Chemical abundances and kinematics of 257 G-, K-type field giants. Setting a base for further analysis of giant-planet properties orbiting evolved stars★

Abstract

We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257 G-and K-type evolved stars from the CORALIE planet search program. To date, only one of these stars is known to harbor a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. 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. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a "gap" in metallicity between the thick-disk and high-α metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B -V colour cut-off, which excludes low-log g stars with high metallicities, and high-log g star with low-[Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars we suggest to use a sub-sample of stars in a "cut-rectangle" in the log g -[Fe/H] diagram to overcome the aforementioned issue.

Constraining planet structure from stellar chemistry: the cases of CoRoT-7, Kepler-10, and Kepler-93

“…The abundances of magnesium (Mg) and silicon (Si) were derived for the three stars following the same methodology as in our previous works (e.g., Adibekyan et al 2012aAdibekyan et al , 2015. We used a LTE analysis relative to the Sun with the 2014 version of the code MOOG (Sneden 1973) and a grid of Kurucz ATLAS9 plane-parallel model atmospheres with no α-enhancement.…”

Searching for Li-rich giants in a sample of 12 open clusters

“…In order to check whether the stars with higher Li show a different abundance pattern from their counterparts in the same cluster, we have derived abundances for 12 refractory elements (α and Fe-peak), in the same way as Adibekyan et al (2015), which will be presented in a separate work (Zaworska et al, in prep.). All the stars within the same cluster show similar abundances within the errors, and no clear enhancement in a given element is observed for any of the Li-enhanced stars.…”

Consistent metallicity scale for cool dwarfs and giants

“…A similar conclusion has been reached by other authors who recently proposed to improve existing line list by customising it to the stars observed, using an empirical approach. This method has been applied to cool dwarfs (Tsantaki et al 2013) and to evolved stars (Adibekyan et al 2015), reaching substantial improvements with respect to what obtained with a not optimised line list.…”