THE DISTANCE TO THE TYPE-IA SUPERNOVA 1972E AND ITS PARENT GALAXY NGC-5253 - A PREDICTION

Sandage et al. have used the HST to obtain a Cepheid-based distance to IC 4182, the parent galaxy of the Type Ia SN 1937C, and intend to do the same for NGC 5253, the parent galaxy of the Type Ia SN 1972E. In an attempt to test the predictive power of Type Ia supernovae as distance indicators, we compare the observational properties of SNs 1937C and 1972E and consider the possibility of intrinsic differences between them. A naive application of a relation between absolute magnitude and postpeak decline rate implies that SN 1972E was intrinsically brighter than SN 1937C and at a distance of 5.2+/-0.6 Mpc. However, because SNs 1937C and 1972E were spectroscopically normal we expect their absolute magnitudes to have been similar and the NGC 5253 distance to be 4.4+/-0.4 Mpc.