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Issue A&A
Volume 427, Number 2, November IV 2004
Page(s) 561 - 566
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20034235



A&A 427, 561-566 (2004)
DOI: 10.1051/0004-6361:20034235

Modeling the gas reservoir of circumstellar disks around young G-type stars

I. Kamp1, 2 and F. Sammar1

1  Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
2  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
    e-mail: kamp@stsci.edu

(Received 27 August 2003 / Accepted 27 July 2004)

Abstract
Interpretation of molecular line observations in tenuous circumstellar disks around young G-type stars in terms of a disk mass is difficult without a model that describes the chemical structure of these disks. This paper discusses the chemistry in tenuous disks around young solar-type stars based on disk models that take into account the presence of a stellar chromosphere. The example of the disk around a 70 Myr old solar-type star shows that the dissociating radiation from the chromosphere is stronger than the interstellar ultraviolet radiation field up to a distance of ~400 AU from the star. Similar to other studies in this research field, it is found that, due to photodissociation, the CO-to-H 2 ratio is far from the canonical value of 10-4 for molecular clouds. Moreover, the dust-to-gas mass ratio as well as the dust grain size plays an important role for the H 2 abundance in these disks.


Key words: stars: chromospheres -- stars: circumstellar matter -- stars: pre-main sequence -- stars: individual: HD 123160

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© ESO 2004


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