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Session 75 - 2MASS.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
During its prototyping phase, the Two Micron All-Sky Survey (2MASS) has surveyed more than 200 square degrees of the sky. Infrared (1.61--1.64\um) spectra of 206 bright (\Ks \leq5.0 mag.) sources identified by the prototype survey have been acquired at the KPNO 0.9m Coudé Feed telescope using the University of Massachusetts NICMOS3 camera (NICMASS) during four observing runs in 1994-95. Many of these stars are heavily obscured and have faint visible counterparts. At the focal plane of the coudé feed telescope, the NICMASS system has a spectral resolving power of R=7200 per pixel pair (20 km s^-1/pixel). The 1.61--1.64\um\ window was chosen for its low telluric absorption and its large number of atomic and molecular lines. There are molecular transitions of CO, OH, and CN in this wavelength region, as well as many metallic lines. The CO bands in particular are diagnostic of effective temperature and luminosity class.
Spectral classification of a subset of the sources indicates that approximately 65% have spectral types typical of asymptotic giant branch stars (M, C, and S). These spectra have high SNR, and there is sufficient detail to differentiate between M, C, and S stars and to determine spectral type to within two subclasses.
We are able to measure relative velocities to a precision of \sim5 km s^-1 by cross correlation. Our long range goal is to use radial velocities together with photometrically determined distances for spectrally identified AGB stars to probe the underlying structure of the Galaxy.
