|A Sensitive Search for OH and H2O in the Cold Outer Layers of a Planet-forming Disk
|cleeves, l. i.
|One of the biggest results that have come from Herschel HIFI is the detection of cold water vapor where it would otherwise be frozen onto grains (Hogerheijde et al. 2011, Bergin et al. 2010). Surprisingly, one unexpected inference of these observations is the requirement that the photo-desorption of water be reduced by nearly an order of magnitude to reproduce the emission line observations. The interpretation of these results was the existence of a population of .dry. (reduced water-ice-coated) grains on the surface of the disk. Emission line data, however, is intrinsically model dependent with many uncertainties, even in the collisional rates. We propose here a test of the models used to reproduce the Herschel observed water emission using an absorption line study of the main photo-desorption products of water, namely gas-phase H2O and OH. This type of study is intrinsically more sensitive as it is a direct measure of the column, without the need to assume anything about the excitation conditions. Both H2O and OH are expected to be predominantly in the ground state, and therefore such a study is the only direct test of the bulk-water-vapor reservoir. This program is designed to optimize the opportunity to find water and OH in a T Tauri disk both with the ideal inclination and continuum. These results will robustly test theories of water formation in disk systems, namely the presence of a cold, UV-photodesorbed layer of water vapor sitting on the disk surface as inferred by Herschel emission measurements of T Tauris.
|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 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_lcleeves_1, SPG v14.2.0. https://doi.org/10.5270/esa-i7cp69k