I. Selection method and first discoveries
Isaac Newton Group, PO Ap. de Correos 321, 38700 Sta. Cruz de la Palma, Spain e-mail: email@example.com
2 Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
3 Instituto de Geofísica y Astronomía, Calle 212, N. 2906, CP 11600, La Habana, Cuba
4 Imperial College of Science, Technology and Medicine, Blackett Laboratory, Exhibition Road, London, SW7 2AZ, UK
5 Centre for Astrophysics Research, STRI, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK
6 N. Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
7 Columbia Astrophysics Laboratory, USA
Accepted: 10 December 2007
Context.The study of symbiotic stars is essential to understand important aspects of stellar evolution in interacting binaries. Their observed population in the Galaxy is however poorly known, and is one to three orders of magnitudes smaller than the predicted population size.
Aims.IPHAS, the INT Photometric Hα survey of the Northern Galactic plane, gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume, and discover a significant number of new systems.
Methods.A method of selecting candidate symbiotic stars by combining IPHAS and near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic binaries from normal stars and most of the other types of Hα emission line stars in the Galaxy. The only exception are T Tauri stars, which can however be recognized because of their concentration in star forming regions.
Results.Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Hα in emission. 1500 to 2000 of them are likely to be Be stars. Among the remaining objects, 1183 fulfill our photometric constraints to be considered candidate symbiotic stars. The spectroscopic confirmation of three of these objects, which are the first new symbiotic stars discovered by IPHAS, proves the potential of the survey and selection method.
Key words: surveys / Galaxy: stellar content / stars: binaries: symbiotic / stars: emission-line, Be / stars: pre-main sequence / ISM: planetary nebulae: general
Based on observations obtained at the 2.5 m INT telescope of the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has also made use of the SIMBAD database, operated at CDS, Strasbourg, France.
© ESO, 2008