THE PEAK BRIGHTNESS OF SN 1895B IN NGC-5253 AND THE HUBBLE CONSTANT

The light curve of the Type Ia supernova SN 1895B (in NGC 5253) is imp ortant because Sandage et al. have measured a distance to the host gal axy by means of Cepheid variables and thus have derived the Hubble con stant. However, the last time the supernova plates were measured was i n 1923, and the resultant photometry is inconsistent at the 0.8 mag le vel. In this paper, I report on the results of my remeasurement of the old supernova plates with a scanning microdensitometer. I find B-magn itudes of >11.3 +/- 0.3, 8.36 +/- 0.07, 8.51 +/- 0.06, 8.54 +/- 0.05, and 9.34 +/- 0.08 on JD 2,413,359, 2,413,383, 2,413,384, 2,413,385, an d 2,413,393, respectively. The last plate was a prism plate, for which I present a flux-calibrated spectrum, taken similar to 15 days after maximum. Even though only loose constraints can be placed on the light curve shape, the firm limit on the peak magnitude (<8.49 +/- 0.03) wi ll provide a firm limit on the Hubble constant. The most likely shape is that of the average Type Ia template of Leibundgut et al., for whic h the best-fit peak B-magnitude is 8.26 +/- 0.11. The deduced probabil ity distribution for H-0 is peaked at 51 +/- 7 km s(-1) Mpc(-1), with extreme limits of 61 +/- 12 and 26 +/- 5 km s(-1) Mpc(-1).