Single-dish spectra and interferometric maps of ( sub- ) millimeter lines of H _ { 2 } ^ { 18 } 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 \sim 110 K and column densities in an 11 ^ { \prime \prime } beam of \sim 2 \times 10 ^ { 14 } cm ^ { -2 } for HDO and \sim 2 \times 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 _ { 2 } ^ { 18 } O and HDO emission is estimated to be 10 – 20 % .
Radiative transfer models indicate that the water abundance is low ( \sim 10 ^ { -6 } ) outside a critical radius corresponding to a temperature in the protostellar envelope of \approx 100 K , and ‘ jumps ’ to H _ { 2 } O/H _ { 2 } \sim 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 \sim 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 _ { 2 } ^ { 18 } O 3 _ { 13 } – 2 _ { 20 } and SO _ { 2 } 12 _ { 0 , 12 } – 11 _ { 1 , 11 } lines , which reveal compact ( Ø \sim 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 \approx 0.8 M _ { \odot } , or \sim 5 % of the mass of the central star .
We speculate that we may be observing a circumstellar disk in an almost face-on orientation .