We present high-resolution echelle spectroscopic observations of the two near- infrared (NIR) Diffuse Interstellar Bands (DIBs) at 13175 A and 11797.5 A. The DIBs have been observed in a number of diffuse interstellar medium sightlines that exhibit a wide range of visual extinctions. Band profiles are similar to those seen in narrow DIBs, clearly asymmetric and can be closely fitted in most cases using two simple Gaussian components. Gaussian fits were generally found to be more successful than fits based on a multiple-cloud model using a template DIB profile. For a sample of 9 objects in which both bands are observed, the strength of both NIR DIBs generally increases with A(V), and we report a correlation between the two observed bands over a large A(V) range and widely-separated lines of sight. The strength of the two bands is also compared against those of two visual DIBs and the diffuse ISM aliphatic dust absorption feature at 3.4 microns previously detected in the same sightlines. We find that the NIR DIBs do not exhibit notable (anti)correlations with either. Implications of these observations on possible DIB carrier species are discussed.
M. Rawlings, A. Adamson and T. Kerr
Mon, 29 Sep 14
Comments: 35 pages; contains 8 figures (including a 3-page Figure 1) and 3 tables. Accepted for publication in the Astrophysical Journal