Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. Ⅷ. SN 1990N in NGC 4639

摘要

Reeated imaging observations have been made of NGC 4639 with the Hubble Space Telescope between 1995 April and July over an interval of 71 days. Images were obtained on 12 epochs in the F555W band and on two epochs in the F814W band. The galaxy is parent to the prototypical Type Ia supernova SN 1990N. A total of 18 definite and six lkely Cepheids were found with periods ranging between 17 and 67 days. The dereddened distance modulus of NGC 639 derived from the Cepheids that could be measured in both passbands is (m - M)_0 = 32.03 + - 0.22, which corresponds to a distance of 25.5 + - 2.5 Mpc.