Supernova 1991T and the Value of the Hubble Constant

Based on multiepoch Hubble Space Telescope observations, we present the discovery of 16 high-quality Cepheid candidates in NGC 4527. Corrected for metallicity effects in the Cepheid period-luminosity relation, we derive a distance, including both random ( r ) and systematic ( s ) uncertainties, of 13.0 ± 0.5( r ) ± 1.2( s ) Mpc. Our result is then used to provide a calibration of the peak B -, V -, and I -band luminosities of the peculiar Type Ia supernova SN 1991T, a resident of NGC 4527. Despite its documented spectroscopic peculiarities, after correction for the decline rate-luminosity correlation, the corrected peak luminosity is indistinguishable from those of so-called "normal" Type Ia SNe. With nine local calibrators now at our disposal, we determine a robust value for the Hubble constant of H 0 = 73 ± 2( r ) ± 7( s ) km s -1 Mpc -1 .