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          Institute: MPI für Astrophysik     Collection: High Energy Astrophysics at MPA     Display Documents

ID: 10719.0, MPI für Astrophysik / High Energy Astrophysics at MPA
Numerical methods for non-LTE line radiative transfer: Performance and convergence characteristics
Authors:van Zadelhoff, G. J.; Dullemond, C. P.; van der Tak, F. F. S.; Yates, J. A.; Doty, S. D.; Ossenkopf, V.; Hogerheijde, M. R.; Juvela, M.; Wiesemeyer, H.; Schoier, F. L.
Date of Publication (YYYY-MM-DD):2002
Title of Journal:Astronomy & Astrophysics
Journal Abbrev.:Astron. Astrophys.
Issue / Number:1
Start Page:373
End Page:384
Review Status:Peer-review
Audience:Experts Only
Abstract / Description:Comparison is made between a number of independent computer programs for radiative transfer in molecular rotational lines. The test models are spherically symmetric circumstellar envelopes with a given density and temperature profile. The first two test models have a simple power law density distribution, constant temperature and a fictive 2-level molecule, while the other two test models consist of an inside- out collapsing envelope observed in rotational transitions of HCO+. For the 2-level molecule test problems all codes agree well to within 0.2%, comparable to the accuracy of the individual codes, for low optical depth and up to 2% for high optical depths (tau = 4800). The problem of the collapsing cloud in HCO+ has a larger spread in results, ranging up to 12% for the J = 4 population. The spread is largest at the radius where the transition from collisional to radiative excitation occurs. The resulting line profiles for the HCO+ J = 4-3 transition agree to within 10%, i.e., within the calibration accuracy of most current telescopes. The comparison project and the results described in this paper provide a benchmark for future code development, and give an indication of the typical accuracy of present day calculations of molecular line transfer.
Free Keywords:stars : formation; molecular processes
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astrophysik
External Affiliations:Leiden Observ, POB 9513, NL-2300 RA Leiden, Netherlands; Leiden Observ, NL-2300 RA Leiden, Netherlands; Max Planck Inst Astrophys, D-85741 Garching, Germany; Max Planck Inst Radioastron, D-53121 Bonn, Germany; Univ Coll London, London WC1E 6BT, England; Denison Univ, Dept Phys & Astron, Granville, OH 43023 USA; Univ Cologne, Inst Phys 1, D-50937 Cologne, Germany; Univ Arizona, Steward Observ, Tucson, AZ 85721 USA; Univ Helsinki, Helsinki Univ Observ, FIN-00014 Helsinki, Finland; Inst Radio Astron Millimetr, F-38406 St Martin Dheres, France
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