Letter to the Editor

PACS and SPIRE spectroscopy of the red supergiant VY CMa^*

¹ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: pierre@ster.kuleuven.be
² Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 Amsterdam, The Netherlands
³ Dept of Physics & Astronomy, University College London, Gower St, London WC1E 6BT, UK
⁴ Space Science and Technology Department, Rutherford Appleton Laboratory, Oxfordshire, OX11 0QX, UK
⁵ Department of Physics, University of Lethbridge, Lethbridge, Alberta, T1J 1B1, Canada
⁶ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁷ Astrophysics Dept, CAB (INTA-CSIC), Crta Ajalvir km4, 28805 Torrejon de Ardoz, Madrid, Spain
⁸ LUTH, Observatoire de Paris-Meudon, LERMA UMR CNRS 8112, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁹ Radio Astronomy Laboratory, University of California at Berkeley, CA 94720, USA
¹⁰ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748, Germany
¹¹ School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff, Wales CF24 3YB, UK
¹² Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
¹³ Blue Sky Spectroscopy, 9/740 4 Ave S, Lethbridge, Alberta T1J 0N9, Canada
¹⁴ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁵ University of Vienna, Department of Astronomy, Türkenschanzstraße 17, 1180 Vienna, Austria
¹⁶ Dept of Astronomy, Stockholm University, AlbaNova University Center, Roslagstullsbacken 21, 10691 Stockholm, Sweden

Received: 31 March 2010
Accepted: 20 April 2010

Abstract

With a luminosity >10⁵  and a mass-loss rate of ~2 × 10^-4  yr^-1, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55–672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ~1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.