Modeling the gas reservoir of circumstellar disks around young G-type stars
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: email@example.com
Accepted: 27 July 2004
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-H2 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 H2 abundance in these disks.
Key words: stars: chromospheres / stars: circumstellar matter / stars: pre-main sequence / stars: individual: HD 123160
© ESO, 2004