Chemical Composition of B-type Stars from LAMOST DR5

We present detailed criteria for the classification of subtypes of B-type supergiants and apply them to 97 supergiants chosen manually from the LAMOST DR5 data set. We obtained the physical parameters (effective temperature, surface gravity, projected rotational velocity) and chemical abundances of C and Si for 103 B-type stars, including 62 supergiants. Non-LTE TLUSTY atmospheric models are employed in our analysis. Projected rotational velocities of B-type stars are found to be systematically smaller than those of the old clusters in the Milky Way. The spectral types and luminosity classes of our manually classified B-type stars are consistent with their effective temperatures and surface gravities derived from the model spectral matching method, respectively. The obtained C and Si abundances for most of our B-type stars are subsolar. Our results indicate that a silicon abundance gradient is -0.0419 ± 0.0226 dex kpc^-1 in the region of 7.1 kpc ≤ R _g ≤ 14.1 kpc, which is in agreement with previous studies.