 100 planets were known on orbits larger than 1 au around evolved stars as defined here, no planets were known on orbits smaller than 0.5 au around evolved stars (Schlaufman & Winn 2013;Villaver et al. 2014;Reffert et al. 2015). ...
... These short-period, Jupiter-sized planets have proven useful for studying planet inflation and star−planet interaction, revealing that planets can become inflated at late times (Grunblatt et al. 2016;Lopez & Fortney 2016;Grunblatt et al. 2017). Studies of planet occurrence have revealed that these planets are more common than predictions suggested (e.g., Schlaufman & Winn 2013), with hot Jupiters being found to be similarly common around main-sequence and evolved stars (Grunblatt et al. 2019). ...
The fate of planets around rapidly evolving stars is not well understood. Previous studies have suggested that, relative to the main-sequence population, planets transiting evolved stars ( P < 100 days) tend to have more eccentric orbits. Here we present the discovery of TOI-4582 b, a 0.94 − 0.12 + 0.09 R J , 0.53 ± 0.05 M J planet orbiting an intermediate-mass subgiant star every 31.034 days. We find that this planet is also on a significantly eccentric orbit ( e = 0.51 ± 0.05). We then compare the population of planets found transiting evolved (log g < 3.8) stars to the population of planets transiting main-sequence stars. We find that the rate at which median orbital eccentricity grows with period is significantly higher for evolved star systems than for otherwise similar main-sequence systems. In general, we observe that mean planet eccentricity 〈 e 〉 = a + b log 10 ( P ) for the evolved population with significant orbital eccentricity where a = −0.18 ± 0.08 and b = 0.38 ± 0.06, significantly distinct from the main-sequence planetary system population. This trend is seen even after controlling for stellar mass and metallicity. These systems do not appear to represent a steady evolution pathway from eccentric, long-period planetary orbits to circular, short-period orbits, as orbital model comparisons suggest that inspiral timescales are uncorrelated with orbital separation or eccentricity. Characterization of additional evolved planetary systems will distinguish effects of stellar evolution from those of stellar mass and composition.
... Finally, as the star evolves off the main-sequence the tidal quality factor can change by orders of magnitude, which dramatically impacts the decay time. This could in-part explain the lack of hot Jupiters observed around sub-giant stars (Villaver & Livio 2009;Hansen 2010;Schlaufman & Winn 2013). ...
... ;Hansen 2010;Schlaufman & Winn 2013). Phase-folded radial velocity measurements for NGTS-23,. ...
We report the discovery of three new hot Jupiters with the Next Generation Transit Survey (NGTS) as well as updated parameters for HATS-54b, which was independently discovered by NGTS. NGTS-23b, NGTS-24b and NGTS-25b have orbital periods of 4.076, 3.468, and 2.823 days and orbit G-, F- and K-type stars, respectively. NGTS-24 and HATS-54 appear close to transitioning off the main-sequence (if they are not already doing so), and therefore are interesting targets given the observed lack of hot Jupiters around sub-giant stars. By considering the host star luminosities and the planets’ small orbital separations (0.037–0.050 au), we find that all four hot Jupiters are above the minimum irradiance threshold for inflation mechanisms to be effective. NGTS-23b has a mass of 0.61 MJ and radius of 1.27 RJ and is likely inflated. With a radius of 1.21 RJ and mass of 0.52 MJ, NGTS-24b has a radius larger than expected from non-inflated models but its radius is smaller than the predicted radius from current Bayesian inflationary models. Finally, NGTS-25b is intermediate between the inflated and non-inflated cases, having a mass of 0.64 MJ and a radius of 1.02 RJ. The physical processes driving radius inflation remain poorly understood, and by building the sample of hot Jupiters we can aim to identify the additional controlling parameters, such as metallicity and stellar age.
... This appears a reasonable conclusion given its age and spectral type (see Table 4). Therefore, it is an interesting target given the rarity of hot Jupiters around sub-giant stars (Villaver & Livio 2009;Hansen 2010;Schlaufman & Winn 2013). We also conclude that HATS-54 and NGTS-23 are both towards the end of their lifetimes on the main-sequence and will evolve off the main-sequence within a few Gyrs. ...
... Finally, as the star evolves off the main-sequence the tidal quality factor can change by orders of magnitude, which dramatically impacts the decay time. This could in-part explain the lack of hot Jupiters observed around sub-giant stars (Villaver & Livio 2009;Hansen 2010;Schlaufman & Winn 2013). ...
We report the discovery of three new hot Jupiters with the Next Generation Transit Survey (NGTS) as well as updated parameters for HATS-54b, which was independently discovered by NGTS. NGTS-23b, NGTS-24b and NGTS-25b have orbital periods of 4.076, 3.468, and 2.823 days and orbit G-, F- and K-type stars, respectively. NGTS-24 and HATS-54 appear close to transitioning off the main-sequence (if they are not already doing so), and therefore are interesting targets given the observed lack of Hot Jupiters around sub-giant stars. By considering the host star luminosities and the planets' small orbital separations (0.037 - 0.050 au), we find that all four hot Jupiters are above the minimum irradiance threshold for inflation mechanisms to be effective. NGTS-23b has a mass of 0.61 and radius of 1.27 and is likely inflated. With a radius of 1.21 and mass of 0.52 , NGTS-24b has a radius larger than expected from non-inflated models but its radius is smaller than the predicted radius from current Bayesian inflationary models. Finally, NGTS-25b is intermediate between the inflated and non-inflated cases, having a mass of 0.64 and a radius of 1.02 . The physical processes driving radius inflation remain poorly understood, and by building the sample of hot Jupiters we can aim to identify the additional controlling parameters, such as metallicity and stellar age.
... In this manuscript, we consider a star to be evolved if its surface gravity g is less than one fourth of the surface gravity of the Sun (i.e., g 6,300 cm s −2 , or log(g) < 3.8). Until recently, though over 100 planets were known on orbits larger than 1 AU around evolved stars as defined here, no planets were known on orbits smaller than 0.5 AU around evolved stars (Schlaufman & Winn 2013;Villaver et al. 2014;Reffert et al. 2015). ...
... These short-period, Jupiter-sized planets have proven useful for studying planet inflation and star-planet interaction, revealing that planets can become inflated at late times (Lopez & Fortney 2016;Grunblatt et al. 2016Grunblatt et al. , 2017. Studies of planet occurrence have revealed that these planets are more common than predictions suggested (e.g., Schlaufman & Winn 2013), with hot Jupiters being found to be similarly common around main sequence and evolved stars (Grunblatt et al. 2019). ...
The fate of planets around rapidly evolving stars is not well understood. Previous studies have suggested that relative to the main sequence population, planets transiting evolved stars (P 100 d) tend to have more eccentric orbits. Here we present the discovery of TOI-4582 b, a 0.94 0.12 R, 0.53 0.05 M planet orbiting an intermediate-mass subgiant star every 31.034 days. We find that this planet is also on a significantly eccentric orbit (e = 0.51 0.05). We then compare the population of planets found transiting evolved (logg 3.8) stars to the population of planets transiting main sequence stars. We find that the rate at which median orbital eccentricity grows with period is significantly higher for evolved star systems than for otherwise similar main sequence systems, particularly for systems with only one planet detected. In general, we observe that mean planet eccentricity = a + blog(P) for the evolved population with a single transiting planet where a = (-0.18 0.08) and b = (0.38 0.06), significantly distinct from the main sequence planetary system population. This trend is seen even after controlling for stellar mass and metallicity. These systems do not appear to represent a steady evolution pathway from eccentric, long-period planetary orbits to circular, short period orbits, as orbital model comparisons suggest inspiral timescales are uncorrelated with orbital separation or eccentricity. Characterization of additional evolved planetary systems will distinguish effects of stellar evolution from those of stellar mass and composition.
... One interpretation is that the initial planet population of high-mass stars is similar to that seen in unevolved sun-like stars, but that the short-period planets are subsequently engulfed during the evolution of their parent stars or ablated by the intense irradiation of their host stars while they are still hot 6 . Another interpretation is that these stars actually have masses similar to the Sun 13 , implying that the paucity of short-period planets among the retired A-stars is indeed a signature of planet engulfment 14 , as sun-like stars do not emit strong ultraviolet radiation with which to ablate their planets 6 . ...
The amount of ultraviolet irradiation and ablation experienced by a planet depends strongly on the temperature of its host star. Of the thousands of extra-solar planets now known, only four giant planets have been found that transit hot, A-type stars (temperatures of 7300-10,000K), and none are known to transit even hotter B-type stars. WASP-33 is an A-type star with a temperature of ~7430K, which hosts the hottest known transiting planet; the planet is itself as hot as a red dwarf star of type M. The planet displays a large heat differential between its day-side and night-side, and is highly inflated, traits that have been linked to high insolation. However, even at the temperature of WASP-33b's day-side, its atmosphere likely resembles the molecule-dominated atmospheres of other planets, and at the level of ultraviolet irradiation it experiences, its atmosphere is unlikely to be significantly ablated over the lifetime of its star. Here we report observations of the bright star HD 195689, which reveal a close-in (orbital period ~1.48 days) transiting giant planet, KELT-9b. At ~10,170K, the host star is at the dividing line between stars of type A and B, and we measure the KELT-9b's day-side temperature to be ~4600K. This is as hot as stars of stellar type K4. The molecules in K stars are entirely dissociated, and thus the primary sources of opacity in the day-side atmosphere of KELT-9b are likely atomic metals. Furthermore, KELT-9b receives ~700 times more extreme ultraviolet radiation (wavelengths shorter than 91.2 nanometers) than WASP-33b, leading to a predicted range of mass-loss rates that could leave the planet largely stripped of its envelope during the main-sequence lifetime of the host star.
... The difficulty of measuring masses for such evolved stars from spectroscopy and stellar isochrones has led to a debate over the reality of the correlation between planet occurrence and stellar mass for gas-giant planets (e.g. Lloyd 2011;Johnson et al. 2013;Schlaufman & Winn 2013). While recent studies focused on asteroseismology as a way to independently test "spectroscopic" masses (Ghezzi & Johnson 2015;Campante et al. 2017;North et al. 2017;Stello et al. 2017), accurate effective temperatures and radii from long-baseline interferometry play a key role for resolving the modeldependent systematic errors. ...
Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass () planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis (, ), 24 Sextantis (, ), Coronae Borealis (, ), HR 6817 (, ), and HR 8641 (, ). We find disagreements of typically 15 per cent in angular diameter and 200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly (15 per cent) lower masses than generally reported in the literature.
... The results of J14 are consistent with a mass in excess of 1.5M , indicating that HD 185351 was an early F-or A-type star on the main sequence (MS). However mass estimates of single stars are based on stellar evolution models which may contain systematic errors, and indeed the accuracy of mass estimates of sub-giant stars has recently been called into question (Lloyd 2011(Lloyd , 2013Schlaufman & Winn 2013), suggesting that sub-giants with masses in excess of 1.5M should be rare in the solar neighbourhood. This issue of mass estimation for this kind of star has implications for the reliability of stellar evolution models as well as our understanding of planet occurrence rates around higher-mass stars which depends on accurate knowledge of the stellar masses (Lloyd 2013;Johnson et al. 2013). ...
The physical parameters of the retired A star HD 185351 were analysed in great detail by Johnson et al. (2014) using interferometry, spectroscopy and asteroseismology. Results from all independent methods are consistent with HD 185351 having a mass in excess of . However, the study also showed that not all observational constraints could be reconciled in stellar evolutionary models, leading to mass estimates ranging from and casting doubts on the accuracy of stellar properties determined from asteroseismology. Here we solve this discrepancy and construct a theoretical model in agreement with all observational constraints on the physical parameters of HD 185351. The effects of varying input physics are examined as well as considering the additional constraint of the observed g-mode period spacing. This quantity is found to be sensitive to the inclusion of additional mixing from the convective core during the main sequence, and can be used to calibrate the overshooting efficiency using low-luminosity red giant stars. A theoretical model with metallicity dex, mixing-length parameter , and convective overshooting efficiency parameter f=0.030 is found to be in complete agreement with all observational constraints for a stellar mass of .
... The anomalously rapid rotation of some hot-Jupiter host stars has been attributed to transfer of the planet's orbital angular momentum (Penev et al. 2016). The absence of hot Jupiters around subgiant stars may be caused by an acceleration of orbital decay when a star leaves the main sequence (Villaver & Livio 2009;Hansen 2010;Schlaufman & Winn 2013). Tidal decay might also be responsible for the lower occurrence of close-in planets around rapidly rotating stars (Teitler & Königl 2014), or the realignment of stars and their planetary orbits (Matsakos & Königl 2015). ...
We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: ms yr and Myr. However, it is difficult to tell whether we have observed orbital decay, or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter is about . If interpreted as precession, the planet's Love number is . Orbital decay appears to be the more parsimonious model: it is favored by despite having two fewer free parameters than the precession model. The decay model implies that WASP-12 was discovered within the final 0.2% of its existence, which is an unlikely coincidence but harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but does require some mechanism to maintain an eccentricity of 0.002 in the face of rapid tidal circularization. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.
... An important confirmation was the radialvelocity measurements in the near-IR recently carried out by Trifonov et al. (2015). The results for giant stars have furthermore been criticized in the sense that the masses of the giant stars could be wrong (Lloyd 2013;Schlaufman & Winn 2013). ...
We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19 0.04) orbit around K2-99, an 11th magnitude subgiant in Virgo. We confirm the planetary nature of the companion with radial velocities, and determine that the star is a metal-rich ([Fe/H] = 0.200.05) subgiant, with mass and radius . The planet has a mass of and a radius . A measured systemic radial acceleration of offers compelling evidence for the existence of a third body in the system, perhaps a brown dwarf orbiting with a period of several hundred days.
... The orbits of hot Jupiters are expected to decay due to tidal dissipation within their host stars (Rasio et al. 1996). While there is considerable indirect evidence of orbital decay in the ensemble properties of hot Jupiter systems (Jackson et al. 2008;Jackson et al. 2009;Hansen 2010;Penev et al. 2012;Schlaufman & Winn 2013;Teitler & Königl 2014), the recent transit timing observations of WASP-12 by Maciejewski et al. (2016) and Patra et al. (2017) could be the first direct evidence of orbital decay of an individual system. They detect a decrease in the orbital period at a rateṖ = −29 ± 3 ms yr −1 . ...
WASP-12 is a hot Jupiter system with an orbital period of , making it one of the shortest-period giant planets known. Recent transit timing observations by Maciejewski et al. (2016) and Patra et al. (2017) find a decreasing period with . This has been interpreted as evidence of either orbital decay due to tidal dissipation or a long term oscillation of the apparent period due to apsidal precession. Here we consider the possibility that it is orbital decay. We show that the parameters of the host star are consistent with either a main sequence star or a subgiant. We find that if the star is on the main sequence, the tidal dissipation is too inefficient to explain the observed . However, if it is a subgiant, the tidal dissipation is significantly enhanced due to nonlinear wave breaking of the dynamical tide near the star's center. The subgiant models have a tidal quality factor and an orbital decay rate that agrees well with the observed . It would also explain why the planet survived for while the star was on the main sequence and yet is now inspiraling on a 3 Myr timescale. Although this suggests that we are witnessing the last of the planet's life, the probability of such a detection is a few percent given the observed sample of hot Jupiters in orbits around hosts.
... As stars ascend the RGB, planets on short periods are rapidly engulfed by the expanding star. Additionally the tidal decay timescale decreases for evolved stars (Schlaufman & Winn 2013), e.g., the Kepler-56 system, where the planets are likely to be engulfed within ∼100 Myr (Li et al. 2014). Even without consideration of tidal decay, for the case of evolved RGB hosts, planets on short periods, and many cases in the Kepler period distribution described above, would have to exist inside the stellar envelope (these cases have been removed from Figure 8). ...
In spite of the huge advances in exoplanet research provided by the NASA Kepler Mission, there remain only a small number of transit detections around evolved stars. Here we present a reformulation of the noise properties of red-giant stars, where the intrinsic stellar granulation, and the stellar oscillations described by asteroseismology play a key role. The new noise model is a significant improvement on the current Kepler results for evolved stars. Our noise model may be used to help understand planet detection thresholds for the ongoing K2 and upcoming TESS missions, and serve as a predictor of stellar noise for these missions. As an application of our noise model, we explore the minimum detectable planet radii for red giant stars, and find that Neptune sized planets should be detectable around low luminosity red giant branch stars.
... However, the mass estimates of the retired A-stars were subsequently called into question by Lloyd (2011), who argued it was statistically unlikely that the sample, which he extracted from the Exoplanet Orbit Database (EOD) (Wright et al. 2011), would include so many relatively massive stars, given their location in the HR-diagram. This led to further investigations by Johnson et al. (2013), Lloyd (2013), and Schlaufman & Winn (2013), but without a clear resolution. ...
To better understand how planets form, it is important to study planet occurrence rates as a function of stellar mass. However, estimating masses of field stars is often difficult. Over the past decade, a controversy has arisen about the inferred occurrence rate of gas-giant planets around evolved intermediate-mass stars -- the so-called `retired A-stars'. The high masses of these red-giant planet hosts, derived using spectroscopic information and stellar evolution models, have been called into question. Here we address the controversy by determining the masses of eight evolved planet-hosting stars using asteroseismology. We compare the masses with spectroscopic-based masses from the Exoplanet Orbit Database that were previously adopted to infer properties of the exoplanets and their hosts. We find a significant one-sided offset between the two sets of masses for stars with spectroscopic masses above roughly 1.6Msun, suggestive of an average 15--20% overestimate of the adopted spectroscopic-based masses. The only star in our sample well below this mass limit is also the only one not showing this offset. Finally, we note that the scatter across literature values of spectroscopic-based masses often exceed their formal uncertainties, making it comparable to the offset we report here.
... These cool, moderately evolved stars occupy a region of the Hertzsprung-Russell diagram where mass discrimination should be easier than further up the RGB. These stars' intermediate masses (M 1.3 M e ) have been challenged on the basis that both their rotational velocities (Lloyd 2011(Lloyd , 2013 and space velocity dispersion (Schlaufman & Winn 2013) are more akin to 1-1.2 M e stars. These claims have been refuted by Johnson et al. (2013) and Ghezzi et al. (2018), the latter of whom argued that at most the masses may be overestimated by 0.12 M e , maintaining their classification as "retired A" stars. ...
We present a study of asteroseismically derived surface gravities, masses, and radii of a sample of red giant stars both with and without confirmed planetary companions using TESS photometric light curves. These red giants were drawn from radial velocity surveys, and their reported properties in the literature rely on more traditional methods using spectroscopy and isochrone fitting. Our asteroseismically derived surface gravities achieved a precision of ∼0.01 dex; however, they were on average ∼0.1 dex smaller than the literature. The systematic larger gravities of the literature could plausibly present as a systematic overestimation of stellar masses, which would in turn lead to overestimated planetary masses of the companions. We find that the fractional discrepancies between our asteroseismically determined parameters and those previously found are typically larger for stellar radii (∼10% discrepancy) than for stellar masses (<5% discrepancy). However, no evidence of a systematic difference between methods was found for either fundamental parameter. Two stars, HD 100065 and HD 18742, showed significant disagreement with the literature in both mass and radii. We explore the impacts of updated stellar properties on inferred planetary properties and caution that red giant radii may be more poorly constrained than uncertainties suggest.
... These cool, moderately evolved stars occupy a region of the Hertzsprung-Russell diagram where mass discrimination should be easier than further up the red giant branch. These stars' intermediate masses (M ≳ 1.3 M ⊙ ) have been challenged on the basis that both their rotational velocities (Lloyd 2011(Lloyd , 2013 and space velocity dispersion (Schlaufman & Winn 2013) are more akin to 1-1.2 M ⊙ stars. These claims have been refuted by Johnson et al. (2013) and Ghezzi et al. (2018), the latter of whom argued that at most the masses may be overestimated by 0.12M ⊙ , maintaining their classification as "retired A" stars. ...
We present a study of asteroseismically derived surface gravities, masses, and radii of a sample of red giant stars both with and without confirmed planetary companions using TESS photometric light curves. These red giants were drawn from radial velocity surveys, and their reported properties in the literature rely on more traditional methods using spectroscopy and isochrone fitting. Our asteroseismically derived surface gravities achieved a precision of 0.01 dex; however, they were on average 0.1~dex smaller than the literature. The systematic larger gravities of the literature could plausibly present as a systematic overestimation of stellar masses, which would in turn lead to overestimated planetary masses of the companions. We find that the fractional discrepancies between our asteroseismically-determined parameters and those previously found are typically larger for stellar radii (10% discrepancy) than for stellar masses (% discrepancy). However, no evidence of a systematic difference between methods was found for either fundamental parameter. Two stars, HD~100065 and HD~18742, showed significant disagreement with the literature in both mass and radii. We explore the impacts on updated stellar properties on inferred planetary properties and caution that red giant radii may be more poorly constrained than uncertainties suggest.
... However, Lloyd (2013) used apparent magnitude-limited weights for the isochrone integration in his 2011 calculations and argued that irrespective of such limit used in target selection, there was a deficit of massive stars in the subgiant and red giant regime compared to what was reported in the literature. Supporting this argument by Lloyd (2013), Schlaufman & Winn (2013) found consistency between the velocity dispersions for their subgiant sample and their main-sequence F5-G5 sample, but not with their main-sequence A0-F5 sample. This consistency led them to conclude that their subgiants are less massive than main sequence A0-F5 stars. ...
One way to understand planet formation is through studying the correlations between planet occurrence rates and stellar mass. However, measuring stellar mass in the red giant regime is very difficult. In particular, the spectroscopic masses of certain evolved stars, often referred to as "retired A-stars", have been questioned in the literature. Efforts to resolve this mass controversy using spectroscopy, interferometry and asteroseismology have so far been inconclusive. A recent ensemble study found a mass-dependent mass offset, but the result was based on only 16 stars. With NASA's Transiting Exoplanet Survey Satellite (TESS), we expand the investigation of the mass discrepancy to a total of 92 low-luminosity stars, synonymous with the retired A-stars. We measure their characteristic oscillation frequency, , and the large frequency separation, , from their TESS photometric time series. Using these measurements and asteroseismic scaling relations, we derive asteroseismic masses and compare them with spectroscopic masses from five surveys, to comprehensively study the alleged mass-dependent mass offset. We find a mass offset between spectroscopy and seismology that increases with stellar mass. However, we note that adopting the seismic mass scale does not have a significant effect on the planet occurrence-mass-metallicity correlation for the so-called retired A-stars. We also report seismic measurements and masses for 157 higher luminosity giants (mostly helium-core-burning) from the spectroscopic surveys.
... The rates of decay can vary depending on the magnitude of the stellar tidal dissipation for a given configuration (Levrard et al. 2009;Matsumura et al. 2010). Population studies offer additional evidence for orbital decay, such as the scarcity of gaseous giants with periods less than 1 day (Jackson et al. 2008;Hansen 2010;Penev et al. 2012;Ogilvie 2014), the unusually rapid rotation of certain hot Jupiters' host stars (Penev et al. 2018), and the rarity of hot Jupiters around subgiants (Hansen 2010;Schlaufman & Winn 2013). ...
Many hot Jupiters may experience orbital decays, which are manifested as long-term transit-timing variations. We have analyzed 7068 transits from the Transiting Exoplanet Survey Satellite (TESS) for a sample of 326 hot Jupiters. These new mid-transit-time data allow us to update ephemerides for these systems. By combining the new TESS transit-timing data with archival data, we searched for possible long-term variations in the orbital period in these hot Jupiters using a linear and a quadratic ephemeris model. We identified 26 candidates that exhibit possible long-term variations of the orbital period, including 18 candidates with decreasing orbital periods and eight candidates with increasing orbital periods. Among them, 12 candidates failed our leave-one-out cross validation test and thus should be considered to be marginal candidates. In addition to tidal interaction, alternative mechanisms such as apsidal precession, the Rømer effect, and the Applegate effect could also contribute to the variations during the observed period. The ephemerides derived in this work are useful for scheduling follow-up observations for these hot Jupiters in the future. The Python code ( PdotQuest , https://github.com/AeoN400/PdotQuest ) used to generate the ephemerides is made available online.
... Alternatively, the velocity dispersion for an assemble of stars is known to correlate with age. The velocity dispersions have been previously used as a relative age proxy to study the hosts of hot Jupiters (7)(8)(9). Specifically, Hamer & Schlaufman found that the hosts of hot Jupiters are on average younger than the field stars, which can be interpreted by the tidal inspiral of hot Jupiters around hosts with modified stellar tidal quality factor Q * ≲ 10 7 (8). In a subsequent work, they showed that hot Jupiter host stars with larger obliquities are older compared to the aligned systems, suggesting those misaligned hot Jupiters arrived at their presently short-period orbits at late times (9). ...
The unexpected discovery of hot Jupiters challenged the classical theory of planet formation inspired by our solar system. Until now, the origin and evolution of hot Jupiters are still uncertain. Determining their age distribution and temporal evolution can provide more clues into the mechanism of their formation and subsequent evolution. Using a sample of 383 giant planets around Sun-like stars collected from the kinematic catalogs of the Planets Across Space and Time project, we find that hot Jupiters are preferentially hosted by relatively younger stars in the Galactic thin disk. We subsequently find that the frequency of hot Jupiters declines with age as F HJ ∝ exp ( − 0.20 ± 0.06 × t Gyr ) . In contrast, the frequency of warm/cold Jupiters shows no significant dependence on age. Such a trend is expected from the tidal evolution of hot Jupiters’ orbits, and our result offers supporting evidence using a large sample. We also perform a joint analysis on the planet frequencies in the stellar age-metallicity plane. The result suggests that the frequencies of hot Jupiters and warm/cold Jupiters, after removing the age dependence are both correlated with stellar metallicities as F HJ ∝ 10 1 . 6 − 0.3 + 0.3 × [ Fe / H ] and F WJ / CJ ∝ 10 1 . 1 − 0.3 + 0.2 × [ Fe / H ] , respectively. Moreover, we show that the above correlations can explain the bulk of the discrepancy in hot Jupiter frequencies inferred from the transit and radial velocity (RV) surveys, given that RV targets tend to be more metal-rich and younger than transits.
... However, it still remains quantitatively unclear how the orbital decay drives the evolution of the entire population of HJs. The two systems with detected decay, for example, may well be atypical cases showing the quickest decays that are easiest to detect, perhaps aided by enhanced tidal dissipation due to host stars evolving off the main sequence (e.g., Schlaufman & Winn 2013;Weinberg et al. 2017). The study of Hamer & Schlaufman (2019) does not relate the velocity dispersion with the absolute age scale. ...
We investigate how the occurrence rate of giant planets (minimum mass > 0.3 M Jup ) around Sun-like stars depends on the age, mass, and metallicity of their host stars. We develop a hierarchical Bayesian framework to infer the number of planets per star (NPPS) as a function of both planetary and stellar parameters. The framework fully takes into account the uncertainties in the latter by utilizing the posterior samples for the stellar parameters obtained by fitting stellar isochrone models to the spectroscopic parameters, Gaia DR3 parallaxes, and 2MASS K s -band magnitudes adopting a certain bookkeeping prior. We apply the framework to 46 Doppler giants found around a sample of 382 Sun-like stars from the California Legacy Survey catalog that publishes spectroscopic parameters and search completeness for all the surveyed stars. We find evidence that the NPPS of hot Jupiters (orbital period P = 1–10 days) decreases roughly in the latter half of the main sequence over the timescale of ( Gyr ) , while that of cold Jupiters ( P = 1–10 yr) does not. Assuming that this decrease is real and caused by tidal orbital decay, the modified stellar tidal quality factor Q ⋆ ′ is implied to be ( 10 6 ) for a Sun-like main-sequence star orbited by a Jupiter-mass planet with P ≈ 3 days.
... Common-envelope evolution (CEE; Paczynski 1976) is a process in which a star engulfs a companion (substellar or otherwise). The known planetary system architectures imply that a large fraction of planets and brown dwarfs (hereafter substellar bodies, SBs) will eventually undergo CEE (Villaver & Livio 2009;Mustill & Villaver 2012;Nordhaus & Spiegel 2013;Schlaufman & Winn 2013;Sun et al. 2018). Throughout this work, we will refer to CEE between a star and an SB as "planetary engulfment," and use "CEE" for the more general interaction between a star and a companion of any mass. ...
The engulfment of substellar bodies (SBs), such as brown dwarfs and planets, by giant stars is a possible explanation for rapidly rotating giants, lithium-rich giants, and the presence of SBs in close orbits around subdwarfs and white dwarfs. We perform three-dimensional hydrodynamical simulations of the flow in the vicinity of an engulfed SB. We model the SB as a rigid body with a reflective surface because it cannot accrete. This reflective boundary changes the flow morphology to resemble that of engulfed compact objects with outflows. We measure the drag coefficients for the ram-pressure and gravitational drag forces acting on the SB, and use them to integrate its trajectory inside the star. We find that engulfment can increase the luminosity of a 1 M ⊙ star by up to a few orders of magnitude. The time for the star to return to its original luminosity is up to a few thousand years when the star has evolved to ≈10 R ⊙ and up to a few decades at the tip of the red giant branch (RGB). No SBs can eject the envelope of a 1 M ⊙ star before it evolves to ≈10 R ⊙ if the orbit of the SB is the only energy source contributing to the ejection. In contrast, SBs as small as ≈10 M Jup can eject the envelope at the tip of the RGB. The numerical framework we introduce here can be used to study planetary engulfment in a simplified setting that captures the physics of the flow at the scale of the SB.
... The role of tidal forces becomes increasingly important in the context of host stars being in an evolved state. There is a higher chance of the planet being destroyed by the evolved star (Kunitomo et al. 2011;Schlaufman & Winn 2013). However, there is no obvious way to estimate these tidal dissipation forces. ...
We report here the discovery of a hot Jupiter at an orbital period of 3.208664 ± 0.000015 d around TOI-1789 (TYC 1962-00303-1, TESS mag = 9.1) based on the TESS photometry, ground-based photometry, and high-precision radial velocity (RV) observations. The high-precision RV observations were obtained from the high-resolution spectrographs, PARAS at Physical Research Laboratory (PRL), India, and TCES at Thüringer Landessternwarte Tautenburg (TLS), Germany, and the ground-based transit observations were obtained using the 0.43-m telescope at PRL with the Bessel-R filter. The host star is a slightly evolved (log g * = 3.943 +0.023 −0.043), late F-type (T eff = 5991 ± 55 K), metal-rich star ([Fe/H] = 0.373 +0.071 −0.086 dex) with a radius of R * = 2.168 +0.036 −0.034 R located at a distance of 223.53 +0.91 −0.90 pc. The simultaneous fitting of the multiple light curves and the RV data of TOI-1789 reveals that TOI-1789 b has a mass of M P = 0.70 ± 0.16 M J , a radius of R P = 1.44 +0.24 −0.14 R J , and a bulk density of ρ P = 0.28 +0.14 −0.12 g cm −3 with an orbital separation of a = 0.04882 +0.00063 −0.0016 au. This puts TOI-1789 b in the category of inflated hot Jupiters. It is one of the few nearby evolved stars with a close-in planet. The detection of such systems will contribute to our understanding of mechanisms responsible for inflation in hot Jupiters and also provide an opportunity to understand the evolution of planets around stars leaving the main-sequence branch.
... Wang et al. (2021) noted that cool stars with a/R 10 tend to have both low obliquity and low eccentricity. This could be due to damping of both obliquity and eccentricity by tides (Section 4.1), although according to standard theoretical assumptions, eccentricity damping is mainly caused by dissipation within planets and obliquity damping is mainly caused by dissipation within the star (see, e.g., Schlaufman & Winn 2013). Rice et al. (2022) found that cool stars with planets on eccentric orbits tend to have higher obliquities than similar stars with planets on low-eccentricity orbits. ...
The rotation of a star and the revolutions of its planets are not necessarily aligned. This article reviews the measurement techniques, key findings, and theoretical interpretations related to the obliquities (spin–orbit angles) of planet-hosting stars. The best measurements are for stars with short-period giant planets, which have been found on prograde, polar, and retrograde orbits. It seems likely that dynamical processes such as planet–planet scattering and secular perturbations are responsible for tilting the orbits of close-in giant planets, just as those processes are implicated in exciting orbital eccentricities. The observed dependence of the obliquity on orbital separation, planet mass, and stellar structure suggests that in some cases, tidal dissipation damps a star’s obliquity within its main-sequence lifetime. The situation is not as clear for stars with smaller or wider-orbiting planets. Although the earliest measurements of such systems tended to find low obliquities, some glaring exceptions are now known in which the star’s rotation is misaligned with respect to the coplanar orbits of multiple planets. In addition, statistical analyses based on projected rotation velocities and photometric variability have found a broad range of obliquities for F-type stars hosting compact multiple-planet systems. The results suggest it is unsafe to assume that stars and their protoplanetary disks are aligned. Primordial misalignments might be produced by neighboring stars or more complex events that occur during the epoch of planet formation.
... hot Jupiters) are rarely found with additional planetary companions, and may have cleared away planet-forming disk material during migration, or ejected other planets dynamically (Latham et al. 2011;Mustill et al. 2015). While it is unclear if a giant planet (or two) is sufficient to amplify mass loss during stellar evolution, the absence of hot Jupiters around subgiant hosts argues that giant planet ingestion does indeed occur (Schlaufman & Winn 2013). ...
White dwarf stars frequently exhibit external pollution by heavy elements, and yet the intrinsically carbon-enriched DQ spectral class members fail to experience this phenomenon, representing a decades-old conundrum. This study reports a high-resolution spectroscopic search for Ca II in classical DQ white dwarfs, finding that these stars are stunted both in pollution frequency and heavy element mass fractions, relative to the wider population. Compared to other white dwarf spectral classes, the average external accretion rate is found to be at least three orders of magnitude lower in the DQ stars. Several hypotheses are considered which need to simultaneously account for i) an apparent lack of accreted metals, ii) a dearth of circumstellar planetary material, iii) an observed deficit of unevolved companions in post-common envelope binaries, iv) relatively low helium mass fractions, and remnant masses that appear smaller than for other spectral classes, v) a high incidence of strong magnetism, and vi) modestly older disk kinematics. Only one hypothesis is consistent with all these constraints, suggesting DQ white dwarfs are the progeny of binary evolution that altered both their stellar structures and their circumstellar environments. A binary origin is already suspected for the warmer and more massive DQ stars, and is proposed here as an inclusive mechanism to expose core carbon material, in a potential evolutionary unification for the entire DQ spectral class. In this picture, DQ stars are not descended from DA or DB white dwarfs that commonly host dynamically-active planetary systems.
... Common-envelope evolution (hereafter CEE;Paczynski 1976) is a process in which the expanding envelope of a postmain-sequence star fills its Roche lobe and engulfs a companion (substellar or otherwise). The known census of planetary system architectures implies that a large fraction of planets and brown dwarfs (hereafter substellar bodies, SBs) in mainsequence systems will eventually undergo CEE (Villaver & Livio 2009;Mustill & Villaver 2012;Nordhaus & Spiegel 2013;Schlaufman & Winn 2013;Sun et al. 2018). The CEE phase often results disassociation of the SB companion, which is caused by tidal disruption, ram pressure stripping, and ablation. ...
The engulfment of substellar bodies (SBs) such as brown dwarfs and planets has been invoked as a possible explanation for the presence of SBs orbiting subdwarfs and white dwarfs, rapidly rotating giants, and lithium-rich giants. We perform three-dimensional hydrodynamical simulations of the flow in the vicinity of an SB engulfed in a stellar envelope. We model the SB as a rigid body with a reflective boundary because it cannot accrete. This reflective boundary changes the flow morphology to resemble that of engulfed compact objects with outflows. We measure the drag coefficients for the ram pressure and gravitational drag forces acting on the SB, and use them to integrate its trajectory during engulfment. We find that SB engulfment can increase the stellar luminosity of a star by up to a few orders of magnitude for timescales of up to a few thousand years when the star is and up to a few decades at the tip of the red giant branch. We find that no SBs can eject the envelope of a star before it evolves to . In contrast, SBs as small as can eject the envelope at the tip of the red giant branch, shrinking their orbits by several orders of magnitude in the process. The numerical framework we introduce here can be used to study the dynamics of planetary engulfment in a simplified setting that captures the physics of the flow at the scale of the SB.
... However, planets at smaller separations were expected to be engulfed due to angular momentum exchange through tides (Hut 1981;Villaver & Livio 2009). Thus less than a decade ago, no planets were known on orbits smaller than 1 au around stars with radii greater than 3 R e and masses above 1 M e (Schlaufman & Winn 2013;Villaver et al. 2014). ...
Giant planets on short-period orbits are predicted to be inflated and eventually engulfed by their host stars. However, the detailed timescales and stages of these processes are not well known. Here, we present the discovery of three hot Jupiters ( P < 10 days) orbiting evolved, intermediate-mass stars ( M ⋆ ≈ 1.5 M ⊙ , 2 R ⊙ < R ⋆ < 5 R ⊙ ). By combining TESS photometry with ground-based photometry and radial velocity measurements, we report masses and radii for these three planets of between 0.4 and 1.8 M J and 0.8 and 1.8 R J . TOI-2337b has the shortest period ( P = 2.99432 ± 0.00008 days) of any planet discovered around a red giant star to date. Both TOI-4329b and TOI-2669b appear to be inflated, but TOI-2337b does not show any sign of inflation. The large radii and relatively low masses of TOI-4329b and TOI-2669b place them among the lowest density hot Jupiters currently known, while TOI-2337b is conversely one of the highest. All three planets have orbital eccentricities of below 0.2. The large spread in radii for these systems implies that planet inflation has a complex dependence on planet mass, radius, incident flux, and orbital properties. We predict that TOI-2337b has the shortest orbital decay timescale of any planet currently known, but do not detect any orbital decay in this system. Transmission spectroscopy of TOI-4329b would provide a favorable opportunity for the detection of water, carbon dioxide, and carbon monoxide features in the atmosphere of a planet orbiting an evolved star, and could yield new information about planet formation and atmospheric evolution.
... By measuring the deviation from a constant orbital period over the course of many observations for a hot Jupiter around subgiant stars, the inspiral timescale and value of ¢ Q for the host can be constrained (e.g., Levrard et al. 2009;Chontos et al. 2019). Planets around evolved stars can also contribute to the resolution of debates about the dependence of planet occurrence on stellar mass, a hotly debated topic over the last decade (Johnson et al. 2010;Lloyd 2013;Schlaufman & Winn 2013;Ghezzi & Johnson 2015). ...
While the population of confirmed exoplanets continues to grow, the sample of confirmed transiting planets around evolved stars is still limited. We present the discovery and confirmation of a hot Jupiter orbiting TOI-2184 (TIC 176956893), a massive evolved subgiant ( M ⋆ = 1.53 ± 0.12 M ⊙ , R ⋆ = 2.90 ± 0.14 R ⊙ ) in the Transiting Exoplanet Survey Satellite (TESS) Southern Continuous Viewing Zone. The planet was flagged as a false positive by the TESS Quick-Look Pipeline due to periodic systematics introducing a spurious depth difference between even and odd transits. Using a new pipeline to remove background scattered light in TESS Full Frame Image data, we combine space-based TESS photometry, ground-based photometry, and ground-based radial velocity measurements to report a planet radius of R p = 1.017 ± 0.051 R J and mass of M p = 0.65 ± 0.16 M J . For a planet so close to its star, the mass and radius of TOI-2184b are unusually well matched to those of Jupiter. We find that the radius of TOI-2184b is smaller than theoretically predicted based on its mass and incident flux, providing a valuable new constraint on the timescale of post-main-sequence planet inflation. The discovery of TOI-2184b demonstrates the feasibility of detecting planets around faint (TESS magnitude > 12) post-main-sequence stars and suggests that many more similar systems are waiting to be detected in the TESS FFIs, whose confirmation may elucidate the final stages of planetary system evolution.
... However, planets at smaller separations were expected to be engulfed due to angular momentum exchange through tides (Hut 1981;Villaver & Livio 2009). Thus less than a decade ago, no planets were known on orbits smaller than 1 AU around stars with radii greater than 3 R and masses above 1 M (Schlaufman & Winn 2013;Villaver et al. 2014). ...
Giant planets on short-period orbits are predicted to be inflated and eventually engulfed by their host stars. However, the detailed timescales and stages of these processes are not well known. Here we present the discovery of three hot Jupiters (P 10 d) orbiting evolved, intermediate-mass stars ( 1.5 M, 2 R 5 R). By combining \tess photometry with ground-based photometry and radial velocity measurements, we report masses and radii for these three planets between 0.4 and 1.8 M and 0.8 and 1.8 R. \planet has the shortest period (P=\period) of any planet discovered around a red giant star to date. Both \planettwo and \planetthree appear to be inflated, but \planet does not show any sign of inflation. The large radii and relatively low masses of \planettwo and \planetthree place them among the lowest density hot Jupiters currently known, while \planet is conversely one of the highest. All three planets have orbital eccentricities below 0.2. The large spread in radii for these systems implies that planet inflation has a complex dependence on planet mass, radius, incident flux, and orbital properties. We predict that \planet has the shortest orbital decay timescale of any planet currently known, but do not detect any orbital decay in this system. Transmission spectroscopy of \planettwo would provide a favorable opportunity for the detection of water, carbon dioxide and carbon monoxide features in the atmosphere of a planet orbiting an evolved star, and could yield new information about planet formation and atmospheric evolution.
... Levrard et al. 2009;Chontos et al. 2019). Planets around evolved stars can also contribute to the resolution of debates about the dependence of planet occurrence on stellar mass, a hotly debated topic over the last decade (Johnson et al. 2010;Lloyd 2013;Schlaufman & Winn 2013;Ghezzi & Johnson 2015). ...
While the population of confirmed exoplanets continues to grow, the sample of confirmed transiting planets around evolved stars is still limited. We present the discovery and confirmation of a hot Jupiter orbiting TOI-2184 (TIC 176956893), a massive evolved subgiant (, ) in the Southern Continuous Viewing Zone. The planet was flagged as a false positive by the Quick-Look Pipeline due to periodic systematics introducing a spurious depth difference between even and odd transits. Using a new pipeline to remove background scattered light in Full Frame Image (FFI) data, we combine space-based photometry, ground-based photometry, and ground-based radial velocity measurements to report a planet radius of and mass of . For a planet so close to its star, the mass and radius of TOI-2184b are unusually well matched to those of Jupiter. We find that the radius of TOI-2184b is smaller than theoretically predicted based on its mass and incident flux, providing a valuable new constraint on the timescale of post-main-sequence planet inflation. The discovery of TOI-2184b demonstrates the feasibility of detecting planets around faint ( magnitude ) post-main sequence stars and suggests that many more similar systems are waiting to be detected in the FFIs, whose confirmation may elucidate the final stages of planetary system evolution.
... The role of tidal forces becomes increasingly important in the context of host stars being in an evolved state. There is a higher chance of the planet being destroyed by the evolved star (Kunitomo et al. 2011;Schlaufman & Winn 2013). However, there is no obvious way to estimate these tidal dissipation forces. ...
We report here the discovery of a hot Jupiter at an orbital period of days around TOI-1789 (TYC 1962-00303-1, = 9.1) based on the TESS photometry, ground-based photometry, and high-precision radial velocity observations. The high-precision radial velocity observations were obtained from the high-resolution spectrographs, PARAS at Physical Research Laboratory (PRL), India, and TCES at Th\"uringer Landessternwarte Tautenburg (TLS), Germany, and the ground-based transit observations were obtained using the 0.43~m telescope at PRL with the Bessel-R filter. The host star is a slightly evolved ( = ), late F-type ( = K), metal-rich star ([Fe/H] = dex) with a radius of {\ensuremath{}} = located at a distance of pc. The simultaneous fitting of the multiple light curves and the radial velocity data of TOI-1789 reveals that TOI-1789b has a mass of = , a radius of = , and a bulk density of = g cm with an orbital separation of a = AU. This puts TOI-1789b in the category of inflated hot Jupiters. It is one of the few nearby evolved stars with a close-in planet. The detection of such systems will contribute to our understanding of mechanisms responsible for inflation in hot Jupiters and also provide an opportunity to understand the evolution of planets around stars leaving the main sequence branch.
... Subgiant and giant stars are observed to have fewer close-in giant planets (see, e.g., Johnson et al. 2010;Ortiz et al. 2015;Reffert et al. 2015). The origin of this is subject to debate, and may be caused by tidal evolution (Rasio et al. 1996;Schlaufman and Winn 2013) or be the result of the higher mass of observed evolved stars compared to observed main-sequence stars (Burkert and Ida 2007;Kretke et al. 2009). Precisely determining the mass and evolutionary stage of these evolved planet-host stars is difficult but may help understand and distinguish between these mechanisms (e.g., Campante et al. 2017;North et al. 2017;Stello et al. 2017;Ghezzi et al. 2018;Malla et al. 2020), in particular for evolved stars around which short-period planets have been detected (see, e.g., Van Eylen et al. 2016;Chontos et al. 2019). ...
The mass of a star is the most fundamental parameter for its structure, evolution, and final fate. It is particularly important for any kind of stellar archaeology and characterization of exoplanets. There exist a variety of methods in astronomy to estimate or determine it. In this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. We then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. The arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. We include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. For all methods uncertainties and restrictions will be discussed. We provide lists of altogether more than 200 benchmark stars with relative mass accuracies between for the covered mass range of , of which are stars burning hydrogen in their core and the other covering all other evolved stages. We close with a recommendation how to combine various methods to arrive at a “mass-ladder” for stars.
... A value close to this was obtained by Weinberg et al. (2017) for the subgiant WASP-12. Note also, that during the post-MS evolution the main reason of planet engulfment is stellar expansion, not tides, so the value of Q on this stage is less important (see, however, Villaver & Livio 2009;Schlaufman & Winn 2013). ...
Orbits of close-in planets can shrink significantly due to dissipation of tidal energy in a host star. This process can result in star–planet coalescence within the Galactic lifetime. In some cases, such events can be accompanied by an optical or/and UV/X-ray transient. Potentially, these outbursts can be observed in near future with new facilities such as LSST from distances about few Mpc. We use a population synthesis model to study this process and derive the rate of star–planet mergers of different types. Mostly, planets are absorbed by red giants. However, these events, happening with the rate about 3 per year, mostly do not produce detectable transients. The rate of mergers with main sequence stars depends on the effectiveness of tidal dissipation; for reasonable values of stellar tidal quality factor, such events happen in a Milky Way-like galaxy approximately once in 70 yr or more rarely. This rate is dominated by planets with low masses. Such events do not produce bright transients having maximum luminosities ≲ 1036.5 erg s−1. Brighter events, related to massive planets, with maximum luminosity ∼1037.5–1038 erg s−1, have the rate nearly five times smaller.
... From these recalculations, Lloyd (2013) showed that there are fewer massive stars than found in the literature, irrespective of the limit used in the target selection (volume-or magnitude-limit). Meanwhile, Schlaufman & Winn (2013) determined model-independent masses from space velocity dispersions. They found that the velocity dispersions of their subgiant sample were larger than for their main-sequence A0-F5 stars but consistent with their main sequence F5-G5 sample. ...
The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a sample of evolved planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology, results were inconclusive. In an attempt to resolve this controversy, we study four more evolved planet-hosting stars in this paper using asteroseismology, and we revisit previous results to make an informed study of the whole ensemble in a self-consistent way. For the four new stars, we measure their masses by locating their characteristic oscillation frequency, νmax, from their radial velocity time series observed by SONG. For two stars, we are also able to measure the large frequency separation, Δν, helped by extended SONG single-site and dual-site observations and new Transiting Exoplanet Survey Satellite observations. We establish the robustness of the νmax-only-based results by determining the stellar mass from Δν, and from both Δν and νmax. We then compare the seismic masses of the full ensemble of 16 stars with the spectroscopic masses from three different literature sources. We find an offset between the seismic and spectroscopic mass scales that is mass dependent, suggesting that the previously claimed overestimation of spectroscopic masses only affects stars more massive than about 1.6 M⊙.
... It would be worthwhile to apply our results to explore the implications of planetary survival in more detail. Schlaufman & Winn (2013) previously found evidence for tidal destruction of hot Jupiters around subgiant stars (out to P orb < 200 d), which requires very efficient dissipation Q ∼ 10 2 − 10 3 . Our results in § 5 and 6 and Fig. 8 indicate that inertial waves may be able to provide such efficient dissipation briefly as the stars evolve off the main sequence, depending on the rotation rate of the star, so it would be worthwhile to revisit this mechanism in more detail with a population-wide study. ...
We study tidal dissipation in stars with masses in the range throughout their evolution, including turbulent effective viscosity acting on equilibrium tides and inertial waves in convection zones, and internal gravity waves in radiation zones. We consider a range of stellar evolutionary models and incorporate the frequency-dependent effective viscosity acting on equilibrium tides based on the latest simulations. We compare the tidal flow and dissipation obtained with the conventional equilibrium tide, which is strictly invalid in convection zones, finding that the latter typically over-predicts the dissipation by a factor of 2-3. Dissipation of inertial waves is computed using a frequency-averaged formalism accounting for realistic stellar structure for the first time, and is the dominant mechanism for binary circularization and synchronization on the main sequence. Dissipation of gravity waves in the radiation zone assumes these waves to be fully damped (e.g.~by wave breaking), and is the dominant mechanism for planetary orbital decay. We calculate the critical planetary mass required for wave breaking as a function of stellar mass and age, and show that this mechanism predicts destruction of many hot Jupiters but probably not Earth-mass planets on the main sequence. We apply our results to compute tidal quality factors following stellar evolution, and tidal evolutionary timescales, for the orbital decay of hot Jupiters, and the spin synchronization and circularization of binary stars. We also provide predictions for shifts in transit arrival times due to tidally-driven orbital decay of hot Jupiters that may be detected with NGTS, TESS or PLATO.
One way to understand planet formation is through studying the correlations between planet occurrence rates and stellar mass. However, measuring stellar mass in the red giant regime is very difficult. In particular, the spectroscopic masses of certain evolved stars, often referred to as ”retired A-stars”, have been questioned in the literature. Efforts to resolve this mass controversy using spectroscopy, interferometry and asteroseismology have so far been inconclusive. A recent ensemble study found a mass-dependent mass offset, but the result was based on only 16 stars. With NASA’s Transiting Exoplanet Survey Satellite (TESS), we expand the investigation of the mass discrepancy to a total of 92 low-luminosity stars, synonymous with the retired A-stars. We measure their characteristic oscillation frequency, νmax, and the large frequency separation, Δν, from their TESS photometric time series. Using these measurements and asteroseismic scaling relations, we derive asteroseismic masses and compare them with spectroscopic masses from five surveys, to comprehensively study the alleged mass-dependent mass offset. We find a mass offset between spectroscopy and seismology that increases with stellar mass. However, we note that adopting the seismic mass scale does not have a significant effect on the planet occurrence-mass-metallicity correlation for the so-called retired A-stars. We also report seismic measurements and masses for 157 higher luminosity giants (mostly helium-core-burning) from the spectroscopic surveys.
White dwarf stars frequently experience external pollution by heavy elements, and yet the intrinsically carbon-enriched DQ spectral class members fail to exhibit this phenomenon, representing a decades-old conundrum. This study reports a high-resolution spectroscopic search for Ca ii in classical DQ white dwarfs, finding that these stars are stunted both in pollution frequency and heavy element mass fractions, relative to the wider population. Compared to other white dwarf spectral classes, the average external accretion rate is found to be at least three orders of magnitude lower in the DQ stars. Several hypotheses are considered which need to simultaneously account for (i) an apparent lack of accreted metals, (ii) a dearth of circumstellar planetary material, (iii) an observed deficit of unevolved companions in post-common envelope binaries, (iv) relatively low helium mass fractions, and remnant masses that appear smaller than for other spectral classes, (v) a high incidence of strong magnetism, and (vi) modestly older disc kinematics. Only one hypothesis is consistent with all these constraints, suggesting DQ white dwarfs are the progeny of binary evolution that altered both their stellar structures and their circumstellar environments. A binary origin is already suspected for the warmer and more massive DQ stars, and is proposed here as an inclusive mechanism to expose core carbon material, in a potential evolutionary unification for the entire DQ spectral class. In this picture, DQ stars are not descended from DA or DB white dwarfs that commonly host dynamically active planetary systems.
Before the launch of the Kepler Space Telescope, models of low-mass planet formation predicted that convergent type I migration would often produce systems of low-mass planets in low-order mean-motion resonances. Instead, Kepler discovered that systems of small planets frequently have period ratios larger than those associated with mean-motion resonances and rarely have period ratios smaller than those associated with mean-motion resonances. Both short-timescale processes related to the formation or early evolution of planetary systems and long-timescale secular processes have been proposed as explanations for these observations. Using a thin disk stellar population’s Galactic velocity dispersion as a relative age proxy, we find that Kepler-discovered multiple-planet systems with at least one planet pair near a period ratio suggestive of a second-order mean-motion resonance have a colder Galactic velocity dispersion and are therefore younger than both single-transiting and multiple-planet systems that lack planet pairs consistent with mean-motion resonances. We argue that a nontidal secular process with a characteristic timescale no less than a few hundred Myr is responsible for moving systems of low-mass planets away from second-order mean-motion resonances. Among systems with at least one planet pair near a period ratio suggestive of a first-order mean-motion resonance, only the population of systems likely affected by tidal dissipation inside their innermost planets has a small Galactic velocity dispersion and is therefore young. We predict that period ratios suggestive of mean-motion resonances are more common in young systems with 10 Myr ≲ τ ≲ 100 Myr and become less common as planetary systems age.
To understand giant planet formation, we need to focus on host stars close to , where the occurrence rate of these planets is the highest. In this initial study, we carry out pebble-driven core accretion planet formation modelling to investigate the trends and optimal conditions for the formation of giant planets around host stars in the range of . We find that giant planets are more likely to form in systems with a larger initial disk radius; higher disk gas accretion rate; pebbles of ∼ millimeter in size; and birth location of the embryo at a moderate radial distance of ∼10 AU. We also conduct a population synthesis study of our model and find that the frequency of giant planets and super-Earths decreases with increasing stellar mass. This contrasts the observational peak at , stressing the need for strong assumptions on stellar mass dependencies in this range. Investigating the combined effect of stellar mass dependent disk masses, sizes, and lifetimes in the context of planet population synthesis studies is a promising avenue to alleviate this discrepancy. The hot-Jupiter occurrence rate in our models is around - similar to RV observations around Sun-like stars, but drastically decreases for higher mass stars.
The mass (M) of a star can be evaluated from its spectroscopically determined effective temperature () and metallicity ([Fe/H]) along with the luminosity (L; derived from parallax), while comparing them with grids of theoretical evolutionary tracks. It has been argued, however, that such a track-based mass () may tend to be overestimated for the case of red giants. Meanwhile, there is an alternative approach of evaluating mass () directly from surface gravity (g), L, and . The practical reliability of was examined for benchmark giants in the Kepler field, for which atmospheric parameters are already determined and the reliable mass () along with the evolutionary status are known from asteroseismology. In addition, similar check was also made for the accuracy of for comparison. It turned out that, while a reasonable correlation is seen between and almost irrespective of the stellar property, its precision is rather insufficient because distributes rather widely within –0.3 dex. In contrast, the reliability of was found to depend on the evolutionary status. Although and are satisfactorily consistent with each other (typical dispersion of is within ∼± 0.1 dex) for H-burning red giants as well as He-burning 2nd clump giants of higher mass, tends to be considerably overestimated as compared to by up to ≲ 0.4 dex for He-burning 1st clump giants of lower mass. Accordingly, and are complementary with each other in terms of their characteristic merit and demerit.
The rotation of a star and the revolutions of its planets are not necessarily aligned. This article reviews the measurement techniques, key findings, and theoretical interpretations related to the obliquities (spin-orbit angles) of planet-hosting stars. The best measurements are for stars with short-period giant planets, which have been found on prograde, polar, and retrograde orbits. It seems likely that dynamical processes such as planet-planet scattering and secular perturbations are responsible for tilting the orbits of close-in giant planets, just as those processes are implicated in exciting orbital eccentricities. The observed dependence of the obliquity on orbital separation, planet mass, and stellar structure suggests that in some cases, tidal dissipation damps a star's obliquity within its main-sequence lifetime. The situation is not as clear for stars with smaller or wider-orbiting planets. Although the earliest measurements of such systems tended to find low obliquities, some glaring exceptions are now known in which the star's rotation is misaligned with respect to the coplanar orbits of multiple planets. In addition, statistical analyses based on projected rotation velocities and photometric variability have found a broad range of obliquities for F-type stars hosting compact multiple-planet systems. The results suggest it is unsafe to assume that stars and their protoplanetary disks are aligned. Primordial misalignments might be produced by neighboring stars or more complex events that occur during the epoch of planet formation.
Context. Radial velocity surveys of evolved stars allow us to probe a higher stellar mass range, on average, compared to main-sequence samples. Hence, differences between the planet populations around the two target classes can be caused by either the differing stellar mass or stellar evolution. To properly disentangle the effects of both variables, it is important to characterize the planet population around giant stars as accurately as possible.
Aims. Our goal is to investigate the giant planet occurrence rate around evolved stars and determine its dependence on stellar mass, metallicity, and orbital period.
Methods. We combine data from three different radial velocity surveys targeting giant stars: the Lick giant star survey, the radial velocity program EXoPlanets aRound Evolved StarS (EXPRESS), and the Pan-Pacific Planet Search (PPPS), yielding a sample of 482 stars and 37 planets. We homogeneously rederived the stellar parameters of all targets and accounted for varying observational coverage, precision and stellar noise properties by computing a detection probability map for each star via injection and retrieval of synthetic planetary signals. We then computed giant planet occurrence rates as a function of period, stellar mass, and metallicity, corrected for incompleteness.
Results. Our findings agree with previous studies that found a positive planet-metallicity correlation for evolved stars and identified a peak in the giant planet occurrence rate as a function of stellar mass, but our results place it at a slightly smaller mass of (1.68 ± 0.59) M ⊙ . The period dependence of the giant planet occurrence rate seems to follow a broken power-law or log-normal distribution peaking at (718 ± 226) days or (797 ± 455) days, respectively, which roughly corresponds to 1.6 AU for a 1 M ⊙ star and 2.0 AU for a 2 M ⊙ star. This peak could be a remnant from halted migration around intermediate-mass stars, caused by stellar evolution, or an artifact from contamination by false positives. The completeness-corrected global occurrence rate of giant planetary systems around evolved stars is 10.7% −1.6% +2.2% for the entire sample, while the evolutionary subsets of RGB and HB stars exhibit 14.2% −2.7% +4.1% and 6.6% −1.3% +2.1% , respectively. However, both subsets have different stellar mass distributions and we demonstrate that the stellar mass dependence of the occurrence rate suffices to explain the apparent change of occurrence with the evolutionary stage.
We present 127 new transit light curves for 39 hot Jupiter systems, obtained over the span of 5 yr by two ground-based telescopes. A homogeneous analysis of these newly collected light curves together with archived spectroscopic, photometric, and Doppler velocimetric data using EXOFASTv2 leads to a significant improvement in the physical and orbital parameters of each system. All of our stellar radii are constrained to accuracies of better than 3%. The planetary radii for 37 of our 39 targets are determined to accuracies of better than 5%. Compared to our results, the literature eccentricities are preferentially overestimated due to the Lucy-Sweeney bias. Our new photometric observations therefore allow for significant improvement in the orbital ephemerides of each system. Our correction of the future transit window amounts to a change exceeding 10 minutes for 10 targets at the time of James Webb Space Telescope's launch, including a 72 minutes change for WASP-56. The measured transit midtimes for both literature light curves and our new photometry show no significant deviations from the updated linear ephemerides, ruling out in each system the presence of companion planets with masses greater than 0.39-5.0 M⊕, 1.23-14.36 M⊕, 1.65-21.18 M⊕, and 0.69-6.75 M⊕ near the 1:2, 2:3, 3:2, and 2:1 resonances with the hot Jupiters, respectively, at a confidence level of ±1σ. The absence of resonant companion planets in the hot Jupiter systems is inconsistent with the conventional expectation from disk migration. © 2021. The American Astronomical Society. All rights reserved.
Context. Most exoplanets detected so far are close-in planets, which are likely to be affected by tidal dissipation in their host star. To obtain a complete picture of the evolution of star–planet systems, we need to consider the effect of tides within stellar radiative and convective zones.
Aims. We aim to provide a general formalism allowing us to assess tidal dissipation in stellar radiative zones for late- and early-type stars, including stellar structure with a convective core and an envelope like in F-type stars. This allows us to study the dynamics of a given system throughout the stellar evolution. On this basis, we investigate the effect of stellar structure and evolution on tidal dissipation in the radiative core of low-mass stars.
Methods. We developed a general theoretical formalism to evaluate tidal dissipation in stellar radiative zones that is applicable to early- and late-type stars. From the study of adiabatic oscillations throughout the star, we computed the energy flux transported by progressive internal gravity waves and the induced tidal torque. By relying on grids of stellar models, we studied the effect of stellar structure and evolution on the tidal dissipation of F-, G-, and K-type stars from the pre-main sequence (PMS) to the red giant branch (RGB).
Results. For a given star–planet system, tidal dissipation reaches a maximum value on the PMS for all stellar masses. On the main sequence (MS), it decreases to become almost constant. The dissipation is then several orders of magnitude smaller for F-type than for G- and K-type stars. During the subgiant phase and the RGB, tidal dissipation increases by several orders of magnitude, along with the expansion of the stellar envelope. We show that the dissipation of the dynamical tide in the convective zone dominates the evolution of the system during most of the PMS and the beginning of the MS, as the star rotates rapidly. Tidal dissipation in the radiative zone then becomes the strongest contribution during the subgiant phase and the RGB as the density at the convective-radiative interface increases. For similar reasons, we also find that the dissipation of a metal-poor star is stronger than the dissipation of a metal-rich star during the PMS, the subgiant phase, and the RGB. The opposite trend is observed during the MS. Finally, we show that the contribution of a convective core for the most massive solar-type stars is negligible compared to that of the envelope because the mass distribution of the core does not favor the dissipation of tidal gravity waves.
In the past few years, significant advances have been made in understanding the distributions of exoplanet populations and the architecture of planetary systems. We review the recent progress of planet statistics, with a focus on the inner ≲1-AU region of the planetary system that has been fairly thoroughly surveyed by the Kepler mission. We also discuss the theoretical implications of these statistical results for planet formation and dynamical evolution.
Expected final online publication date for the Annual Review of Astronomy and Astrophysics, Volume 59 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Context. As part of the search for planets around evolved stars, we can understand planet populations around significantly higher-mass stars than the Sun on the main sequence. This population is difficult to study any other way, such as using radial-velocities to measure planet masses and orbital mechanics, since the stars are too hot and rotate too fast to present the quantity of narrow stellar spectral lines that is necessary for measuring velocities at the level of a few m s ⁻¹ .
Aims. Our goal is to estimate stellar parameters for all of the giant stars from the EXPRESS project, which aims to detect planets orbiting evolved stars, and study their occurrence rate as a function of stellar mass.
Methods. We analysed the high-resolution echelle spectra of these stars and computed their atmospheric parameters by measuring the equivalent widths for a set of iron lines, using an updated method implemented during this work. Physical parameters, such as mass and radius, were computed by interpolating through a grid of stellar evolutionary models, following a procedure that carefully takes into account the post-main sequence evolutionary phases. The atmospheric parameters, as well as the photometric and parallax data, are used as constraints during the interpolation process. The probabilities of the star being in the red giant branch (RGB) or the horizontal branch (HB) are estimated from the derived distributions.
Results. We obtained atmospheric and physical stellar parameters for the whole EXPRESS sample, which comprises a total of 166 evolved stars. We find that 101 of them are most likely first ascending the RGB phase, while 65 of them have already reached the HB phase. The mean derived mass is 1.41 ± 0.46 M ⊙ and 1.87 ± 0.53 M ⊙ for RGB and HB stars, respectively. To validate our method, we compared our derived physical parameters with data from interferometry and asteroseismology studies. In particular, when comparing to stellar radii derived from interferometric angular diameters, we find: Δ R inter = −0.11 R ⊙ , which corresponds to a 1.7% difference. Similarly, when comparing with asteroseismology, we obtain the following results: Δ log g = 0.07 cgs (2.4%), Δ R = −0.12 R ⊙ (1.5%), Δ M = 0.08 M ⊙ (6.2%), and Δage = −0.55 Gyr (11.9%). Additionally, we compared our derived atmospheric parameters with previous spectroscopic studies. We find the following results: Δ T eff = 22 K (0.5%), Δ log g = −0.03 (1.0%) and Δ[Fe/H] = −0.04 dex (2%). We also find a mean systematic difference in the mass with respect to those presented in the EXPRESS original catalogue of Δ M = −0.28 ± 0.27 M ⊙ , corresponding to a systematic mean difference of 16%. For the rest of the atmospheric and physical parameters we find a good agreement between the original catalogue and the results presented here. Finally, we find excellent agreement between the spectroscopic and trigonometric log g values, showing the internal consistency and robustness of our method.
Conclusions. We show that our method, which includes a re-selection of iron lines and changes in the interpolation of evolutionary models, as well as Gaia parallaxes and newer extinction maps, can greatly improve the estimates of stellar parameters for giant stars compared to those presented in our previous work. This method also results in smaller mass estimates, an issue that has been described in results for giant stars from spectroscopy studies in the literature. The results provided here will improve the physical parameter estimates of planetary companions found orbiting these stars and give us insights into their formation and the effect of stellar evolution on their survival.
We report the discovery of planetary companions orbiting four low-luminosity giant stars with M ⋆ between 1.04 and 1.39 M ⊙ . All four host stars have been independently observed by the EXoPlanets aRound Evolved StarS (EXPRESS) program and the Pan-Pacific Planet Search (PPPS). The companion signals were revealed by multi-epoch precision radial velocities obtained in nearly a decade. The planetary companions exhibit orbital periods between ~1.2 and 7.1 yr, minimum masses of m p sin i ~ 1.8–3.7 M J , and eccentricities between 0.08 and 0.42. With these four new systems, we have detected planetary companions to 11 out of the 37 giant stars that are common targets in the EXPRESS and PPPS. After excluding four compact binaries from the common sample, we obtained a fraction of giant planets ( m p ≳ 1– 2 M J ) orbiting within 5 AU from their parent star of f = 33.3 −7.1 +9.0 %. This fraction is slightly higher than but consistent at the 1 σ level with previous results obtained by different radial velocity surveys. Finally, this value is substantially higher than the fraction predicted by planet formation models of gas giants around stars more massive than the Sun.
We report precise Doppler measurements of seven subgiants from Keck Observatory. All seven stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. The host stars have masses ranging from 1.1 ≤ / ≤ 1.9 , radii 3.4 ≤ / ≤ 6.1 , and metallicities -0.21 ≤ [Fe/H] ≤ +0.26 . The planets are all more massive than Jupiter ( sin > 1 ) and have semimajor axes > 1 AU . We present millimagnitude photometry from the T3 0.4 m APT at Fairborn Observatory for five of the targets. Our monitoring shows these stars to be photometrically stable, further strengthening the interpretation of the observed radial velocity variability. The orbital characteristics of the planets thus far discovered around former A-type stars are very different from the properties of planets around dwarf stars of spectral type F, G, and K, and suggests that the formation and migration of planets is a sensitive function of stellar mass. Three of the planetary systems show evidence of long-term, linear trends indicative of additional distant companions. These trends, together with the high planet masses and increased occurrence rate, indicate that A-type stars are very promising targets for direct-imaging surveys.
We report on the detection of four extrasolar planets orbiting evolved intermediate-mass stars from a precise Doppler survey
of G-K giants at Okayama Astrophysical Observatory. All of the host stars are considered to be formerly early F-type or A-type
dwarfs when they were on the main sequence. 14 And (K0 III) is a clump giant with a mass of 2.2 and has a planet of minimum mass sini = 4.8 in a nearly circular orbit with a 186d period. This is one of the innermost planets around evolved intermediate-mass stars,
and such planets have only been discovered in clump giants. 81 Cet (G5 III) is a clump giant with 2.4 hosting a planet of sini = 5.3 in a 953d orbit with an eccentricity of e= 0.21. 6 Lyn (K0 IV) is a less-evolved subgiant with 1.7, and has a planet of sini = 2.4 in a 899d orbit with e= 0.13. HD167042 (K1 IV) is also a less-evolved star with 1.5 hosting a planet of sini = 1.6 in a 418d orbit with e= 0.10. This planet was independently announced by Johnson et al. (2008, ApJ, 675, 784). All of the host stars have solar or sub-solar metallicity, which supports the lack of a metal-rich tendency
in planet-harboring giants in contrast to the case of dwarfs.
Aims: Our primary goal is to search for planets around intermediate mass stars. We are also interested in studying the nature of radial velocity (RV) variations of K giant stars. Methods: We selected about 55 early K giant (K0-K4) stars brighter than fifth magnitude that were observed using BOES, a high resolution spectrograph attached to the 1.8 m telescope at BOAO (Bohyunsan Optical Astronomy Observatory). BOES is equipped with I 2 absorption cell for high precision RV measurements. Results: We detected a periodic radial velocity variations in the K0 III star gamma1 Leonis with a period of P = 429 days. An orbital fit of the observed RVs yields a period of P = 429 days, a semi-amplitude of K = 208 ms-1, and an eccentricity of e = 0.14. To investigate the nature of the RV variations, we analyzed the photometric, Ca II lambda 8662 equivalent width, and line-bisector variations of gamma1 Leonis. We conclude that the detected RV variations can be best explained by a planetary companion with an estimated mass of m sin i = 8.78 M_Jupiter and a semi-major axis of a = 1.19 AU, assuming a stellar mass of 1.23 M&sun;. ARRAY(0x382ecc0)
Received; accepted Abstract. Our aim is to confirm the nature of the long period radial velocity measurements forGem first found by Hatzes & Cochran (1993). We present precise stellar radial velocity measurements for the K giant starGem spanning over 25 years. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry was also made to discern the true nature of the long period radial velocity variations. The radial velocity data show that the long period, low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. Furthermore, the Ca II K emission, spectral line bisectors, and Hipparcos photometry show no significant variations of these quantities with the radial velocity period. An orbital solution assuming a stellar mass of 1.7 M⊙ yields a period, P = 589.6 days, a minimum mass of 2.3 MJupiter, and a semi-major axis, a = 1.6 AU. The orbit is nearly circular (e = 0.02). The data presented here confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). � Gem is the sixth intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.
We report precise radial velocity measurements of the K giant ι Dra
(HD 137759, HR 5744, HIP 75458), carried out at Lick Observatory, which
reveal the presence of a substellar companion orbiting the primary star.
A Keplerian fit to the data yields an orbital period of about 536 days
and an eccentricity of 0.70. Assuming a mass of 1.05 Msolar
for ι Dra, the mass function implies a minimum companion mass
m2sini of 8.9 MJ, making it a planet candidate.
The corresponding semimajor axis is 1.3 AU. The nondetection of the
orbital motion by Hipparcos allows us to place an upper limit of 45
MJ on the companion mass, establishing the substellar nature
of the object. We estimate that transits in this system could occur
already for inclinations as low as 81.5d, as a result of the large
diameter of the giant star. The companion to ι Dra is the first
brown dwarf or planet found to orbit a giant rather than a main-sequence
star. Based on observations obtained at Lick Observatory, which is
operated by the University of California.
Aims. The purpose of the present study is to research the origin of planetary
companions by using a precise radial velocity (RV) survey.
Methods. The high-resolution spectroscopy of the fiber-fed Bohyunsan
Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy
Observatory (BOAO) is used from September 2008 to June 2012.
Results. We report the detection of two exoplanets in orbit around HD 208527
and HD 220074 exhibiting periodic variations in RV of 875.5 +/- 5.8 and 672.1
+/- 3.7 days. The RV variations are not apparently related to the surface
inhomogeneities and a Keplerian motion of the planetary companion is the most
likely explanation. Assuming possible stellar masses of 1.6 +/- 0.4 and 1.2 +/-
0.3 M_Sun, we obtain the minimum masses for the exoplanets of 9.9 +/- 1.7 and
11.1 +/- 1.8 M_Jup around HD 208527 and HD 220074 with an orbital semi-major
axis of 2.1 +/- 0.2 and 1.6 +/- 0.1 AU and an eccentricity of 0.08 and 0.14,
respectively. We also find that the previously known spectral classification of
HD 208527 and HD 220074 was in error: Our new estimation of stellar parameters
suggest that both HD 208527 and HD 220074 are M giants. Therefore, HD 208527
and HD 220074 are so far the first candidate M giants to harbor a planetary
companion.
We report the detection of a giant planet in a 6.4950 day orbit around the 1.68 M ☉ subgiant HD 102956. The planet has a semimajor axis a = 0.081 AU and a minimum mass MP sin i =0.96 M Jup. HD 102956 is the most massive star known to harbor a hot Jupiter, and its planet is only the third known to orbit within 0.6 AU of a star more massive than 1.5 M ☉. Based on our sample of 137 subgiants with M >1.45 M ☉, we find that 0.5%-2.3% of A-type stars harbor a close-in planet (a < 0.1 AU) with MP sin i > 1 M Jup, consistent with hot-Jupiter occurrence for Sun-like stars. Thus, the paucity of planets with 0.1 AU < a < 1.0 AU around intermediate-mass stars may be an exaggerated version of the "period valley" that is characteristic of planets around Sun-like stars.
We present an analysis of ~5 years of Lick Observatory radial velocity measurements targeting a uniform sample of 31 intermediate-mass (IM) subgiants (1.5 M
*/M
☉ 2.0) with the goal of measuring the occurrence rate of Jovian planets around (evolved) A-type stars and comparing the distributions of their orbital and physical characteristics to those of planets around Sun-like stars. We provide updated orbital solutions incorporating new radial velocity measurements for five known planet-hosting stars in our sample; uncertainties in the fitted parameters are assessed using a Markov-Chain Monte Carlo method. The frequency of Jovian planets interior to 3 AU is 26+9–8%, which is significantly higher than the 5%-10% frequency observed around solar-mass stars. The median detection threshold for our sample includes minimum masses down to {0.2, 0.3, 0.5, 0.6, 1.3} M
Jup within {0.1, 0.3, 0.6, 1.0, 3.0} AU. To compare the properties of planets around IM stars to those around solar-mass stars we synthesize a population of planets based on the parametric relationship dN ∝ M
αP
βdlnMdlnP, the observed planet frequency, and the detection limits we derived. We find that the values of α and β for planets around solar-type stars from Cumming et al. fail to reproduce the observed properties of planets in our sample at the 4σ level, even when accounting for the different planet occurrence rates. Thus, the properties of planets around A stars are markedly different than those around Sun-like stars, suggesting that only a small (~50%) increase in stellar mass has a large influence on the formation and orbital evolution of planets.
We report the detection of a planetary-mass companion to the G9 III giant star HD 104985 from precise Doppler velocity measurements made using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. The radial velocity variability of this star is best explained by an orbital motion with a period of 198.2 ± 0.3 days, a velocity semiamplitude of 161 ± 2 m s-1, and an eccentricity of 0.03 ± 0.02. Assuming a stellar mass of 1.6 M☉, we obtained a minimum mass and a semimajor axis of 6.3MJ and 0.78 AU, respectively, for the companion. A probable upper limit to the stellar mass of 3 M☉ yielded m2 sin i = 9.6MJ, which falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.
We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong Station and Okayama Astrophysical Observatory (OAO) reveal Keplerian velocity variations with an orbital period of 326.03 ± 0.32 days, a semiamplitude of 302.8 ± 2.6 m s−1, and an eccentricity of 0.231 ± 0.005. Adopting a stellar mass of 2.7 ± 0.3 M☉, the minimum mass of the companion is 19.4 ± 1.5 MJ, well above the deuterium-burning limit, and the semimajor axis is 1.29 ± 0.05 AU. This is the first result from a joint planet-search program between China and Japan aimed at revealing the statistics of substellar companions around intermediate-mass giants. 11 Com b emerged from 300 targets of the planet-search program at OAO. The program's current detection rate of brown dwarf candidates seems to be comparable to the rate of such detections around solar-type stars with orbital separations of 3 AU.
We report the detection of 18 Jovian planets discovered as part of our Doppler survey of subgiant stars at Keck Observatory, with follow-up Doppler and photometric observations made at McDonald and Fairborn Observatories, respectively. The host stars have masses 0.927 ≤ M
/M
☉ ≤ 1.95, radii 2.5 ≤ R
/R
☉ ≤ 8.7, and metallicities –0.46 ≤ [Fe/H] ≤+0.30. The planets have minimum masses 0.9 M
Jup ≤ MPsin i 13 M
Jup and semimajor axes a ≥ 0.76 AU. These detections represent a 50% increase in the number of planets known to orbit stars more massive than 1.5 M
☉ and provide valuable additional information about the properties of planets around stars more massive than the Sun.
We report precise Doppler measurements of two stars, obtained at Lick Observatory as part of our search for planets orbiting intermediate-mass subgiants. Periodic variations in the radial velocities of both stars reveal the presence of substellar orbital companions. These two stars are notably massive with stellar masses of 1.80 and 1.64 M⊙, respectively, indicating that they are former A-type dwarfs that have evolved off of the main sequence and are now K-type subgiants. The planet orbiting K CrB has a minimum mass Mp sin i = 1.8 MJup, eccentricity e = 0.146 and a 1208 day period, corresponding to a semimajor axis a = 2.7 AU. The planet around HD 167042 has a minimum mass Mp sin i = 1.7 MJup and a 412.6 day orbit, corresponding to a semimajor axis a = 1.3 AU. The eccentricity of HD 167042b is consistent with circular (e = 0.027 ± 0.04), adding to the rare class of known exoplanets in long-period, circular orbits similar to the solar system gas giants. Like all of the planets previously discovered around evolved A stars, K CrBb and HD 167042b orbit beyond 0.8 AU. © 2008. The American Astronomical Society. All rights reserved.
We report radial velocity (RV) measurements of the G-type subgiants 24 Sextanis (= HD 90043) and HD 200964. Both are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets. Photometric monitoring with the T12 0.80 m APT at Fairborn Observatory demonstrates both stars to be constant in brightness to ≤0.002 mag, thus strengthening the planetary interpretation of the RV variations. Based on our dynamical analysis of the RV time series, 24 Sex b, c have orbital periods of 452.8 days and 883.0 days, corresponding to semimajor axes 1.333 AU and 2.08 AU, and minimum masses 1.99 M
Jup and 0.86 M
Jup, assuming a stellar mass M
= 1.54 M
☉. HD 200964 b, c have orbital periods of 613.8 days and 825.0 days, corresponding to semimajor axes 1.601 AU and 1.95 AU, and minimum masses 1.99 M
Jup and 0.90 M
Jup, assuming M
= 1.44 M
☉. We also carry out dynamical simulations to properly account for gravitational interactions between the planets. Most, if not all, of the dynamically stable solutions include crossing orbits, suggesting that each system is locked in a mean-motion resonance that prevents close encounters and provides long-term stability. The planets in the 24 Sex system likely have a period ratio near 2:1, while the HD 200964 system is even more tightly packed with a period ratio close to 4:3. However, we caution that further RV observations and more detailed dynamical modeling will be required to provide definitive and unique orbital solutions for both cases, and to determine whether the two systems are truly resonant.
We introduce the Pan-Pacific Planet Search, a survey of 170 metal-rich
Southern hemisphere subgiants using the 3.9m Anglo-Australian Telescope. We
report the first discovery from this program, a giant planet orbiting 7 CMa (HD
47205) with a period of 763+/-17 days, eccentricity e=0.14+/-0.06, and m sin
i=2.6+/-0.6 M_jup. The host star is a K giant with a mass of 1.5+/-0.3 M_sun
and metallicity [Fe/H]=0.21+/-0.10. The mass and period of 7 CMa b are typical
of planets which have been found to orbit intermediate-mass stars (M*>1.3
M_sun). Hipparcos photometry shows this star to be stable to 0.0004 mag on the
radial-velocity period, giving confidence that this signal can be attributed to
reflex motion caused by an orbiting planet.
We report the detection of five Jovian-mass planets orbiting high-metallicity stars. Four of these stars were first observed as part of the N2K program, and exhibited low rms velocity scatter after three consecutive observations. However, follow-up observations over the last 3 years now reveal the presence of longer period planets with orbital periods ranging from 21 days to a few years. HD 11506 is a G0 V star with a planet of M sin i = 4.74 MJup in a 3.85 yr orbit. HD 17156 is a G0 V star with a 3.12 MJup planet in a 21.2 day orbit. The eccentricity of this orbit is 0.67, one of the highest known for a planet with a relatively short period. The orbital period for this planet places it in a region of parameter space where relatively few planets have been detected. HD 125612 is a G3 V star with a planet of M sin i = 3.5 MJup in a 1.4 yr orbit. HD 170469 is a G5 IV star with a planet of M sin i = 0.67 MJup in a 3.13 year orbit. HD 231701 is an F8 V star with planet of 1.08 MJup in a 142 day orbit. All of these stars have supersolar metallicity. Three of the five stars were observed photometrically, but showed no evidence of brightness variability. A transit search conducted for HD 17156 was negative, but covered only 25% of the search space, and so is not conclusive.
We report precision Doppler measurements of three intermediate-mass subgiants obtained at Lick and Keck Observatories. All three stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. We find a planet with a minimum mass MP sin i = 2.5 MJ in a 351.5 day orbit around HD 192699, a planet with a minimum mass of 2.0 MJ in a 341.1 day orbit around HD 210702, and a planet with a minimum mass of 0.61 MJ in a 297.3 day orbit around HD 175541. Mass estimates from stellar interior models indicate that all three stars were formerly A-type, main-sequence dwarfs with masses ranging from 1.65 to 1.85 M☉. These three long-period planets would not have been detectable during their stars' main-sequence phases due to the large rotational velocities and stellar jitter exhibited by early-type dwarfs. There are now nine "retired" (evolved) A-type stars (M* > 1.6 M☉) with known planets. All nine planets orbit at distances a ≥ 0.78 AU, which is significantly different from the semimajor axis distribution of planets around lower mass stars.
We present a catalog of nearby exoplanets. It contains the 172 known low-mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc. We include five previously unpublished exoplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148, and HD 164922. We update orbits for 83 additional exoplanets, including many whose orbits have not been revised since their announcement, and include radial velocity time series from the Lick, Keck, and Anglo-Australian Observatory planet searches. Both these new and previously published velocities are more precise here due to improvements in our data reduction pipeline, which we applied to archival spectra. We present a brief summary of the global properties of the known exoplanets, including their distributions of orbital semimajor axis, minimum mass, and orbital eccentricity.
We have recently carried out spectral synthesis modeling to determine Teff, log g, v sin i, and [Fe/H] for 1040 FGK-type stars on the Keck, Lick, and Anglo-Australian Telescope planet search programs. This is the first time that a single, uniform spectroscopic analysis has been made for every star on a large Doppler planet search survey. We identify a subset of 850 stars that have Doppler observations sufficient to detect uniformly all planets with radial velocity semiamplitudes K > 30 m s-1 and orbital periods shorter than 4 yr. From this subset of stars, we determine that fewer than 3% of stars with -0.5 < [Fe/H] < 0.0 have Doppler-detected planets. Above solar metallicity, there is a smooth and rapid rise in the fraction of stars with planets. At [Fe/H] > +0.3 dex, 25% of observed stars have detected gas giant planets. A power-law fit to these data relates the formation probability for gas giant planets to the square of the number of metal atoms. High stellar metallicity also appears to be correlated with the presence of multiple-planet systems and with the total detected planet mass. This data set was examined to better understand the origin of high metallicity in stars with planets. None of the expected fossil signatures of accretion are observed in stars with planets relative to the general sample: (1) metallicity does not appear to increase as the mass of the convective envelopes decreases, (2) subgiants with planets do not show dilution of metallicity, (3) no abundance variations for Na, Si, Ti, or Ni are found as a function of condensation temperature, and (4) no correlations between metallicity and orbital period or eccentricity could be identified. We conclude that stars with extrasolar planets do not have an accretion signature that distinguishes them from other stars; more likely, they are simply born in higher metallicity molecular clouds.
We report the discovery of two new planets: a 1.94 MJup planet in a 1.8 yr orbit of HD 5319, and a 2.51 MJup planet in a 1.1 yr orbit of HD 75898. The measured eccentricities are 0.12 for HD 5319b and 0.10 for HD 75898b, and Markov chain Monte Carlo simulations based on the derived orbital parameters indicate that the radial velocities of both stars are consistent with circular planet orbits. With low eccentricity and 1 AU < a < 2 AU, our new planets have orbits similar to terrestrial planets in the solar system. The radial velocity residuals of both stars have significant trends, likely arising from substellar or low-mass stellar companions.
Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd called into question the masses of subgiant stars targeted by Doppler surveys. Lloyd argues that very few observable subgiants have masses greater than 1.5 M
☉, and that most of them have masses in the range 1.0-1.2 M
☉. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to negligibly small systematic errors in stellar mass estimates, in contrast to the ≈50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars with masses greater than 1.5 M
☉, primarily because the inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 M
☉. We conclude that, within the context of our present-day understanding of stellar structure and evolution, many of the subgiants observed in Doppler surveys are indeed as massive as main-sequence A stars.
We present radial velocities with an accuracy of 0.1 km/s for 2046 stars of
spectral type F,G,K, and M, based on 29000 spectra taken with the Keck I
telescope. We also present 131 FGKM standard stars, all of which exhibit
constant radial velocity for at least 10 years, with an RMS less than 0.03
km/s. All velocities are measured relative to the solar system barycenter.
Spectra of the Sun and of asteroids pin the zero-point of our velocities,
yielding a velocity accuracy of 0.01 km/s for G2V stars. This velocity
zero-point agrees within 0.01 \kms with the zero-points carefully determined by
Nidever et al. (2002) and Latham et al. (2002). For reference we compute the
differences in velocity zero-points between our velocities and standard stars
of the IAU, the Harvard-Smithsonian Center for Astrophysics, and l'Observatoire
de Geneve, finding agreement with all of them at the level of 0.1 km/s. But our
radial velocities (and those of all other groups) contain no corrections for
convective blueshift or gravitational redshifts (except for G2V stars), leaving
them vulnerable to systematic errors of 0.2 \kms for K dwarfs and ~0.3 km/s for
M dwarfs due to subphotospheric convection, for which we offer velocity
corrections. The velocities here thus represent accurately the radial component
of each star's velocity vector. The radial velocity standards presented here
are designed to be useful as fundamental standards in astronomy. They may be
useful for Gaia (Crifo et al. 2010, Gilmore et al. 2012} and for dynamical
studies of such systems as long-period binary stars, star clusters, Galactic
structure, and nearby galaxies, as will be carried out by SDSS, RAVE, APOGEE,
SkyMapper, HERMES, and LSST.
The discovery of a planetary companion to the intermediate-mass late-type giant star HD173416 from precise Doppler surveys of G and K giants at Xinglong station and Okayama Astrophysical Observatory (OAO) is presented in this letter. The planet has a minimum mass of 2.7 M J , an eccentricity of 0.21, a semimajor axis of 1.16 AU and an orbital period of 324 days.
We report the discovery of a unique object, BD+48 740, a lithium overabundant
giant with A(Li)=2.33 +/- 0.04 (where A(Li) = log(n_Li/n_H) + 12), that
exhibits radial velocity (RV) variations consistent with a 1.6 M_J companion in
a highly eccentric, e = 0.67 +/- 0.17 and extended, a=1.89 AU (P=771 d), orbit.
The high eccentricity of the planet is uncommon among planetary systems
orbiting evolved stars and so is the high lithium abundance in a giant star.
The ingestion by the star of a putative second planet in the system originally
in a closer orbit, could possibly allow for a single explanation to these two
exceptional facts. If the planet candidate is confirmed by future RV
observations, it might represent the first example of the remnant of a multiple
planetary system possibly affected by stellar evolution.
The Pulkovo Compilation of Radial Velocities (PCRV) has been made to study the stellar kinematics in the local spiral arm.
The PCRV contains weighted mean absolute radial velocities for 35 495 Hipparcos stars of various spectral types and luminosity
classes over the entire celestial sphere mainly within 500 pc of the Sun. The median accuracy of the radial velocities obtained
is 0.7 km s−1. Results from 203 publications were used in the catalogue. Four of them were used to improve the radial velocities of standard
stars from the IAU list. The radial velocities of 155 standard stars turned out to be constant within 0.3 km s−1. These stars were used to analyze 47 768 mean radial velocities for 37 200 stars from 12 major publications (∼80% of all
the data used). Zero-point discrepancies and systematic dependences on radial velocity, B-V color index, right ascension, and declination were found in radial velocity differences of the form “publication minus IAU
list of standards.” These discrepancies and dependences were approximated and taken into account when calculating the weighted
mean radial velocities. 1128 stars whose independent radial-velocity determinations were available at least in three of these
publications and agreed within 3 km s−1 were chosen as the work list of secondary standards. Radial-velocity differences of the form “publication minus list of secondary
standards” were used by analogy to correct the zero points and systematic dependences in the radial velocities from 33 more
publications (∼ 13% of the data used). In addition, the radial velocities from 154 minor publications (∼7% of the data used)
pertaining to well-known instruments were used without any corrections.
We use precise radial velocity measurements and photometric data to derive
the frequency spacing of the p-mode oscillation spectrum of the planet-hosting
star Beta Gem. This spacing along with the interferometric radius for this star
is used to derive an accurate stellar mass. A long time series of over 60 hours
of precise stellar radial velocity measurements of Beta Gem were taken with an
iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred
Jensch Telescope. Complementary photometric data for this star were also taken
with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial
velocity data reveals the presence of up to 17 significant pulsation modes in
the frequency interval 10-250 micro-Hz. Most of these fall on a grid of
equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An
analysis of 3.6 days of high precision photometry taken with the MOST space
telescope shows the presence of up to 16 modes, six of which are consistent
with modes found in the spectral (radial velocity) data. This frequency spacing
is consistent with high overtone radial pulsations; however, until the
pulsation modes are identified we cannot be sure if some of these are nonradial
modes or even mixed modes. The radial velocity frequency spacing along with
angular diameter measurements of Beta Gem via interferometry results in a
stellar mass of M = 1.91 +/- 0.09 solar masses. This value confirms the
intermediate mass of the star determined using stellar evolutionary tracks.
Beta Gem is confirmed to be an intermediate mass star. Stellar pulsations in
giant stars along with interferometric radius measurements can provide accurate
determinations of the stellar mass of planet hosting giant stars. These can
also be used to calibrate stellar evolutionary tracks.
We determine the fraction of F, G, and K dwarfs in the Solar Neighborhood
hosting hot jupiters as measured by the California Planet Survey from the Lick
and Keck planet searches. We find the rate to be 1.2\pm0.38%, which is
consistent with the rate reported by Mayor et al. (2011) from the HARPS and
CORALIE radial velocity surveys. These numbers are more than double the rate
reported by Howard et al. (2011) for Kepler stars and the rate of Gould et al.
(2006) from the OGLE-III transit search, however due to small number statistics
these differences are of only marginal statistical significance. We explore
some of the difficulties in estimating this rate from the existing radial
velocity data sets and comparing radial velocity rates to rates from other
techniques.
A precise radial velocity survey conducted by a Korean-Japanese planet search
program revealed a planetary companion around the intermediate-mass clump giant
HD 100655. The radial velocity of the star exhibits a periodic Keplerian
variation with a period, semi-amplitude and eccentricity of 157.57 d, 35.2 m
s^-1 and 0.085, respectively. Adopting an estimated stellar mass of 2.4 M_Sun,
we confirmed the presence of a planetary companion with a semi-major axis of
0.76 AU and a minimum mass of 1.7 M_Jup. The planet is the lowest-mass planet
yet discovered around clump giants with masses greater than 1.9 M_Sun.
The Hipparcos and Tycho Catalogues are the primary products of the
European Space Agency's astrometric mission, Hipparcos. The satellite,
which operated for four years, returned high quality scientific data
from November 1989 to March 1993.
Each of the catalogues contains a large quantity of very high quality
astrometric and photometric data. In addition there are associated
annexes featuring variability and double/multiple star data, and solar
system astrometric and photometric measurements. In the case of the
Hipparcos Catalogue, the principal parts are provided in both printed
and machine-readable form (on CDROM). In the case of the Tycho
Catalogue, results are provided in machine-readable form only (on
CDROM). Although in general only the final reduced and calibrated
astrometric and photometric data are provided, some auxiliary files
containing results from intermediate stages of the data processing, of
relevance for the more-specialised user, have also been retained for
publication. (Some, but not all, data files are available from the
Centre de Donnees astronomiques de Strasbourg.)
The global data analysis tasks, proceeding from nearly 1000 Gbit of raw
satellite data to the final catalogues, was a lengthy and complex
process, and was undertaken by the NDAC and FAST Consortia, together
responsible for the production of the Hipparcos Catalogue, and the Tycho
Consortium, responsible for the production of the Tycho Catalogue. A
fourth scientific consortium, the INCA Consortium, was responsible for
the construction of the Hipparcos observing programme, compiling the
best-available data for the selected stars before launch into the
Hipparcos Input Catalogue. The production of the Hipparcos and Tycho
Catalogues marks the formal end of the involvement in the mission by the
European Space Agency and the four scientific consortia.
For more complete and detailed information on the data, the user is
advised to refer to Volume 1 ("Introduction and Guide to the Data", ESA
SP-1200) of the printed Hipparcos and Tycho Catalogues. The user should
also note that in order to convert the Double and Multiple Systems
(Component solutions) data file hipdmc.dat into FITS format
it is first necessary to filter the file according to whether the entry
is a component record (identified by COMP in field DCM5) or a
correlation record (identified by CORR in field DCM5) because of the
different structures of the respective records. On a Unix system this
can be achieved as follows:
grep COMP hipdmc.dat > hdmcom.dat grep CORR
hipdmc.dat > hdmcor.dat
The catalogue description file (this file) gives the relevant
information for converting the main data files, including
hdmcor.dat and hdmcom.dat, into FITS format.
The machine readable data files (i.e. those available on CD-ROM and the
subset available from the CDS) contain several extra fields in addition
to the data from the printed catalogue. These fields are identified by
the letter `M' in the data label (e.g. the field DGM1 contains data only
available in the machine readable file hipdmg.dat).
(19 data files).
The new reduction of the Hipparcos data presents a very significant
improvement in the overall reliability of the astrometric catalogue
derived from this mission. Improvements by up to a factor 4 in the
accuracies for in particular brighter stars have been obtained. This has
been achieved mainly through careful study of the satellite dynamics,
and incorporating results from these studies in the attitude modelling.
Data correlations, caused by attitude-modelling errors in the original
catalogue, have all but disappeared. This book provides overviews of the
new reduction as well as on the use of the Hipparcos data in a variety
of astrophysical implementations. A range of new results, like cluster
distances and luminosity calibrations, is presented. The Hipparcos data
provide a unique opportunity for the study of satellite dynamics. The
orbit covered a wide range of altitudes, showing in detail the different
torques acting on the satellite. One part of the book details these
studies and their impact on the new reduction. It furthermore presents
an extensive summary on a wide range of spacecraft and payload
calibrations, which provide a detailed record of the conditions under
which these unique Hipparcos data have been obtained. The book is
accompanied by a DVD with the new catalogue and the underlying data.
Link:
http://www.springer.com/east/home?SGWID=5-102-22-173741445-0&changeHeader=true
Context: 11 UMi and HD 32518 belong to a sample of 62 K giant stars that
has been observed since February 2004 using the 2m Alfred Jensch
telescope of the Thüringer Landessternwarte (TLS) to measure
precise radial velocities (RVs). Aims: The aim of this survey is
to investigate the dependence of planet formation on the mass of the
host star by searching for planetary companions around intermediate-mass
giants. Methods: An iodine absorption cell was used to obtain
accurate RVs for this study. Results: Our measurements reveal
that the RVs of 11 UMi show a periodic variation of 516.22 days with a
semiamplitude of K = 189.70 m s-1. An orbital solution yields
a mass function of f(m) = (3.608 ± 0.441) × 10-7
solar masses (M⊙) and an eccentricity of e = 0.083
± 0.03. The RV curve of HD 32518 shows sinusoidal variations with
a period of 157.54 days and a semiamplitude of K = 115.83 m
s-1. An orbital solution yields an eccentricity, e = 0.008
± 0.03 and a mass function, f(m) = (2.199 ± 0.235) ×
10-8 M⊙. The HIPPARCOS photometry as well as
our Hα core flux measurements reveal no variability with the RV
period. Thus, Keplerian motion is the most likely explanation for the
observed RV variations for both giant stars. Conclusions: An
exoplanet with a “minimum mass” of m sin i = 10.50 ±
2.47 Jupiter masses (MJup) orbits the K giant 11 UMi. The K1
III giant HD 32518 hosts a planetary companion with a “minimum
mass” of m sin i = 3.04 ± 0.68 MJup in a nearly
circular orbit. These are the 4th and 5th planets published from this
TLS survey.
Tables 2 and 5 are only available in electronic form at the CDS via
anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/505/1311
The radial velocity and spectral variations are calculated for
low-amplitude nonradial pulsations in slowly rotating stars (v sin i = 3
km s^-1). Sectoral modes (l = -m) in the range l = 1-8 are considered.
An empirical equation relating the pulsational amplitude to the
"observed" stellar radial velocity amplitude is derived and this
indicates that precise radial velocity techniques should be able to
detect low-amplitude (<1 km s^-1) pulsations for sectoral modes as
high as l = 6. The spectral variations manifest themselves via changes
in the span and curvature of the line bisector which are maximized for m
= 4. These spectral variations can be used to distinguish between radial
velocity variations due to pulsations from those due to the reflex
motion of the star caused by the presence of a low-mass companion.
However, these measurements require data taken at high resolution
(lambda/delta-lambad > 100,000) and high signal-to-noise ratios (S/N
> 500). (SECTION: Stars)
Precise relative radial velocities were measured for three K giants
Alpha Tau, Alpha Boo, and Beta Gem to detect planetary companions.
Results reveal strong evidence for long term periodic behavior in the
radial velocities: 233 days for Alpha Boo, 643 days for Alpha Tau, and
558 days for Beta Gem. These periods are considered to be too long to be
due to radial pulsations. The fact that all three stars exhibit similar
periods and give comparable companion masses suggests that the
variability is intrinsic to the star (either rotational modulation or
pulsations).
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THE recent discovery1 and confirmation2 of a possible planetary companion orbiting the solar-type star 51 Pegasi represent a breakthrough in the search for extrasolar planetary systems. Analysis of systematic variations in the velocity of the star indicate that the mass of the companion is approximately that of Jupiter, and that it is travelling in a nearly circular orbit at a distance from the star of 0.05 AU (about seven stellar radii). Here we show that, if the companion is indeed a gas-giant planet, it is extremely unlikely to have formed at its
present location. We suggest instead that the planet probably formed by gradual accretion of solids and capture of gas at a much larger distance from the star (~5 AU), and that it subsequently migrated inwards through interactions with the remnants of the circumstellar disk. The planet's migration may have stopped in its present orbit as a result of tidal interactions with the star, or through truncation of the inner circumstellar disk by the stellar magnetosphere.
This paper reviews the rich corpus of observational evidence for tidal
effects, mostly based on photometric and radial-velocity measurements.
This is done in a period when the study of binaries is being
revolutionized by large-scaled photometric surveys that are detecting
many thousands of new binaries and tens of extrasolar planets.
We begin by examining the short-term effects, such as ellipsoidal
variability and apsidal motion. We next turn to the long-term
effects, of which circularization was studied the most: a transition
period between circular and eccentric orbits has been derived for
eight coeval samples of binaries. The study of synchronization and
spin-orbit alignment is less advanced. As binaries are supposed to
reach synchronization before circularization, one can expect finding
eccentric binaries in pseudo-synchronization state, the evidence for
which is reviewed. We also discuss synchronization in PMS and young
stars, and compare the emerging timescale with the circularization
timescale.
We next examine the tidal interaction in close binaries that are
orbited by a third distant companion, and review the effect of
pumping the binary eccentricity by the third star. We elaborate on the
impact of the pumped eccentricity on the tidal evolution of close
binaries residing in triple systems, which may shrink the binary separation.
Finally we consider the extrasolar planets and the observational
evidence for tidal interaction with their parent stars. This includes
a mechanism that can induce radial drift of short-period planets,
either inward or outward, depending on the planetary radial position
relative to the corotation radius. Another effect is the
circularization of planetary orbits, the evidence for which can be
found in eccentricity-versus-period plot of the planets already known.
Whenever possible, the paper attempts to address the possible
confrontation between theory and observations, and to point out
noteworthy cases and observations that can be performed in the future
and may shed some light on the key questions that remain open.
We present a uniform catalog of stellar properties for 1040 nearby F, G, and K stars that have been observed by the Keck, Lick, and AAT planet search programs. Fitting observed echelle spectra with synthetic spectra yielded effective temperature, surface gravity, metallicity, projected rotational velocity, and abundances of the elements Na, Si, Ti, Fe, and Ni, for every star in the catalog. Combining V-band photometry and Hipparcos parallaxes with a bolometric correction based on the spectroscopic results yielded stellar luminosity, radius, and mass. Interpolating Yonsei-Yale isochrones to the luminosity, effective temperature, metallicity, and α-element enhancement of each star yielded a theoretical mass, radius, gravity, and age range for most stars in the catalog. Automated tools provide uniform results and make analysis of such a large sample practical. Our analysis method differs from traditional abundance analyses in that we fit the observed spectrum directly, rather than trying to match equivalent widths, and we determine effective temperature and surface gravity from the spectrum itself, rather than adopting values based on measured photometry or parallax. As part of our analysis, we determined a new relationship between macroturbulence and effective temperature on the main sequence. Detailed error analysis revealed small systematic offsets with respect to the Sun and spurious abundance trends as a function of effective temperature that would be inobvious in smaller samples. We attempted to remove these errors by applying empirical corrections, achieving a precision per spectrum of 44 K in effective temperature, 0.03 dex in metallicity, 0.06 dex in the logarithm of gravity, and 0.5 km s-1 in projected rotational velocity. Comparisons with previous studies show only small discrepancies. Our spectroscopically determined masses have a median fractional precision of 15%, but they are systematically 10% higher than masses obtained by interpolating isochrones. Our spectroscopic radii have a median fractional precision of 3%. Our ages from isochrones have a precision that varies dramatically with location in the Hertzsprung-Russell diagram. We plan to extend the catalog by applying our automated analysis technique to other large stellar samples.
We report the detection of an extrasolar planet orbiting Tau, one of the giant stars in the Hyades open cluster. This is the first planet ever discovered in an open cluster. Precise Doppler measurements of this star from Okayama Astrophysical Observatory have revealed Keplerian velocity variations with an orbital period of 594.9 ± 5.3 days, a semiamplitude of 95.9 ± 1.8 m s-1, and an eccentricity of 0.151 ± 0.023. The minimum mass of the companion is 7.6 ± 0.2 MJ, and the semimajor axis is 1.93 ± 0.03 AU adopting a stellar mass of 2.7 ± 0.1 M☉. The age of 625 Myr for the cluster sets the most secure upper limit ever on the timescale of giant planet formation. The mass of 2.7 M☉ for the host star is robustly determined by isochrone fitting, which makes the star the heaviest among planet-harboring stars. Putting together the fact that no planets have been found around about 100 low-mass dwarfs in the cluster, the frequency of massive planets is suggested to be higher around high-mass stars than around low-mass ones.
The ever-expanding depth and quality of photometric and spectroscopic observations of stellar populations increase the need for theoretical models in regions of age-composition parameter space that are largely unexplored at present. Stellar evolution models that employ the most advanced physics and cover a wide range of compositions are needed to extract the most information from current observations of both resolved and unresolved stellar populations. The Dartmouth Stellar Evolution Database is a collection of stellar evolution tracks and isochrones that spans a range of [Fe/H] from –2.5 to +0.5, [α/Fe] from –0.2 to +0.8 (for [Fe/H] ≤ 0) or +0.2 (for [Fe/H] > 0), and initial He mass fractions from Y = 0.245 to 0.40. Stellar evolution tracks were computed for masses between 0.1 and 4 M☉, allowing isochrones to be generated for ages as young as 250 Myr. For the range in masses where the core He flash occurs, separate He-burning tracks were computed starting from the zero age horizontal branch. The tracks and isochrones have been transformed to the observational plane in a variety of photometric systems including standard UBV(RI)C, Stromgren uvby, SDSS ugriz, 2MASS JHKs, and HST ACS/WFC and WFPC2. The Dartmouth Stellar Evolution Database is accessible through a Web site at http://stellar.dartmouth.edu/~models/ where all tracks, isochrones, and additional files can be downloaded.
We report on the detection of a planetary companion in orbit around the primary star of the binary system γ Cephei. High-precision radial velocity measurements using four independent data sets spanning the time interval 1981-2002 reveal long-lived residual radial velocity variations superposed on the binary orbit that are coherent in phase and amplitude with a period or 2.48 yr (906 days) and a semiamplitude of 27.5 m s-1. We performed a careful analysis of our Ca II H and K S-index measurements, spectral line bisectors, and Hipparcos photometry. We found no significant variations in these quantities with the 906 day period. We also reanalyzed the Ca II λ8662 measurements of Walker et al., which showed possible periodic variations with the "planet" period when first published. This analysis shows that periodic Ca II equivalent width variations were only present during 1986.5-1992 and absent during 1981-1986.5. Furthermore, a refined period for the Ca II λ8662 variations is 2.14 yr, significantly less than the residual radial velocity period. The most likely explanation of the residual radial velocity variations is a planetary-mass companion with M sin i = 1.7MJ and an orbital semimajor axis of a2 = 2.13 AU. This supports the planet hypothesis for the residual radial velocity variations for γ Cep first suggested by Walker et al. With an estimated binary orbital period of 57 yr, γ Cep is the shortest period binary system in which an extrasolar planet has been found. This system may provide insights into the relationship between planetary and binary star formation.
We present rotational and radial velocities for a sample of 761 giants selected from the Hipparcos Catalogue to lie within 100 pc of the Sun. Our original goal was to examine stellar rotation in field giants using spectroscopic line broadening to look for evidence of excess rotation that could be attributed to planets that were engulfed as the parent stars expanded. Thus we were obliged to investigate other sources of line broadening, including tidal coupling in close binaries and macroturbulence. For all the binaries in our sample with periods shorter than 20 days the orbits have been circularized, while about half the orbits with periods in the range 20-100 days still show significant eccentricity. All our primaries in orbits shorter than 30 days show line broadening consistent with synchronized rotation, while about half the primaries with periods in the range 30-120 days are synchronized. To study the dependence of rotation on stellar evolution when tidal effects are not important, we used a subsample of single stars and members in wide binaries. We found evidence to suggest that the first dredge-up may play a role in speeding up the rotation of the observable outer layers of giants and that the rotational velocity of horizontal branch stars is larger by a few km s−1 than that of first-ascent giants with similar mass, effective temperature, and radius. Finally, we found three giants that rotate more rapidly than expected. We conjecture that they acquired their excess angular momentum by ingesting planets.
Recent radial-velocity surveys for GK clump giants have revealed that planets also exist around ~1.5-3 M
☉ stars. However, no planets have been found inside 0.6 AU around clump giants, in contrast to solar-type main-sequence stars, many of which harbor short-period planets such as hot Jupiters. In this study, we examine the possibility that planets were engulfed by host stars evolving on the red-giant branch (RGB). We integrate the orbital evolution of planets in the RGB and helium-burning phases of host stars, including the effects of stellar tide and stellar mass loss. Then we derive the critical semimajor axis (or the survival limit) inside which planets are eventually engulfed by their host stars after tidal decay of their orbits. Specifically, we investigate the impact of stellar mass and other stellar parameters on the survival limit in more detail than previous studies. In addition, we make detailed comparisons with measured semimajor axes of planets detected so far, which no previous study has done. We find that the critical semimajor axis is quite sensitive to stellar mass in the range between 1.7 and 2.1 M
☉, which suggests a need for careful comparison between theoretical and observational limits of the existence of planets. Our comparison demonstrates that all planets orbiting GK clump giants that have been detected are beyond the survival limit, which is consistent with the planet-engulfment hypothesis. However, on the high-mass side (>2.1M
☉), the detected planets are orbiting significantly far from the survival limit, which suggests that engulfment by host stars may not be the main reason for the observed lack of short-period giant planets. To confirm our conclusion, the detection of more planets around clump giants, especially with masses 2.5M
☉, is required.
We report homogeneous spectroscopic determinations of the effective temperature, metallicity, and projected rotational velocity for the host stars of 56 transiting planets. Our analysis is based primarily on the stellar parameter classification (SPC) technique. We investigate systematic errors by examining subsets of the data with two other methods that have often been used in previous studies (Spectroscopy Made Easy (SME) and MOOG). The SPC and SME results, both based on comparisons between synthetic spectra and actual spectra, show strong correlations between T
eff, [Fe/H], and log g when solving for all three quantities simultaneously. In contrast the MOOG results, based on a more traditional curve-of-growth approach, show no such correlations. To combat the correlations and improve the accuracy of the temperatures and metallicities, we repeat the SPC analysis with a constraint on log g based on the mean stellar density that can be derived from the analysis of the transit light curves. Previous studies that have not taken advantage of this constraint have been subject to systematic errors in the stellar masses and radii of up to 20% and 10%, respectively, which can be larger than other observational uncertainties, and which also cause systematic errors in the planetary mass and radius.
This paper describes three-dimensional (3D) large eddy simulations of stellar surface convection using realistic model physics.
The simulations include the present Sun, a subgiant of one solar mass and a lower-gravity subgiant, also of one solar mass.
We examine the thermal structure (superadiabaticity) after modification by 3D turbulence, the overshoot of convective motions
into the radiative atmosphere and the range of convection cell sizes. Differences between models based on the mixing length
theory (MLT) and the simulations are found to increase significantly in the more evolved stages as the surface gravity decreases.
We find that the full width at half maximum (FWHM) of the turbulent vertical velocity correlation provides a good objective
measure of the vertical size of the convective cells. Just below the convection surface, the FWHM is close to the mean vertical
size of the granules and 2 × FWHM is close to the mean horizontal diameter of the granules. For the Sun, 2 × FWHM = 1200 km,
a value close to the observed mean granule size. For all the simulations, the mean horizontal diameter is close to 10 times
the pressure scaleheight at the photospheric surface, in agreement with previous work.
Precise stellar radial velocity (RV) measurements (σ≈ 20 m s-1 ) spanning more than 2 yr are presented for the K giant star π Herculis. These show variability with a period of 613 ± 57 d and an amplitude of 150 ± 12 m s-1 . Radial pulsations can be excluded as a mechanism for this variability because the observed period is more than an order of magnitude greater than the expected period of the fundamental radial mode. Tenable hypotheses for the RV variability include rotational modulation by surface structure, non-radial pulsations, or a substellar companion of mass at least 27 MJupiter in orbit 3 au from the star. An upper limit of 1400 d to the rotational period for π Herculis is determined using published values of the angular diameter and distance to π Herculis as well as an estimate of the projected rotational velocity. Rotational modulation is thus a viable mechanism for the RV variability. The RV variations were also fitted using two models: (i) a stellar surface covered with cool spots and (ii) non-radial pulsations. Both models could adequately reproduce the RV curve although the spot model predicts photometric variations of Δ V ∼ 0.1 mag. As a result of the long period, non-radial pulsations may be g-mode or r-mode oscillations, which implies that most of the atmospheric motion of the star is in the horizontal direction. If these modes are indeed present then the corresponding photometric amplitude for non-radial pulsations may be quite small. The radial velocity variations were also measured using subsections of the spectral region. Weak spectral lines yielded an RV amplitude of ≈ 140 m s-1 whereas the stronger lines yielded an RV amplitude of ≈ 220 m s-1 with a phase shift of about 60 ° with respect to the weaker lines. This seems to support the pulsation hypothesis as the cause of the RV variability, although an analysis of more lines is needed to confirm this. Also, a period of 90.3 d with an amplitude 50 m s-1 is found in the residual RV measurements after subtracting the 613-d component. The presence of two periods also argues in favour of non-radial pulsations, although at the present time one cannot exclude low-mass companions or surface structure as a cause for at least one of the observed periods. Photometric measurements as well as detailed analysis of the changes in the spectral line shapes using high-resolution data may be required to distinguish between the companion object and non-radial pulsation hypotheses.
We present analytic formulae that approximate the evolution of stars for a wide range of mass M and metallicity Z. Stellar luminosity, radius and core mass are given as a function of age, M and Z, for all phases from the zero-age main sequence up to, and including, the remnant stages. For the most part we find continuous
formulae accurate to within 5 per cent of detailed models. These formulae are useful for purposes such as population synthesis
that require very rapid but accurate evaluation of stellar properties, and in particular for use in combination with N-body codes. We describe a mass-loss prescription that can be used with these formulae, and investigate the resulting stellar
remnant distribution.
Self-consistent evolutionary models were computed for our Sun, using Los
Alamos interior opacities and Sharp molecular opacities, starting with
contraction on the Hayashi track, and fitting the observed present solar
L, R, and Z/X at the solar age. This resulted in presolar Y = 0.274 and
Z = 0.01954, and in present solar 37Cl and 71Ga
neutrino capture rates of 6.53 and 123 SNU, respectively.
We explored the Sun's future. While on the hydrogen-burning main
sequence, the Sun's luminosity grows from 0.7 Lsun, 4.5 Gyr
ago, to 2.2 Lsun, 6.5 Gyr from now. A luminosity of 1.1
Lsun will be reached in 1.1 Gyr, and 1.4 Lsun in
3.5 Gyr; at these luminosities, Kasting predicts "moist greenhouse" and
"runaway greenhouse" catastrophes, respectively, using a cloud-free
climate model of the Earth; clouds could delay these catastrophes
somewhat. As the Sun ascends the red giant branch (RGB), its convective
envelope encompasses 75% of its mass (diluting remaining 7Li
by two orders of magnitude; 4He is enhanced by 8%,
3He by a factor of 5.7, 13C by a factor of 3, and
14N by a factor of 1.5). The Sun eventually reaches a
luminosity of 2300 Lsun and a radius of 170 Rsun
on the RGB, shedding 0.275 Msun and engulfing the planet
Mercury. After the horizontal branch stage (core helium burning), the
Sun climbs the asymptotic giant branch (AGB), encountering four thermal
pulses there; at the first thermal pulse, the Sun reaches its largest
radial extent of 213 Rsun (0.99 AU), which is surprisingly
close to Earth's present orbit. However, at this point the Sun's mass
has been reduced to 0.591 Msun, and the orbits of Venus and
Earth have moved out to 1.22 and 1.69 AU, respectively they both escape
being engulfed. The Sun reaches a peak luminosity of 5200
Lsun at the fourth thermal pulse. It ends up as a white dwarf
with a final mass of 0.541 Msun, shifting the orbits of the
planets outward such that Venus and Earth end up at 1.34 and 1.85 AU,
respectively. These events on the AGB are strongly mass-loss dependent;
somewhat less mass loss can result in engulfment of Venus, or even
Earth. Our preferred mass-loss rate was a Reimers wind with a mass-loss
parameter η = 0.6 normalized from inferred mass loss in globular
cluster stars. For reasonable mass-loss rates (0.8 > η > 0.4),
the Sun's final white dwarf mass is between 0.51 and 0.58
Msun.
The Sun spends 11 Gyr on the main sequence, 0.7 Gyr cooling toward the
RGB, 0.6 Gyr ascending the RGB, 0.1 Gyr on the horizontal branch, 0.02
Gyr on the early AGB, 0.0004 Gyr on the thermally pulsing AGB, and
0.0001 Gyr on the traverse to the planetary nebula stage (the last three
of these time scales depend sensitively on the amount of mass loss).