Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627

Abstract

Repeated imaging observations have been made of NGC 3627 with theHubble Space Telescope in 1997-1998 over an interval of 58 days.Images were obtained on 12 epochs in the F555W band and on fiveepochs in the F814W band. The galaxy hosted the prototypical,``Branch normal,'' type Ia supernova SN 1989B. A total of 83 variableshave been found, of which 68 are definite Cepheid variables withperiods ranging from 75 to 3.85 days. The dereddened distance modulusis determined to be (m-M)_0=30.22+/-0.12 (internal uncertainty)using a subset of the Cepheid data whose reddening and errorparameters are secure. The photometric data of Wells and coworkerscombined with the Cepheid data for NGC 3627 give M_B(max)=-19.36+/-0.18and M_V(max)=-19.34+/-0.16 for SN 1989B. The previous six calibrationsin this program combined with two additional calibrations determinedby others gives the mean absolute magnitudes at maximum of =-19.48+/-0.07 and =-19.48+/-0.07 for ``Branch normal''SNe Ia at this interim stage in the calibration program. Using theargument by Wells et al. that SN 1989B here is virtually identicalin decay rate and colors at maximum with SN 1980N in NGC 1316 inthe Fornax cluster, and that such identity means nearly identicalabsolute magnitude, it follows that the difference in the distancemodulus of NGC 3627 and NGC 1316 is 1.62+/-0.03 mag. Thus the NGC3627 modulus implies that (m-M)_0=31.84 for NGC 1316. Thesecond-parameter correlations of M(max) of blue SNe Ia with decayrate, color at maximum, and Hubble type are reinvestigated. Thedependence of on decay rate is nonlinear, showing a minimumfor decay rates between 1.0