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 over 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 function and the magnitude of the tip of the first ascent giant branch are consistent with theoretical values derived from isochrones with appropriate age and metallicity. We use the relationship between [Fe/H] and the giant branch slope derived from near-lR observations of metal-rich globular clusters by Kuchinski et al. [AJ, 109, 1131 (1995)] to calculate the mean metallicity for several bulge fields along the minor axis. For Baade's Window we derive ([Fe/H]) = - 0.28 +/- 0.16, consistent with the recent estimate of McWilliam & Rich [ApJS, 91, 749 (1994)], but somewhat lower than previous estimates based on CO and TiO absorption 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 gradient 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 derive 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 empirical derivations based on observations of globular cluster and local field stars. However, for the redder M giants we find, as did Frogel & Whitford [ApJ, 320, 199 (1987)], that the bolometric corrections differ by several tenths of a magnitude from those derived for field giants and subsequently used in the Revised Yale Isochrones. This difference most 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 luminosity function for Baade's Window and our bolometric corrections we 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 Tonry & Schneider [AJ, 96, 807 (1988)], with the distance to M31 and M32 used for calibration. (C) 1995 American Astronomical Society.