Diffuse interstellar bands in Upper Scorpius: Probing variations in the
  DIB spectrum due to changing environmental conditions
  We study the effects of local environmental conditions affecting the diffuse
interstellar band (DIB) carriers within the Upper Scorpius subgroup of the Sco
OB2 association. We obtained optical spectra with FEROS, and measured the
equivalent widths of five DIBs (at 5780, 5797, 6196, 6379, and 6613 Angstrom)
as well as those of absorption lines of di-atomic molecules (CH, CH+, CN) and
atoms (KI, CaI) towards 89 targets in the direction of Upper Scorpius. We
construct a simple radiative transfer and chemical network model of the diffuse
interstellar medium (ISM) sheet in front of Upp Sco to infer the effective
radiation field. Both the interstellar radiation field strength, I_UV, and the
molecular hydrogen fraction, f_H2, have been derived for 55 sightlines probing
the Upp Sco ISM. We discuss the relations between DIB strengths, CH and CH+
line strengths, E(B-V), I_UV, and f_H2. The ratio between the 5780 and 5797
DIBs reveals a (spatial) dependence on the local environment in terms of cloud
density and exposure to the interstellar radiation field, reflecting the
molecular nature of these DIB carriers.
