THE UNIQUE SPECTRUM OF THE BROWN DWARF CANDIDATE GD 165B AND COMPARISON TO THE SPECTRA OF OTHER LOW-LUMINOSITY OBJECTS

The 6300-9000 angstrom spectrum of the brown dwarf candidate GD 165B is presented and compared to spectra of three of the lowest luminosity, red objects known: LHS 2924, LHS 2065, and PC 0025+0447. The features found in the spectrum of GD 165B may not correspond to the familiar molecular absorptions seen in these objects, and they do not match the molecular absorptions found in spectra of the Jovian planets. New, previously unidentified molecules may be present. Recent model energy distributions for M dwarfs do not predict spectra like the one presented here, so a temperature for this object is estimated using extrapolations to absolute magnitude versus temperature for low-mass stars. Two estimates are given for the location of GD 165B on the H-R diagram-one using our temperature estimate and the other using the temperature quoted in Zuckerman & Becklin. Neither data point yields an unambiguous classification as either star or brown dwarf for this unusual object. It can be concluded, nonetheless, that GD 165B has redder colors and fainter absolute magnitudes than any known main-sequence star-with a spectrum unlike that of any known M dwarf.