Publications (13)24.07 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: There have been previous hints that the transiting planet WASP3 b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The radialvelocity data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period.  [Show abstract] [Hide abstract]
ABSTRACT: Transit and radial velocity observations continuously discover an increasing number of exoplanets. However, when it comes to the composition of the observed planets the data are compatible with several interior structure models. Thus, a planetary parameter sensitive to the planet's density distribution could help constrain this large number of possible models even further. We aim to investigate to what extent an exoplanet's interior can be constrained in terms of core mass and envelope metallicity by taking the tidal Love number k_2 into account as an additional possibly observable parameter. Because it is the only planet with an observationally determined k_2, we constructed interior models for the Hot Jupiter exoplanet HATP13b by solving the equations of hydrostatic equilibrium and mass conservation for different boundary conditions. In particular, we varied the surface temperature and the outer temperature profile, as well as the envelope metallicity within the widest possible parameter range. We also considered atmospheric conditions that are consistent with nongray atmosphere models. For all these models we calculated the Love number k_2 and compared it to the allowed range of k_2 values that could be obtained from eccentricity measurements of HATP13b. We use the example of HATP13b to show the general relationships between the quantities temperature, envelope metallicity, core mass, and Love number of a planet. For any given k_2 value a maximum possible core mass can be determined. For HATP13b we find Mcore < 27 ME, based on the latest eccentricity measurement. We are able to constrain both the envelope and bulk metallicity of HATP13b to 1  11 times stellar metallicity and the extension of the isothermal layer in the planet's atmosphere to 3  44 bar. Assuming equilibrium tidal theory, we find lower limits on the tidal Q consistent with 10^3  10^5.  [Show abstract] [Hide abstract]
ABSTRACT: For the solar sytem giant planets the measurement of the gravitational moments J2 and J4 provided valuable information about the interior structure. However, for extrasolar planets the gravitational moments are not accessible. Nevertheless, an additional constraint for extrasolar planets can be obtained from the tidal Love number k2, which, to first order, is equivalent to J2. k2 quantifies the quadrupolic gravity field deformation at the surface of the planet in response to an external perturbing body and depends solely on the planet's internal density distribution. On the other hand, the inverse deduction of the density distribution of the planet from k2 is nonunique. The Love number k2 is a potentially observable parameter that can be obtained from tidally induced apsidal precession of closein planets (Ragozzine & Wolf 2009) or from the orbital parameters of specific twoplanet systems in apsidal alignment (Mardling 2007). We find that for a given k2, a precise value for the core mass cannot be derived. However, a maximum core mass can be inferred which equals the core mass predicted by homogeneous zero metallicity envelope models. Using the example of the extrasolar transiting planet HATP13b we show to what extend planetary models can be constrained by taking into account the tidal Love number k2.  [Show abstract] [Hide abstract]
ABSTRACT: We present the Young Exoplanet Transit Initiative (YETI), in which we use several 0.2 to 2.6m telescopes around the world to monitor continuously young (< 100 Myr), nearby (< 1 kpc) stellar clusters mainly to detect young transiting planets (and to study other variability phenomena on timescales from minutes to years). The telescope network enables us to observe the targets continuously for several days in order not to miss any transit. The runs are typically one to two weeks long, about three runs per year per cluster in two or three subsequent years for about ten clusters. There are thousands of stars detectable in each field with several hundred known cluster members, e.g. in the first cluster observed, Tr37, a typical cluster for the YETI survey, there are at least 469 known young stars detected in YETI data down to R=16.5 mag with sufficient precision of 50 millimag rms (5 mmag rms down to R=14.5 mag) to detect transits, so that we can expect at least about one young transiting object in this cluster. If we observe 10 similar clusters, we can expect to detect approximately 10 young transiting planets with radius determinations. The precision given above is for a typical telescope of the YETI network, namely the 60/90cm Jena telescope (similar brightness limit, namely within +/1 mag, for the others) so that planetary transits can be detected. For planets with mass and radius determinations, we can calculate the mean density and probe the internal structure. We aim to constrain planet formation models and their timescales by discovering planets younger than 100 Myr and determining not only their orbital parameters, but also measuring their true masses and radii, which is possible so far only by the transit method. Here, we present an overview and first results. (Abstract shortened)  [Show abstract] [Hide abstract]
ABSTRACT: In order to accurately model giant planets, a whole set of observational constraints is needed. As the conventional constraints for extrasolar planets like mass, radius, and temperature allow for a large number of acceptable models, a new planetary parameter is desirable in order to further constrain planetary models. Such a parameter may be the tidal Love number k2. In this paper we aim to study the capability of k2 to reveal further information about the interior structure of a planet. With theoretical planetary models we investigate how the tidal Love number k2 responds to the internal density distribution of a planet. In particular, we demonstrate the effect of the degeneracy of k2 due to a density discontinuity in the envelope of a threelayer planetary model. The effect of a possible outer density discontinuity masks the effect of the core mass on the Love number k2. Hence, there is no unique relationship between the Love number k2 and the core mass of a planet. We show that the degeneracy of k2 with respect to a layer boundary in the envelope also occurs in existing planets, e.g. Saturn and the Hot Neptune GJ436b. As a result of the degeneracy, the planetary parameter k2 cannot be used to further constrain Saturnian models and for GJ436b only a maximum possible core mass can be derived from a given k2. To significantly narrow the uncertainty about the core mass of GJ436b the combined knowledge of k2 and atmospheric metallicity and temperature profile is necessary.  [Show abstract] [Hide abstract]
ABSTRACT: Transiting exoplanets (TEPs) observed just about 10 Myrs after formation of their host systems may serve as the Rosetta Stone for planet formation theories. They would give strong constraints on several aspects of planet formation, e.g. timescales (planet formation would then be possible within 10 Myrs), the radius of the planet could indicate whether planets form by gravitational collapse (being larger when young) or accretion growth (being smaller when young). We present a survey, the main goal of which is to find and then characterise TEPs in very young open clusters.  [Show abstract] [Hide abstract]
ABSTRACT: Photometric followups of transiting exoplanets (TEPs) may lead to discoveries of additional, less massive bodies in extrasolar systems. This is possible by detecting and then analysing variations in transit timing of transiting exoplanets. In 2009 we launched an international observing campaign, the aim of which is to detect and characterise signals of transit timing variation (TTV) in selected TEPs. The programme is realised by collecting data from 0.62.2m telescopes spread worldwide at different longitudes. We present our observing strategy and summarise first results for WASP3b with evidence for a 15 Earthmass perturber in an outer 2:1 orbital resonance.  [Show abstract] [Hide abstract]
ABSTRACT: The planet GJ 1214b is the second known superEarth with a measured mass and radius. Orbiting a quiet M star, it receives considerably less massloss driving Xray and UV radiation than CoRoT7b, so that the interior may be quite dissimilar in composition, including the possibility of a large fraction of water. We model the interior of GJ 1214b assuming a twolayer (envelope+rock core) structure where the envelope material is either H/He, pure water, or a mixture of H/He and H2O. Within this framework, we perform models of the thermal evolution and contraction of the planet. We discuss possible compositions that are consistent with Mp = 6.55 M ⊕, Rp = 2.678 R ⊕, an age τ = 310 Gyr, and the irradiation level of the atmosphere. These conditions require that if water exists in the interior, it must remain in a fluid state, with important consequences for magnetic field generation. These conditions also require the atmosphere to have a deep isothermal region extending down to 80800 bar, depending on composition. Our results bolster the suggestion of a metalenriched H/He atmosphere for the planet, as we find waterworld models that lack an H/He atmosphere to require an implausibly large watertorock ratio of more than 6:1. We instead favor an H/He/H2O envelope with high water mass fraction (~0.50.85), similar to recent models of the deep envelope of Uranus and Neptune. Even with these high water mass fractions in the H/He envelope, generally the bulk composition of the planet can have subsolar water:rock ratios. Dry, waterenriched, and pure water envelope models differ to an observationally significant level in their tidal Love numbers k 2 of, respectively, ~0.018, ~0.15, and ~0.7.  [Show abstract] [Hide abstract]
ABSTRACT: We present new results in modeling the interiors of Giant Planets (GP) and Brown Dwarfs (BD). In general models of the interior rely on equation of state data for planetary materials which have considerable uncertainties in the highpressure domain. Our calculations are based on ab initio equation of state (EOS) data for hydrogen, helium, hydrogenhelium mixtures and water as the representative of all heavier elements or ices using finitetemperature density functional theory molecular dynamics (FTDFTMD) simulations. We compare results for the BD Gliese 229B calculated with SaumonChabrierVan Horn EOS (SCVH95) and our EOS data. 
Article: Interior structure models of GJ 436b
[Show abstract] [Hide abstract]
ABSTRACT: GJ 436b is the first extrasolar planet discovered that resembles Neptune in mass and radius. The particularly interesting property of Neptunesized planets is that their mass Mp and radius Rp are close to theoretical MR relations of water planets. Given Mp, Rp, and equilibrium temperature, however, various internal compositions are possible. A broad set of interior structure models is presented here that illustrates the dependence of internal composition and possible phases of water occurring in presumably waterrich planets, such as GJ 436b on the uncertainty in atmospheric temperature profile and mean density. We show how the set of solutions can be narrowed down if theoretical constraints from formation and model atmospheres are applied or potentially observational constraints for the atmospheric metallicity Z1 and the tidal Love number k2. We model the interior by assuming either three layers (hydrogenhelium envelope, water layer, rock core) or two layers (H/He/H2O envelope, rocky core). For water, we use the equation of state H2OREOS based on FTDFTMD simulations. Some admixture of H/He appears mandatory for explaining the measured radius. For the warmest considered models, the H/He mass fraction can reduce to 10^3, still extending over ~0.7 REarth. If water occurs, it will be essentially in the plasma phase or in the superionic phase, but not in an ice phase. Metalfree envelope models have 0.02<k2<0.2, and the core mass cannot be determined from a measurement of k2. In contrast, models with 0.3<k2<0.82 require high metallicities Z1<0.89 in the outer envelope. The uncertainty in core mass decreases to 0.4 Mp, if k2>0.3, and further to 0.2 Mp, if k2>0.5, and core mass and Z1 become sensitive functions of k2. To further narrow the set of solutions, a proper treatment of the atmosphere and the evolution is necessary. Comment: 9 pages, accepted to A&A  [Show abstract] [Hide abstract]
ABSTRACT: The planet GJ 1214b is the second known superEarth with a measured mass and radius. Orbiting a quiet Mstar, it receives considerably less massloss driving Xray and UV radiation than CoRoT7b, so that the interior may be quite dissimilar in composition, including the possibility of a large fraction of water. We model the interior of GJ 1214b assuming a twolayer (envelope+rock core) structure where the envelope material is either H/He, pure water, or a mixture of H/He and H2O. Within this framework we perform models of the thermal evolution and contraction of the planet. We discuss possible compositions that are consistent with Mp=6.55 ME, Rp=2.678 RE, an age tau=310 Gyr, and the irradiation level of the atmosphere. These conditions require that if water exists in the interior, it must remain in a fluid state, with important consequences for magnetic field generation. These conditions also require the atmosphere to have a deep isothermal region extending down to 80800 bar, depending on composition. Our results bolster the suggestion of a metalenriched H/He atmosphere for the planet, as we find waterworld models that lack an H/He atmosphere to require an implausibly large watertorock ratio of more than 6:1. We instead favor a H/He/H2O envelope with high water mass fraction (~0.50.85), similar to recent models of the deep envelope of Uranus and Neptune. Even with these high water mass fractions in the H/He envelope, generally the bulk composition of the planet can have subsolar water:rock ratios. Dry, waterenriched, and pure water envelope models differ to an observationally significant level in their tidal Love numbers k2 of respectively ~0.018, 0.15, and 0.7.  [Show abstract] [Hide abstract]
ABSTRACT: We present new results for the interior of solar as well as extrasolar giant planets based on ab initio molecular dynamics simulations for the most abundant planetary materials hydrogen, helium, and water. The equation of state, the electrical conductivity and reflectivity can be calculated up to high pressures; very good agreement with shock‐wave experimental results is found. The nonmetal‐to‐metal transition in hydrogen and the subsequent demixing of hydrogen from helium is of great importance for the interior of Jovian planets. The superionic phase predicted for water at high pressures is relevant for Neptune‐like giant planets. Advanced planetary models can be constructed based on the new ab initio data.  [Show abstract] [Hide abstract]
ABSTRACT: We have performed quantum molecular dynamics simulations using finitetemperature density functional theory (FTDFTMD) to calculate accurate equation of state data for the most abundant materials in giant planets hydrogen, helium, and water in the warm dense matter region. We discuss the phase diagram of water up to ultrahigh pressures and identify the location of the superionic phase which might occur in the deep interior of Neptune, Uranus or even in Saturn. These ab initio data sets were used to calculate the interior structure models of solar giant planets within the standard threelayer model and to determine their core mass and metallicity. We have also determined possible compositions of extrasolar giant planets such as GJ 436b for which the massradius relation and the surface temperature are measured. We discuss also the impact of highpressure effects such as the nonmetaltometal transition in hydrogen and the demixing of hydrogen and helium on the interior structure of giant planets.
Publication Stats
129  Citations  
24.07  Total Impact Points  
Top Journals
Institutions

20092013

University of Rostock
 Institut für Physik
Rostock, MecklenburgVorpommern, Germany
