FINAL RESULTS FROM THE HUBBL E SPACE T EL ESCOPE KEY PROJECT TO MEASURE THE

We present here the —nal results of the Hubble Space Telescope (HST ) Key Project to measure the Hubble constant. We summarize our method, the results, and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. Our results are based on a Cepheid calibration of several secondary distance methods applied over the range of about 60¨400 Mpc. The analysis presented here bene—ts from a number of recent improvements and re—nements, including (1) a larger LMC Cepheid sample to de—ne the —ducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. We adopt a distance modulus to the LMC (relative to which the more distant galaxies are measured) of mag, or 50 kpc. New, revised distances are given for the 18 spiral galaxies for k 0 (LMC) 18.50 ^ 0.10 which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we —nd values (in km s~1 Mpc~1) of (random) ^ 6 (systematic) (Type Ia supernovae), H 0 71 ^ 2