An IPHAS-based search for accreting very low-mass objects using VO tools

¹ Instituto de Astrofísica de Canarias, C/ vía Láctea, s/n, 38200 La Laguna, Tenerife, Spain e-mail: [lval;ege;bouy]@iac.es
² University of Central Florida, Dept. of Physics, PO Box 162385, Orlando, FL 32816-2385, USA
³ Astronomy Department, University of California, Berkeley, CA 94720, USA
⁴ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), Apdo.78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: [esm;raul]@laeff.inta.es
⁵ Spanish Virtual Observatory Thematic Network, Spain
⁶ Imperial College of Science, Technology and Medicine, Blackett Laboratory, Exhibition Road, London, SW7 2AZ, UK e-mail: j.drew@imperial.ac.uk
⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
⁸ Institut für Physik, Universität Graz, Universitätsplatz 5, 8010 Graz, Austria e-mail: rgreimel@gmail.com
⁹ Isaac Newton Group of Telescopes, Apartado de correos 321, 38700 Santa Cruz de la Palma, Tenerife, Spain
¹⁰ Astrophysics Group, Blackett Laboratory, Imperial College London, SW7 2AZ, UK e-mail: y.unruh@imperial.ac.uk
¹¹ Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland, UK e-mail: jsv@arm.ac.uk

Received: 26 May 2008
Accepted: 12 October 2008

Abstract

Context. The main goal of this paper is to prove that accreting very low-mass stars and brown dwarfs can be identified in IPHAS, an Hα emission survey of the northern Milky Way. Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be useful in identifying very low-mass accreting objects near to and far from well-known star-forming regions.

Aims. We have used Virtual Observatory tools to cross-match the IPHAS catalogue with the 2MASS catalogue. We defined photometric criteria to identify Hα emission sources with near-infrared colours similar to those of known young very low-mass stars and brown dwarfs. 4000 candidates were identified that met our criteria over an area of 1600 square degrees. We present low-resolution optical spectra of 113 candidates. Spectral types have been derived for the 33 candidates that have spectroscopically confirmed Hα emission, negligible reddening and spectral class M. We have also measured Hα emission and investigated the NaI doublet (818.3 nm, 819.5 nm) in these 33 objects.

Methods. We confirm that 33 IPHAS candidates have strong Hα emission indicative of disc accretion for their spectral type. Twenty-three of them have spectral class M4 or later, of which ten have classes in the range M5.5–M7.0 and could thus be very young brown dwarfs. Many objects also have a weak NaI doublet, an indication of low surface gravity.

Results. IPHAS provides a very valuable database for identifying accreting very low-mass stars and brown dwarfs. Virtual Observatory tools provide an efficient method for identifying these objects over large areas of the sky. Based on our success rate of 23 Hα emission objects with spectral type in the range M4–M7 out of 113 candidates with spectroscopic follow-up, we estimate that there could be hundreds of such objects in the full IPHAS survey.