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Astron. Astrophys. 347, 235-242 (1999)


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On the relation between diffuse interstellar bands and simple molecular species *

J. Kreowski 1, P. Ehrenfreund 2, B.H. Foing 3, T.P. Snow 4, T. Weselak 1, S. Ó. Tuairisg 2, G.A. Galazutdinov 5 and F.A. Musaev 5

1 Center for Astronomy, Nicholas Copernicus University, Gagarina 11, PL-87-100 Toru, Poland
2 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands
3 ESA Space Science Department, ESTEC/SCI-SO, 2200 AG Noordwijk, The Netherlands and IAS/CNRS, France
4 University of Colorado, CASA, Campus Box 391, Boulder, CO 80309, USA
5 Special Astrophysical Observatory, Nizhnij Arkhyz 357147, Russia

Received 25 January 1999 / Accepted 21 April 1999

Abstract

We present observations of the major diffuse interstellar bands (DIBs) at 5780 and 5797 Å as well as literature data and our own observations of the violet lines of CH and [FORMULA], in the lines of sight toward some 70 stars representing various degrees of the interstellar reddening. The correlations are shown and discussed in the context of indicators such as far-UV extinction parameters and neutral molecular abundances. The results show that the DIBs in question ([FORMULA][FORMULA]5797 and 5780) both probably form in diffuse cloud interiors, in a related regime where CH and H2 form. The ratio of the two DIBs correlates with CH abundance, confirming that the [FORMULA]5797 carrier is favoured in enhanced molecular gas regions over the [FORMULA]5780 carrier. The ratio of the two DIBs correlates poorly with CH+ abundance. Our compilation of observational data also suggests that the DIB ratio may be equally useful as a cloud type indicator as is RV, the ratio of total to selective extinction, and much more readily observed.

Key words: ISM: dust, extinction – ISM: molecules – infrared: ISM: lines and bands

* Based on observations obtained at the Russian Special Astrophysical Observatory (SAO), Terskol Observatory (TER), Canada France Hawaii Telescope (CFHT), European Southern Observatory (ESO), Observatoire de Haute-Provence (OHP)

Send offprint requests to: P. Ehrenfreund

© European Southern Observatory (ESO) 1999

Online publication: June 18, 1999

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