Supernova type ia luminosities, their dependence on second parameters, andthe value of H-0

A sample of 35 Type Ia supernovae (SNe Ia) with good to excellent photometr y in B and V, minimum internal absorption, and 1200 < upsilon less than or similar to 30,000 km s(-1) is compiled from the literature. As far as their spectra are known, they are all Branch-normal. For 29 of the SNe Ia, peak magnitudes in I are also known. The SNe Ia have uniform colors at maximum, i.e., [B-V] = -0.012 mag (sigma = 0.051) and [V-I] = -0.276 mag (sigma = 0. 078). In the Hubble diagram, they define a Hubble line with a scatter of si gma(M) = 0.21-0.16 mag, decreasing with wavelength. The scatter is further reduced if the SNe Ia are corrected for differences in decline rate, Delta m(15), or color (B-V). A combined correction reduces the scatter to sigma l ess than or similar to 0.13 mag. After the correction, no significant depen dence remains on Hubble type or Galactocentric distance. The Hubble line su ggests some curvature that can be differently interpreted. A consistent sol ution is obtained for a cosmological model with Omega(M) = 0.3, Omega(Lambd a) = 0.7, which is also indicated by much more distant SNe Ia. Absolute mag nitudes are available for eight equally blue (Branch-normal) SNe Ia in spir als whose Cepheid distances are known. If their well-defined mean values of M-B, M-V, and M-I are used to fit the Hubble line to the above sample of S Ne Ia, one obtains H-0 = 58.3 km s(-1) Mpc(-1), or, after adjusting all SNe Ia to the average values of Delta m(15) and (B-V), H-0 = 60.9 km s(-1) Mpc (-1). Various systematic errors are discussed whose elimination tends to de crease H-0. The value finally adopted at the 90% level, including random an d systematic errors, is H-0 = 58.5 +/- 6.3 km s(-1) Mpc(-1). Several higher values of H-0 from SNe Ia, as suggested in the literature, are found to de pend on large corrections for variations of the light-curve parameter and/o r on an unwarranted reduction of the Cepheid distances of the calibrating S Ne Ia.