Hot subdwarf stars identified in Gaia DR2 with spectra of LAMOST DR6 and DR7 I. Single-lined spectra

TL;DR

This study identifies and classifies 182 hot subdwarf stars from Gaia DR2 using LAMOST spectra, revealing new discoveries, analyzing their atmospheric parameters, and discussing their origins and evolutionary implications.

Contribution

The paper presents a large, spectroscopically classified sample of hot subdwarfs from Gaia DR2, including new discoveries and detailed atmospheric analysis, advancing understanding of their origins.

Findings

108 hot subdwarfs are newly discovered.

The atmospheric parameters confirm two He sequences.

The hot subdwarf fraction varies between 10% and 60%.

Abstract

182 single-lined hot subdwarf stars are identified by using spectra from the sixth and seventh data release (DR6 and DR7) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey. We classified all the hot subdwarf stars using a canonical classification scheme, and got 89 sdB, 37 sdOB, 26 sdO, 24 He-sdOB, 3 He-sdO and 3 He-sdB stars, respectively. Among these stars, 108 hot subdwarfs are newly discovered, while 74 stars were reported by previous catalogs. The atmospheric parameters of these stars were obtained by fitting the hydrogen (H) and helium (He) lines with non-local thermodynamic equilibrium (non-LTE) model atmospheres. The atmospheric parameters confirm the two He sequences and the two subgroups of He-sdOB stars in our samples, which were found by previous studies in the T eff -log(nHe/nH) diagram. Our results demonstrate different origins of field hot subdwarf stars and extreme horizontal branch (EHB) stars in globular clusters (GCs), and provide strict observational limits on the formation and evolution models of the different sub-types of these evolved objects. Based on the results, we evaluated the completeness of the Geier et al. (2019) catalog. We found the fraction of hot subdwarf stars is between 10% and 60%, depending on the brightness of the sample. A more accurate estimation for the hot subdwarf fraction can be obtained when similar results from composite spectra will become available.