Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk

Astronomy and Astrophysics (Impact Factor: 4.38). 07/2010; 521(33). DOI: 10.1051/0004-6361/201015104
Source: OAI


We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane. Comment: 5 pages, 3 figures. Accepted for publication in the Herschel HIFI special issue of A&A

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Available from: Umut A. Yildiz,
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    • "Observations of H 2 O lines with HIFI may improve our understanding of protoplanetary disks, but the expected signals are weak so that only few objects can be observed. The spectrum of DM Tau does not show H 2 O lines at all which gives a firm upper limit on the H 2 O abundance (Bergin et al., 2010). The implication of this observation is that the dust in this disk has already settled to the midplane and probably started coagulating, which makes photodesorption less effective. "
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