Discovery of s-process enhanced stars in the LAMOST survey

Brodie Norfolk, Andrew Casey, Amanda Karakas, Matthew T. Miles, Alex Kemp, Kevin C Schlaufman, Melissa K. Ness, Anna Ho, John Lattanzio, Alexander P. Ji

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Abstract

Here we present the discovery of 895 s-process-rich candidates from 454 180 giant stars observed by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) using a data-driven approach. This sample constitutes the largest number of s-process enhanced stars ever discovered. Our sample includes 187 s-process-rich candidates that are enhanced in both barium and strontium, 49 stars with significant barium enhancement only and 659 stars that show only a strontium enhancement. Most of the stars in our sample are in the range of effective temperature and log g typical of red giant branch (RGB) populations, which is consistent with our observational selection bias towards finding RGB stars. We estimate that only a small fraction (∼0.5 per cent) of binary configurations are favourable for s-process enriched stars. The majority of our s-process-rich candidates (95 per cent) show strong carbon enhancements, whereas only five candidates (<3 per cent) show evidence of sodium enhancement. Our kinematic analysis reveals that 97 per cent of our sample are disc stars, with the other 3 per cent showing velocities consistent with the Galactic halo. The scaleheight of the disc is estimated to be zh = 0.634 ± 0.063 kpc, comparable with values in the literature. A comparison with yields from asymptotic giant branch (AGB) models suggests that the main neutron source responsible for the Ba and Sr enhancements is the 13C(α,n)16O reaction. We conclude that s-process-rich candidates may have received their overabundances via mass transfer from a previous AGB companion with an initial mass in the range 1-3 M☉.

Original languageEnglish
Pages (from-to)2219-2227
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume490
Issue number2
DOIs
Publication statusPublished - 1 Dec 2019

Keywords

  • Stars: abundances - stars: chemically peculiar

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