2011A&A...525A.123S

Binaries provide empirically derived key constraints for star formation theories, including the overall binary fraction, mass ratio distribution, and the separation distribution. They play crucial roles in calibrating the output of theoretical models, such as absolute magnitudes, colors, and effective temperature depending on mass, metallicity, and age. We present first results of our ongoing high-resolution imaging survey of late type brown dwarfs. The survey aims at resolving tight brown dwarf binary systems to better constrain the T dwarf binary fraction. We intend to follow up on the individual binaries to determine orbital parameters. Using NACO at the VLT, we performed AO-assisted near-infrared observations of SDSS J2052-1609. High-spatial resolution images of the T1 dwarf were obtained in H and K_S filters. We resolved SDSS J2052-1609 into a binary system with a separation of 0.1009±0.001''. Archival data from HST/NICMOS taken one year before our observations proves the components are co-moving. Using the flux ratio between the components we infer J, H, and K_S magnitudes for the resolved system. From the near-IR colors, we estimate spectral types of T1⁺¹_–4 for component A and T2.5±1 for component B. A first estimate of the total system mass yields M_tot≥78M_Jup, when assuming a circular orbit.