Name/Affiliation: ZengHua Zhang (Instituto de Astrofísica de Canarias)
Characterizing metal-deficient brown dwarfs
Metal-deficient brown dwarfs are kinematically assosiated with the Galactic halo and thick disc. Our knowledge of halo brown dwarfs are limited due to the lack of known L subdwarfs and well tested low-metallicity atmospheric models. There are only 20 L subdwarfs (some are d/sdL) been published in the literature (see Kirkpatrick et al. 2014). I started to search for mid-late type L subdwarfs in UKIDSS and SDSS in 2010, and have confirmed 20 new L subdwarfs with spectra so far, including five (e)sdL6+ (e.g. Zhang et al 2013b). Wer are expecting more new L subdwafs in our GTC/OSIRIS run in 2014A. I will summarize the current sample of mid-late type subdwarfs, and discuss responses of L subdwarf spectra to changes of metallicity and effective temperature (mass). Then disscuss the spectroscopic indicators for L subdwarfs and halo brown dwarfs. I found that the substellar subdwarf gap is likely between (e)sdL4 and (e)sdL6 (Zhang et al. 2013a). I will also compare our L subdwarf sample with Drift (Witte et al. 2009) and BT-settl (Allard et al. 2009) model spectra to support my conclutions. Then I will discuss how future facilities will help us to understand halo brown dwarf population, and how halo brown dwarfs could help us to understand the evolution of brown dwarfs and Galactic halo.