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