Cepheid calibration of the peak brightness of SNe Ia V SN 1981B in NGC 4536

Observations have been made with the Hubble Space Telescope between 1994 June and August over a 67 day interval, comprising 17 epochs in the F555W band and 5 epochs in the F814W band. The target was a region of an outlying spiral arm of NGC 4536 [Sbc(s)I-II], a galaxy that was parent to the type Ia supernova SN 1981B. Seventy-three Cepheids were found with periods ranging between 5.4 and 65 days. The apparent distance modulus of NGC 4536 is (m - M)(AV) = 31.23 +/- 0.05 and (m - M)(AB) = 31.27 +/- 0.05. There is no statistically significant differential absorption between the Cepheids inside and outside the spiral arm, or between the Cepheids and the position of the supernova (SN). The resulting absolute magnitudes of SN 1981B are M(V)(max) = - 19.32 +/- 0.12 and M(B)(max) = -19.29 +/- 0.13 using the apparent modulus of NGC 4536 and the apparent magnitudes of SN 1981B as if there is no differential extinction between them. If we correct the SN for reddening, determined independently of the Cepheids, and then use the true modulus of NGC 4536 of (m - M)(o) = 31.10 +/- 0.13, the SN values are M(B)(max) = - 19.46 +/- 0.24 and M(V)(max) = - 19.44 +/- 0.21. Combining these calibrations with the three calibrations previously available for the SNe 1895B, 1937C, and 1972E, determined in the first four papers of this series, gives the interim calibrations of [M(B)(max)] = -19.48 +/- 0.12 and [M(V)(max)] = -19.47 +/- 0.10. These require interim Hubble constants of H-0(B) = 55 +/- 3(internal) km s(-1) Mpc(-1), and H-0(V) = 58 +/- 3(internal) km s(-1) Mpc(-1). Improvement is expected when the fifth and sixth calibrators, SN 1960F in NGC 4496A and SN 1990N in NGC 4639, are added to the four available here. When these data are available, any putative decay rate-absolute magnitude correlation can also begin to be studied directly from the Cepheid calibrations themselves.