Water in the envelopes and disks around young high-mass stars

Single-dish spectra and interferometric maps of (sub-)millimeter lines of H 18 2 O 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 ∼2 x 10 14 cm -2 for HDO and ∼2 x 10 17 cm -2 for H 2 O, with the N(HDO)/N(H 2 O) ratio increasing with decreasing temperature. Simultaneous observations of CH 3 OH and SO 2 indicate that 20-50% of the single-dish line flux arises in the molecular outflows of these objects. The outflow contribution to the H 18 2 O 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 H 2 O/H 2 ∼ 10 -4 inside this radius. This value corresponds to the observed abundance of solid water and together with the derived HDO/H 2 O 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 1 10 -1 11 , H 18 2 O 3 13 -2 20 and SO 2 12 0,12 -1 1,11 lines, which reveal compact (O ∼ 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 M ○. , 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.