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Spectrally Resolved Pure Rotational Lines of Water in Protoplanetary Disks

Pontoppidan, Klaus M. and Salyk, Colette and Blake, Geoffrey A. and Käufl, Hans Ulrich (2010) Spectrally Resolved Pure Rotational Lines of Water in Protoplanetary Disks. Astrophysical Journal Letters, 722 (2). L173-L177. ISSN 2041-8205.

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We present ground-based high-resolution N-band spectra (Δv = 15 km s^(−1)) of pure rotational lines of water vapor in two protoplanetary disks surrounding the pre-main-sequence stars AS 205N and RNO 90, selected based on detections of rotational water lines by the Spitzer InfraRed Spectrograph. Using VISIR on the Very Large Telescope, we spectrally resolve individual lines and show that they have widths of 30–60 km s^(−1), consistent with an origin in Keplerian disks at radii of ~ 1AU. The water lines have similar widths to those of the CO at 4.67 μm, indicating that the mid-infrared water lines trace similar radii. The rotational temperatures of the water are 540 and 600 K in the two disks, respectively. However, the line ratios show evidence of non-LTE excitation, with low-excitation line fluxes being overpredicted by two-dimensional disk LTE models. Due to the limited number of observed lines and the non-LTE line ratios, an accurate measure of the water ortho/para (O/P) ratio is not available, but a best estimate for AS 205N is O/P = 4.5±1.0, apparently ruling out a low-temperature origin of the water. The spectra demonstrate that high-resolution spectroscopy of rotational water lines is feasible from the ground, and further that ground-based high-resolution spectroscopy is likely to significantly improve our understanding of the inner disk chemistry revealed by recent Spitzer observations.

Item Type:Article
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URLURL TypeDescription
Pontoppidan, Klaus M.0000-0001-7552-1562
Salyk, Colette0000-0003-3682-6632
Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 2010 The American Astronomical Society. Received 2010 August 6; accepted 2010 September 16; published 2010 September 29. Based on observations made at the ESO Paranal Observatory under program IDs 084.C-0635 and 179.C-0151. The authors acknowledge valuable discussions with Alain Smette.
Subject Keywords:astrochemistry; protoplanetary disks; planetary systems
Issue or Number:2
Classification Code:PACS: 97.82.Jw; 95.30.Ky; 95.30.Ft; 97.21.+a
Record Number:CaltechAUTHORS:20101102-110121416
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Official Citation:Klaus M. Pontoppidan et al 2010 ApJ 722 L173 doi: 10.1088/2041-8205/722/2/L173
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:20640
Deposited By: Ruth Sustaita
Deposited On:02 Nov 2010 20:11
Last Modified:09 Dec 2019 21:59

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