OBSERVING A COLUMN-DEPENDENT $\zeta$ IN THE HORSEHEAD PDR
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Date
2010
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Ohio State University
Abstract
The molecules CCH, C$_4$H, HCO$^+$, and HC$_3$N have been observed at the edge of the Horsehead Nebula in abundances far higher than those predicted by Photodissociation Region (PDR) models, 885 (2005)}. Using a column-dependent cosmic ray ionization rate ($\zeta$), 619 (2009)}, we model the edge of the Horsehead Nebula as a one-dimensional nearly-``edge-on'' heterogeneous PDR with temperature ranging from 15-250 K, number density from $10^3$ - $5 \times 10^5$ cm$^{-3}$, and $\zeta = 10^{-16}$ - $10^{-14}$ s$^{-1}$. The resulting abundances for the molecules listed above are much closer to the observed abundances. In this talk, we will discuss this method, its results, and the usefulness of incorporating a column-dependent $\zeta$ in astrochemical PDR models, especially in the advent of ALMA.
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Author Institution: Department of Physics, Ohio State University, Columbus, OH 43210; Institute of Astronomy and Astrophysics, Academia Sinica, Tapei 11677, Taiwan; Observatoire de Paris, LUTH and Universite Denis Diderot, Place J. Janssen 92190 Meudon, France; Departments of Astronomy, Physics, and Chemistry, Ohio State University, Columbus, OH 43210