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The H2CO abundance in the inner warm regions of low mass protostellar envelopes

Maret, S., Ceccarelli, C., Caux, E., Tielens, A. G. G. M., Jorgensen, J. K., van Dishoeck, E., Bacmann, A., Castets, A., Lefloch, B., Loinard, L., Parise, Berengere and Schoier, F. L. 2004. The H2CO abundance in the inner warm regions of low mass protostellar envelopes. Astronomy and Astrophysics 416 (2) , pp. 577-594. 10.1051/0004-6361:20034157

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Abstract

We present a survey of the formaldehyde emission in a sample of eight Class 0 protostars obtained with the IRAM and JCMT millimeter telescopes. The range of energies of the observed transitions allows us to probe the physical and chemical conditions across the protostellar envelopes. The data have been analyzed with three different methods with increasing level of sophistication. We first analyze the observed emission in the LTE approximation, and derive rotational temperatures between 11 and 40 K, and column densities between 1 and 20 x 10{13} cm -2. Second, we use a LVG code and derive higher kinetic temperatures, between 30 and 90 K, consistent with subthermally populated levels and densities from 1 to 6 x 10{5} cm -3. The column densities from the LVG modeling are within a factor of 10 with respect to those derived in the LTE approximation. Finally, we analyze the observations based upon detailed models for the envelopes surrounding the protostars, using temperature and density profiles previously derived from continuum observations. We approximate the formaldehyde abundance across the envelope with a jump function, the jump occurring when the dust temperature reaches 100 K, the evaporation temperature of the grain mantles. The observed formaldehyde emission is well reproduced only if there is a jump of more than two orders of magnitude, in four sources. In the remaining four sources the data are consistent with a formaldehyde abundance jump, but the evidence is more marginal ( ${\leq} 2 ~ \sigma ). The inferred inner H 2CO abundance varies between 1 x 10{-8} and 6 x 10{-6}. The absolute values of the jump in the H 2CO abundance are uncertain by about one order of magnitude, because of the uncertainties in the density, ortho to para ratio, temperature and velocity profiles of the inner region, as well as the evaporation temperature of the ices. We discuss the implications of these jumps for our understanding of the origin and evolution of ices in low mass star forming regions. Finally, we give predictions for the submillimeter H 2CO lines, which are particularly sensitive to the abundance jumps.

Item Type: Article
Status: Published
Schools: Physics and Astronomy
Subjects: Q Science > QB Astronomy
Uncontrolled Keywords: ISM: abundances; ISM: molecules; stars: formation; ISM: general
Additional Information: Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 17/04/2014)
Publisher: EDP Sciences
ISSN: 0004-6361
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 May 2023 20:19
URI: https://orca.cardiff.ac.uk/id/eprint/52829

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