A sample of 35 SNe Ia with good to excellent photometry in B and V , minimum internal absorption , and 1200 < v \stackrel { { } _ { < } } { { } _ { \sim } } 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 also peak magnitudes in I are known .
The SNe Ia have uniform colors at maximum , i.e . < B - V > = - 0 \stackrel { { } ^ { m } } { { } _ { . } } 012 ( \sigma =0.051 ) and < V - I > = - 0 \stackrel { { } ^ { m } } { { } _ { . } } 276 ( \sigma =0.078 ) .
In the Hubble diagram they define a Hubble line with a scatter of \sigma _ { M } =0 \stackrel { { } ^ { m } } { { } _ { . } } 21-0 \stackrel { { } ^ { m } } { { } _ { . } } 16 , 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 \stackrel { { } _ { < } } { { } _ { \sim } } 0 \stackrel { { } ^ { m } } { { } _ { . } } 13 .
After the correction no significant dependence remains on Hubble type or galactocentric distance .
The Hubble line suggests some curvature which can be differently interpreted .
A consistent solution is obtained for a cosmological model with \Omega _ { M } =0.3 , \Omega _ { \Lambda } =0.7 , which is indicated also by much more distant SNe Ia .
Absolute magnitudes are available for eight equally blue ( Branch-normal ) SNe Ia in spirals , 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 SNe 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 decrease H _ { 0 } .
The finally adopted value at the 90-percent level , including random and systematic errors , is H _ { 0 } =58.5 \pm 6.3 km s ^ { -1 } Mpc ^ { -1 } .
Several higher values of H _ { 0 } from SNe Ia , as suggested in the literature , are found to depend on large corrections for variations of the light curve parameter and/or on an unwarranted reduction of the Cepheid distances of the calibrating SNe Ia .