Program: GN-2009B-DD-6

We propose to obtain a JHK spectroscopy of an ultracool brown dwarf candidate, CFBDS013302+023128, identified as an i-band dropout in the CFHTLS survey and through its extreme z-J and J-H colours in follow-up photometry. Those suggest that it is at least as cold as the coldest known brown dwarfs, and is most likely to show the NH3 absorption that characterizes the proposed Y spectral class. The primary goal of the proposed spectroscopic observations is to explore atmospheric physics in a new temperature domain, intermediate between the currently known brown dwarfs and the giant planets.