| Abstract | Following the approach by Paczyński & Stanek, we compare the red clump stars with parallaxes known to better than 10% in the Hipparcos catalog with the red clump stars observed in three fields in M31 using the Hubble Space Telescope. There are ~600 and ~6300 such stars in the two data sets, respectively. The local red clump luminosity function is well represented by a Gaussian with the peak at MI,m=-0.23 and the dispersion σRC~0.2 mag. This allows a single-step determination of the distance modulus to M31, μ0,M31=24.471+/-0.035+/-0.045 mag (statistical plus systematic error), and the corresponding distance, RM31=784+/-13+/-17 kpc. The number of red clump stars is large enough that the formal statistical error in the distance is only <~2%. We also correct the treatment of the local interstellar extinction by Paczyński & Stanek, and we obtain the Galactocentric distance modulus, μ0,GC=14.57+/-0.04+/-0.04 mag (statistical plus systematic error), and the corresponding Galactocentric distance, R0=8.2+/-0.15+/-0.15 kpc. |
