Radial velocity variability fractions of different types of hot subdwarf stars

• Published in: arXiv.org 2024-12
• Main Authors: He, Ruijie, Meng, Xiangcun, Lei, Zhenxin, Huahui Yan, Shunyi Lan
• Format: Article
• Language: English
• Subjects: B stars; Horizontal branch stars; Massive stars; Radial velocity; Subdwarf stars; Variability
• ISSN: 2331-8422

Different types of hot subdwarfs may have different origins, which will cause them to present different radial velocity (RV) variability properties. Only 6\(\pm\)4% of our single-lined He-rich hot subdwarfs that only show spectroscopic features of hot subdwarfs are found to be RV variable, which is lower than the fraction of single-lined He-poor sdB stars (31\(\pm\)3%). Single-lined sdB stars with effective temperatures (\(T_{\rm eff}\)) \(\sim\) 25,000 \(-\) 33,000 K show an RV-variability fraction of 34\(\pm\)5%, while lower RV-variability fractions are observed for single-lined sdB stars cooler than about 25,000 K (11\(\pm\)4%), single-lined sdB/OB stars with \(T_{\rm eff}\) \(\sim\) 33,000 \(-\) 40,000 K and surface gravities about 5.7 \(-\) 6.0 (13\(\pm\)3%), as well as single-lined sdO/B stars with \(T_{\rm eff}\) \(\sim\) 45,000 \(-\) 70,000 K (10\(\pm\)7%). Single-lined hot subdwarfs with \(T_{\rm eff}\) \(\sim\) 35,000 \(-\) 45,000 K located above the extreme horizontal branch (EHB) show a similar RV-variability fraction of 34\(\pm\)9% as single-lined sdB stars at about 25,000 \(-\) 33,000 K. The largest RV-variability fraction of 51\(\pm\)8% is found in single-lined hot subdwarfs below the canonical EHB. The detected RV-variability fraction of our composite hot subdwarfs with an infrared excess in their spectral energy distributions is 9\(\pm\)3%, which is lower than that fraction of single-lined hot subdwarfs. Since the average RV uncertainty we measured in the LAMOST spectra is about 7.0 km/s, the lower detected RV-variability fraction for composite hot subdwarfs is expected because the RV amplitudes associated with long-period systems are lower.