The Type Ia Supernova 1998bu in M96 and the Hubble Constant

We present optical and near-infrared photometry and spectroscopy of the Type Ia SN 1998bu in the Leo I Group galaxy M96 (NGC 3368). The data set consists of 356 photometric measurements and 29 spectra of SN 1998bu between UT 1998 May 11 and July 15. The well-sampled light curve indicates the supernova reached maximum light in B on UT 1998 May 19.3 (JD 2450952.8 ± 0.8) with B = 12.22 ± 0.03 and V = 11.88 ± 0.02. Application of a revised version of the Multicolor Light Curve Shape (MLCS) method yields an extinction toward the supernova of AV = 0.94 ± 0.15 mag, and indicates the supernova was of average luminosity compared to other normal Type Ia supernovae. Using the HST Cepheid distance modulus to M96 and the MLCS fitted parameters for the supernova, we derive an extinction-corrected absolute magnitude for SN 1998bu at maximum, MV = -19.42 ± 0.22. Our independent results for this supernova are consistent with those of Suntzeff et al. Combining SN 1998bu with three other well-observed local calibrators and 42 supernovae in the Hubble flow yields a Hubble constant, H0 = 64img1.gif km s-1 Mpc-1, where the error estimate incorporates possible sources of systematic uncertainty including the calibration of the Cepheid period-luminosity relation, the metallicity dependence of the Cepheid distance scale, and the distance to the LMC.