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The enormous abundance of D2CO in IRAS 16293-2422
L. Loinard 1,
A. Castets 2,
C. Ceccarelli 3,
A.G.G.M. Tielens 4,
A. Faure 3,
E. Caux 5 and
G. Duvert 3
Received 7 April 2000 / Accepted 16 May 2000
Ceccarelli et al. (1998) recently reported the detection of D2CO in the low-luminosity protostar IRAS 16293-2422. Using the data available at the time, they found that the abundance of D2CO might be as high as 1/10th that of its hydrogenated counterpart H2CO. Here we describe and analyse new multi-transition observations of D2CO, HDCO, H2CO, and H213CO towards IRAS 16293-2422. Correcting for the opacity of the H2CO lines, we find that the abundance of D2CO is 5 that of H2CO. In addition, we find a component in absorption - also associated to IRAS 16293-2422, but at larger radius - where the abundance of D2CO compared to H2CO could be even higher.
Though slightly lower than initially claimed, the abundance of D2CO in IRAS 16293-2422 is extremely high, more than one order of magnitude higher than in Orion KL, the only other source where D2CO has ever been detected. Because the gas temperature (T = 20-50 K) is too high, deuteration in the gas-phase is very insufficient to explain such high abundances. We conclude that D2CO is most likely not currently formed in the gas phase, but is evaporated from the dust grains, where it has been accumulating during the cold, dense pre-collapse period.
Key words: stars: formation ISM: abundances ISM: molecules ISM: individual objects: IRAS 16293-2422
Send offprint requests to: L. Loinard (email@example.com)
Online publication: July 13, 2000