DISCOVERY OF THE LOWEST MASS BROWN DWARF IN THE PLEIADES

We have imaged the Pleiades open cluster at I and Z in a search for lo w-mass stars and brown dwarfs. One very red object, which we have call ed PIZ 1, at I=19.64, I-Z=1.33 has been detected within an area of 100 arcmin(2). Follow-up infrared photometry verifies that this object is extremely red with a K magnitude of 15.5. We have also obtained a spe ctrum which exhibits the spectral features indicative of an extremely cool M dwarf. We estimate the effective temperature and mass of PIZ 1 to be 2300 K and 0.038 M., respectively.