Volume 588, April 2016
|Number of page(s)||15|
|Section||Interstellar and circumstellar matter|
|Published online||25 March 2016|
Observations and modelling of CO and [C i] in protoplanetary disks
First detections of [C i] and constraints on the carbon abundance⋆
1 Leiden Observatory, PO Box 9513, 2300 RA, Leiden, The Netherlands
2 Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
3 SRON Netherlands Institute for Space Research, 3584, The Netherlands
4 Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
5 NOVA, J.H. Oort Building, PO Box 9513, 2300 RA Leiden, The Netherlands
6 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
7 Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, The Netherlands
8 ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
9 Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Sloneczna 36, 60-286 Poznan, Poland
10 UK Astronomy Technology Center, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
11 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
12 Department of Physics and Astronomy, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606, USA
13 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Received: 19 June 2015
Accepted: 5 January 2016
Context. The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The principal gas-phase carbon carriers CO, C0, and C+ can now be observed regularly in disks.
Aims. The gas-phase carbon abundance in disks has thus far not been well characterized observationally. We obtain new constraints on the [C]/[H] ratio in a large sample of disks, and compile an overview of the strength of [C i] and warm CO emission.
Methods. We carried out a survey of the CO 6–5 line and the [C i] 1–0 and 2–1 lines towards 37 disks with the APEX telescope, and supplemented it with [C ii] data from the literature. The data are interpreted using a grid of models produced with the DALI disk code. We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties.
Results. The CO 6–5 line is detected in 13 out of 33 sources, [C i] 1–0 in 6 out of 12, and [C i] 2–1 in 1 out of 33. With separate deep integrations, the first unambiguous detections of the [C i] 1–0 line in disks are obtained, in TW Hya and HD 100546.
Conclusions. Gas-phase carbon abundance reductions of a factor of 5–10 or more can be identified robustly based on CO and [C i] detections, assuming reasonable constraints on other parameters. The atomic carbon detection towards TW Hya confirms a factor of 100 reduction of [C]/[H]gas in that disk, while the data are consistent with an ISM-like carbon abundance for HD 100546. In addition, BP Tau, T Cha, HD 139614, HD 141569, and HD 100453 are either carbon-depleted or gas-poor disks. The low [C i] 2–1 detection rates in the survey mostly reflect insufficient sensitivity for T Tauri disks. The Herbig Ae/Be disks with CO and [C ii] upper limits below the models are debris-disk-like systems. An increase in sensitivity of roughly order of magnitude compared to our survey is required to obtain useful constraints on the gas-phase [C]/[H] ratio in most of the targeted systems.
Key words: surveys / protoplanetary disks / submillimeter: planetary systems
The reduced spectra (FITS files) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A108
© ESO, 2016
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