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Astron. Astrophys. 357, L9-L12 (2000)


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Letter to the Editor

The hot core of the solar-type protostar IRAS 16293-2422: H2CO emission

C. Ceccarelli 1, L. Loinard 2, A. Castets 3, A.G.G.M. Tielens 4 and E. Caux 5

1 Laboratoire d'Astrophysique, Observatoire de Grenoble, B.P. 53, 38041 Grenoble cedex 09, France
2 Institut de Radio Astronomie Millimétrique, 300 rue de la piscine, 38406 St. Martin d'Hères, France
3 Observatoire de Bordeaux, B.P. 89, 33270 Floirac, France
4 SRON, P.O. Box 800, 9700 AV Groningen, The Netherlands
5 CESR CNRS-UPS, B.P. 4346, 31028 Toulouse cedex 04, France

Received 24 January 2000 / Accepted 30 March 2000

Abstract

We model the H2CO and H[FORMULA]CO line emission observed towards the solar-type protostar IRAS16293-2422. Based upon previous analysis of the physical structure of the envelope surrounding IRAS16293-2422, we develop a model in which the H2CO lines are emitted by two components: a cold H2CO-poor outer envelope and a warm H2CO-rich core. We find that the model reproduces successfully all the available H2CO and H[FORMULA]CO data for a H2CO abundance equal to [FORMULA] in the outer and [FORMULA] in the inner regions of the envelope respectively. We interpret this increase of the H2CO abundance as due to the evaporation of the grain mantles when the dust temperature exceeds 100 K at about 150 AU from the center, forming a hot core like region. Assuming that all mantle constituents evaporate and are detected in the gas phase, we derive that the H2CO-ice abundance is about 3% of the H2O-ice abundance. This is the first measurement of the H2CO abundance in grain mantles around a low-mass protostar.

Key words: stars: formation – ISM: jets and outflows – ISM: individual objects: – infrared: ISM: lines and bands

Send offprint requests to: Ceccarelli.Cecilia@obs.ujf-grenoble.fr

© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000

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