Research Note

IPHAS and the symbiotic stars^*

II. New discoveries and a sample of the most common mimics

¹ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain e-mail: rcorradi@iac.es
² Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³ INAF, Osservatorio Astronomico di Padova, via dell'Osservatorio 8, 36012 Asiago (VI), Italy
⁴ Department of Astronomy, University of Padova, Asiago Astrophysical Observatory, 36012 Asiago (VI), Italy
⁵ Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK
⁶ Instituto de Geofísica y Astronomía, Calle 212, N. 2906, CP 11600, La Habana, Cuba
⁷ Institut für Physik, Karl-Franzen Universität Graz, Universitätsplatz 5, 8010 Graz, Austria
⁸ Isaac Newton Group of Telescopes, Apart. de Correos 321, 38700 Santa Cruz de la Palma, Spain
⁹ Jodrell Bank Centre for Astrophysics, Alan Turing Building, University of Manchester, Manchester, M13 9PL, UK
¹⁰ Department of Physics, Macquarie University, Sydney, NSW 2109, Australia
¹¹ Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
¹² Astrophysics Group, Imperial College of Science, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
¹³ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
¹⁴ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁶ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 Gl Nijmegen, the Netherlands
¹⁷ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Street, Manchester M13 9PL, UK
¹⁸ Institute of Astronomy, Cambridge University, Madingley Road, Cambridge, CB3 0HA, UK

Received: 2 September 2009
Accepted: 10 October 2009

Abstract

Context. Knowledge of the total population of symbiotic stars in the Galaxy is important for understanding basic aspects of stellar evolution in interacting binaries and the relevance of this class of objects in the formation of supernovae of type Ia.

Aims. In a previous paper, we presented the selection criteria needed to search for symbiotic stars in IPHAS, the INT Hα survey of the Northern Galactic plane. IPHAS gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume.

Methods. Follow-up spectroscopy at different telescopes worldwide of a sample of sixty two symbiotic star candidates is presented.

Results. Seven out of nineteen S-type candidates observed spectroscopically are confirmed to be genuine symbiotic stars. The spectral type of their red giant components, as well as reddening and distance, were computed by modelling the spectra. Only one new D-type symbiotic system, out of forty-three candidates observed, was found. This was as expected (see discussion in our paper on the selection criteria). The object shows evidence for a high density outflow expanding at a speed ≥65 km s^-1.
Most of the other candidates are lightly reddened classical T Tauri stars and more highly reddened young stellar objects that may be either more massive young stars of HAeBe type or classical Be stars. In addition, a few notable objects have been found, such as three new Wolf-Rayet stars and two relatively high-luminosity evolved massive stars. We also found a helium-rich source, possibly a dense ejecta hiding a WR star, which is surrounded by a large ionized nebula.

Conclusions. These spectroscopic data allow us to refine the selection criteria for symbiotic stars in the IPHAS survey and, more generally, to better understand the behaviour of different Hα emitters in the IPHAS and 2MASS colour-colour diagrams.