%0 Journal Article
%T S stars and s-process in the Gaia era
%T I. Stellar parameters and chemical abundances in a sub-sample of S stars with new MARCS model atmospheres
%+ Institut d'Astronomie et d'Astrophysique
%+ Instituut voor Sterrenkunde [Leuven]
%+ Université libre de Bruxelles (ULB)
%+ Laboratoire Univers et Particules de Montpellier (LUPM)
%A Shetye, S.
%A van Eck, S.
%A Jorissen, A.
%A van Winckel, H.
%A Siess, L.
%A Goriely, S.
%A Escorza, A.
%A Karinkuzhi, D.
%A Plez, Bertrand
%< avec comité de lecture
%@ 0004-6361
%J Astronomy and Astrophysics - A&A
%I EDP Sciences
%V 620
%P A148
%8 2018-12
%D 2018
%Z 1810.07105
%R 10.1051/0004-6361/201833298
%Z Physics [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR]Journal articles
%X S stars are transition objects between M-type giants and carbon stars on the asymptotic giant branch (AGB). They are characterized by overabundances of s-process elements. Roughly half of them are enhanced in technetium (Tc), an s-process element with no stable isotope, while the other half lack technetium. This dichotomy arises from the fact that Tc-rich S stars are intrinsically producing s-process elements and have undergone third dredge-up (TDU) events, while Tc-poor S stars owe their s-process overabundances to a past pollution by a former AGB companion. Our aim is to analyse the abundances of S stars and gain insights into their evolutionary status and on the nucleosynthesis of heavy s-process elements taking place in their interior. In particular, the location of extrinsic and intrinsic S stars in the HR diagram will be compared with the theoretical onset of the TDU on the thermally-pulsing AGB. A sample of 19 S-type stars was analysed by combining HERMES high-resolution spectra, accurate Gaia Data Release 2 (GDR2) parallaxes, stellar-evolution models, and newly-designed MARCS model atmospheres for S-type stars. Combining the derived parameters with GDR2 parallaxes allows a joint analysis of the location of the stars in the Hertzsprung-Russell diagram and of their surface abundances. For all 19 stars, Zr and Nb abundances are derived, complemented by abundances of other s-process elements for the three Tc-rich S stars. These abundances agree within the uncertainties with nucleosynthesis predictions for stars of corresponding mass, metallicity and evolutionary stage. Most extrinsic S stars lie close to the tip of the red giant branch (RGB), and a few are located along the early AGB. The location of intrinsic S stars in the HR diagram is compatible with them being thermally-pulsing AGB stars.
%G English
%L hal-01971966
%U https://hal.science/hal-01971966
%~ IN2P3
%~ CNRS
%~ LUPM
%~ UNIV-MONTPELLIER
%~ LUPM_AS
%~ UM-2015-2021