Diffuse interstellar bands as probes of small-scale interstellar structure

TL;DR

This study uses diffuse interstellar bands to investigate small-scale structures in the interstellar medium, revealing variations over 0.25 parsecs and stability over 10 AU scales, with some unusual spectral features.

Contribution

It provides new observational evidence of small-scale interstellar structure using DIBs, including velocity shifts and stability over different spatial scales.

Findings

Significant DIB differences over 0.25 pc separation.

No DIB variation over ~10 AU in Kappa Vel.

Detection of an unusual DIB spectrum.

Abstract

We present observations which probe the small-scale structure of the interstellar medium using diffuse interstellar bands (DIBs). Towards HD 168075/6 in the Eagle Nebula, significant differences in DIB absorption are found between the two lines of sight, which are separated by 0.25 pc, and {\lambda}5797 exhibits a velocity shift. Similar data are presented for four stars in the {\mu} Sgr system. We also present a search for variations in DIB absorption towards {\kappa} Vel, where the atomic lines are known to vary on scales of ~10 AU. Observations separated by ~9 yr yielded no evidence for changes in DIB absorption strength over this scale, but do reveal an unusual DIB spectrum.