Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-11-22
Astrophys.J. 581 (2002) L105-L108
Astronomy and Astrophysics
Astrophysics
12 pages, 3 figures, accepted by Astrophysical Journal Letters
Scientific paper
10.1086/346014
We present SWAS observations of water vapor in two cold star-less clouds, B68 and Core D in rho Ophiuchus. Sensitive non-detections of the 1(10)-1(01) transition of o-H2O are reported for each source. Both molecular cores have been previously examined by detailed observations that have characterized the physical structure. Using these rather well defined physical properties and a Monte-Carlo radiation transfer model we have removed one of the largest uncertainties from the abundance calculation and set the lowest water abundance limit to date in cold low-mass molecular cores. These limits are < 3 x 10^{-8} (relative to H2) and < 8 x 10^{-9} in B68 and rho Oph D, respectively. Such low abundances confirm the general lack of ortho-water vapor in cold (T < 20 K) cores. Provided that the ortho/para ratio of water is not near zero, these limits are well below theoretical predictions and appear to support the suggestion that most of the water in dense low-mass cores is frozen onto the surfaces of cold dust grains.
Bergin Edwin A.
Snell Ronald L.
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