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

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.

T Tauri candidates and accretion rates using IPHAS: method and application to IC 1396

“…In the case of multiple photometric detections due to overlapping or repeated CCD pointings, we averaged the photometry and show the object only once. We note that no extremely low-mass candidates are found beyond (r −i ) > 2.5, which is in agreement with the low density of such objects in IPHAS as previously found by Valdivielso et al (2009).…”

DE0823−49 is a juvenile binary brown dwarf at 20.7 pc

“…DE0823−49 thus appears isolated in terms of membership, although there may exist numerous very-low-mass few-member young associations that are not recognised yet in the solar neighbourhood. Searches for young very-low-mass stars outside starforming regions indicate that they are typically near larger starforming regions but not inside them (Martin & Kun 1996;Valdivielso et al 2009). …”

The IPHAS-POSS-I proper motion survey of the Galactic plane

“…Valdivielso et al (2009) have produced a sample of young, low‐mass objects using IPHAS data. Clearly identifying the proper motions of such objects could establish a connection with a known star‐forming association or moving group.…”

“…With the number density of stars highly concentrated on the plane, IPHAS and EGAPS provide ideal tools to study a whole range of stellar and Galactic research topics. They have already yielded significant discoveries in fields such as cataclysmic variables (Witham et al 2008), planetary nebulae (Mampaso et al 2006; Wesson et al 2008), young low‐mass objects (Valdivielso et al 2009), star‐forming regions (Vink et al 2008) and extinction in the Galactic plane (Sale, Drew & Unruh 2009). Large‐scale CCD‐based astronomical surveys such as IPHAS provide accurate photometric and astrometric data on large numbers of astronomical objects.…”