THE PEAK BRIGHTNESS OF SUPERNOVAE IN THE U BAND AND THE HUBBLE CONSTANT

The peak magnitudes of Type I supernovae in the U band can be used to answer various questions relating to supernovae and the Hubble constan t: (1) Well-observed normal Type Ia supernovae are placed in a color-c olor diagram along the extinction line of (B - V) = 1.25(U - B) + 0.15 with a scatter of 0.1 mag in each color. (2) The peak B - V colors me asured at the Asiago Observatory are far from this relation, hence sup porting the earlier conclusions that these data are unreliable. (3) Th e intrinsic B - V at B peak of normal Type Ia events is 0.00 +/- 0.04 or perhaps slightly redder, hence implying that these are good standar d candles. (4) The dereddened absolute magnitude in the U band at the time of B peak is - 18.88 +/- 0.15 for H-0 = 75. (5) The U- and H-band light curves of SN 1972E yield low values for the Hubble constant.