HDO abundance in the envelope of the solar-type protostar IRAS 16293–2422

Free access article

Issue		A&A Volume 431, Number 2, February IV 2005


Page(s)		547 - 554
Section		Interstellar and circumstellar matter
DOI		http://dx.doi.org/10.1051/0004-6361:20041899

A&A 431, 547-554 (2005)
DOI: 10.1051/0004-6361:20041899

HDO abundance in the envelope of the solar-type protostar IRAS 16293-2422

B. Parise¹, E. Caux¹, A. Castets², C. Ceccarelli³, L. Loinard⁴, A. G. G. M. Tielens⁵, A. Bacmann², S. Cazaux⁶, C. Comito⁷, F. Helmich^{5, 8}, C. Kahane³, P. Schilke⁷, E. van Dishoeck⁹, V. Wakelam² and A. Walters¹

¹ Centre d'Étude Spatiale des Rayonnements, BP 4346, 31028 Toulouse Cedex 04, France
e-mail: parise@cesr.fr
² Observatoire de Bordeaux, BP 89, 33270 Floirac, France
³ Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
⁴ Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apartado Postal 72-3 (Xangari), 58089 Morelia, Michoacán, Mexico
⁵ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁶ INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁸ SRON National Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
⁹ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands

(Received 25 August 2004 / Accepted 14 October 2004 )

Abstract
We present IRAM 30 m and JCMT observations of HDO lines towards the solar-type protostar IRAS 16293-2422. Five HDO transitions have been detected on-source, and two were unfruitfully searched for towards a bright spot of the outflow of IRAS 16293-2422. We interpret the data by means of the Ceccarelli et al. (1996) model, and derive the HDO abundance in the warm inner and cold outer parts of the envelope. The emission is well explained by a jump model, with an inner abundance $x{^{\tiny\rm {HDO}}_{\rm in}} = 1\times10^{-7}$ and an outer abundance $x{^{\tiny\rm {HDO}}_{\rm out}}\,\leq\,1\times10^{-9}$ (3 $\sigma$ ). This result is in favor of HDO enhancement due to ice evaporation from the grains in the inner envelope. The deuteration ratio HDO/H ₂O is found to be $f_{\rm in}=3\%$ and $f_{\rm out} \le 0.2\%$ (3 $\sigma$ ) in the inner and outer envelope respectively and therefore, the fractionation also undergoes a jump in the inner part of the envelope. These results are consistent with the formation of water in the gas phase during the cold prestellar core phase and storage of the molecules on the grains, but do not explain why observations of H ₂O ices consistently derive a H ₂O ice abundance of several 10 ^-5 to 10 ^-4, some two orders of magnitude larger than the gas phase abundance of water in the hot core around IRAS 16293-2422.

Key words: ISM: molecules -- stars: formation -- stars: individual: IRAS 16293-2422

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