Program: GN-2013B-Q-7

Over the past ~20 years, discoveries of brown dwarfs have prompted intensive study of the low-mass end of the IMF and the atmospheric properties of these ultracool objects. Yet in spite of these efforts, constraints on the local mass function remain weak, and models have yet to successfully reproduce the observed spectral features of brown dwarfs, particularly in the transition from L dwarfs to T dwarfs. As part of the PI’s first 699 project, we have cross-matched the PS1 (optical) and WISE (mid-IR) catalogs to produce a unique multi-wavelength database for finding ultracool dwarfs. We are using this database to conduct a volume-limited census of nearby L/T transition dwarfs. Previous large scale searches have been incomplete for L/T dwarfs, because these objects are faint in optical bands and have near-infrared colors that are difficult to distinguish from background stars. Our search is significantly filling a known gap in the solar neighborhood census, including discovery of some of the nearest, brightest objects and identification of spectroscopic variables (Best et al. ApJ, submitted March 2013). Our limiting distance of 25 pc matches several previous surveys of the solar neighborhood. We are using low resolution near-infrared spectra to confirm the identity of our candidates, mostly with IRTF/SpeX. However, IRTF has a northerly declination limit of +70°. We propose 2 hours on Gemini/GNIRS to obtain near-infrared spectra of six promising northern L/T transition dwarf candidates within 25 pc of the Sun. These observations will help us to complete a well-defined sample of over 80 late L and early T dwarfs, which we will use to model the evolution of brown dwarfs through the L/T transition.