Hot Subdwarf Atmospheric Parameters, Kinematics, and Origins Based on 1587 Hot Subdwarf Stars Observed in Gaia DR2 and LAMOST DR7
Yangping Luo et al 2021 ApJS 256 28
Categorization of hot subdwarfs — stars with temperatures similar to O and B stars but with lower masses — based on helium abundance reveals four separate stellar populations that likely have different origins.