Hot Subdwarf Stars Identified in LAMOST DR8 with Single-lined and Composite Spectra

• Published in: The Astrophysical journal Vol. 942; no. 2; pp. 109 - 123
• Main Authors: Lei, Zhenxin, He, Ruijie, Németh, Péter, Vos, Joris, Zou, Xuan, Hu, Ke, Xiao, Huaping, Yan, Huahui, Zhao, Jingkun
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.01.2023; IOP Publishing
• Subjects: Astrophysics; B subdwarf stars; Binary stars; Helium; Line spectra; Spectra; Stellar evolution; Subdwarf stars; Wide binary stars
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aca542

Abstract A total of 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. A total of 15 composite sdB stars fall in the high-probability binary region of the 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-spectrum sample, but we could not come to a conclusion as to whether this feature is connected to the formation history of hot subdwarf stars before their binary natures are confirmed.