The diffuse interstellar bands at 5797, 6379 and 6613 Angstroms. Ionization properties of the carriers
Abstract
We present a study of the behaviour and ionization properties of three narrow Diffuse Interstellar Bands (DIBs) at lambda lambda 5797, 6379 and 6613 Angstroms. In all three DIBs substructures have recently been detected, indicating large gaseous molecular carriers. Studying DIBs in regions with drastically different physical properties in terms of UV flux and density enables us to monitor the behaviour of the carriers and hence to constrain their nature. We observed these three DIBs along 40 different lines-of-sight (35 program stars and 5 standard stars) consisting of HII regions, dark clouds, molecular clouds and reflection nebulae. The DIB variations at low reddening are explained by a new model of photoionization equilibrium of the DIB carriers. This model takes into account the penetration depth of UV ionizing photons throughout the cloud. The slope of the variation of DIB strength as a function of reddening thus allows us to estimate the effective ionization potentials of the carriers. Following this new analysis, the carriers of the lambda 5797 and lambda 6613 Angstroms DIBs would have ionization potentials above 10eV, reminiscent of large PAHs or fullerenes which have a single positive charge. The estimated ionization potential (7--9eV) of the lambda 6379 Angstroms DIB seems to indicate a large neutral carrier. Based on observations with OHP 1.93m Telescope and Elalie spectrograph.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 1997
- Bibcode:
- 1997A&A...327.1215S
- Keywords:
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- ISM: MOLECULES;
- ISM: MOLECULAR CLOUDS;
- HII REGIONS;
- MOLECULAR PROCESSES;
- LINE: IDENTIFICATION