GALACTOCENTRIC DISTANCE WITH THE OGLE AND HIPPARCOS RED CLUMP STARS

We compare red clump stars with parallaxes known to better than 10% in the Hipparcos catalog and corrected for interstellar extinction with the OGLE red clump stars in Baade's Window, also corrected for interst ellar extinction. There are similar to 600 and similar to 10,000 such stars in the two data sets, respectively. We find empirically that the average I-band magnitude of red clump stars does not depend on their intrinsic color in the range 0.8 < (V-I)(0) < 1.4. The red clump lumin osity function is well represented by a Gaussian with the peak at M-I0 ,M-m = -0.28 and the dispersion sigma(RC) approximate to 0.2 mag. This allows a single-step determination of the distance to the Galactic ce nter and gives R-0 = 8.4 +/- 0.4 kpc. The number of red clump stars is so large that the formal statistical error is only similar to 1%. The local stars are relatively blue and have a small color dispersion: <( V -I)> = 1.01 and sigma(V-1) = 0.08, while for the bulge stars <(V-I)( 0)> = 1.22 and sigma((V-1)0) = 0.14. Presumably, the bulge population has a broader range and a higher average metallicity than the local di sk population.