Volume 447, Number 3, March I 2006
|Page(s)||1011 - 1025|
|Section||Interstellar and circumstellar matter|
|Published online||10 February 2006|
Water in the envelopes and disks around young high-mass stars
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
3 Observatoire de Bordeaux, L3AB, UMR 5804, BP 89, 33270 Floirac, France
4 Laboratoire Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble, France
Accepted: 21 October 2005
Single-dish spectra and interferometric maps of (sub-)millimeter lines of HO and HDO are used to study the chemistry of water in eight regions of high-mass star formation. The spectra indicate HDO excitation temperatures of ~110 K and column densities in an 11'' beam of cm-2 for HDO and cm-2 for H2O, with the N(HDO)/N(H2O) ratio increasing with decreasing temperature. Simultaneous observations of CH3OH and SO2 indicate that 20-50% of the single-dish line flux arises in the molecular outflows of these objects. The outflow contribution to the HO and HDO emission is estimated to be 10-20%. Radiative transfer models indicate that the water abundance is low (~10-6) outside a critical radius corresponding to a temperature in the protostellar envelope of ≈100 K, and “jumps” to H2O/H2 ~ 10-4 inside this radius. This value corresponds to the observed abundance of solid water and together with the derived HDO/H2O abundance ratios of ~10-3 suggests that the origin of the observed water is evaporation of grain mantles. This idea is confirmed in the case of AFGL 2591 by interferometer observations of the HDO , HO and SO2 lines, which reveal compact (Ø ~ 800 AU) emission with a systematic velocity gradient. This size is similar to that of the 1.3 mm continuum towards AFGL 2591, from which we estimate a mass of ≈0.8 , or ~5% of the mass of the central star. We speculate that we may be observing a circumstellar disk in an almost face-on orientation.
Key words: ISM: molecules / molecular processes / stars: formation / astrochemistry
© ESO, 2006
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