2002/05/17 by S. D. Doty, E. F. van Dishoeck, F. F. S. van der Tak +1 · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1051/0004-6361:20020597
18 pages, 16 figures
arxiv created 2002/05/17 · arxiv updated 2009/12/01
We present detailed thermal and gas-phase chemical models for the envelope of the massive star-forming region AFGL 2591. Time- and space-dependent chemistry are used to study the physical structure proposed by van der Tak et al. (1999; 2000), and the chemical evolution of this region. The model is compared with observations for 29 species covering a wide range of conditions within the source. Taking appropriate care when comparing models with both emission and absorption measurements, we find that the majority of the chemical structure can be well-explained. In particular, we find that the nitrogen and hydrocarbon chemistry can be significantly affected by temperature, with the possibility of high-temperature pathways to HCN. While we cannot determine the sulphur reservoir, the observations can be explained by models with the majority of the sulphur in CS in the cold gas, SO2 in the warm gas, and atomic sulphur in the warmest gas. The observed abundances of ions such as HCO+ and N2H+ and the cold gas-phase production of HCN constrain the cosmic-ray ionization rate to ∼ 5.6 × 10-17 s-1, to within a factor of three. Finally, we find that the model and observations can simultaneously agree at a reasonable level and often to within a factor of three for 7 × 103 ≤ t(yrs) ≤ 5 × 104, with a strong preference for t ∼ 3 × 104 yrs since the collapse and formation of the central luminosity source.