Volume 559, November 2013
|Number of page(s)||22|
|Section||Interstellar and circumstellar matter|
|Published online||20 November 2013|
DIGIT survey of far-infrared lines from protoplanetary disks
1 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
2 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
3 Naval Research Laboratory, Code 7211, Washington, DC 20375, USA
4 Kavli Institute for Astronomy and Astrophysics, Yi He Yuan Lu 5, 100871, Beijing, PR China
5 National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719, USA
6 University of Texas at Austin, Department of Astronomy, 2515 Speedway, Stop C1400, Austin TX 78712-1205, USA
7 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
8 Universidad Autónoma de Madrid, Dpt. Física Teórica, Campus Cantoblanco, Spain
9 Universität Wien, Dr.-Karl-Lueger-Ring 1, 1010 Wien, Austria
Received: 16 January 2013
Accepted: 26 July 2013
We present far-infrared (50−200 μm) spectroscopic observations of young pre-main-sequence stars taken with Herschel/PACS as part of the DIGIT key project. The sample includes 16 Herbig AeBe and 4 T Tauri sources observed in SED mode covering the entire spectral range. An additional 6 Herbig AeBe and 4 T Tauri systems have been observed in SED mode with a limited spectral coverage. Multiple atomic fine structure and molecular lines are detected at the source position: [O i], [C ii], CO, OH, H2O, CH+. The most common feature is the [O i] 63 μm line detected in almost all of the sources, followed by OH. In contrast with CO, OH is detected toward both Herbig AeBe groups (flared and non-flared sources). An isothermal LTE slab model fit to the OH lines indicates column densities of 1013 < NOH < 1016 cm-2, emitting radii 15 < r < 100 AU and excitation temperatures 100 < Tex < 400 K. We used the non-LTE code RADEX to verify the LTE assumption. High gas densities (n ≥ 1010 cm-3) are needed to reproduce the observations. The OH emission thus comes from a warm layer in the disk at intermediate stellar distances. Warm H2O emission is detected through multiple lines toward the T Tauri systems AS 205, DG Tau, S CrA and RNO 90 and three Herbig AeBe systems HD 104237, HD 142527, HD 163296 (through line stacking). Overall, Herbig AeBe sources have higher OH/H2O abundance ratios across the disk than do T Tauri disks, from near- to far-infrared wavelengths. Far-infrared CH+ emission is detected toward HD 100546 and HD 97048. The slab model suggests moderate excitation (Tex ~ 100 K) and compact (r ~ 60 AU) emission in the case of HD 100546. Off-source [O i] emission is detected toward DG Tau, whose origin is likely the outflow associated with this source. The [C ii] emission is spatially extended in all sources where the line is detected. This suggests that not all [C ii] emission is associated with the disk and that there is a substantial contribution from diffuse material around the young stars. The flux ratios of the atomic fine structure lines ([O i] 63 μm, [O i] 145 μm, [C ii]) are analyzed with PDR models and require high gas density (n ≳ 105 cm-3) and high UV fluxes (Go ~ 103 − 107), consistent with a disk origin for the oxygen lines for most of the sources.
Key words: stars: variables: T Tauri, Herbig Ae/Be / astrochemistry / protoplanetary disks
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2013
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