Near-Infrared Diffuse Interstellar Bands towards Her 36
  Discovered almost a century ago, the Diffuse Interstellar Bands (DIBs) still
lack convincing and comprehensive identification. Hundreds of DIBs have now
been observed in the near-ultraviolet (NUV), visible and near-infrared (NIR).
They are widely held to be molecular in origin, and modelling of their band
profiles offers powerful constraints on molecular constants. Herschel 36, the
illuminating star of the Lagoon Nebula, has been shown to possess unusually
broad and asymmetric DIB profiles in the visible, and is also bright enough for
NIR observation. We present here high-resolution spectroscopic observations
targeting the two best-known NIR DIBs at 11797.5 and 13175 A toward this object
and a nearby comparison O-star, 9 Sgr, using the GNIRS instrument on Gemini
North. We show a clear detection of the 13175 A DIB in both stars, and find (i)
that it does not exhibit the unusual wing structure of some of the visual DIBs
in Her 36 and (ii) that the depth of the band in the two objects is very
similar, also contrary to the behaviour of the visual DIBs. We discuss the
implications of these results for multiple DIB carrier candidates, and the
location of their carriers along the observed lines of sight.
