A study of the ISM with large massive-star optical spectroscopic surveys
  We are conducting a study on the imprint of the ISM on optical spectra based
on two types of ongoing spectroscopic massive-star surveys: on the one hand,
intermediate-resolution (R = 2500) green-blue spectra for ~3000 stars obtained
with the Galactic O Star Spectroscopic Survey (GOSSS). On the other hand,
high-resolution (R = 23 000 - 65 000) optical spectra for 600 stars obtained
from three different surveys, OWN, IACOB, and NoMaDS. The R = 2500 data allows
us to reach a larger sample with an average larger extinction while the R = 23
000 - 65 000 sample provides access to more diffuse interstellar bands (DIBs)
and allows for the resolution in velocity of some ISM features. For each
spectrum we are measuring the equivalent widths, FWHMs, and central wavelengths
of 10-40 DIBs and interstellar lines (e.g. Ca II H+K, Na I D1+D2) and, in the
case of GOSSS, the existence of an H II region around the star. We have also
derived from auxiliary data or compiled from the literature values for the
reddening, extinction law, H I column density, parallax, and H alpha emission.
All of this constitutes the most complete collection ever of optical
information on the ISM within 3 kpc of the Sun. We are analyzing the
correlations between all of the collected quantities to discriminate between
different possible origins of the DIBs.
