A dataset provided by the European Space Agency

Name OT2_dteyssie_2
Title Unveiling the water puzzle in cold PDRs: The Horsehead case


DOI 10.5270/esa-xwvf1s1
Author teyssier, d.
Description While Herschel observations of water vapour in warm regions (T_gas >> 100 K) driven by energetic processes (outfows, shocks, hot cores, etc.) have confirmed large abundances of water vapour (~10^-5), the inferred gas phase H2O abundance in dark clouds is very low, ~10^-10. A detailed balance between freeze-out, ice-mantle desorption and gas-phase chemistry is required to explain this orders-of-magnitude abundance difference. The Horsehead nebula is particularly well-suited to investigate grain surface chemistry in a UV irradiated environment. Its relatively low UV illumination (~60 in Draine units) implies low dust grain temperatures, from T_dust=30K in the PDR to T_dust=20K deeper inside the cloud. Therefore, the release of the grain mantle products into the gas phase, water vapour in particular, is dominated by UV-induced photo-desorption and not by thermal evaporation (as in other warm PDRs such as the Orion Bar). Besides, owing to its simple edge-on geometry, the Horsehead is very close to the prototypical kind of source needed to serve as model benchmark. A relatively low water vapour beam-averaged abundances (~5x10^-9) was derived from a single position of the o-H2O ground-state line towards the so-called "IR peak" of the Horsehead PDR. However a detailed comparison with sophisticated PDR models including gas and grain chemistry is not possible due to our complete ignorance about the true H2O spatial distribution as one moves from the UV-illuminated cloud surface to the inner shielded cloud. We propose here to map with HIFI the o-H2O 557 GHz line on a cut across the PDR front, and extract the spatial information required to constrain the role of water freeze-out and water ice photodesorption as a function of cloud depth.
Instrument HIFI_HifiPoint_fs
Temporal Coverage 2012-09-20T10:05:26Z/2012-09-20T14:52:53Z
Version SPG v14.1.0
Mission Description Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 ┬Ám range, bridging the gap between earlier infrared space missions and groundbased facilities.
Creator Contact https://support.cosmos.esa.int/herschel/
Date Published 2013-03-20T14:05:03Z
Publisher And Registrant European Space Agency
Credit Guidelines European Space Agency, 2013-03-20T14:05:03Z, OT2_dteyssie_2, SPG v14.1.0. https://doi.org/10.5270/esa-xwvf1s1