Herschel observations of EXtra-Ordinary Sources (HEXOS): The?present and?future of spectral surveys with Herschel/HIFI

摘要

We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI.The HIFI instrument offers unprecedented sensitivity, as well ascontinuous spectral coverage across the gaps imposed by the atmosphere,opening up a largely unexplored wavelength regime to high-resolutionspectroscopy. We show the spectrum of Orion KL between 480 and 560 GHzand from 1.06 to 1.115THz. From these data, we confirm that HIFIseparately measures the dust continuum andspectrally resolves emission lines in Orion KL. Based on thiscapability we demonstrate thatthe line contribution to the broad-band continuum in this molecule-richsource is 20-40% below 1THz and declines to a few percentat higher frequencies. We also tentatively identify multiple transitions of HD18Oin the spectra. The first detection of this rare isotopologue in theinterstellar medium suggests that HDO emission is optically thick inthe Orion hot core with HDO/H2O 0.02. Wediscuss the implications of this detection for the water D/H ratio in hot cores.Key words: ISM: abundances - ISM: molecules - submillimeter: ISM