- ID:
- ivo://CDS.VizieR/J/ApJ/774/148
- Title:
- Ab initio EOS for hydrogen-helium mixtures
- Short Name:
- J/ApJ/774/148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using density functional molecular dynamics simulations, we determine the equation of state (EOS) for hydrogen-helium mixtures spanning density-temperature conditions typical of giant-planet interiors, ~0.2-9g/cm3 and 1000-80000K for a typical helium mass fraction of 0.245. In addition to computing internal energy and pressure, we determine the entropy using an ab initio thermodynamic integration technique. A comprehensive EOS table with 391 density-temperature points is constructed and the results are presented in the form of a two-dimensional free energy fit for interpolation. Deviations between our ab initio EOS and the semi-analytical EOS model by Saumon and Chabrier (1992PhRvA..46.2084S, 1995ApJS...99..713S) are analyzed in detail, and we use the results for initial revision of the inferred thermal state of giant planets with known values for mass and radius. Changes are most pronounced for planets in the Jupiter mass range and below. We present a revision to the mass-radius relationship that makes the hottest exoplanets increase in radius by ~0.2 Jupiter radii at fixed entropy and for masses greater than ~0.5 Jupiter mass. This change is large enough to have possible implications for some discrepant "inflated giant exoplanets."
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- ID:
- ivo://CDS.VizieR/J/ApJ/806/228
- Title:
- Ab initio EOS for water-hydrogen mixtures
- Short Name:
- J/ApJ/806/228
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from ab initio simulations of liquid water-hydrogen mixtures in the range from 2 to 70GPa and from 1000 to 6000K, covering conditions in the interiors of ice giant planets and parts of the outer envelope of gas giant planets. In addition to computing the pressure and the internal energy, we derive the Gibbs free energy by performing a thermodynamic integration. For all conditions under consideration, our simulations predict hydrogen and water to mix in all proportions. The thermodynamic behavior of the mixture can be well described with an ideal mixing approximation. We suggest that a substantial fraction of water and hydrogen in giant planets may occur in homogeneously mixed form rather than in separate layers. The extent of mixing depends on the planet's interior dynamics and its conditions of formation, in particular on how much hydrogen was present when icy planetesimals were delivered. Based on our results, we do not predict water-hydrogen mixtures to phase separate during any stage of the evolution of giant planets. We also show that the hydrogen content of an exoplanet is much higher if the mixed interior is assumed.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A72
- Title:
- Absolute Refletivity of Jupiter and Saturn
- Short Name:
- J/A+A/607/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide measurements of the absolute reflectivity of Jupiter and Saturn along their central meridians in filters covering a wide range of visible and near-infrared wavelengths (from 0.38 to 1.7um) that are not often presented in the literature. We also give measurements of the geometric albedo of both planets and discuss the limb-darkening behavior and temporal variability of their reflectivity values for a period of four years (2012-2016). This work is based on observations with the PlanetCam-UPV/EHU instrument at the 1.23m and 2.2m telescopes in Calar Alto Observatory (Spain). The instrument simultaneously observes in two channels: visible (VIS; 0.38-1.0um) and short-wave infrared (SWIR; 1.0-1.7um). We obtained high-resolution observations via the lucky-imaging method. We show that our calibration is consistent with previous independent determinations of reflectivity values of these planets and, for future reference, provide new data extended in the wavelength range and in the time. Our results have an uncertainty in absolute calibration of 10-20%. We show that under the hypothesis of constant geometric albedo, we are able to detect absolute reflectivity changes related to planetary temporal evolution of about 5-10%.
- ID:
- ivo://CDS.VizieR/J/MNRAS/370/163
- Title:
- Abundance distribution of stars with planets
- Short Name:
- J/MNRAS/370/163
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a uniform, high-precision spectroscopic metallicity study of 136 G-type stars from the Anglo-Australian Planet Search, 20 of which are known to harbour extrasolar planets (as at 2005 July). Abundances in Fe, C, Na, Al, Si, Ca, Ti and Ni are presented, along with Stroemgen photometric metallicities. This study is one of several recent studies examining the metallicities of a sample of planet-host and non-planet-host stars that were obtained from a single sample, and analysed in an identical manner, providing an unbiased estimate of the metallicity trends for planet-bearing stars. We find that non-parametric tests of the distribution of metallicities for planet-host and non-planet-host stars are significantly different at a level of 99.4 per cent confidence. We confirm the previously observed trend for planet-host stars to have higher mean metallicities than non-planet-host stars, with a mean metallicity for planet-host stars of [Fe/H]=0.06+/-0.03dex compared with [Fe/H]=0.09+/-0.01dex for non-host-stars in our sample. This enrichment is also seen in the other elements studied. Based on our findings, we suggest that this observed enhancement is more likely a relic of the original gas cloud from which the star and its planets formed, rather than being due to 'pollution' of the stellar photosphere.
- ID:
- ivo://CDS.VizieR/J/A+A/458/997
- Title:
- Abundances for 6 transiting planet host stars
- Short Name:
- J/A+A/458/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used the UVES spectrograph (VLT-UT2 telescope) to obtain high-resolution spectra of 6 stars hosting transiting planets, namely for OGLE-TR-10, 56, 111, 113, 132, and TrES-1. These spectra are now used to derive and discuss the chemical abundances for C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn.
- ID:
- ivo://CDS.VizieR/J/A+A/449/723
- Title:
- Abundances in atmospheres of stars with planets
- Short Name:
- J/A+A/449/723
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform and homogeneous study of the abundances of Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg and Al in 100 stars with and 94 without known planetary companions. The main purpose of this work is to make a deep investigation of the abundance of refractory elements, using an enlarged set of data which includes new observations, especially for the sample of stars without known planets. The new comparison sample spans metallicity range -0.70<[Fe/H]<0.50 and fills the gap that previously existed, mainly at high metallicities, in the number of field "single" comparison stars. Furthermore, we improved the line list previously studied by other authors: on average we analysed 90 spectral lines in every spectrum and carefully measured more than 16 600 equivalent widths (EW) to calculate the abundances. We investigate possible differences between the chemical abundances of the two groups of stars, with and without planets. The results are globally comparable to those obtained by other authors, and in most cases the abundance trends of planet-host stars are very similar to those of the comparison sample. This work represents a step towards the comprehension of recently discovered planetary systems. These results could also be useful for verifying galactic models at high metallicities and consequently improve our knowledge of stellar nucleosynthesis and galactic chemical evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/87
- Title:
- Abundances in G-type stars with exoplanets
- Short Name:
- J/ApJ/736/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We confirm the difference in chemical abundance between stars with and without exoplanets and present the relation between chemical abundances and physical properties of exoplanets, such as planetary mass and the semimajor axis of planetary orbit. We obtained the spectra of 52 G-type stars from the Bohyunsan Optical Astronomy Observatory (BOAO) Echelle Spectrograph and carried out abundance analyses for 12 elements: Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, and Ni. We first found that the [Mn/Fe] ratios of planet-host stars are higher than those of comparison stars over the entire metallicity range, and we then found that in metal-poor stars of [Fe/H]<-0.4 the abundance difference was larger than in metal-rich samples, especially for the elements of Mg, Al, Sc, Ti, V, and Co. After examining the relation between planet properties and metallicities of planet-host stars, we observed that planet-host stars with low metallicities tend to have several low-mass planets (<M_J_) instead of a massive gas-giant planet.
- ID:
- ivo://CDS.VizieR/J/ApJ/768/L12
- Title:
- Abundances in host stars XO-2S and XO-2N
- Short Name:
- J/ApJ/768/L12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the aim of connecting the compositions of stars and planets, we present the abundances of carbon and oxygen, as well as iron and nickel, for the transiting exoplanet host star XO-2N and its wide-separation binary companion XO-2S. Stellar parameters are derived from high-resolution, high signal-to-noise spectra, and the two stars are found to be similar in their T_eff_, log g, iron ([Fe/H]), and nickel ([Ni/H]) abundances. Their carbon ([C/H]) and oxygen ([O/H]) abundances also overlap within errors, although XO-2N may be slightly more C-rich and O-rich than XO-2S. The C/O ratios of both stars (~0.60+/-0.20) may also be somewhat larger than solar (C/O~0.50). The XO-2 system has a transiting hot Jupiter orbiting one binary component but not the other, allowing us to probe the potential effects planet formation might have on the host star composition. Additionally, with multiple observations of its atmosphere the transiting exoplanet XO-2b lends itself to compositional analysis, which can be compared to the natal chemical environment established by our binary star elemental abundances. This work sets the stage for determining how similar or different exoplanet and host star compositions are, and the implications for planet formation, by discussing the C/O ratio measurements in the unique environment of a visual binary system with one star hosting a transiting hot Jupiter.
- ID:
- ivo://CDS.VizieR/J/A+A/438/251
- Title:
- Abundances in stars with giant planets
- Short Name:
- J/A+A/438/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Na, Mg and Al abundances in a set of 98 stars with known giant planets, and in a comparison sample of 41 "single" stars. The results show that the [X/H] abundances (with X = Na, Mg and Al) are, on average, higher in stars with giant planets, a result similar to the one found for iron. However, we did not find any strong difference in the [X/Fe] ratios, for a fixed [Fe/H], between the two samples of stars in the region where the samples overlap. The data was used to study the Galactic chemical evolution trends for Na, Mg and Al and to discuss the possible influence of planets on this evolution. The results, similar to those obtained by other authors, show that the [X/Fe] ratios all decrease as a function of metallicity up to solar values. While for Mg and Al this trend then becomes relatively constant, for Na we find indications of an upturn up to [Fe/H] values close to 0.25dex. For metallicities above this value the [Na/Fe] becomes constant.
- ID:
- ivo://CDS.VizieR/J/ApJ/720/1592
- Title:
- Abundances of solar analogs with planets
- Short Name:
- J/ApJ/720/1592
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a fully differential chemical abundance analysis using very high resolution ({lambda}/{delta}{lambda}>~85000) and very high signal-to-noise (S/N~800 on average) HARPS and UVES spectra of 7 solar twins and 95 solar analogs, of which 24 are planet hosts and 71 are stars without detected planets. The whole sample of solar analogs provides very accurate Galactic chemical evolution trends in the metallicity range -0.3<[Fe/H]<0.5. Solar twins with and without planets show similar mean abundance ratios. We have also analyzed a sub-sample of 28 solar analogs, 14 planet hosts, and 14 stars without known planets, with spectra at S/N~850 on average, in the metallicity range 0.14<[Fe/H]<0.36, and find the same abundance pattern for both samples of stars with and without planets. This result does not depend on either the planet mass, from 7 Earth masses to 17.4 Jupiter masses, or the orbital period of the planets, from 3 to 4300 days. In addition, we have derived the slope of the abundance ratios as a function of the condensation temperature for each star and again find similar distributions of the slopes for both stars with and without planets. In particular, the peaks of these two distributions are placed at a similar value but with the opposite sign to that expected from a possible signature of terrestrial planets. In particular, two of the planetary systems in this sample, each of them containing a super-Earth-like planet, show slope values very close to these peaks, which may suggest that these abundance patterns are not related to the presence of terrestrial planets.
