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Session 58 - Future of Antarctic Astrophysics.
Display session, Wednesday, June 10
The two major tracers of neutral carbon gas, CI and CO, have been observed in 11 southern hemisphere high Galactic latitude (|b| \gtrsim 10\deg) molecular clouds (HLCs) using the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO). Observations of the lowest-lying (^3P_1\rightarrow ^3P_0) transition of neutral carbon [CI], at 492 GHz, as well as the (J = 2--1) and (J = 4--3) rotational transitions of CO, at 230 and 461 GHz, respectively, are presented. HLCs are nearby (d\sim 100\,pc) translucent clouds (A_v \sim 1--5) associated with infrared cirrus. Since the clouds are translucent, destruction of H_2 and CO by the ambient far-ultraviolet (FUV) radiation field dominates their structure. As such they are the simplest regions in which to study molecule formation in the interstellar medium (ISM) in the presence of FUV radiation. The HLCs are probably representative of much of the molecular ISM: \sim 50% of the molecular gas in the Galaxy is translucent. Due to the extremely low submillimeter atmospheric opacity above the Antarctic plateau, AST/RO enables observation of the weak CI and CO lines in translucent clouds with unprecedented sensitivity. Estimates are made of the abundances of CI and CO in the observed clouds. A complete census of carbon gas is possible for a subset of the clouds, which have also been observed in ionized carbon (C^+) emission with the Infrared Space Observatory (ISO). The two transitions of CO are used to constrain physical conditions, and the abundances of C^+, CI, and CO are compared with chemical models.
This research was supported in part by the National Science Foundation under a cooperative agreement with the Center for Astrophysical Research in Antarctica (CARA), grant number NSF OPP 89-20223. CARA is a National Science Foundation Science and Technology Center.
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