Program: GN-2010A-Q-81

We request 13 hours with GMOS-N to obtain i-band and z-band photometry of eight T7.5-T9.0 dwarfs with 800 > T_eff K > 500. Such data currently do not exist. The far-red colors of cool dwarfs are very red, but are calculated to turn to the blue for T_eff < 700K as the gaseous K I condenses to KCl, weakening the extremely strong K I absorption at 0.77um, which falls in the i-band. It is important to understand the alkali chemistry of brown dwarfs as it plays a critical role in shaping the energy distributions of both L and T dwarfs (and is even important in exosolar planetary atmospheres), and so we must determine the currently unknown behaviour at the coolest temperatures, where the alkalis should be completely removed from the photosphere. Also, knowledge of these colors is fundamental to the search for more and cooler examples of the rare very low-mass brown dwarfs, as far-red/very-near-IR surveys are ongoing or planned which use the izYJ bands to identify such objects (e.g. CFHTBDS, UKIDSS, Pan-Starrs, VISTA, LSST).