STUDIES OF DIFFUSE INTERSTELLAR BANDS V. PAIRWISE CORRELATIONS OF EIGHT STRONG DIBs AND NEUTRAL HYDROGEN, MOLECULAR HYDROGEN, AND COLOR EXCESS
- Space Telescope Science Institute, Baltimore, MD 21218 (United States)
- Department of Astronomy and Astrophysics and the Enrico Fermi Institute, University of Chicago, Chicago, IL (United States)
- Departments of Chemistry, Astronomy, and Physics, University of Illinois at Urbana-Champaign, IL (United States)
- Department of Physics and Astronomy, Carthage College, Kenosha, WI (United States)
- Department of Astronomy, University of Illinois at Urbana-Champaign, IL (United States)
- Department of Astronomy, University of Virginia, Charlottesville, VA (United States)
- Department of Physics, Embry-Riddle Aeronautical University, Prescott, AZ (United States)
We establish correlations between equivalent widths of eight diffuse interstellar bands (DIBs), and examine their correlations with atomic hydrogen, molecular hydrogen, and E{sub B-V}. The DIBs are centered at {lambda}{lambda} 5780.5, 6204.5, 6283.8, 6196.0, 6613.6, 5705.1, 5797.1, and 5487.7, in decreasing order of Pearson's correlation coefficient with N(H) (here defined as the column density of neutral hydrogen), ranging from 0.96 to 0.82. We find the equivalent width (EW) of {lambda}5780.5 is better correlated with column densities of H than with E{sub B-V} or H{sub 2}, confirming earlier results based on smaller data sets. We show that the same is true for six of the seven other DIBs presented here. Despite this similarity, the eight strong DIBs chosen are not correlated well enough with each other to suggest they come from the same carrier. We further conclude that these eight DIBs are more likely to be associated with H than with H{sub 2}, and hence are not preferentially located in the densest, most UV shielded parts of interstellar clouds. We suggest that they arise from different molecules found in diffuse H regions with very little H{sub 2} (molecular fraction f < 0.01). Of the 133 stars with available data in our study, there are three with significantly weaker {lambda}5780.5 than our mean H-{lambda}5780.5 relationship, all of which are in regions of high radiation fields, as previously noted by Herbig. The correlations will be useful in deriving interstellar parameters when direct methods are not available. For instance, with care, the value of N(H) can be derived from W{sub {lambda}}(5780.5).
- OSTI ID:
- 21567609
- Journal Information:
- Astrophysical Journal, Vol. 727, Issue 1; Other Information: DOI: 10.1088/0004-637X/727/1/33; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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