Astronomy and Astrophysics, volume 462, 221-230 (2007/1-4)
The depletion of NO in pre-protostellar cores.
AKYILMAZ M., FLOWER D.R., HILY-BLANT P., PINEAU DES FORETS G. and WALMSLEY C.M.
Abstract (from CDS):
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. We observed the 150GHz and 250GHz transitions of NO and the 93GHz transitions of N2H+ towards L1544 and L183 using the IRAM 30m 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. 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 104cm–3) mainly in atomic form; the grain sticking probabilities of atomic C, N and, probably, O are significantly smaller than unity.
molecular processes - stars: formation - dust, extinction - ISM: molecules - ISM: abundances - radio lines: ISM