Extracting interstellar diffuse absorption bands from cool star spectra:
  Application to bulge clump giants in Baade's window
  Interstellar diffuse bands are usually extracted from hot star spectra
because they are characterized by smooth continua. It introduces a strong
limitation on the number of available targets, and reduces potential studies of
the IS matter and the use of absorptions for cloud mapping. We have developed a
new automatic fitting method appropriate to interstellar absorptions in spectra
of cool stars that possess stellar atmospheric parameters. We applied this
method to the extraction of three DIBs in high resolution VLT FLAMES/GIRAFFE
spectra of red clump stars from the bulge. By combining all stellar synthetic
spectra, HITRAN-LBLRTM atmospheric transmission spectra and diffuse band
empirical absorption profiles, we determine the 6196, 6204, and 6284 A DIB
strength toward the 219 target stars and discuss the sources of uncertainties.
In order to test the sensitivity of the DIB extraction, we intercompare the
three results and compare the DIB equivalent widths with the reddening derived
from an independent extinction map based on OGLE photometric data. Most stellar
spectra could be well reproduced by the composite stellar, atmospheric and
interstellar models. Measurement uncertainties on the EWs are smaller for the
broad and strong 6284 A DIB, and are of the order of 10-15%. Uncertainties on
the two narrow and weaker DIBs are larger, as expected, and found to be highly
variable from one target to the other. They strongly depend on the radial
velocity of the star . DIB-DIB correlations among the three bands demonstrate
that a meaningful signal is extracted. For the 6284 and 6204 A DIBs, the
star-to-star variability of the equivalent width (EW) also reflects features of
the OGLE extinction map...
