Röllig, M. and Abel, N. P. and Bell, T. and Bensch, F. and Black, J. and Ferland, G. J. and Jonkheid, B. and Kamp, I. and Kaufman, M. J. and Le Bourlot, J. and Le Petit, F. and Meijerink, R. and Morata, O. and Ossenkopf, V. and Roueff, E. and Shaw, G. and Spaans, M. and Sternberg, A. and Stutzki, J. and Thi, W.-F. and van Dishoeck, E. F. and van Hoof, P. A. M. and Viti, S. and Wolfire, M. G. (2007) A photon dominated region code comparison study. Astronomy and Astrophysics, 467 (1). pp. 187-206. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20091117-135414524
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Aims. We present a comparison between independent computer codes, modeling the physics and chemistry of interstellar photon dominated regions (PDRs). Our goal was to understand the mutual differences in the PDR codes and their effects on the physical and chemical structure of the model clouds, and to converge the output of different codes to a common solution. Methods. A number of benchmark models have been created, covering low and high gas densities n = 10^3, 10^(5.5) cm^(-3) and far ultraviolet intensities χ = 10, 10^5 in units of the Draine field (FUV: 6 < h υ < 13.6 eV). The benchmark models were computed in two ways: one set assuming constant temperatures, thus testing the consistency of the chemical network and photo-processes, and a second set determining the temperature self consistently by solving the thermal balance, thus testing the modeling of the heating and cooling mechanisms accounting for the detailed energy balance throughout the clouds. Results. We investigated the impact of PDR geometry and agreed on the comparison of results from spherical and plane-parallel PDR models. We identified a number of key processes governing the chemical network which have been treated differently in the various codes such as the effect of PAHs on the electron density or the temperature dependence of the dissociation of CO by cosmic ray induced secondary photons, and defined a proper common treatment. We established a comprehensive set of reference models for ongoing and future PDR model bench-marking and were able to increase the agreement in model predictions for all benchmark models significantly. Nevertheless, the remaining spread in the computed observables such as the atomic fine-structure line intensities serves as a warning that there is still a considerable uncertainty when interpreting astronomical data with our models.
|Additional Information:||© ESO 2007. Received 27 June 2006. Accepted 2 February 2007 We thank the Lorentz Center, Leiden, for hosting the workshop and for the perfect organization, supplying a very productive environment. The workshop and this work was partly funded by the Deutsche Forschungs Gesellschaft DFG via Grant SFB494 and by a Spinoza grant from the Netherlands Organization for Scientific Research (NWO). We also would like to thank the referee and the editor for making helpful suggestions which helped to improve the manuscript.|
|Subject Keywords:||ISM : abundances; astrochemistry; ISM : clouds; ISM : general; radiative transfer; methods : numerical|
|Official Citation:||A photon dominated region code comparison study M. Röllig, N. P. Abel, T. Bell, F. Bensch, J. Black, G. J. Ferland, B. Jonkheid, I. Kamp, M. J. Kaufman, J. Le Bourlot, F. Le Petit, R. Meijerink, O. Morata, V. Ossenkopf, E. Roueff, G. Shaw, M. Spaans, A. Sternberg, J. Stutzki, W.-F. Thi, E. F. van Dishoeck, P. A. M. van Hoof, S. Viti and M. G. Wolfire A&A 467 (1) 187-206 (2007) DOI: 10.1051/0004-6361:20065918|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Nov 2009 19:40|
|Last Modified:||26 Dec 2012 11:34|
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