Letter to the Editor

Herschel-SPIRE FTS spectroscopy of the carbon-rich objects AFGL 2688, AFGL 618, and NGC 7027 ^*,**

¹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK e-mail: rwesson@star.ucl.ac.uk
² Astrophysics Dept, CAB (INTA-CSIC), Crta Ajalvir km4, 28805 Torrejon de Ardoz, Madrid, Spain
³ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁴ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
⁵ Universiteit van Amsterdam, Sterrenkundig Instituut “Anton Pannekoek”, Science Park 904, 1098 XH Amsterdam, The Netherlands
⁶ Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
⁷ Space Science and Technology Department, Rutherford Appleton Laboratory, Oxfordshire, OX11 0QX, UK
⁸ Institute for Space Imaging Science, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, T1K 3M4, Canada
⁹ LUTH, Observatoire de Paris-Meudon, 5 Place Jules Janssen, 92190 Meudon, France
¹⁰ Radio Astronomy Laboratory, University of California at Berkeley, CA 94720, USA
¹¹ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, Wales CF24 3AA, UK
¹² Blue Sky Spectroscopy, 9/740 4 Ave S, Lethbridge, Alberta T1J 0N9, Canada
¹³ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁴ Dept of Astronomy, Stockholm University, AlbaNova University Center, Roslagstulsbacken 21, 10691 Stockholm, Sweden
¹⁵ Dept. of Physics and Astronomy, University of Denver, Mail Stop 6900, Denver, CO 80208, USA

Received: 30 March 2010
Accepted: 10 May 2010

Abstract

We present far-infrared and submillimetre spectra of three carbon-rich evolved objects, AFGL 2688, AFGL 618 and NGC 7027. The spectra were obtained with the SPIRE Fourier-transform spectrometer on board the Herschel Space Observatory, and cover wavelengths from 195–670 μm, a region of the electromagnetic spectrum hitherto difficult to study in detail. The far infrared spectra of these objects are rich and complex, and we measure over 150 lines in each object. Lines due to 18 different species are detected. We determine physical conditions from observations of the rotational lines of several molecules, and present initial large velocity gradient models for AFGL 618. We detect water in AFGL 2688 for the first time, and confirm its presence in AFGL 618 in both ortho and para forms. In addition, we report the detection of the J = 1–0 line of CH⁺ in NGC 7027.