An Infrared Diffuse Circumstellar Band? The Unusual 1.5272 Micron DIB In the Red Square Nebula

TL;DR

This study analyzes a peculiar diffuse interstellar band in the Red Square Nebula using high-resolution spectra, suggesting a circumstellar origin and providing insights into the nature of DIB carriers in a unique environment.

Contribution

It presents the first evidence of a circumstellar origin for a DIB feature, using APOGEE spectra to analyze the 1.5272 micron DIB in the Red Square Nebula.

Findings

Approximately half of the DIB absorption is circumstellar in origin.

The asymmetric DIB profile indicates a complex environment.

The velocities and reddening ratios support a circumstellar interpretation.

Abstract

The molecular carriers of the ubiquitous absorption features called the diffuse interstellar bands (DIBs) have eluded identification for many decades, in part because of the enormous parameter space spanned by the candidates and the limited set of empirical constraints afforded by observations in the diffuse interstellar medium. Detection of these features in circumstellar regions, where the environmental properties are more easily measured, is thus a promising approach to understanding the chemical nature of the carriers themselves. Here, using high resolution spectra from the APOGEE survey, we present an analysis of the unusually asymmetric 1.5272 micron DIB feature along the sightline to the Red Square Nebula and demonstrate the likely circumstellar origin of about half of the DIB absorption in this line of sight. This interpretation is supported both by the velocities of the feature components and by the ratio of foreground to total reddening along the line of sight. The Red Square Nebula sightline offers the unique opportunity to study the behavior of DIB carriers in a constrained environment and thus to shed new light on the carriers themselves.