MK-like spectral classification for hot subdwarf stars with LAMOST spectra.

This article focuses on applying an MK-like spectral classification scheme to 1,224 hot subdwarf stars using low-resolution spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) Data Release 9 (DR9). The stars were categorized into four groups based on spectral line characteristics: He-normal, He-weak, He-strong C (carbon-rich), and He-strong, with each star assigned a spectral class, luminosity class, and helium class by comparison to selected LAMOST standard stars. The study demonstrates consistency between the spectral classifications and atmospheric parameters such as effective temperature, surface gravity, and helium abundance, and provides linear fitting formulae to facilitate automated spectral classification of hot subdwarfs in future analyses. This work expands the application of the MK-like classification system, originally proposed by Drilling et al., to a large sample of hot subdwarfs, contributing valuable data for astrophysical research on these stars.