WISE/2MASS-SDSS brown dwarfs candidates using Virtual Observatory tools

Context. Massive far-red and infrared imaging surveys in different bandpasses are the main contributors to the discovery of brown dwarfs (BDs). The Virtual Observatory (VO) represents an adequate framework to handle these vast datasets efficiently and filter them out according to specific requirements. A statistically significant number of BDs is mandatory for understanding their general properties better for identifing peculiar objects. WISE, an all-sky survey in the mid-infrared, provides an excellent opportunity to increase the number of BDs significantly, in particular those at the lower end of the temperature scale. Aims. We aim to demonstrate that VO tools are efficient in identifing and characterizing BDs by cross-correlating public catalogues released by large surveys. Methods. Using VO tools we performed a cross-match of the WISE Preliminary Release, the 2MASS Point Source and the SDSS Data Release 7 catalogues over the whole area of sky that they have in common (similar to 4000 deg(2)). Photometric and proper motion criteria were used to obtain a list of BD candidates. A temperature estimate is provided for each candidate based on their spectral energy distribution using VOSA, a VO tool for spectral energy distribution (SED) fitting. We derive the spectral types from the effective temperatures. Distances, calculated from the absolute magnitude-spectral type relation, place our candidates at 14-80 pc from the Sun, assuming that they are single. Results. We have identified 31 BD candidates, 25 of which have already been reported in the literature. The remaining six candidates have been classified as L- (four) and T-type (two) objects. The high rate of recovery of known BDs (similar to 90% of the T dwarfs catalogued in 2MASS) demonstrates the validity of our strategy to identify them with VO tools. An application of this method for a deeper search that covers the whole sky in common to WISE and UKIDSS will be presented in a forthcoming work.