Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...281..517j&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 281, no. 2, p. 517-525
Astronomy and Astrophysics
Astrophysics
29
Abundance, Astronomical Spectroscopy, Cosmic Dust, Interstellar Extinction, Interstellar Matter, Molecular Clouds, Orion Nebula, Visible Spectrum, H Ii Regions, Hydrogen, Molecular Gases, Monatomic Gases, Stellar Spectra
Scientific paper
Four Diffuse Intersellar Bands (DIB) have been measured in 22 lines of sight towards Orion and GMC214-13. The paper reports on the environment dependence of DIB strength, using reddening, the total extinction in the visual, and column densities of various forms of hydrogen as indicators of line of sight conditions. In lines of sight with small reddening, EB-V less than 0.08 mag, a weakening of lambda(6284) and lambda(5785) is found relative to reddening (= all matter), but no weakening relative to atomic + molecular hydrogen (= all neural matter). This probably implies that the DIB carriers are absent in the ionised HII medium. At higher reddening, where a significant part of hydrogen is an molecular form, all DIBs in Orion decrease with increasing EB-V in a similar way as is known for the Taurus and Ophiuchus dark clouds. In Taurus, where even in low reddened lines of sight a significant part of hydrogen is in molecular form, lambda(6284) is weakened compared to diffuse medium values at lower reddening than lambda (6196). In lines of sight towards the Orion Nebula, where molecular hydrogen is mostly dissociated, lambda(6284) is some 70% stronger, while lambda(6196) is a factor of 5 weaker than expected from the above dependence. The results are discussed in the context that the carrier of the diffuse bands might be a large molecule in ionised form. The dissociation and ionisation state of hydrogen is used as an indicator of the UV field. The results above indicate that the lambda(6284) carrier is both ionised and destroyed by higher energy photons than the lambda(6196) carrier, which is consistent with a molecular carrier.
Ehrenfreund Pascale
Foing Bernard
Jenniskens Peter
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