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: email@example.com
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
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.