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We report observations of two nearby Type Ia supernovae (SNe Ia) for whichobservations of Cepheid variables in the host galaxies have been obtained withthe Hubble Space Telescope: SN 1994ae in NGC 3370 and SN 1998aq in NGC 3982.For NCG 3370, we used the Advanced Camera for Surveys to observe 64 Cepheidsthat yield a distance of 29 Mpc, the farthest direct measurement of Cepheids.We have measured emission lines from H II regions in both host galaxies whichprovide metallicity-dependent corrections to their period-luminosity relations.These two SNe Ia double the sample of ``ideal'' luminosity calibrators: objectswith well-observed and well-calibrated light curves of typical shape and withlow reddening. By comparing them to all similarly well-measured SNe Ia in theHubble flow, we find that H_0 = 73 +/- 4 (statistical) +/- 5 (systematic). Adetailed analysis demonstrates that most of the past disagreement over thevalue of H_0 as determined from SNe Ia is abated by the replacement of past,problematic data by more accurate and precise, modern data.Comment: Accepted to ApJ, 66 pages, truncated data tables, 12 figures (some  condensed to jpeg

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Cepheid Calibrations from the<i>Hubble Space Telescope</i>of the Luminosity of Two Recent Type Ia Supernovae and a Redetermination of the Hubble Constant

Cepheid Calibrations from theHubble Space Telescopeof the Luminosity of Two Recent Type Ia Supernovae and a Redetermination of the Hubble Constant