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Session 75 - 2MASS.
Display session, Wednesday, January 17
North Banquet Hall, Convention Center
Several important ground-- and HST--based surveys in recent years have defined the shapes of the stellar luminosity function (LF) and initial mass function (IMF) of low mass stars in the Galactic disk with greater precision. While the LF and IMF have been shown to peak near 0.3 solar masses, and decline to about 0.1--0.15 solar masses, all of the surveys lack enough detections below 0.15 solar masses for the slope beyond that point to be well determined. The faintest magnitude bins are also of critical importance because of the possibility that young brown dwarfs may exist at these detectable luminosities, before they fade out.
2MASS offers the opportunity to search most of the sky in a complete, unbiased way for very low luminosity stars in the solar neighborhood, and for any brown dwarfs of similar or lower luminosity. This survey offers two advantages over "deeper" pencil-beam surveys of limited area: much larger numbers of stellar objects near the mass limit could be found, and (2) these will be closer, brighter, and hence more amenable to the follow-up observations critical to determining their luminosities, other parameters, and evolutionary state.
The red star candidate list for each 2MASS field will be produced by pairing up point sources identified in the two databases our group has access to -- 2MASS and the POSS--II Schmidt plates measured with the U.S. Naval Observatory Precision Measuring Machine (PMM) at Flagstaff. These include a blue (IIIaJ) magnitude, a red (IIIaF) magnitude, and in some cases a near--infrared (IV-N) magnitude. Thus the goal is to produce a catalogue of candidates in each field with B,R,I,J,H,K magnitudes or limits, and a positional accuracy of 0.25 arc seconds. The catalogue will include measured proper motions for candidates detected and measured by the PMM on earlier POSS plates. The prototype camera observations with the KPNO 1.3--m at high Galactic latitude fields are being analyzed as a test of the sensitivity and accuracy of the all-sky survey.
