Abstract
Abstract The Submillimeter Wave Astronomy Satellite ( SWAS ), launched in December 1998, is a NASA mission dedicated to the study of star formation through direct measurements of: (1) molecular cloud composition and chemistry; (2) the cooling mechanisms that facilitate cloud collapse; and, (3) the large-scale structure of the UV-illuminated cloud surfaces. To achieve these goals, SWAS is conducting pointed observations of dense ( n (H 2 )>10 3 cm −3 ) molecular clouds throughout our Galaxy in either the ground-state or a low-lying transition of five astrophysically important species: H 2 O, H 2 18 O, O 2 , CI, and 13 CO. By observing these lines SWAS is: (1) testing long-standing theories that predict that these species are the dominant coolants of molecular clouds during the early stages of their collapse to form stars and planets; and (2) supplying previously missing information about the abundance of key species central to the chemical models of dense interstellar gas. SWAS carries two independent Schottky barrier diode mixers — passively cooled to ∼ 175 K — coupled to a 54 × 68-cm off-axis Cassegrain antenna. During its baseline three-year mission, SWAS is observing giant and dark cloud cores with the objective of detecting or setting a 3σ upper limit on the water and molecular oxygen abundance of 3 × 10 −6 (relative to H 2 ). In addition, advantage is being taken of SWAS 's relatively large beamsize of 3.3 × 4.5 arcminutes at 553 GHz and 3.5 × 5.0 arcminutes at 490 GHz to obtain large-area (∼1° × 1°) maps of giant and dark clouds in the 13 CO and CI lines. With the use of a 1.4 GHz bandwidth acousto-optical spectrometer, SWAS has the ability to simultaneously observe either the H 2 O, O 2 , CI, and 13 CO lines or the H 2 18 O, O 2 , and CI lines with a velocity resolution ∼- 1 km s −1 .
Published Version
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