Are some CEMP-s stars the daughters of spinstars?

Arthur Choplin (1), Raphael Hirschi (2,3,4), Georges Meynet (1) and Sylvia Ekstrom (1)

1 - Geneva Observatory, University of Geneva, Maillettes 51, CH-1290 Sauverny, Switzerland
2 - Astrophysics Group, Lennard-Jones Labs 2.09, Keele University, ST5 5BG, Staffordshire, UK
3 - Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, 5-1-5
Kashiwanoha, Kashiwa, 277-8583, Japan
4 - UK Network for Bridging the Disciplines of Galactic Chemical Evolution (BRIDGCE)

Carbon-Enhanced Metal-Poor (CEMP)-s stars are long-lived low-mass stars with a very low iron content as well as overabundances of carbon and s-elements. Their peculiar chemical pattern is often explained by pollution from an asymptotic giant branch (AGB) star companion.
Recent observations have shown that most CEMP-s stars are in binary systems, providing support to the AGB companion scenario. A few CEMP-s stars, however, appear to be single. We inspect four apparently single CEMP-s stars and discuss the possibility that they formed from the ejecta of a previous-generation massive star, referred to as the ''source'' star. In order to investigate this scenario, we computed low-metallicity massive-star models with and without rotation and including complete s-process nucleosynthesis. We find that non-rotating source stars cannot explain the observed abundance of any of the four CEMP-s stars. Three out of the four CEMP-s stars can be explained by a 25 $M_{\odot}$ source star with $v_{\rm ini} \sim 500$ km s$^{-1}$ (spinstar). The fourth CEMP-s star has a high Pb abundance that cannot be explained by any of the models we computed. Since spinstars and AGB predict different ranges of [O/Fe] and [ls/hs], these ratios could be an interesting way to further test these two scenarios.

Reference: arXiv:1710.05564, Accepted in A&A
Status: Manuscript has been accepted