The degree of CO depletion in pre-stellar cores

Free access article

Issue		A&A Volume 389, Number 1, July I 2002


Page(s)		L6 - L10
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20020652

A&A 389, L6-L10 (2002)
DOI: 10.1051/0004-6361:20020652

Letter

The degree of CO depletion in pre-stellar cores

A. Bacmann¹, B. Lefloch², C. Ceccarelli^{3, 2}, A. Castets³, J. Steinacker¹ and L. Loinard⁴

¹ Astrophysikalisches Institut und Universitäts Sternwarte (AIU), Schillergäßchen 2-3, 07745 Jena, Germany
    e-mail: stein@astro.uni-jena.de
² Laboratoire d'Astrophysique, Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
    e-mail: lefloch@obs.ujf-grenoble.fr
³ Observatoire de Bordeaux, 2 rue de l'Observatoire, BP 89, 33270 Floirac, France
    e-mail: ceccarel@observ.u-bordeaux.fr,castets@observ.u-bordeaux.fr
⁴ Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacán, Mexico
    e-mail: l.loinard@astrosmo.unam.mx

(Received 5 March 2002 / Accepted 24 April 2002 )

Abstract
We present new results on CO depletion in a sample of nearby pre-stellar cores, based on observations of the millimeter C ¹⁷O and C ¹⁸O lines and the 1.3 mm dust emission with the IRAM 30 m telescope. In most cases, the distribution of CO is much flatter than that of the dust, whereas other tracers, like $\rm N_2H^{+}$ , still probe the latter. In the centre of these objects, we estimate CO to be underabundant by a factor 4-15 depending on the cores. The CO underabundance is more pronounced in the central regions and appears to decrease with increasing distance from the core centre. This underabundance is most likely due to the freezing out of CO onto the dust grains in the cold, dense parts of the cores. We find evidence for an increase of the CO depletion degree with the core density.

Key words: ISM: molecules -- dust, extinction -- stars: formation

Offprint request: A. Bacmann, bacmann@astro.uni-jena.de

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