Volume 397, Number 3, January III 2003
|Page(s)||789 - 802|
|Published online||21 January 2003|
Axi-symmetric models of ultraviolet radiative transfer with applications to circumstellar disk chemistry
Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Dept. of Earth and Planetary Sciences, Kobe University, 1-1 Rokkoudai, Nada-ku, Kobe, 657-8501, Japan
3 Steward Observatory, The University of Arizona, 933 N. Cherry Ave. Tucson AZ, USA
Corresponding author: G. J. van Zadelhoff, email@example.com
Accepted: 29 October 2002
A new two-dimensional axi-symmetric ultraviolet radiative transfer code is presented, which is used to calculate photodissociation and ionization rates for use in chemistry models of flaring circumstellar disks. Scattering and absorption of photons from the central star and from the interstellar radiation field are taken into account. The molecules are effectively photodissociated in the surface layer of the disk, but can exist in the intermediate, moderately warm layers. A comparison has been made with an approximate 2D ray-tracing method and it was found that the latter underestimates the ultraviolet field and thus the molecular photodissociation rates below the disk surface. The full 2D results show significantly higher abundances of radicals such as CN and C2H than previous work, partly due to the fact that CO is dissociated to greater depths. Results for different stellar radiation fields are also presented. The CN/HCN ratio shows a strong dependence on the stellar spectrum, whereas other ratios such as HCO+/CO show only little variation.
Key words: ISM: molecules / stars: pre-main sequence / stars: circumstellar matter / stars: planetary systems: protoplanetary disks / radiative transfer / line: profiles
© ESO, 2003
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