New hot subdwarf stars identified in Gaia DR2 with LAMOST DR5 spectra

TL;DR

This study identifies 294 new hot subdwarf stars in the Galaxy by combining Gaia DR2 data with LAMOST DR5 spectra, revealing two distinct helium sequences and expanding the known population of these stars.

Contribution

It presents a large sample of newly identified hot subdwarf stars with detailed atmospheric parameters, utilizing combined Gaia and LAMOST data for the first time at this scale.

Findings

Discovery of 294 hot subdwarf stars, including various spectral types.

Identification of two distinct helium sequences in the T_eff - log g diagram.

Demonstration of Gaia and LAMOST data synergy in uncovering new hot subdwarfs.

Abstract

We selected 4593 hot subdwarf candidates from the Gaia DR2 Hertzsprung-Russell (HR) diagram. By combining the sample with LAMOST DR5, we identified 294 hot subdwarf stars, including 169 sdB, 63 sdOB, 31 He-sdOB, 22 sdO, 7 He-sdO and 2 He-sdB stars. The atmospheric parameters (e.g., T_{eff} , log g, log(nHe/nH)) are obtained by fitting the hydrogen (H) and helium (He) line profiles with synthetic spectra. Two distinct He sequences of hot subdwarf stars are clearly presented in the T_{eff} - log g diagram. We found that the He-rich sequence consists of the bulk of sdB and sdOB stars as well as all of the He-sdB, He-sdO and He-sdOB stars in our samples, while all the stars in the He-weak sequence belong to the sdO spectral type, combined with a few sdB and sdOB stars. We demonstrated that the combination of Gaia DR2 and LAMOST DR5 allows one to uncover a huge number of new hot subdwarf stars in our Galaxy.