AN INFRARED DIFFUSE CIRCUMSTELLAR BAND? THE UNUSUAL 1.5272μm DIB IN THE RED SQUARE NEBULA

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 Apache Point Observatory Galactic Evolution Experiment survey, we present an analysis of the unusually asymmetric 1.5272 μm DIB feature along the sightline to the Red Square Nebula (RSN) 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 RSN 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.

Medium-resolution échelle spectroscopy of the Red Square Nebula, MWC 922

“…Some of these emission bands were also compared to the diffuse interstellar bands (DIBs), molecular features which are usually seen in absorption in diffuse interstellar clouds. The Red Rectangle seems unique in this respect as it shows the same molecular features (DIBs) seen in emission (Sarre 1991;Scarrott et al 1992;Sarre et al 1995;Van Winckel et al 2002;Wehres et al 2011 of the Red Square, although one particular IR DIB has been argued to arise from circumstellar material in the nebula itself (Zasowski et al 2015). An overview of the X-shooter spectrum is given in Fig.…”

Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

“…9. Mapping the interstellar medium using Diffuse Interstellar Bands (Zasowski et al 2015a(Zasowski et al , 2015b, or dust reddening effects (Schultheis et al 2014). …”

The Data-Driven Approach to Spectroscopic Analyses

“…This figure shows a feature not captured in The Cannon's model which has high residuals only very near the plane, and is dispersed in radial velocity. This feature corresponds to the strongest diffuse interstellar band identified in the APOGEE spectra (see Zasowski et al 2015).…”