IMPLICATIONS OF NEW JHK PHOTOMETRY AND A DEEP INFRARED LUMINOSITY FUNCTION FOR THE GALACTIC BULGE

We present deep near-IR photometry for Galactic bulge stars in Baade's Window, (l, b) = (1.0 degrees, - 3.9 degrees), and another minor axis field at (l, b) = (0 degrees, - 6 degrees). We combine our data with previously published photometry and construct a luminosity function ov er the range 5.5 less than or equal to K-0 less than or equal to 16.5, deeper than any previously published, The slope of this luminosity fu nction and the magnitude of the tip of the first ascent giant branch a re consistent with theoretical values derived from isochrones with app ropriate age and metallicity. We use the relationship between [Fe/H] a nd the giant branch slope derived from near-lR observations of metal-r ich globular clusters by Kuchinski et al. [AJ, 109, 1131 (1995)] to ca lculate the mean metallicity for several bulge fields along the minor axis. For Baade's Window we derive ([Fe/H]) = - 0.28 +/- 0.16, consist ent with the recent estimate of McWilliam & Rich [ApJS, 91, 749 (1994) ], but somewhat lower than previous estimates based on CO and TiO abso rption bands and the JHK colors of M giants by Frogel et al. [ApJ, 353 , 494 (1990)]. Between b = - 3 degrees and - 12 degrees we find a grad ient in ([Fe/H]) of - 0.06 +/- 0.03 dex/deg or - 0.43 +/- 0.21 dex/kpc for R(0) = 8 kpc, consistent with other independent derivations. We d erive a helium abundance for Baade's Window with the R and R' methods and find that Y = 0.27 +/- 0.03 implying Delta Y/ Delta Z = 3.3 +/- 1. 3. Next, we find that the bolometric corrections for bulge K giants (V - K less than or equal to 2) are in excellent agreement with empirica l derivations based on observations of globular cluster and local fiel d stars. However, for the redder M giants we find, as did Frogel & Whi tford [ApJ, 320, 199 (1987)], that the bolometric corrections differ b y several tenths of a magnitude from those derived for field giants an d subsequently used in the Revised Yale Isochrones. This difference mo st likely arises from the stronger molecular blanketing in the V and I bands of the bulge giants relative to that in field stars. From the l uminosity function for Baade's Window and our bolometric corrections w e calculate that (m - M)(0) = 14.43 +/- 0.35 or R(0) = 7.7 +/- 1.2 kpc to the bulge based on the surface-brightness fluctuation method of To nry & Schneider [AJ, 96, 807 (1988)], with the distance to M31 and M32 used for calibration. (C) 1995 American Astronomical Society.