CHOH abundance in low mass protostars

¹ Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 09, France e-mail: smaret@umich.edu
² Space Research Organization of the Netherlands, PO Box 800, 9700 AV Groningen, The Netherlands
³ Centre d'Etude Spatiale des Rayonnements, CESR/CNRS-UPS, BP 4346, 31028 Toulouse Cedex 04, France
⁴ Observatoire de Bordeaux, BP 79, 33270 Floirac, France
⁵ Physics Department, The University, Durham DH1 3LE, UK

Received: 17 February 2005
Accepted: 1 July 2005

Abstract

We present observations of methanol lines in a sample of Class 0 low mass protostars. Using a 1-D radiative transfer model, we derive the abundances in the envelopes. In two sources of the sample, the observations can only be reproduced by the model if the methanol abundance is enhanced by about two order of magnitude in the inner hot region of the envelope. Two other sources show similar jumps, although at a lower confidence level. The observations for the other three sources are well reproduced with a constant abundance, but the presence of a jump cannot be ruled out. The observed methanol abundances in the warm gas around low mass protostars are orders of magnitude higher than gas phase chemistry models predict. Hence, in agreement with other evidence, this suggests that the high methanol abundance reflects recent evaporation of ices due to the heating by the newly formed star. The observed abundance ratios of CH₃OH, H₂CO and CO are in good agreement with grain surface chemistry models. However, the absolute abundances are more difficult to reproduce and may indicate the presence of multiple ice components in these regions.