Query : 2013A&A...550A..56R

2013A&A...550A..56R - Astronomy and Astrophysics, volume 550A, 56-56 (2013/2-1)

Carbon fractionation in photo-dissociation regions.


Abstract (from CDS):

We upgraded the chemical network from the UMIST Database for Astrochemistry 2006 to include isotopes such as 13C and 18O. This includes all corresponding isotopologues, their chemical reactions and the properly scaled reaction rate coefficients. We study the fractionation behavior of astrochemically relevant species over a wide range of model parameters, relevant for modelling of photo-dissociation regions (PDRs). We separately analyze the fractionation of the local abundances, fractionation of the total column densities, and fractionation visible in the emission line ratios. We find that strong C+ fractionation is possible in cool C+ gas. Optical thickness as well as excitation effects produce intensity ratios between 40 and 400. The fractionation of CO in PDRs is significantly different from the diffuse interstellar medium. PDR model results never show a fractionation ratio of the CO column density larger than the elemental ratio. Isotope-selective photo-dissociation is always dominated by the isotope-selective chemistry in dense PDR gas. The fractionation of C, CH, CH+ and HCO+ is studied in detail, showing that the fractionation of C, CH and CH+ is dominated by the fractionation of their parental species. The light hydrides chemically derive from C+, and, consequently, their fractionation state is coupled to that of C+. The fractionation of C is a mixed case depending on whether formation from CO or HCO+ dominates. Ratios of the emission lines of [CII], [CI], 13CO, and H13CO+ provide individual diagnostics to the fractionation status of C+, C, and CO.

Abstract Copyright:

Journal keyword(s): astrochemistry - ISM: abundances - ISM: structure - ISM: clouds - photon-dominated region (PDR)

Simbad objects: 6

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Number of rows : 6
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 RAFGL 5077 HII 02 43 28.62213 +62 57 08.7770           ~ 70 0
2 TMC-1 MoC 04 41 45.9 +25 41 27           ~ 1620 0
3 M 42 HII 05 35 17 -05 23.4           ~ 4024 0
4 NAME Orion Bright Bar reg 05 35 22.30 -05 24 33.0           ~ 841 0
5 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13898 0
6 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 390 1

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