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