Detection of warm water vapour in Taurus protoplanetary discs by Herschel^⋆

¹ Centro de Astrobiología – Depto. Astrofísica (CSIC–INTA), POB 78, 28691 Villanueva de la Cañada, Spain
e-mail: riviere@cab.inta-csic.es
² UJF-Grenoble 1 / CNRS-INSU, Institut de Planétologie et d’Astrophysique (IPAG) UMR 5274, 38041 Grenoble, France
³ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
⁴ Dep. de Física Teórica, Fac. de Ciencias, UAM Campus Cantoblanco, 28049 Madrid, Spain
⁵ University of Vienna, Dept. of Astronomy, Türkenschanzstr. 17, 1180 Vienna, Austria
⁶ UK Astronomy Technology Centre, Royal Observatory, Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ SUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, UK
⁸ SOFIA-USRA, NASA Ames Research Center, USA
⁹ ALMA, Avda Apoquindo 3846, Piso 19, Edificio Alsacia, Las Condes, Santiago, Chile
¹⁰ Department of Physics & Astronomy, The Open University, Milton Keynes MK7 6AA, UK
¹¹ The Rutherford Appleton Laboratory, Chilton, Didcot OX11 OQL, UK
¹² Calar Alto Observatory, Centro Astronómico Hispano-Alemán C/Jesús Durbán Remón, 2-2, 04004 Almería, Spain

Received: 14 November 2011
Accepted: 15 December 2011

Abstract

Line spectra of 68 Taurus T Tauri stars were obtained with the Herschel-PACS (Photodetector Array Camera and Spectrometer) instrument as part of the GASPS (GAS evolution in Protoplanetary Systems) survey of protoplanetary discs. A careful examination of the linescans centred on the [OI] 63.18 μm fine-structure line unveiled a line at 63.32 μm in some of these spectra. We identify this line with the 8₁₈ → 7₀₇ transition of ortho-water. It is detected confidently (i.e.,  >3σ) in eight sources, i.e.,  ~24% of the sub-sample with gas-rich discs. Several statistical tests were used to search for correlations with other disc and stellar parameters such as line fluxes of [O i] 6300 Å  and 63.18 μm; X-ray luminosity and continuum levels at 63 μm and 850 μm. Correlations are found between the water line fluxes and the [O i] 63.18 μm line luminosity, the dust continuum, and possibly with the stellar X-ray luminosity. This is the first time that this line of warm water vapour has been detected in protoplanetary discs. We discuss its origins, in particular whether it comes from the inner disc and/or disc surface or from shocks in outflows and jets. Our analysis favours a disc origin, with the observed water vapour line produced within 2–3 AU from the central stars, where the gas temperature is of the order of 500–600 K.