Spectral classification of B stars: The empirical sequence using SDSS-IV/APOGEE near-IR data

Abstract

We present a semi-empirical spectral classification scheme for normal B-type stars using near-infrared spectra (1.5-1.7 $\mu$m) from the SDSS APOGEE2-N DR14 database. The main motivation for working with B-type stars is their importance in the evolution of young stellar clusters, however we also take advantage of having a numerous sample (316 stars) of B-type star candidates in APOGEE2-N, for which we also have optical (3600-9100 \angstrom) counterparts from the LAMOST survey. By first obtaining an accurate spectral classification of the sources using the LAMOST DR3 spectra and the canonical spectral classification scheme Gray & Corbally 2009, we found a linear relation between optical spectral types and the equivalent widths of the hydrogen lines of the Brackett series in the APOGEE2-N NIR spectra. This relation extends smoothly from a similar relation for O and early-B stars found by Roman-Lopes et al. (2018). This way, we obtain a catalog of B-type sources with features in both the optical and NIR, and a classification scheme refined down to one spectral sub-class.

arXiv comment11 pages, 7 figures and 1 table

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• Stellar Properties for a Comprehensive Collection of Star Forming Regions in the SDSS APOGEE-2 Survey
• ABYSS I: Targeting strategy for APOGEE & BOSS young star survey in SDSS-V
• Simultaneous J-, H-, K- and L-band spectroscopic observations of galactic Be stars. I. IR atlas
• tonalli: an asexual genetic code to characterise APOGEE-2 stellar spectra. I. Validation with synthetic and solar spectra
• Astrophotometric search for massive stars in the Milky way. Confronting Random Forest predictions with available spectroscopy
• Zeta-Payne: a fully automated spectrum analysis algorithm for the Milky Way Mapper program of the SDSS-V survey