A&A 462, 221-230 (2007)
The depletion of NO in pre-protostellar coresM. Akyilmaz1, D. R. Flower1, P. Hily-Blant2, G. Pineau des Forêts3, 4, and C. M. Walmsley5
1 Physics Department, The University, Durham DH1 3LE, UK
2 IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
3 IAS (UMR 8617 du CNRS), Université de Paris-Sud, 91405 Orsay, France
4 LERMA (UMR 8112 du CNRS), Observatoire de Paris, 61 Avenue de l'Observatoire, 75014 Paris, France
5 INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
(Received 28 July 2006 / Accepted 24 October 2006)
Aims.Understanding the depletion of heavy elements is a fundamental step towards determining the structure of pre-protostellar cores just prior to collapse. We study the dependence of the NO abundance on position in the pre-protostellar cores L1544 and L183.
Methods.We observed the 150 GHz and 250 GHz transitions of NO and the 93 GHz transitions of N2H+ towards L1544 and L183 using the IRAM 30 m telescope. We compare the variation of the NO column density with position in these objects with the H column density derived from dust emission measurements.
Results.We find that NO behaves differently from N2H+ and appears to be partially depleted in the high density core of L1544. Other oxygen-containing compounds are also likely to be partially depleted in dense-core nuclei. The principal conclusions are that: the prestellar core L1544 is likely to be "carbon-rich"; the nitrogen chemistry did not reach equilibrium prior to gravitational collapse, and nitrogen is initially (at densities of the order of 104 cm-3) mainly in atomic form; the grain sticking probabilities of atomic C, N and, probably, O are significantly smaller than unity.
Key words: molecular processes -- stars: formation -- dust, extinction -- ISM: molecules -- ISM: abundances -- radio lines: ISM
© ESO 2007