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Session 14 - Various Stellar Surveys.
Display session, Wednesday, January 07
Exhibit Hall,
Late M-type dwarfs, recently discovered in Two-Micron All Sky Survey (2MASS) scan observations, have been observed at the MMT, Palomar, and Keck. Comparison to their positions on the POSS-I plates show some of these to have sufficient proper motions to warrant inclusion in the LHS (Luyten Half Second) and/or NLTT (New Luyten Two Tenths) catalogs, but were missed. We discuss and show spectra for examples of these, including one very cool object with an M10+ spectral type, and a proper motion of 1.28"/yr. This star is probably cool enough that it is at least a "transition mass" object (i.e., able to sustain only limited nuclear burning), or is a young brown dwarf. Another 2MASS discovery, of type M7.5, was found to have a motion of 0.61"/yr. The number of such field objects already reported from the southern DENIS and 2MASS infrared surveys implies that such low-luminosity objects are not infrequent. These two 2MASS discoveries are also very nearby objects (photometric distances \le10 pc), and thus represent a missing component of the nearby star census. A kinematically-unbiased survey will be possible by combining 2MASS and POSS survey fields over at least the northern two thirds of the sky. Our initial detections permit preliminary comments on the likely level of completeness of Luyten's mammoth efforts through the 1980s.
