Probing stellar evolution with S stars and Gaia

TL;DR

This paper uses Gaia data and high-resolution spectroscopy to determine atmospheric parameters of S stars, helping to distinguish intrinsic from extrinsic types and understand their evolutionary stages.

Contribution

It provides a detailed analysis of S star atmospheric parameters using Gaia parallaxes and MARCS models, improving understanding of their evolution and s-process element enrichment.

Findings

Intrinsic and extrinsic S stars are accurately located in the HR diagram.

Atmospheric parameters are derived despite their entanglement.

Enhanced s-process element abundance analysis is enabled.

Abstract

S-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The intrinsic S stars are on the AGB and have undergone third dredge-up events. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. These atmospheric parameters are also entangled within each other. Nevertheless, high-resolution spectroscopic data of S stars combined with the Gaia Data Release 2 (GDR2) parallaxes and with the MARCS model atmospheres for S-type stars were used to derive effective temperatures, surface gravities, and luminosities. These parameters not only allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell (HR) diagram but also allow the accurate abundance analysis of the s-process elements.