Letter to the Editor

The Herschel view of GAS in Protoplanetary Systems (GASPS)^*

First comparisons with a large grid of models

¹ Université Joseph-Fourier – Grenoble 1/CNRS, Laboratoire d'Astrophysique de Grenoble (LAOG) UMR 5571, BP 53, 38041 Grenoble Cedex 09, France e-mail: christophe.pinte@obs.ujf-grenoble.fr
² School of Physics, University of Exeter, UK
³ SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁴ UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁵ School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
⁶ Astronomy Department, University of California, Berkeley, CA 94720-3411, USA
⁷ Kapteyn Astronomical Institute, Postbus 800, 9700 AV Groningen, The Netherlands
⁸ Dep. de Física Teórica, Fac. de Ciencias, UAM Campus Cantoblanco, 28049 Madrid, Spain
⁹ Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822, USA
¹⁰ SOFIA-USRA, NASA Ames Research Center, Mailstop 211-3 Moffett Field CA 94035, USA
¹¹ Eureka Scientific and Exoplanets and Stellar Astrophysics Lab, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD, 20771, USA
¹² ALMA, Joint ALMA Office, Avda Apoquindo 3846, Piso 19, Edificio Alsacia, Las Condes, Santiago, Chile
¹³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
¹⁴ Unidad de Archivo de Datos, Depto. Astrofísica, Centro de Astrobiología (INTA-CSIC), P.O. Box 78, 28691 Villanueva de la Cañada, Spain
¹⁵ Spanish Virtual Observatory
¹⁶ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA, USA
¹⁷ NASA Herschel Science Center, California Institute of Technology, Pasadena, USA
¹⁸ Calar Alto Observatory, Centro Astronómico Hispano-Alemán C/Jesús Durbán Remón 2-2, 04004 Almería, Spain
¹⁹ LAEX, Depto. Astrofísica, Centro de Astrobiología (INTA-CSIC), PO Box 78, 28691 Villanueva de la Cañada, Spain
²⁰ Clemson University
²¹ NASA Exoplanet Science Institute/Caltech 770 South Wilson Avenue, Mail Code: 100-22, Pasadena, CA USA 91125
²² NASA Goddard Space Flight Center, Exoplanets & Stellar Astrophysics, Code 667, Greenbelt, MD 20771, USA
²³ Max Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁴ Johns Hopkins University Dept. of Physics and Astronomy, 3701 San Martin drive Baltimore, MD 21210 USA
²⁵ Research and Scientific Support Department-ESA/ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
²⁶ Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität, Schillergäßchen 2-3, 07745 Jena, Germany
²⁷ Department of Radio and Space Science, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁸ ESA-ESAC Gaia SOC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
²⁹ Spitzer Science Center, California Institute of Technology, 1200 E California Blvd, 91125 Pasadena, USA
³⁰ Department of Astronomy, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
³¹ CEA/IRFU/SAp, AIM UMR 7158, 91191 Gif-sur-Yvette, France
³² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
³⁴ Exoplanets and Stellar Astrophysics Lab, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD, 20771, USA
³⁵ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
³⁶ The Rutherford Appleton Laboratory, Chilton, Didcot, OX11 OQL, UK
³⁷ Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK

Received: 30 March 2010
Accepted: 5 May 2010

Abstract

The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300 000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs.