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- Title
High abundance ratio of <sup>13</sup>CO to C<sup>13</sup>O toward photon-dominated regions in the Orion-A giant molecular cloud.
- Authors
Yoshito Shimajiri; Yoshimi Kitamura; Masao Saito; Munetake Momose; Fumitaka Nakamura; Kazuhito Dobashi; Tomomi Shimoikura; Hiroyuki Nishitani; Akifumi Yamabi; Chihomi Hara; Sho Katakura; Takashi Tsukagoshi; Tomohiro Tanaka; Ryohei Kawabe
- Abstract
Aims. We derive physical properties such as the optical depths and the column densities of 13CO and C18O to investigate the relationship between the far ultraviolet (FUV) radiation and the abundance ratios between 13CO and C18O. Methods. We have carried out wide-field (0.4 deg2) observations with an angular resolution of 25.8" (∼0.05 pc) in 13CO (J = 1-0) and C18O (J = 1-0) toward the Orion-A giant molecular cloud using the Nobeyama 45 m telescope in the on-the-fly mode. Results. Overall distributions and velocity structures of the 13CO and C18O emissions are similar to those of the 12CO (J = 1-0) emission. The optical depths of the 13CO and C18O emission lines are estimated to be 0.05 < τ13CO < 1.54 and 0.01 < τC18O < 0.18, respectively. The column densities of the 13CO and C18O emission lines are estimated to be 0.2 × 1016 < N13CO < 3.7 × 1017 cm-2 and 0.4 × 1015 < NC18O < 3.5 × 1016 cm-2, respectively. The abundance ratios between 13CO and C18O, X13CO/XCC18O, are found to be 5.7-33.0. The mean value of X13CO/XC18O in the nearly edge-on photon-dominated regions is found to be 16.47 ± 0.10, which is a third larger than that the solar system value of 5.5. The mean value of X13CO/XC18O in the other regions is found to be 12.29 ± 0.02. The difference of the abundance ratio is most likely due to the selective FUV photodissociation of C18O.
- Subjects
MOLECULAR clouds; ORION (Patrol aircraft); INTERSTELLAR medium; PHOTODISSOCIATION; FIELD theory (Physics)
- Publication
Astronomy & Astrophysics / Astronomie et Astrophysique, 2014, Vol 564, p1
- ISSN
0004-6361
- Publication type
Article
- DOI
10.1051/0004-6361/201322912