A catalog of early-type stars toward the Galactic center
  It is still unclear whether the Sagittarius spiral arm is a major spiral arm
in the Galaxy or whether it just outlines a region of enhanced star formation
because of the local compression of gas. The best way to separate these
scenarios out is to study the kinematics across the arm to determine the
velocity perturbation it induces. A survey of early-type stars in the direction
of the Galactic center is performed covering an area of 100 square degrees with
the aim of identifying candidates for a radial velocity study. Objective prism
plates were obtained with the 4deg prism on the ESO Schmidt telescope using
IIaO, 4415, and IIIaJ emulsions. The plates were digitized and more than 100k
spectra were extracted down to a limiting magnitude of B = 15m. The spectra
were cross-correlated with a template with Balmer lines, which yielded a
candidate list of 12675 early-type stars. Magnitudes and equivalent widths of
strong lines were calculated from the spectra, which allowed us to estimate the
individual extinctions and distances for 11075 stars. The survey identified
9571 candidate stars with a spectral type earlier than A1 and B < 14.5m out to
distances of more than 2kpc, which is beyond the Sagittarius arm. This is
indicated by the increase of absorption in the plane at distances larger than
0.5kpc.
