THE CEPHEID DISTANCE TO NGC-5253 - CALIBRATION OF M(MAX) FOR THE TYPE-IA SUPERNOVAE SN-1972E AND SN-1895B

The apparent V distance modulus of NGC 5253, parent galaxy to the Type Ia supernovae SN 1972E and SN 1895B, is (m - M)AV = 28.06 +/- 0.06 mag (internal error) determined from 11 Cepheid variables discovered with the Hubble Space Telescope. The internal differential absorption between the Cepheids and the two SNs is taken to be zero based on four independent methods. The absolute magnitudes of SN Ia 1972E are M(B)(max) = - 19.53 +/- 0.12, and M(V)(max) = - 19.46 +/- 0.12. The absolute magnitude of SN Ia 1895B is M(B)(max) = - 19.69 +/- 0.21, based on B(max) = - 8.4 +/- 0.2 determined by correcting Walker's comparison stars, in 1923, to the modem photoelectric zero point in B. Combining these data with the data for SN 1937C in IC 4182 determined earlier gives mean values of [M(B)(max)] = - 19.55 +/- 0.08 mag based now on three SNs calibrations relative to Cepheids, and [M(V)(max)] = - 19.58 +/- 0.09 mag based on two Cepheid determinations. Using the extant Hubble diagrams in B and V for SNs la gives the global values of the Hubble constant as H-0(B) = 52 +/- 8 km s-1 Mpc-1, and H-0(V) = 55 +/- 8 km s-1 Mpc-1. The quoted error is the external uncertainty assuming an intrinsic dispersion of 0.3 mag about the Hubble diagram for SNs Ia.