Diffuse interstellar bands in RAVE Survey spectra

TL;DR

This study analyzes diffuse interstellar bands in RAVE spectra, confirming the strongest DIB at 8620.4 Ang and its correlation with reddening, while questioning the reality of weaker bands and their stellar line blends.

Contribution

First detailed analysis of DIBs in RAVE spectra, confirming the 8620.4 Ang DIB as a reddening indicator and clarifying the nature of other weak DIBs.

Findings

DIB at 8620.4 Ang correlates tightly with reddening.

Presence of a DIB at 8648 Ang is confirmed.

Weak DIBs at 8531 and 8572 Ang are likely blends with stellar lines.

Abstract

We have used spectra of hot stars from the RAVE Survey in order to investigate the visibility and properties of five diffuse interstellar bands previously reported in the literature. The RAVE spectroscopic survey for Galactic structure and kinematics records CCD spectra covering the 8400-8800 Ang wavelength region at 7500 resolving power. The spectra are obtained with the UK Schmidt at the AAO, equipped with the 6dF multi-fiber positioner. The DIB at 8620.4 Ang is by far the strongest and cleanest of all DIBs occurring within the RAVE wavelength range, with no interference by underlying absorption stellar lines in hot stars. It correlates so tightly with reddening that it turns out to be a reliable tool to measure it, following the relation E(B-V) = 2.72 (+/- 0.03) x E.W.(Ang), valid throughout the general interstellar medium of our Galaxy. The presence of a DIB at 8648 Ang is confirmed. Its intensity appears unrelated to reddening, in agreement with scanty and preliminary reports available in the literature, and its measurability is strongly compromised by severe blending with underlying stellar HeI doublet at 8649 Ang. The two weak DIBS at 8531 and 8572 Ang do not appear real and should actually be blends of underlying stellar lines. The very weak DIB at 8439 Ang cannot be resolved within the profile of the much stronger underlying hydrogen Paschen 18 stellar line.