High abundance ratio of $^{13}$CO to C$^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud

Yoshito Shimajiri (1, 2, 3) , Yoshimi Kitamura (4) , Masao Saito (5, 2) , Munetake Momose (6) , Fumitaka Nakamura (2) , Kazuhito Dobashi (7) , Tomomi Shimoikura (7) , Hiroyuki Nishitani (2, 3) , Akifumi Yamabi (7) , Chihomi Hara (2, 8) , Sho Katakura (7) , Takashi Tsukagoshi (6) , Tomohiro Tanaka (9) , Ryohei Kawabe (2, 5)

1 AIM (UMR7158 / UMR_E_9005 / UM_112) - Astrophysique Interprétation Modélisation
2 NAOJ - National Astronomical Observatory of Japan
3 Nobeyama Radio Observatory
4 ISAS - Institute of Space and Astronautical Science
5 JAO - Joint ALMA Observatory
6 Ibaraki University
7 Tokyo Gakugei University
8 UTokyo - The University of Tokyo
9 Osaka Prefecture University

$Aims$.We derive physical properties such as the optical depths and the column densities of $^{13}$CO to C$^{18}$O to investigate the relationship between the far ultraviolet (FUV) radiation and the abundance ratios between $^{13}$CO to C$^{18}$O. $Methods$. We have carried out wide-field (0.4 deg$^2$) observations with an angular resolution of 25.8''(∼0.05 pc) in $^{13}$CO (J = 1–0) and C$^{18}$O (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 $^{13}$CO to C$^{18}$O emissions are similar to those of the $^{12}$CO (J = 1–0) emission. The optical depths of the $^{13}$CO to C$^{18}$O emission lines are estimated to be 0.05<$\tau_{13}_{CO}$<1.54 and 0.01<$\tau_{C}^{18}$_O$<0.18, respectively. The column densities of the $^{13}$CO and C$^{18}$O emission lines are estimated to be 0.2×10$^{16}$

Keywords: ISM: individual objects: Orion-A; ISM: clouds; ISM: abundances; photon-dominated region

Domains: Physics [physics]; Astrophysics [astro-ph]

Yoshito Shimajiri, Yoshimi Kitamura, Masao Saito, Munetake Momose, Fumitaka Nakamura, et al.. High abundance ratio of $^{13}$CO to C$^{18}$O toward photon-dominated regions in the Orion-A giant molecular cloud. Astronomy and Astrophysics - A&A, 2014, 564, pp.A68. ⟨10.1051/0004-6361/201322912⟩. ⟨cea-01236279⟩