Herschel observations of EXtra-Ordinary Sources (HEXOS): Observations of H2O and its isotopologues towards Orion?KL

摘要

We report the detection of more than 48 velocity-resolved groundrotational state transitions of HO, HO, and HO - most for the first time -in both emission and absorption toward OrionKL using Herschel/HIFI.We show that a simplefit, constrained to match the known emission and absorption componentsalong theline of sight, is in excellent agreement with the spectral profiles ofall the water lines. Using the measured HOline fluxes, whichare lessaffected by line opacity than their HO counterparts, and an escapeprobability method,the column densities of HO associated with eachemission component are derived. We infer total water abundances of7.410-5,1.010-5,and 1.610-5for theplateau, hot core, and extended warm gas, respectively. In the case ofthe plateau, this value is consistent with previous measures of theOrion-KL water abundance as well as those of other molecular outflows.In the case of the hot core and extended warm gas, these values aresomewhat higher than water abundances derived for other quiescentclouds, suggesting that theseregions are likely experiencing enhanced water-ice sublimation from(and reducedfreeze-out onto) grain surfaces due to the warmer dust in thesesources.Key words: ISM: abundances - ISM: molecules