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Revised orbits of the two nearest Jupiters
Abstract
With its near-to-mid-infrared high-contrast imaging capabilities, JWST is ushering us into a golden age of directly imaging Jupiter-like planets. As the two closest cold Jupiters, ε Ind A b and ε Eridani b have sufficiently wide orbits and adequate infrared emissions to be detected by JWST. To detect more Jupiter-like planets for direct imaging, we develop a gost-based method to analyse radial velocity data and multiple Gaia data releases simultaneously. Without approximating instantaneous astrometry by catalogue astrometry, this approach enables the use of multiple Gaia data releases for detection of both short-period and long-period planets. We determine a mass of MJup and a period of yr for ε Ind A b. We also find a mass of MJup , a period of yr, and an eccentricity of 0.26 MJup, for ε Eridani b. The eccentricity differs from that given by some previous solutions, probably due to the sensitivity of orbital eccentricity to noise modelling. Our work refines the constraints on orbits and masses of the two nearest Jupiters and demonstrate the feasibility of using multiple Gaia data releases to constrain Jupiter-like planets.
... By minimising the difference between fitted and catalog astrometry, we are able to uncover the nonlinear reflex motion of a star. This approach has been successfully applied to refine the orbits of cold Jupiters around nearby stars (e.g., Ind A b and Eridani b, Feng et al. 2023). In this study, we present the discovery of a long-period super-Jupiter, orbiting a metal-poor nearby star HD 222237 on an eccentric orbit. ...
... Since the Gaia IAD is not available, we use GOST to predict the Gaia observations. The choice of Hipparcos version has negligible impact on our analyses, because we directly model the systematics in Hipparcos IAD using offsets and jitters for a given target (see Appendix B), and we are focusing on the temporal baseline between two satellites (∼ 25 yr) when applying for long-period systems (Feng et al. 2023). ...
... The complete methodology of jointly modelling RV and astrometry has been detailed in our previous work (Feng et al. 2019b(Feng et al. , 2021(Feng et al. , 2023; therefore, we provide a relatively brief introduction about the basic process. Further theoretical formulations can be found in the Appendix B. ...
Giant planets on long period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g., transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located pc away. By combining RV data, Hipparcos and multi-epoch Gaia astrometry, we estimate the planetary mass to be , with an eccentricity of and a period of yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F1550C filter () is approximately , which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star () combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet-metallicity correlation and the formation scenarios of giant planets.
... 3)). A long-term radial-velocity trend 4,5 and an astrometric acceleration 6,7 led to claims of a giant planet 2,8,9 orbiting the nearby star (3.6384 ± 0.0013 pc; ref. 10). Here we report JWST coronagraphic images which reveal a giant exoplanet that is consistent with these radial and astrometric measurements but inconsistent with the previously claimed planet properties. ...
... We observed Eps Ind A with the mid-infrared instrument (MIRI) 11 coronagraph onboard the James Webb Space Telescope ( JWST) on 3 July 2023 using two narrowband filters (10.65 and 15.50 µm). Figure 1 shows a bright point source detected in the north-east quadrant at a separation of 4.11″. This is the opposite quadrant than expected based on previous orbital solutions 2,8,9 . The source is unresolved, has apparent magnitudes 13.16 and 11.20 mag at 10.65 and 15.50 µm, and is consistent with a cold, Jupiter-sized object at the host star distance. ...
... These orbits are also consistent with all in-hand dynamical data. Curiously, several previous works had derived properties of the claimed planet Eps Ind Ab and found consistent results 2,8,9 , but these results are inconsistent with the planet observed in this work. This may be due to overfitting of the in-hand data, as fitting accurate orbits with insufficient orbital phase coverage is notoriously hard 56 , or it may hint at another component in the system that biased the previous one-planet fits. ...
Of the approximately 25 directly imaged planets to date, all are younger than 500 Myr, and all but six are younger than 100 Myr (ref. ¹). Eps Ind A (HD209100, HIP108870) is a K5V star of roughly solar age (recently derived as 3.7–5.7 Gyr (ref. ²) and 3.5−1.3+0.8 Gyr (ref. ³)). A long-term radial-velocity trend4,5 and an astrometric acceleration6,7 led to claims of a giant planet2,8,9 orbiting the nearby star (3.6384 ± 0.0013 pc; ref. ¹⁰). Here we report JWST coronagraphic images which reveal a giant exoplanet that is consistent with these radial and astrometric measurements but inconsistent with the previously claimed planet properties. The new planet has a temperature of approximately 275 K and is remarkably bright at 10.65 and 15.50 µm. Non-detections between 3.5 and 5.0 µm indicate an unknown opacity source in the atmosphere, possibly suggesting a high-metallicity, high carbon-to-oxygen ratio planet. The best-fitting temperature of the planet is consistent with theoretical thermal evolution models, which were previously untested at this temperature range. The data indicate that this is probably the only giant planet in the system, and therefore we refer to it as b, despite it having significantly different orbital properties than the previously claimed planet b.
... Following initial indications of a potential wide-orbit companion in the RV data (Endl et al. 2002), continued efforts have been made to monitor and image this companion, culminating in the first successful image captured by Matthews et al. (2024) using JWST/MIRI. The imaging of this system was guided by combined analyses of RV and Hipparcos-Gaia data (Feng et al. 2019b;Philipot et al. 2023a;Feng et al. 2023). The solutions and data from these studies are summarized in Table 2. ...
... We revisit the orbital solution of HD 28185 using the method developed in Feng et al. (2023) and applied in Xiao et al. (2024). By incorporating the astrometric contribution from the inner planet, HD 28185 b, with its year-long orbit, we derive the inclination and absolute mass of the inner companion. ...
The detection and constraint of the orbits of long-period giant planets is essential for enabling their further study through direct imaging. Recently, Venner et al. (2024) highlighted discrepancies between the solutions presented by Feng et al. (2022) and those from other studies, which primarily use orvara. We address these concerns by reanalyzing the data for HD 28185, GJ 229, HD 211847, GJ 680, HD 111031, and eps Ind A, offering explanations for these discrepancies. Based on a comparison between the methods used by Feng et al. (2022) and orvara, we find the discrepancies are primarily data-related rather than methodology-related. Our re-analysis of HD 28185 highlights many of the data-related issues and particularly the importance of parallax modeling for year-long companions. The case of eps Ind A b is instructive to emphasize the value of an extended RV baseline for accurately determining orbits of long period companions. Our orbital solutions highlight other causes for discrepancies between solutions including the combination of absolute and relative astrometry, clear definitions of conventions, and efficient posterior sampling for the detection of wide-orbit giant planets.
... To address the parallax inconsistency and to determine the inclination angle of the orbit, we analysed the Gaia catalogue data from both DR2 and DR3 as well as the RV data and sampled the posterior of the RV and astrometric models using the adaptive MCMC adapted from the Delayed-Rejection Adaptive Metropolis (DRAM) algorithm 6,23 . This method has been successfully applied to constrain the orbits of the two nearest Jupiter-like planets, ε Ind A b and ε Eridani b 24 . ...
The mass distribution of black holes identified through X-ray emission suggests a paucity of black holes in the mass range of 3 to 5 solar masses. Modified theories have been devised to explain this mass gap, and it is suggested that natal kicks during a supernova explosion can more easily disrupt binaries with lower-mass black holes. Although recent Laser Interferometer Gravitational-Wave Observatory observations reveal the existence of compact remnants within this mass gap, the question of whether low-mass black holes can exist in binaries remains a matter of debate. Such a system is expected to be non-interacting and without X-ray emission, and can be searched for using radial-velocity and astrometric methods. Here we report on Gaia Data Release 3 (DR3) 3425577610762832384, which is a wide binary system that includes a red giant star and an unseen object, exhibiting an orbital period of approximately 880 days and a near-zero eccentricity. Through the combination of radial-velocity measurements from the Large Aperture Multi-Object Spectroscopic Telescope and astrometric data from Gaia DR2 and DR3 catalogues, we determine a mass of of the unseen component. If the unseen companion is a black hole, its mass would fall within the gap and it would strongly suggest the existence of binary systems containing low-mass black holes. More notably, the formation of its surprisingly wide circular orbit challenges current binary evolution and supernova explosion theories.
... However, this method faces significant information loss in transforming astrometry into a propermotion anomaly, making it inadequate for constraining the mass of Jupiter analogs 4 and distinguishing between retrograde and prograde orbits (Li et al. 2021). To address this limitation, a method proposed by Feng et al. (2023) utilizes Gaia DR2 and DR3 five-parameter astrometry, along with Hipparcos intermediate astrometric data (IAD), combined with radial velocity data. This approach successfully constrains the orbit and mass of nearby Jupiter analogs, such as ò Eridani b, with a mass of 0.76 0.11 0.14 -+ M Jup and an orbital period of 7.36 0.05 0.04 -+ yr. ...
Hidden within the Gaia satellite’s multiple data releases lies a valuable cache of dark companions. To facilitate the efficient and reliable detection of these companions via combined analyses involving the Gaia, Hipparcos, and Tycho-2 catalogs, we introduce an astrometric modeling framework. This method incorporates analytical least-square minimization and nonlinear parameter optimization techniques to a set of common calibration sources across the different space-based astrometric catalogs. This enables us to discern the error inflation, astrometric jitter, differential parallax zero-points, and frame rotation of various catalogs relative to Gaia Data Release 3 (DR3). Our findings yield the most precise Gaia DR2 calibration parameters to date, revealing notable dependencies on magnitude and color. Intriguingly, we identify submilliarcsecond frame rotation between Gaia DR1 and DR3, along with an estimated astrometric jitter of 2.16 mas for the revised Hipparcos catalog. In a thorough comparative analysis with previous studies, we offer recommendations on calibrating and utilizing different catalogs for companion detection. Furthermore, we provide a user-friendly pipeline ( https://github.com/ruiyicheng/Download_HIP_Gaia_GOST ) for catalog download and bias correction, enhancing accessibility and usability within the scientific community.
... ò Indi A is orbited every ∼45 yr by a Jovian mass exoplanet, ò Indi Ab, which has been detected in both RV and astrometry (Feng et al. 2019). ò Indi Ab is the nearest cold Jupiter-type planet to Earth and its infrared emission is expected to be sufficiently high to be measured by JWST (Feng et al. 2023). ...
We have detected solar-like oscillations in the mid-K-dwarf ϵ Indi A, making it the coolest dwarf to have measured oscillations. The star is noteworthy for harboring a pair of brown dwarf companions and a Jupiter-type planet. We observed ϵ Indi A during two radial velocity campaigns, using the high-resolution spectrographs HARPS (2011) and UVES (2021). Weighting the time series, we computed the power spectra and established the detection of solar-like oscillations with a power excess located at 5265 ± 110 μ Hz—the highest frequency solar-like oscillations so far measured in any star. The measurement of the center of the power excess allows us to compute a stellar mass of 0.782 ± 0.023 M ⊙ based on scaling relations and a known radius from interferometry. We also determine the amplitude of the peak power and note that there is a slight difference between the two observing campaigns, indicating a varying activity level. Overall, this work confirms that low-amplitude solar-like oscillations can be detected in mid-K-type stars in radial velocity measurements obtained with high-precision spectrographs.
The detection of stellar variability often relies on the measurement of selected activity indicators, such as coronal emission lines and nonthermal emissions. On the flip side, the effective stellar temperature is normally seen as one of the key fundamental parameters (with mass and radius) to understanding the basic physical nature of a star and its relation with its environment (e.g., planetary instellation). We present a novel approach for measuring disk-averaged temperature variations to sub-Kelvin accuracy inspired by algorithms developed for precision radial velocity (pRV). This framework uses the entire content of the spectrum, not just preidentified lines, and can be applied to existing data obtained with high-resolution spectrographs. We demonstrate the framework by recovering the known rotation periods and temperature modulation of Barnard star and AU Mic in data sets obtained in the infrared with SPIRou at CHFT and at optical wavelengths on ϵ Eridani with HARPS at ESO 3.6 m telescope. We use observations of the transiting hot Jupiter HD189733b, obtained with SPIRou, to show that this method can unveil the minute temperature variation signature expected during the transit event, an effect analogous to the Rossiter–McLaughlin effect but in temperature space. This method is a powerful new tool for characterizing stellar activity, and in particular temperature and magnetic features at the surfaces of cool stars, affecting both pRV and transit spectroscopic observations. We demonstrate this method in the context of high-resolution spectroscopy but it could be used at lower resolution.
Giant planets on long period orbits around the nearest stars are among the easiest to directly image. Unfortunately these planets are difficult to fully constrain by indirect methods, e.g., transit and radial velocity (RV). In this study, we present the discovery of a super-Jupiter, HD 222237 b, orbiting a star located 11.445 ± 0.002 pc away. By combining RV data, Hipparcos and multi-epoch Gaia astrometry, we estimate the planetary mass to be , with an eccentricity of and a period of yr, making HD 222237 b a promising target for imaging using the Mid-Infrared Instrument (MIRI) of JWST. A comparative analysis suggests that our method can break the inclination degeneracy and thus differentiate between prograde and retrograde orbits of a companion. We further find that the inferred contrast ratio between the planet and the host star in the F1550C filter () is approximately 1.9 × 10−4, which is comparable with the measured limit of the MIRI coronagraphs. The relatively low metallicity of the host star () combined with the unique orbital architecture of this system presents an excellent opportunity to probe the planet-metallicity correlation and the formation scenarios of giant planets.
This study aims to identify potential exoplanet signals from nearby stars with resolved debris discs. However, the high activity of many stars with debris discs limits the detection of periodic signals. Our study is constrained to a sample of 29 stars that have appropriate radial velocity data and debris disc measurements sufficient to resolve their inclination. Our results confirm and update previous findings for exoplanets around HD 10647, HD 115617, HD 69830, GJ 581, HD 22049, and HD 142091, and we identify long-term activity signals around HD 207129 and HD 202628. We utilize the inclination angles of the debris discs, assuming co-planarity between debris disc and exoplanet orbit, to determine the “disc-aligned” masses of radial velocity exoplanets in this study. The “disc-aligned” masses of HD 69830 b, HD 69830 c, and 61 Vir b suggests that they may be classified as ‘hot’ or ‘warm’ Jupiters and so might be nearby examples of planets that have undergone recent type-II disc migration.
The Closeby Habitable Exoplanet Survey (CHES) constitutes a mission intricately designed to systematically survey approximately 100 solar-type stars located within the immediate proximity of the solar system, specifically within a range of 10 pc. The core objective of this mission is the detection and characterization of potentially habitable Earth-like planets or super-Earths within the habitable zone of these stars. The CHES mission obtains high-precision astrometric measurements of planets orbiting the target stars by observing angular distance variations between the target star and reference stars. As a result, we surveyed the relevant parameters of both target and reference stars in detail, conducting a thorough analysis and calculation of the required observation accuracy, the number of observations, and the priority assigned to each target star. Observational emphasis will be concentrated on targets considered of higher priority, ensuring the effectiveness of their observation capabilities. Through this approach, we formulate a 5 yr observation strategy that will cover all the target stars within a 6 month time frame. The strategy not only fulfills the required observing capability but also exhibits high efficiency simultaneously, providing an executable program for future mission. Over the span of the mission’s 5 yr duration, a cumulative observation time of 29,220 hr will be available. Approximately 86% of this, totaling 25,120 hr, is allocated for the observation of target stars. This allocation leaves approximately 4100 hr for extended scientific observation programs. We have also performed simulated observations based on this strategy and verified its observational capability for exoplanets.
The detection of stellar variability often relies on the measurement of selected activity indicators such as coronal emission lines and non-thermal emissions. On the flip side, the effective stellar temperature is normally seen as one of the key fundamental parameters (with mass and radius) to understanding the basic physical nature of a star and its relation with its environment (e.g., planetary instellation). We present a novel approach for measuring disk-averaged temperature variations to sub-Kelvin accuracy inspired by algorithms developed for precision radial velocity. This framework uses the entire content of the spectrum, not just pre-identified lines, and can be applied to existing data obtained with high-resolution spectrographs. We demonstrate the framework by recovering the known rotation periods and temperature modulation of Barnard star and AU Mic in datasets obtained in the infrared with SPIRou at CHFT and at optical wavelengths on Eridani with HARPS at ESO 3.6-m telescope. We use observations of the transiting hot Jupiter HD189733\,b, obtained with SPIRou, to show that this method can unveil the minute temperature variation signature expected during the transit event, an effect analogous to the Rossiter-McLaughlin effect but in temperature space. This method is a powerful new tool for characterizing stellar activity, and in particular temperature and magnetic features at the surfaces of cool stars, affecting both precision radial velocity and transit spectroscopic observations. We demonstrate the method in the context of high-resolution spectroscopy but the method could be used at lower resolution.
The Closeby Habitable Exoplanet Survey (CHES) constitutes a mission intricately designed to systematically survey approximately 100 solar-type stars located within the immediate proximity of the solar system, specifically within a range of 10 parsecs. The core objective of this mission is the detection and characterization of potentially habitable Earth-like planets or super-Earths within the habitable zone of these stars. The CHES mission obtains high-precision astrometric measurements of planets orbiting the target stars by observing angular distance variations between the target star and reference stars. As a result, we surveyed the relevant parameters of both target and reference stars in detail, conducting a thorough analysis and calculation of the required observation accuracy, the number of observations, and the priority assigned to each target star. Observational emphasis will be concentrated on targets considered of higher priority, ensuring the effectiveness of their observation capabilities. Through this approach, we formulate a five-year observation strategy that will cover all the target stars within a six-month timeframe. The strategy not only fulfills the required observing capability but also exhibit high efficiency simultaneously, providing an executable program for future mission. Over the span of the mission's five-year duration, a cumulative observation time of 29,220 hours will be available. Approximately 86 percent of this, totaling 25,120 hours, is allocated for the observation of target stars. This allocation leaves approximately 4,100 hours for extended scientific observation programs. We have also performed simulated observations based on this strategy and verified its observational capability for exoplanets.
Context . Though efforts to detect them have been made with a variety of methods, no technique can claim a successful, confirmed detection of a moon outside the Solar System yet. Moon detection methods are restricted in capability to detecting moons of masses beyond what formation models would suggest, or they require surface temperatures exceeding what tidal heating simulations allow.
Aims . We expand upon spectroastrometry, a method that makes use of the variation of the centre of light with wavelength as the result of an unresolved companion, which has previously been shown to be capable of detecting Earth-analogue moons around nearby exo-Jupiters, with the aim to place bounds on the types of moons detectable using this method.
Methods . We derived a general, analytic expression for the spectroastrometric signal of a moon in any closed Keplerian orbit, as well as a new set of estimates on the noise due to photon noise, pointing inaccuracies, background and instrument noise, and a pixelated detector. This framework was consequently used to derive bounds on the temperature required for Solar System-like moons to be observable around super-Jupiters in nearby systems, with ∈ Indi Ab as an archetype.
Results . We show that such a detection is possible with the ELT for Solar System-like moons of moderate temperatures (150–300 K) in line with existing literature on tidal heating, and that the detection of large (Mars-sized or greater) icy moons of temperatures such as those observed in our Solar System in the very nearest systems may be feasible.
We revisit the Hipparcos 2007 re-reduction and find improvements to the catalog by leveraging Gaia EDR3. We show that including a constant residual offset and additional dispersion (two free parameters in total) in the Hipparcos 2007 IAD creates a new catalog with significantly better agreement with Gaia EDR3. The astrometric parameters, after recalibration, have z-scores that follow a unit-Gaussian when measured against Gaia EDR3 values. We have expanded the Python astrometry tool, htof, to recalibrate the IAD on-the-fly. On a second front, we find that a merged set of IAD from the 1997 and 2007 Hipparcos reductions is not possible in an internally consistent manner. This can be understood if Hipparcos 2007 is an improved, but overfit, model to the underlying along-scan data. For this reason, we recommend using the recalibrated Hipparcos 2007 astrometric parameters, or those from the Hipparcos-Gaia Catalog of Accelerations – because the signatures of overfitting are calibrated out. We advise caution in fitting orbits to the IAD from either Hipparcos 2 as-published or the recalibrated version presented here.
Introduction: The China Space Station Telescope (CSST) will enter a low Earth orbit around 2024 and operate for 10 years, with seven of those years devoted to surveying the area of the median-to-high Galactic latitude and median-to-high Ecliptic latitude of the sky. To maximize the scientific output of CSST, it is important to optimize the survey schedule. We aim to evaluate the astrometric capability of CSST for a given survey schedule and to provide independent suggestions for the optimization of the survey strategy.
Methods: We first construct the astrometric model and then conduct simulated observations based on the given survey schedule. The astrometric solution is obtained by analyzing the simulated observation data. And then we evaluate the astrometric capability of CSST by analyzing the properties of the astrometric solution.
Results: The accuracy of parallax and proper motion of CSST is better than 1 mas (⋅ yr ⁻¹ ) for the sources of 18–22 mag in g band, and about 1∼10 mas (⋅ yr ⁻¹ ) for the sources of 22–26 mag in g band, respectively. The results from real survey could be worse since the assumptions are optimistic and simple.
Discussion: Optimizing the survey schedule can improve the astrometric accuracy of CSST. In the future, we will improve the astrometric capability of CSST by continuously iterating and optimizing the survey schedule.
A wealth of Earth-sized exoplanets will be discovered in the coming years, providing a large pool of candidates from which the targets for the search for life beyond the solar system will be chosen. The target selection process will require the leveraging of all available information in order to maximize the robustness of the target list and make the most productive use of follow-up resources. Here, we present the results of a suite of n -body simulations that demonstrate the degree to which the orbital architecture of the solar system impacts the variability of Earth’s orbital elements. By varying the orbit of Jupiter and keeping the initial orbits of the other planets constant, we demonstrate how subtle changes in solar system architecture could alter the Earth’s orbital evolution—a key factor in the Milankovitch cycles that alter the amount and distribution of solar insolation, thereby driving periodic climate change on our planet. The amplitudes and frequencies of Earth’s modern orbital cycles fall in the middle of the range seen in our runs for all parameters considered—neither unusually fast nor slow, neither large nor small. This finding runs counter to the “Rare Earth” hypothesis, which suggests that conditions on Earth are so unusual that life elsewhere is essentially impossible. Our results highlight how dynamical simulations of newly discovered exoplanetary systems could be used as an additional means to assess the potential targets of biosignature searches, and thereby help focus the search for life to the most promising targets.
Context. Orbital motion in binary and planetary systems is the main source of precise stellar and planetary mass measurements, and the joint analysis of data obtained using multiple observational methods can both lift degeneracies and improve precision.
Aims. We set out to measure the masses of individual stars in binary systems using all the information brought by the H IPPARCOS and Gaia absolute astrometric missions.
Methods. We present BINARYS, a tool that uses the H IPPARCOS and Gaia absolute astrometric data and combines them with relative astrometry and/or radial velocity measurements to determine the orbit of a binary system. This tool rigorously combines the H IPPARCOS and Gaia data (here EDR3) and can use the H IPPARCOS Transit Data as needed for binaries where H IPPARCOS detects significant flux from the secondary component. It also supports the case where Gaia has resolved the system, giving an astrometric solution for both components.
Results. We determine model-independent individual masses for the first time for three systems: the two mature binaries Gl 494 ( M 1 = 0.584 ± 0.003 M ⊙ and M 2 = 87 ± 1 M Jup ) and HIP 88745 ( M 1 = 0.96 ± 0.02 M ⊙ and 0.62 -0.008 +0.009 ), and the younger AB Dor member GJ 2060 (1926 -6 ⁺⁷ and 0.882 -0.005 +0.004 ). The latter provides a rare test of evolutionary model predictions at young ages in the low-stellar-mass range and sets a lower age limit of 100 Myr for the moving group.
Context. Thanks to more than 20 years of monitoring, the radial velocity (RV) method has detected long-period companions (P > 10yr) around several dozens of stars. Yet, the true nature of these companions remains unclear because of the uncertainty as to the inclination of the companion orbital plane. Aims. We wish to constrain the orbital inclination and the true mass of long-period single companions. Methods. We used a Markov Chain Monte Carlo (MCMC) fitting algorithm to combine RV measurements with absolute astrometry and, when available, relative astrometry data. Results. We have lifted the sin(i) indetermination for 7 seven long-period companions. We find true masses in the planetary mass range for the candidate planets detected in the following systems: Epsilon Indi A, HD 13931, HD 115954, and HD 222155. The mass of HD 219077 b is close to the deuterium-burning limit and its nature is uncertain because of the imprecise mass of the host star. Using additional RV measurements, we refine the orbital parameters of HIP 70849 b and find a mass in the planetary range. By combining RV data with absolute and relative astrometry, we significantly improve the characterization of HD 211847 B and properly determine its mass, which appears to be in the low-mass star range. This work illustrates how Gaia and Hipparcos allow for the orbital properties and masses of long-period RV companions to be further constrained.
Context: Gaia DR3 time series data may contain spurious signals related to the time-dependent scan angle. Aims: We aim to explain the origin of scan-angle dependent signals and how they can lead to spurious periods, provide statistics to identify them in the data, and suggest how to deal with them in Gaia DR3 data and in future releases. Methods: Using real Gaia data, alongside numerical and analytical models, we visualise and explain the features observed in the data. Results: We demonstrated with Gaia data that source structure (multiplicity or extendedness) or pollution from close-by bright objects can cause biases in the image parameter determination from which photometric, astrometric and (indirectly) radial velocity time series are derived. These biases are a function of the time-dependent scan direction of the instrument and thus can introduce scan-angle dependent signals, which in turn can result in specific spurious periodic signals. Numerical simulations qualitatively reproduce the general structure observed in the spurious period and spatial distribution of photometry and astrometry. A variety of statistics allows for identification of affected sources. Conclusions: The origin of the scan-angle dependent signals and subsequent spurious periods is well-understood and is in majority caused by fixed-orientation optical pairs with separation <0.5" (amongst which binaries with P>>5y) and (cores of) distant galaxies. Though the majority of sources with affected derived parameters have been filtered out from the Gaia archive, there remain Gaia DR3 data that should be treated with care (e.g. gaia_source was untouched). Finally, the various statistics discussed in the paper can not only be used to identify and filter affected sources, but alternatively reveal new information about them not available through other means, especially in terms of binarity on sub-arcsecond scale.
The ESA global astrometry space mission Gaia has been monitoring the position of a billion stars since 2014. The analysis of such a massive dataset is challenging in terms of the data processing involved. In particular, the blind detection and characterization of single or multiple companions to stars (planets, brown dwarfs, or stars) using Gaia astrometry requires highly efficient algorithms. In this article, we present a set of analytical methods to detect and characterize companions in scanning space astrometric time series as well as via a combination of astrometric and radial velocity time series. We propose a general linear periodogram framework and we derive analytical formulas for the false alarm probability (FAP) of periodogram peaks. Once a significant peak has been identified, we provide analytical estimates of all the orbital elements of the companion based on the Fourier decomposition of the signal. The periodogram, FAP, and orbital elements estimates can be computed for the astrometric and radial velocity time series separately or in tandem. These methods are complementary with more accurate and more computationally intensive numerical algorithms (e.g., least-squares minimization, Markov chain Monte-Carlo, genetic algorithms). In particular, our analytical approximations can be used as an initial condition to accelerate the convergence of numerical algorithms. Our formalism has been partially implemented in the Gaia exoplanet pipeline for the third Gaia data release. Since the Gaia astrometric time series are not yet publicly available, we illustrate our methods on the basis of H ipparcos data, together with on-ground CORALIE radial velocities, for three targets known to host a companion: HD 223636 (HIP 117622), HD 17289 (HIP 12726), and HD 3277 (HIP 2790).
We analyze 5108 AFGKM stars with at least five high-precision radial velocity points, as well as Gaia and Hipparcos astrometric data, utilizing a novel pipeline developed in previous work. We find 914 radial velocity signals with periods longer than 1000 days. Around these signals, 167 cold giants and 68 other types of companions are identified, through combined analyses of radial velocity, astrometry, and imaging data. Without correcting for detection bias, we estimate the minimum occurrence rate of the wide-orbit brown dwarfs to be 1.3%, and find a significant brown-dwarf valley around 40 M Jup . We also find a power-law distribution in the host binary fraction beyond 3 au, similar to that found for single stars, indicating no preference of multiplicity for brown dwarfs. Our work also reveals nine substellar systems (GJ 234 B, GJ 494 B, HD 13724 b, HD 182488 b, HD 39060 b and c, HD 4113 C, HD 42581 d, HD 7449 B, and HD 984 b) that have previously been directly imaged, and many others that are observable at existing facilities. Depending on their ages, we estimate that an additional 10–57 substellar objects within our sample can be detected with current imaging facilities, extending the imaged cold (or old) giants by an order of magnitude.
We present the third data release of the European Space Agency's Gaia mission, GDR3. The GDR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. The GDR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G, and G pass-bands already present in the Early Third Data Release. GDR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges and , have new determinations of their mean radial velocities based on data collected by Gaia. We provide G magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The GDR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BPRP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. GDR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some astrometric, spectroscopic and eclipsing binaries. More than Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BPRP spectral data are published for about 60\,000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey (abridged)
Gaia Data Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release. They were produced by the Astrophysical parameters inference system (Apsis) within the Gaia Data Processing and Analysis Consortium. The aim of this paper is to describe the overall content of the astrophysical parameters in Gaia Data Release 3 and how they were produced. In Apsis we use the mean BP/RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification and probabilities for 1.6 billion objects, interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galactic extinction map, 6 million redshifts of quasar candidates and 1.4 million redshifts of galaxy candidates, along with an analysis of 50 million outlier sources through an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for up to 470 million sources. These comprise Teff, logg, and m_h (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), H-alpha equivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 thousand). This catalogue is the most extensive homogeneous database of astrophysical parameters to date, and it is based uniquely on Gaia data.
The last decade of direct imaging (DI) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. These results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of DI companions. It is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. We present the results of the COPAINS Survey conducted with SPHERE/VLT, searching for sub-stellar companions to stars showing significant proper motion differences (Δμ) between different astrometric catalogues. We observed twenty-five stars and detected ten companions, including four new brown dwarfs: HIP 21152 B, HIP 29724 B, HD 60584 B and HIP 63734 B. Our results clearly demonstrates how astrometric signatures, in the past only giving access to stellar companions, can now thanks to Gaia reveal companions well in the sub-stellar regime. We also introduce FORECAST (Finley Optimised REtrieval of Companions of Accelerating STars), a tool which allows to check the agreement between position and mass of the detected companions with the measured Δμ. Given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with FORECAST, the results of COPAINS represent a significant increase of the number of potential benchmarks for brown dwarf and planet formation and evolution theories.
The distortions of absorption line profiles caused by photospheric brightness variations on the surfaces of cool, main-sequence stars can mimic or overwhelm radial velocity (RV) shifts due to the presence of exoplanets. The latest generation of precision RV spectrographs aims to detect velocity amplitudes ≲ 10 cm s ⁻¹ , but requires mitigation of stellar signals. Statistical techniques are being developed to differentiate between Keplerian and activity-related velocity perturbations. Two important challenges, however, are the interpretability of the stellar activity component as RV models become more sophisticated, and ensuring the lowest-amplitude Keplerian signatures are not inadvertently accounted for in flexible models of stellar activity. For the K2V exoplanet host ϵ Eridani, we separately used ground-based photometry to constrain Gaussian processes for modeling RVs and TESS photometry with a light-curve inversion algorithm to reconstruct the stellar surface. From the reconstructions of TESS photometry, we produced an activity model that reduced the rms scatter in RVs obtained with EXPRES from 4.72 to 1.98 m s ⁻¹ . We present a pilot study using the CHARA Array and MIRC-X beam combiner to directly image the starspots seen in the TESS photometry. With the limited phase coverage, our spot detections are marginal with current data but a future dedicated observing campaign should allow for imaging, as well as allow the stellar inclination and orientation with respect to the debris disk to be definitively determined. This work shows that stellar surface maps obtained with high-cadence, time-series photometric and interferometric data can provide the constraints needed to accurately reduce RV scatter.
Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2.
Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results.
Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity. Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the ( G BP − G RP ) colour are also available. The passbands for G , G BP , and G RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia -CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3.
Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30–40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G , G BP , and G RP is valid over the entire magnitude and colour range, with no systematics above the 1% level
Context. The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph has been mounted since 2003 at the ESO 3.6 m telescope in La Silla and provides state-of-the-art stellar radial velocity (RV) measurements with a precision down to ∼1 m s ⁻¹ . The spectra are extracted with a dedicated data-reduction software (DRS), and the RVs are computed by cross-correlating with a numerical mask.
Aims. This study has three main aims: (i) Create easy access to the public HARPS RV data set. (ii) Apply the new public SpEctrum Radial Velocity AnaLyser (SERVAL) pipeline to the spectra, and produce a more precise RV data set. (iii) Determine whether the precision of the RVs can be further improved by correcting for small nightly systematic effects.
Methods. For each star observed with HARPS, we downloaded the publicly available spectra from the ESO archive and recomputed the RVs with SERVAL. This was based on fitting each observed spectrum with a high signal-to-noise ratio template created by coadding all the available spectra of that star. We then computed nightly zero-points (NZPs) by averaging the RVs of quiet stars.
Results. By analyzing the RVs of the most RV-quiet stars, whose RV scatter is < 5 m s ⁻¹ , we find that SERVAL RVs are on average more precise than DRS RVs by a few percent. By investigating the NZP time series, we find three significant systematic effects whose magnitude is independent of the software that is used to derive the RV: (i) stochastic variations with a magnitude of ∼1 m s ⁻¹ ; (ii) long-term variations, with a magnitude of ∼1 m s ⁻¹ and a typical timescale of a few weeks; and (iii) 20–30 NZPs that significantly deviate by a few m s ⁻¹ . In addition, we find small (≲1 m s ⁻¹ ) but significant intra-night drifts in DRS RVs before the 2015 intervention, and in SERVAL RVs after it. We confirm that the fibre exchange in 2015 caused a discontinuous RV jump that strongly depends on the spectral type of the observed star: from ∼14 m s ⁻¹ for late F-type stars to ∼ − 3 m s ⁻¹ for M dwarfs. The combined effect of extracting the RVs with SERVAL and correcting them for the systematics we find is an improved average RV precision: an improvement of ∼5% for spectra taken before the 2015 intervention, and an improvement of ∼15% for spectra taken after it. To demonstrate the quality of the new RV data set, we present an updated orbital solution of the GJ 253 two-planet system.
Conclusions. Our NZP-corrected SERVAL RVs can be retrieved from a user-friendly public database. It provides more than 212 000 RVs for about 3000 stars along with much auxiliary information, such as the NZP corrections, various activity indices, and DRS-CCF products.
The ability to make independent detections of the signatures of exoplanets with complementary telescopes and instruments brings a new potential for robust identification of exoplanets and precision characterization. We introduce PEXO, a package for Precise EXOplanetology to facilitate the efficient modeling of timing, astrometry, and radial velocity data, which will benefit not only exoplanet science but also various astrophysical studies in general. PEXO is general enough to account for binary motion and stellar reflex motions induced by planetary companions and is precise enough to treat various relativistic effects both in the solar system and in the target system. We also model the post-Newtonian barycentric motion for future tests of general relativity in extrasolar systems. We benchmark PEXO with the pulsar timing package TEMPO2 and find that PEXO produces numerically similar results with timing precision of about 1 ns, space-based astrometry to a precision of 1 μas, and radial velocity of 1 μm s−1 and improves on TEMPO2 for decade-long timing data of nearby targets, due to its consideration of third-order terms of Roemer delay. PEXO is able to avoid the bias introduced by decoupling the target system and the solar system and to account for the atmospheric effects that set a practical limit for ground-based radial velocities close to 1 cm s−1. Considering the various caveats in barycentric correction and ancillary data Required to realize cm s−1 modeling, we recommend the preservation of original observational data. The PEXO modeling package is available at GitHub (https://github.com/phillippro/pexo) and Zenodo (Feng et al. 2019).
Context . The census of stellar and substellar companions of nearby stars is largely incomplete, in particular toward the low-mass brown dwarf and long-period exoplanets. It is, however, fundamentally important in the understanding of the stellar and planetary formation and evolution mechanisms. Nearby stars are particularly favorable targets for high precision astrometry.
Aims . We aim to characterize the presence of physical companions of stellar and substellar mass in orbit around nearby stars.
Methods . Orbiting secondary bodies influence the proper motion of their parent star through their gravitational reflex motion. Using the HIPPARCOS and Gaia ’s second data release (GDR2) catalogs, we determined the long-term proper motion of the stars common to these two catalogs. We then searched for a proper motion anomaly (PMa) between the long-term proper motion vector and the GDR2 (or HIPPARCOS ) measurements, indicative of the presence of a perturbing secondary object. We focussed our analysis on the 6741 nearby stars located within 50 pc, and we also present a catalog of the PMa for ≳99% of the HIPPARCOS catalog (≈117 000 stars).
Results . 30% of the stars studied present a PMa greater than 3 σ . The PMa allows us to detect orbiting companions, or set stringent limits on their presence. We present a few illustrations of the PMa analysis to interesting targets. We set upper limits of 0.1−0.3 M J to potential planets orbiting Proxima between 1 and 10 au ( P orb = 3 to 100 years). We confirm that Proxima is gravitationally bound to α Cen. We recover the masses of the known companions of ϵ Eri, ϵ Ind, Ross 614 and β Pic. We also detect the signature of a possible planet of a few Jovian masses orbiting τ Ceti.
Conclusions . Based on only 22 months of data, the GDR2 has limitations. But its combination with the HIPPARCOS catalog results in very high accuracy PMa vectors, that already enable us to set valuable constraints on the binarity of nearby objects. The detection of tangential velocity anomalies at a median accuracy of σ (Δ v T ) = 1.0 m s ⁻¹ per parsec of distance is already possible with the GDR2. This type of analysis opens the possibility to identify long period orbital companions otherwise inaccessible. For long orbital periods, Gaia ’s complementarity to radial velocity and transit techniques (that are more sensitive to short orbital periods) already appears to be remarkably powerful.
Barnard’s star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs¹, it is the closest single star to the Sun; only the three stars in the α Centauri system are closer. Barnard’s star is also among the least magnetically active red dwarfs known2,3 and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging4–6, astrometry7,8 and direct imaging⁹, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard’s star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard’s star, making it an excellent target for direct imaging and astrometric observations in the future.
The young massive Jupiters discovered with high-contrast imaging provide a unique opportunity to study the formation and early evolution of gas giant planets. A key question is to what extent gravitational energy from accreted gas contributes to the internal energy of a newly formed planet. This has led to a range of formation scenarios from 'cold' to 'hot' start models. For a planet of a given mass, these initial conditions govern its subsequent evolution in luminosity and radius. Except for upper limits from radial velocity studies, disk modelling, and dynamical instability arguments, no mass measurements of young planets are yet available to distinguish between these different models. Here we report on the detection of the astrometric motion of Beta Pictoris, the 21 Myr-old host star of an archetypical directly-imaged gas giant planet, around the system's centre of mass. Subtracting the highly accurate Hipparcos-Gaia proper motion from the internal 3-yr Hipparcos astrometric data reveals the reflex motion of the star, giving a model-independent planet mass of M=11+-2 MJup. This is consistent with scenarios in which the planet is formed in a high-entropy state as assumed by hot start models. The ongoing data collection by Gaia will in the near future lead to mass measurements of other young gas giants and form a great asset to further constrain early evolution scenarios.
Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system.
Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results.
Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0.5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the GBP (330–680 nm) and GRP (630–1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia -CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.
Context. The CARMENES survey is a high-precision radial velocity (RV) programme that aims to detect Earth-like planets orbiting low-mass stars.
Aims. We develop least-squares fitting algorithms to derive the RVs and additional spectral diagnostics implemented in the SpEctrum Radial Velocity AnaLyser (SERVAL), a publicly available python code.
Methods. We measured the RVs using high signal-to-noise templates created by coadding all available spectra of each star. We define the chromatic index as the RV gradient as a function of wavelength with the RVs measured in the echelle orders. Additionally, we computed the differential line width by correlating the fit residuals with the second derivative of the template to track variations in the stellar line width.
Results. Using HARPS data, our SERVAL code achieves a RV precision at the level of 1 m/s. Applying the chromatic index to CARMENES data of the active star YZ CMi, we identify apparent RV variations induced by stellar activity. The differential line width is found to be an alternative indicator to the commonly used full width half maximum.
Conclusions. We find that at the red optical wavelengths (700–900 nm) obtained by the visual channel of CARMENES, the chromatic index is an excellent tool to investigate stellar active regions and to identify and perhaps even correct for activity-induced RV variations.
Over the last 20 years Hubble Space Telescope Fine Guidance Sensor interferometric astrometry has produced precise and accurate parallaxes of astrophysical interesting stars and mass estimates for stellar companions. We review parallax results, and binary star and exoplanet mass determinations, and compare a subset of these parallaxes with preliminary Gaia results. The approach to single-field relative astrometry described herein may continue to have value for targets fainter than the Gaia limit in the coming era of 20-30m telescopes.
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7.
Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release.
Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue.
Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼ 3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼ 0.3 mas should be added to the parallax uncertainties. For the subset of ∼ 94 000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼ 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼ 0.03 mag over the magnitude range 5 to 20.7.
Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important
limitations to the data quality which should be carefully considered before drawing conclusions from the data.
In this article, we describe the MIRI Imager module (MIRIM), which provides
broad-band imaging in the 5 - 27 microns wavelength range for the James Webb
Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed
view of 74"x113". The remainder of its nominal 113"x113" field is occupied by
the coronagraphs and the low resolution spectrometer. We present the instrument
optical and mechanical design. We show that the test data, as measured during
the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton
Laboratory, and at the NASA Goddard Space Flight Center, indicate that the
instrument complies with its design requirements and goals. We also discuss the
operational requirements (multiple dithers and exposures) needed for optimal
scientific utilization of the MIRIM.
MIRI (the Mid-Infrared Instrument for the James Webb Space Telescope (JWST))
operates from 5 to 28.5 microns and combines over this range: 1.) unprecedented
sensitivity levels; 2.) sub-arcsec angular resolution; 3.) freedom from
atmospheric interference; 4.) the inherent stability of observing in space; and
5.) a suite of versatile capabilities including imaging, low and medium
resolution spectroscopy (with an integral field unit), and coronagraphy. We
illustrate the potential uses of this unique combination of capabilities with
various science examples: 1.) imaging exoplanets; 2.) transit and eclipse
spectroscopy of exoplanets; 3.) probing the first stages of star and planet
formation, including identifying bioactive molecules; 4.) determining star
formation rates and mass growth as galaxies are assembled; and 5.)
characterizing the youngest massive galaxies. This paper is the introduction to
a series of ten covering all aspects of the instrument.
We present observations of Epsilon Eridani from the Submillimeter Array (SMA)
at 1.3 millimeters and from the Australia Telescope Compact Array (ATCA) at 7
millimeters that reach an angular resolution of ~4" (13 AU). These first
millimeter interferometer observations of Epsilon Eridani, which hosts the
closest debris disk to the Sun, reveal two distinct emission components: (1)
the well-known outer dust belt, which, although patchy, is clearly resolved in
the radial direction, and (2) an unresolved source coincident with the position
of the star. We use direct model-fitting of the millimeter visibilities to
constrain the basic properties of these two components. A simple Gaussian shape
for the outer belt fit to the SMA data results in a radial location of
AU and FWHM of AU (fractional width
. Similar results are obtained taking a power law radial
emission profile for the belt, though the power law index cannot be usefully
constrained. Within the noise obtained (0.2 mJy/beam), these data are
consistent with an axisymmetric belt model and show no significant azimuthal
structure that might be introduced by unseen planets in the system. These data
also limit any stellocentric offset of the belt to AU, which disfavors the
presence of giant planets on highly eccentric () and wide (10's of AU)
orbits. The flux density of the unresolved central component exceeds
predictions for the stellar photosphere at these long wavelengths, by a
marginally significant amount at 1.3 millimeters but by a factor of a few at 7
millimeters (with brightness temperature K for a source size
of the optical stellar radius). We attribute this excess emission to ionized
plasma from a stellar corona or chromosphere.
Context. The first release of astrometric data from Gaia will contain the
mean stellar positions and magnitudes from the first year of observations, and
proper motions from the combination of Gaia data with Hipparcos prior
information (HTPM).
Aims. We study the potential of using the positions from the Tycho-2
Catalogue as additional information for a joint solution with early Gaia data.
We call this the Tycho-Gaia astrometric solution (TGAS).
Methods. We adapt Gaia's Astrometric Global Iterative Solution (AGIS) to
incorporate Tycho information, and use simulated Gaia observations to
demonstrate the feasibility of TGAS and to estimate its performance.
Results. Using six to twelve months of Gaia data, TGAS could deliver
positions, parallaxes and annual proper motions for the 2.5 million Tycho-2
stars, with sub-milliarcsecond accuracy. TGAS overcomes some of the limitations
of the HTPM project and allows its execution half a year earlier. Furthermore,
if the parallaxes from Hipparcos are not incorporated in the solution, they can
be used as a consistency check of the TGAS/HTPM solution.
The Automated Planet Finder (APF) is a facility purpose-built for the
discovery and characterization of extrasolar planets through high-cadence
Doppler velocimetry of the reflex barycentric accelerations of their host
stars. Located atop Mt. Hamilton, the APF facility consists of a 2.4-m
telescope and its Levy spectrometer, an optical echelle spectrometer optimized
for precision Doppler velocimetry. APF features a fixed format spectral range
from 374 nm - 970 nm, and delivers a "Throughput" (resolution * slit width
product) of 114,000 arc-seconds, with spectral resolutions up to 150,000.
Overall system efficiency (fraction of photons incident on the primary mirror
that are detected by the science CCD) on blaze at 560 nm in planet-hunting mode
is 15%. First-light tests on the RV standard stars HD 185144 and HD 9407
demonstrate sub-meter per second precision (RMS per observation) held over a
3-month period. This paper reviews the basic features of the telescope, dome,
and spectrometer, and gives a brief summary of first-light performance.
Doppler spectroscopy has uncovered or confirmed all the known planets orbiting nearby stars. Two main techniques are used to obtain precision Doppler measurements at optical wavelengths. The first approach is the gas cell method, which consists of least-squares matching of the spectrum of iodine imprinted on the spectrum of the star. The second method relies on the construction of a stabilized spectrograph externally calibrated in wavelength. The most precise stabilized spectrometer in operation is the High Accuracy Radial velocity Planet Searcher (HARPS), operated by the European Southern Observatory in La Silla Observatory, Chile. The Doppler measurements obtained with HARPS are typically obtained using the cross-correlation function (CCF) technique. This technique consists of multiplying the stellar spectrum by a weighted binary mask and finding the minimum of the product as a function of the Doppler shift. It is known that CCF is suboptimal in exploiting the Doppler information in the stellar spectrum. Here we describe an algorithm to obtain precision radial velocity measurements using least-squares matching of each observed spectrum to a high signal-to-noise ratio template derived from the same observations. This algorithm is implemented in our software HARPS-TERRA (Template-Enhanced Radial velocity Re-analysis Application). New radial velocity measurements on a representative sample of stars observed by HARPS are used to illustrate the benefits of the proposed method. We show that, compared with CCF, template matching provides a significant improvement in accuracy, especially when applied to M dwarfs.
The Lick planet search program began in 1987 when the first spectrum of
Ceti was taken with an iodine cell and the Hamilton Spectrograph.
Upgrades to the instrument improved the Doppler precision from about 10 m/s in
1992 to about 3 m/s in 1995. The project detected dozens of exoplanets with
orbital periods ranging from a few days to several years. The Lick survey
identified the first planet in an eccentric orbit (70 Virginis) and the first
multi-planet system around a normal main sequence star (Upsilon Andromedae).
These discoveries advanced our understanding of planet formation and orbital
migration. Data from this project helped to quantify a correlation between host
star metallicity and the occurrence rate of gas giant planets. The program also
served as a test bed for innovation with testing of a tip-tilt system at the
coud{\'e} focus and fiber scrambler designs to stabilize illumination of the
spectrometer optics. The Lick planet search with the Hamilton spectrograph
effectively ended when a heater malfunction compromised the integrity of the
iodine cell. Here, we present more than 14,000 velocities for 386 stars that
were surveyed between 1987 and 2011.
We present htof , an open-source tool for interpreting and fitting the intermediate astrometric data (IAD) from both the 1997 and 2007 reductions of Hipparcos, the scanning law of Gaia, and future missions such as the Nancy Grace Roman Space Telescope (NGRST). htof solves the astrometric parameters of any system for any arbitrary combination of absolute astrometric missions. In preparation for later Gaia data releases, htof supports arbitrarily high-order astrometric solutions (e.g., five-, seven-, and nine-parameter fits). Using htof , we find that the IAD of 6617 sources in Hipparcos 2007 might have been affected by a data corruption issue. htof integrates an ad hoc correction that reconciles the IAD of these sources with their published catalog solutions. We developed htof to study masses and orbital parameters of substellar companions, and we outline its implementation in one orbit fitting code ( orvara ). We use htof to predict a range of hypothetical additional planets in the β Pic system, which could be detected by coupling NGRST astrometry with Gaia and Hipparcos. htof is pip installable and available at https://github.com/gmbrandt/htof .
We provide an overview of the design and capabilities of the near-infrared spectrograph (NIRSpec) onboard the James Webb Space Telescope. NIRSpec is designed to be capable of carrying out low-resolution ( R = 30−330) prism spectroscopy over the wavelength range 0.6–5.3 μm and higher resolution ( R = 500−1340 or R = 1320−3600) grating spectroscopy over 0.7–5.2 μm, both in single-object mode employing any one of five fixed slits, or a 3.1 × 3.2 arcsec ² integral field unit, or in multiobject mode employing a novel programmable micro-shutter device covering a 3.6 × 3.4 arcmin ² field of view. The all-reflective optical chain of NIRSpec and the performance of its different components are described, and some of the trade-offs made in designing the instrument are touched upon. The faint-end spectrophotometric sensitivity expected of NIRSpec, as well as its dependency on the energetic particle environment that its two detector arrays are likely to be subjected to in orbit are also discussed.
We present an open-source Python package, Orbits from Radial Velocity, Absolute, and/or Relative Astrometry ( orvara ), to fit Keplerian orbits to any combination of radial velocity, relative astrometry, and absolute astrometry data from the Hipparcos-Gaia Catalog of Accelerations. By combining these three data types, one can measure precise masses and sometimes orbital parameters even when the observations cover a small fraction of an orbit. The computational performance of orvara is achieved with an eccentric anomaly solver 5–10 times faster than commonly used approaches and low-level memory management to avoid Python overheads and by analytically marginalizing out parallax, barycenter proper motion, and instrument-specific radial velocity zero-points. Through its integration with the Hipparcos and Gaia intermediate astrometry package htof , orvara can properly account for the epoch astrometry measurements of Hipparcos and the measurement times and scan angles of individual Gaia epochs. We configure orvara with modifiable .ini configuration files tailored to any specific stellar or planetary system. We demonstrate orvara with a case study application to a recently discovered white dwarf/main-sequence system, HD 159062. By adding absolute astrometry to literature radial velocity and relative astrometry data, our comprehensive Markov Chain Monte Carlo analysis improves the precision of HD 159062B’s mass by more than an order of magnitude to 0.6083 − 0.0073 + 0.0083 M ☉ . We also derive a low eccentricity and large semimajor axis, establishing HD 159062AB as a system that did not experience Roche lobe overflow.
Eridani is a young planetary system hosting a complex multibelt debris disk and a confirmed Jupiter-like planet orbiting at 3.48 au from its host star. Its age and architecture are thus reminiscent of the early Solar System. The most recent study of Mawet et al., which combined radial-velocity data and Ms-band direct imaging upper limits, started to constrain the planet's orbital parameters and mass, but are still affected by large error bars and degeneracies. Here we make use of the most recent data compilation from three different techniques to further refine Eridani b's properties: RVs, absolute astrometry measurements from the Hipparcos and Gaia missions, and new Keck/NIRC2 Ms-band vortex coronagraph images. We combine this data in a Bayesian framework. We find a new mass, Mb=0.66-0.09+0.12 MJup, and inclination, i=78.81-22.41+29.34, with at least a factor 2 of improvement over previous uncertainties. We also report updated constraints on the longitude of the ascending node, the argument of the periastron, and the time of periastron passage. With these updated parameters, we can better predict the position of the planet at any past and future epoch, which can greatly help define the strategy and planning of future observations and with subsequent data analysis. In particular, these results can assist the search for a direct detection with JWST and the Nancy Grace Roman Space Telescope's coronagraph instrument. © 2021. The American Astronomical Society. All rights reserved..
To fully constrain the orbits of low mass circumstellar companions, we conduct combined analyses of the radial velocity data as well as the Gaia and Hipparcos astrometric data for eight nearby systems. Our study shows that companion-induced position and proper motion differences between Gaia and Hipparcos are significant enough to constrain orbits of low mass companions to a precision comparable with previous combined analyses of direct imaging and radial velocity data. We find that our method is robust to whether we use Gaia DR2 or Gaia EDR3, as well as whether we use all of the data, or just proper motion differences. In particular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time. With a mass of 1.8±0.2 MJup and an effective temperature of 123-176 K and orbiting around a Sun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass and orbit, belonging to a small sample of fully characterized Jupiter analogs. It is separated from its primary star by 0.25″ and thus may be suitable for direct imaging by the CGI instrument of the Roman Space Telescope.
We demonstrate the feasibility of determining magnitudes of stars on archival photographic plates using a commercially available scanner. We describe one photometric approach that could serve as a useful example for other studies. In particular, we measure and calibrate stellar magnitudes from a 1903 photographic plate from the Yerkes Observatory collection, and demonstrate that the overall precision from our methods is better than 0.10 mag. Notably, these measurements are dominated by intrinsic plate noise, rather than noise introduced through the scanning/digitization process. The low expense of this approach expands the scientific potential to study variable stars in the archives of observatory plate collections. We use the serendipitous discovery of a candidate transient at photographic magnitude pg = 16.60 in the spiral galaxy NGC 7331 to illustrate our photometric methods. If this unknown source is a supernova, it would represent the fourth known supernova in NGC 7331.
The presence of Jupiter is crucial to the architecture of the Solar system and models underline this to be a generic feature of planetary systems. We find the detection of the difference between the position and motion recorded by the contemporary astrometric satellite Gaia and its precursor Hipparcos can be used to discover Jupiter-like planets. We illustrate how observations of the nearby star ϵ Indi A giving astrometric and radial velocity data can be used to independently find the orbit of its suspected companion. The radial velocity and astrometric data provide complementary detections which allow for a much stronger solution than either technique would provide individually. We quantify ϵ Indi A b as the closest Jupiter-like exoplanet with a mass of 3 MJup on a slightly eccentric orbit with an orbital period of 45 yr. While other long-period exoplanets have been discovered, ϵ Indi A b provides a well-constrained mass and along with the well-studied brown dwarf binary in orbit around ϵ Indi A means that the system provides a benchmark case for our understanding of the formation of gas giant planets and brown dwarfs.
orbitize! is an open-source, object-oriented software package for fitting the orbits of directly-imaged objects. It packages the Orbits for the Impatient (OFTI) algorithm and a parallel-tempered Markov Chain Monte Carlo (MCMC) algorithm into a consistent and intuitive Python API. orbitize! makes it easy to run standard astrometric orbit fits; in less than 10 lines of code, users can read in data, perform one fit using OFTI and another using MCMC, and make two publication-ready figures. Extensive pedagogical tutorials, intended to be navigable by both orbit-fitting novices and seasoned experts, are available on our documentation page. We have designed the orbitize! API to be flexible and easy to use/modify for unique cases. orbitize! was designed by members of the exoplanet imaging community to be a central repository for algorithms, techniques, and know-how developed by this community. We intend for it to continue to expand and change as the field progresses and new techniques are developed, and call for community involvement in this process. Complete and up-to-date documentation is available at this http URL.
Context. Positions and proper motions of Gaia sources are expressed in a reference frame that ideally should be non-rotating relative to distant extragalactic objects, coincident with the International Celestial Reference System (ICRS), and consistent across all magnitudes. For sources fainter than 16th magnitude, this is achieved through Gaia ’s direct observations of quasars. At brighter magnitudes, it is difficult to validate the quality of the reference frame because comparison data are scarce.
Aims. The aim of this paper is to examine the use of very long baseline interferometry (VLBI) observations of radio stars to determine the spin and orientation of the bright reference frame of current and future Gaia data releases.
Methods. Simultaneous estimation of the six spin and orientation parameters makes optimal use of VLBI data and makes it possible to include even single-epoch VLBI observations in the solution. The method is applied to Gaia Data Release 2 (DR2) using published VLBI data for 41 radio stars.
Results. The VLBI data for the best-fitting 26 sources indicate that the bright reference frame of Gaia DR2 rotates relative to the faint quasars at a rate of about 0.1 mas yr ⁻¹ , which is significant at the 2 σ level. This supports a similar conclusion based on a comparison with stellar positions in the H IPPARCOS frame. The accuracy is currently limited because only a few radio sources are included in the solution, by uncertainties in the Gaia DR2 proper motions, and by issues related to the astrophysical nature of the radio stars.
Conclusions. While the origin of the indicated rotation is understood and can be avoided in future data releases, it remains important to validate the bright reference frame of Gaia by independent observations. This can be achieved using VLBI astrometry, which may require re-observing the old sample of radio stars as well as measuring new objects. The unique historical value of positional measurements is stressed and VLBI observers are urged to ensure that relevant positional information is preserved for the future.
The radial velocity (RV) method plays a major role in the discovery of nearby exoplanets. To efficiently find planet candidates from the data obtained in high-precision RV surveys, we apply a signal diagnostic framework to detect RV signals that are statistically significant, consistent in time, robust in the choice of noise models, and do not correlated with stellar activity. Based on the application of this approach to the survey data of the Planet Finder Spectrograph, we report 15 planet candidates located in 14 stellar systems. We find that the orbits of the planet candidates around HD 210193, 103949, 8326, and 71135 are consistent with temperate zones around these stars (where liquid water could exist on the surface). With periods of 7.76 and 15.14 days, respectively, the planet candidates around star HIP 54373 form a 1:2 resonance system. These discoveries demonstrate the feasibility of automated detection of exoplanets from large RV surveys, which may provide a complete sample of nearby Earth analogs.
We present the most sensitive direct imaging and radial velocity (RV) exploration of Eridani to date. Eridani is an adolescent planetary system, reminiscent of the early solar system. It is surrounded by a prominent and complex debris disk that is likely stirred by one or several gas giant exoplanets. The discovery of the RV signature of a giant exoplanet was announced 15 yr ago, but has met with scrutiny due to possible confusion with stellar noise. We confirm the planet with a new compilation and analysis of precise RV data spanning 30 yr, and combine it with upper limits from our direct imaging search, the most sensitive ever performed. The deep images were taken in the Ms band (4.7 μm) with the vortex coronagraph recently installed in W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive window for planet searches around nearby adolescent systems. The RV data and direct imaging upper limit maps were combined in an innovative joint Bayesian analysis, providing new constraints on the mass and orbital parameters of the elusive planet. Eridani b has a mass of M Jup and is orbiting Eridani at about 3.48 ± 0.02 au with a period of 7.37 ± 0.07 yr. The eccentricity of Eridani b's orbit is an order of magnitude smaller than early estimates and consistent with a circular orbit. We discuss our findings from the standpoint of planet-disk interactions and prospects for future detection and characterization with the James Webb Space Telescope. © 2019. The American Astronomical Society. All rights reserved.
This paper presents a cross-calibrated catalog of Hipparcos and Gaia astrometry to enable their use in measuring changes in proper motion, i.e., accelerations in the plane of the sky. The final catalog adopts the reference frame of the second Gaia data release (DR2) and locally cross-calibrates both the scaled Hipparcos-Gaia DR2 positional differences and the Hipparcos proper motions themselves to this frame. This gives three nearly independent proper motion measurements per star, with the scaled positional difference usually being the most precise. We find that a linear combination of the two Hipparcos reductions is superior to either reduction on its own and address error inflation for both Hipparcos and Gaia DR2. Our adopted error inflation is additive (in quadrature) for Hipparcos and multiplicative for Gaia. We provide the covariance matrices along with the central epochs of all measurements. Our final proper motion differences are accurately Gaussian with the appropriate variances and are suitable for acceleration measurements and orbit fitting. The catalog is constructed with an eye toward completeness; it contains nearly 98% of the Hipparcos stars. It also includes a handful of spurious entries and a few stars with poor Hipparcos reductions that the user must vet by hand. Statistical distributions of accelerations derived from this catalog should be interpreted with caution. © 2018. The American Astronomical Society. All rights reserved.
We present the first ALMA observations of the closest known extrasolar debris disc. This disc orbits the star ε Eri, a K-type star just 3.2 pc away. Due to the proximity of the star, the entire disc cannot fit within the ALMA field of view. Therefore, the observations have been centred 18″ North of the star, providing us with a clear detection of the northern arc of the ring, at a wavelength of 1.3 mm. The observed disc emission is found to be narrow with a width of just 11-13 AU. The fractional disc width we find is comparable to that of the Solar System’s Kuiper Belt and makes this one of the narrowest debris discs known. If the inner and outer edges are due to resonances with a planet then this planet likely has a semi-major axis of 48 AU. We find tentative evidence for clumps in the ring, although there is a strong chance that at least one is a background galaxy. We confirm, at much higher significance, the previous detection of an unresolved emission at the star that is above the level of the photosphere and attribute this excess to stellar chromospheric emission.
We describe a 20-year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck-I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf stars. We provide here 60,949 precision radial velocities for 1,624 stars contained in that survey. We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star. Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as "significant" signals that require confirmation by additional data before rising to classification as planet candidates. Of particular interest is our detection of a candidate planet with a minimum mass of 3.9 Earth masses and an orbital period of 9.9 days orbiting Lalande 21185, the fourth-closest main sequence star to the Sun. For each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the Keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. We also tabulate 18 Keplerian-like signals that we classify as likely arising from stellar activity.
The EXtreme PREcision Spectrograph (EXPRES) is an optical fiber fed echelle instrument being designed and built at the Yale Exoplanet Laboratory to be installed on the 4.3-meter Discovery Channel Telescope operated by Lowell Observatory. The primary science driver for EXPRES is to detect Earth-like worlds around Sun-like stars. With this in mind, we are designing the spectrograph to have an instrumental precision of 15 cm/s so that the on-sky measurement precision (that includes modeling for RV noise from the star) can reach to better than 30 cm/s. This goal places challenging requirements on every aspect of the instrument development, including optomechanical design, environmental control, image stabilization, wavelength calibration, and data analysis. In this paper we describe our error budget, and instrument optomechanical design.
The doppler measurements of stars are diluted and distorted by stellar activity noise. Different choices of noise models and statistical methods have led to much controversy in the confirmation of exoplanet candidates obtained through analysing radial velocity data. To quantify the limitation of various models and methods, we compare different noise models and signal detection criteria for various simulated and real data sets in the Bayesian framework. According to our analyses, the white noise model tend to interpret noise as signal, leading to false positives. On the other hand, the red noise models are likely to interprete signal as noise, resulting in false negatives. We find that the Bayesian information criterion combined with a Bayes factor threshold of 150 can efficiently rule out false positives and confirm true detections. We further propose a Goldilocks principle aimed at modeling radial velocity noise to avoid too many false positives and too many false negatives. We propose that the noise model with RHK-dependent jitter is used in combination with the moving average model to detect planetary signals for M dwarfs. Our work may also shed light on the noise modeling for hotter stars, and provide a valid approach for finding similar principles in other disciplines.
Lowell Observatory's Discovery Channel Telescope is a 4.3m telescope
designed for optical and near infrared astronomical observation. At
first light, the telescope will have a cube capable of carrying five
instruments and the wave front sensing and guider system at the f/6.1 RC
focus. The corrected RC focus field of view is 30’ in diameter.
Nasmyth and prime focus can be instrumented subsequently. Early
commissioning work with the installed primary mirror and its support
system started out using one of the wave front sensing probes mounted at
prime focus, and has continued at RC with the recent installation of the
secondary mirror. We will report on the on-sky pointing and tracking
performance of the telescope, initial assessment of the functionality of
the active optics support system, and tests of the early image quality
of the telescope and optics. We will also describe the suite of first
light instruments, and early science operations.
We describe the design and construction of the ESO UV-visual echelle spectrograph and the performance that was measured during its commissioning 1999. UVES is a dual-beam, grating crossdispersed echelle spectrograph. The resolution for a 1 arcsecond slit is 40,000. With narrower slits, resolutions of up to 80,000 and 115,000 are achieved with adequate sampling. UVES provides order separations of minimum 10 arcseconds at any wavelength between 320 and 1050 nm. The wavelength coverage is 100 nm in the blue arm and 200 or 400 nm in the red arm, with possibility to use a dichroic. Some concepts pioneered in UVES are now increasingly being used in other echelle spectrograph for large telescopes: a white pupil design, very steep replicated mosaic echelles, and large refractive cameras with external focus. Regular observations are starting in April 2000 at the Nasmyth focus of Kueyen, Unit Telescope 2 of the VLT array.
Exoplanet Doppler surveys are currently the most efficient means to detect
low-mass companions to nearby stars. Among these stars, the light M dwarfs
provide the highest sensitivity to detect low-mass exoplanet candidates.
Evidence is accumulating that a substantial fraction of these low-mass planets
are found in high-multiplicity planetary systems. GJ 163 is a nearby inactive M
dwarf with abundant public observations obtained using the HARPS spectrograph.
We obtain and analyse radial velocities from the HARPS public spectra of GJ 163
and investigate the presence of a planetary companions orbiting it. The number
of planet candidates detected might depend on some prior assumptions. Since the
impact of prior choice has not been investigated throughly previously, we study
the effects of different prior densities on the detectability of planet
candidates around GJ 163. We use Bayesian tools, i.e. posterior samplings and
model comparisons, when analysing the GJ 163 velocities. We consider models
accounting for the possible correlations of subsequent measurements. We also
search for activity-related counterparts of the signals we observe and test the
dynamical stability of the planetary systems corresponding to our solutions
using direct numerical integrations of the orbits. We find that there are at
least three planet candidates orbiting GJ 163. The existence of a fourth planet
is supported by the data but the evidence in favor of the corresponding model
is not yet conclusive. The second innermost planet candidate in the system with
an orbital period of 25.6 days and a minimum mass of 8.7 Me is inside the
liquid-water habitable zone of the star.