2013ApJ...774...72K

Diffuse interstellar bands (DIBs) can trace different conditions of the interstellar medium (ISM) along the sightline toward the observed stars. A small survey was made in optical wavelengths, producing high-resolution and high signal-to-noise spectra. We present measurements of 19 DIBs' properties in 50 sightlines toward hot stars, distributed at a variety of galactic coordinates and interstellar reddening. Equivalent widths were obtained by fitting asymmetric Gaussian and variable continua to DIBs. Conditions of the ISM were calculated from eight atomic and molecular interstellar lines. Two distinctly different types of DIBs were identified by carefully comparing correlation coefficients between DIBs and reddening and by different behavior in UV-shielded (ζ) and nonshielded (σ) sightlines. A ratio of DIBs at 5780 Å and 5797 Å proved to be reliable enough to distinguish between two different sightline types. Based on the linear relations between DIB equivalent width and reddening for σ and ζ sightlines, we divide DIBs into type I (where both linear relations are similar) and type II (where they are significantly different). The linear relation for ζ type sightlines always shows a higher slope and larger x-intercept parameter than the relation for σ sightlines. Scatter around the linear relation is reduced after the separation, but it does not vanish completely. This means that UV shielding is the dominant factor of the DIB equivalent width versus reddening relation shape for ζ sightlines, but in σ sightlines other physical parameters play a major role. No similar dependency on gas density, electron density, or turbulence was observed. A catalog of all observed interstellar lines is made public.