Hot subdwarf stars identified in LAMOST DR8 with single-lined and composite spectra

TL;DR

This study identifies 222 hot subdwarf stars in LAMOST DR8, analyzes their spectra, discovers new binary systems with unusual properties, and highlights features in their companion temperature distribution, advancing understanding of their formation and binary evolution.

Contribution

It provides the first large-scale spectral analysis of hot subdwarfs in LAMOST DR8, discovering new binary systems and examining their properties in detail.

Findings

Discovery of two long-period composite sdB binaries with high eccentricity.

Identification of a temperature gap among cool companions in composite spectra.

Many composite sdB stars are likely in binary systems requiring further study.

Abstract

222 hot subdwarf stars were identified with LAMOST DR8 spectra, among which 131 stars show composite spectra and have been decomposed, while 91 stars present single-lined spectra. Atmospheric parameters of all sample stars were obtained by fitting Hydrogen (H) and Helium (He) line profiles with synthetic spectra. Two long-period composite sdB binaries were newly discovered by combining our sample with the non-single star data from Gaia DR3. One of the new systems presents the highest eccentricity (i.e., 0.5 +/- 0.09) among known wide sdB binaries, which is beyond model predictions. 15 composite sdB stars fall in the high probability binary region of RUWE-AEN plane, and deserve priority follow-up observations to further study their binary nature. A distinct gap is clearly presented among temperatures of cool companions for our composite-spectra sample. But we could not come to a conclusion whether this feature is connected to the formation history of hot subdwarf stars before their binary natures are confirmed.