- ID:
- ivo://CDS.VizieR/J/A+A/558/A106
- Title:
- Chemical abundances for 83 transit hosts
- Short Name:
- J/A+A/558/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precise stellar parameters are crucial in exoplanet research for correctly determining of the planetary parameters. For stars hosting a transiting planet, determining of the planetary mass and radius depends on the stellar mass and radius, which in turn depend on the atmospheric stellar parameters. Different methods can provide different results, which leads to different planet characteristics. In this paper, we use a uniform method to spectroscopically derive stellar atmospheric parameters, chemical abundances, stellar masses, and stellar radii for a sample of 90 transit hosts. Surface gravities are also derived photometrically using the stellar density as derived from the light curve. We study the effect of using these different surface gravities on the determination of the chemical abundances and the stellar mass and radius. A spectroscopic analysis based on Kurucz models in LTE was performed through the MOOG code to derive the atmospheric parameters and the chemical abundances. The photometric surface gravity was determined through isochrone fitting and the use of the stellar density, directly determined from the light curve. Stellar masses and radii are determined through calibration formulae. Spectroscopic and photometric surface gravities differ, but this has very little effect on the precise determination of the stellar mass in our spectroscopic analysis. The stellar radius, and hence the planetary radius, is most affected by the surface gravity discrepancies. For the chemical abundances, the difference is, as expected, only noticable for the abundances derived from analyzing of lines of ionized species.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/378/1141
- Title:
- Chemical abundances in 31 stars with planet
- Short Name:
- J/MNRAS/378/1141
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of detailed spectroscopic abundance analyses for 18 elements in 31 nearby stars with planets (SWPs). The resulting abundances are combined with other similar studies of nearby SWPs and compared to a sample of nearby stars without detected planets. We find some evidence for abundance differences between these two samples for Al, Si and Ti. Some of our results are in conflict with a recent study of SWPs in the SPOCS data base. We encourage continued study of the abundance patterns of SWPs to resolve these discrepancies.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/1900
- Title:
- Chemical abundances of 257 giant stars
- Short Name:
- J/MNRAS/450/1900
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a uniform and detailed abundance analysis of 12 refractory elements for a sample of 257 G- and K-type evolved stars from the CORALIE planet search program. This sample, being homogeneously analyzed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an LTE abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations both a purely kinematical approach and a chemical method were applied.
- ID:
- ivo://CDS.VizieR/J/A+A/547/A36
- Title:
- Chemical abundances of 87 KOIs
- Short Name:
- J/A+A/547/A36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent studies showed that at low metallicities Doppler-detected planet-hosting stars have preferably high alpha-content and belong to the thick disk.We used the reconnaissance spectra of 87 Kepler planet candidates and data available from the HARPS planet search survey to explore this phenomena. Using the traditional spectroscopic abundance analysis methods we derived Ti, Ca, and Cr abundances for the Kepler stars. In the metallicity region -0.65<[Fe/H]<-0.3dex the fraction of Ti-enhanced thick-disk HARPS planet harboring stars is 12.3+/-4.1% and for their thin-disk counterparts this fraction is 2.2+/-1.3%. The binomial statistics gives a probability of 0.008 that this could have occurred by chance. Combining the two samples (HARPS + Kepler) reinforces the significance of this result (P~99.97%). Since most of these stars are harboring small-mass/size planets we can assume that, although terrestrial planets can be found at low-iron regime, they are mostly enhanced by alpha-elements. This implies that early formation of rocky planets could get started in the Galactic thick disk, where the chemical conditions for their formation were more favorable.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A87
- Title:
- Chemical abundances of solar analogues
- Short Name:
- J/A+A/592/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- During the past decade, several studies reported a correlation between chemical abundances of stars and condensation temperature (also known as Tc trend). However, the real astrophysical nature of this correlation is still debated. The main goal of this work is to explore the possible dependence of the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality spectra of about 40 stars observed with the HARPS and UVES spectrographs to derive precise stellar parameters, chemical abundances, and stellar ages. A differential line-by-line analysis was applied to achieve the highest possible precision in the chemical abundances. We confirm previous results that [X/Fe] abundance ratios depend on stellar age and that for a given age, some elements also show a dependence on Rmean. When using the whole sample of stars, we observe a weak hint that the Tc trend depends on Rmean. The observed dependence is very complex and disappears when only stars with similar ages are considered. To conclude on the possible dependence of the Tc trend on the formation place of stars, a larger sample of stars with very similar atmospheric parameters and stellar ages observed at different Galactocentric distances is needed.
- ID:
- ivo://CDS.VizieR/J/A+A/497/563
- Title:
- Chemical abundances of 451 stars
- Short Name:
- J/A+A/497/563
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform study of the chemical abundances of 12 elements (Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Na, Mg, and Al) derived from the spectra of 451 stars observed as part of one of the HARPS GTO planet search programs. Sixty eight of these are planet-bearing stars. The main goals of our work are: i) the investigation of possible differences between the abundances of stars with and without planets; ii) the study of the possible differences in the abundances of stars in the thin and the thick disc. We confirm that there is a systematically higher metallicity in planet host stars, when compared to non planet-hosts, common to all studied species. We also found that there is no difference in the galactic chemical evolution trends of the stars with and without planets. Stars that harbour planetary companions simply appear to be in the high metallicity tail of the distribution. We also confirm that Neptunian and super-Earth class planets may be easier to find at lower metallicities. A statistically significative abundance difference between stars of the thin and the thick disc was found for [Fe/H]<0. However, the populations from the thick and the thin disc cannot be clearly separated.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A20
- Title:
- Circumstellar debris discs
- Short Name:
- J/A+A/579/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tentative correlations between the presence of dusty circumstellar debris discs and low-mass planets have recently been presented. In parallel, detailed chemical abundance studies have reported different trends between samples of planet and non-planet hosts. Whether these chemical differences are indeed related to the presence of planets is still strongly debated. We aim to test whether solar-type stars with debris discs show any chemical peculiarity that could be related to the planet formation process. We determine in a homogeneous way the metallicity, [Fe/H], and abundances of individual elements of a sample of 251 stars including stars with known debris discs, stars harbouring simultaneously debris discs and planets, stars hosting exclusively planets, and a comparison sample of stars without known discs or planets. High-resolution echelle spectra (R~57000) from 2-3m class telescopes are used. Our methodology includes the calculation of the fundamental stellar parameters (T_eff_, logg, microturbulent velocity, and metallicity) by applying the iron ionisation and equilibrium conditions to several isolated Fe i and Fe ii lines, as well as individual abundances of 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/441/195
- Title:
- Circumstellar disks in Trapezium cluster
- Short Name:
- J/A+A/441/195
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present results on the size distribution of circumstellar disks in the Trapezium cluster as measured from HST/WFPC2 data. Direct diameter measurements of a sample of 135 bright proplyds and 14 silhouettes disks suggest that there is a single population of disks well characterized by a power-law distribution with an exponent of -1.9+/-0.3 between disk diameters 100-400AU. For the stellar mass sampled (from late G to late M stars) we find no obvious correlation between disk diameter and stellar mass. We also find that there is no obvious correlation between disk diameter and the projected distance to the ionizing Trapezium OB stars. We estimate that about 40% of the disks in the Trapezium have radius larger than 50AU. We suggest that the origin of the Solar system's (Kuiper belt) outer edge is likely to be due to the star formation environment and disk destruction processes (photo-evaporation, collisions) present in the stellar cluster on which the Sun was probably formed. Finally, we identified a previously unknown proplyd and named it 266-557, following convention.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/20
- Title:
- C/O and Mg/Si for solar neighborhood's stars
- Short Name:
- J/ApJ/831/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon-to-oxygen ratio in a protoplanetary disk can have a dramatic influence on the compositions of any terrestrial planets formed. In regions of high C/O, planets form primarily from carbonates, and in regions of low C/O, the ratio of magnesium to silicon determines the types of silicates that dominate the compositions. We present C/O and Mg/Si ratios for 852 F, G, and K dwarfs in the solar neighborhood. We find that the frequency of carbon-rich dwarfs in the solar neighborhood is <0.13% and that 156 known planet hosts in the sample follow a similar distribution as all of the stars as a whole. The cosmic distribution of Mg/Si for these same stars is broader than the C/O distribution and peaks near 1.0, with ~60% of systems having 1<=Mg/Si<2, leading to rocky planet compositions similar to the Earth. This leaves 40% of systems that can have planets that are silicate-rich and that may have very different compositions than our own.
- ID:
- ivo://CDS.VizieR/J/ApJ/814/91
- Title:
- Comparative habitability of transiting exoplanets
- Short Name:
- J/ApJ/814/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Exoplanet habitability is traditionally assessed by comparing a planet's semimajor axis to the location of its host star's "habitable zone", the shell around a star for which Earth-like planets can possess liquid surface water. The Kepler space telescope has discovered numerous planet candidates near the habitable zone, and many more are expected from missions such as K2, TESS, and PLATO. These candidates often require significant follow-up observations for validation, so prioritizing planets for habitability from transit data has become an important aspect of the search for life in the universe. We propose a method to compare transiting planets for their potential to support life based on transit data, stellar properties and previously reported limits on planetary emitted flux. For a planet in radiative equilibrium, the emitted flux increases with eccentricity, but decreases with albedo. As these parameters are often unconstrained, there is an "eccentricity-albedo degeneracy" for the habitability of transiting exoplanets. Our method mitigates this degeneracy, includes a penalty for large-radius planets, uses terrestrial mass-radius relationships, and, when available, constraints on eccentricity to compute a number we call the "habitability index for transiting exoplanets" that represents the relative probability that an exoplanet could support liquid surface water. We calculate it for Kepler objects of interest and find that planets that receive between 60% and 90% of the Earth's incident radiation, assuming circular orbits, are most likely to be habitable. Finally, we make predictions for the upcoming TESS and James Webb Space Telescope missions.
