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For refcode 1999ApJ...522..802S:
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1999ApJ...522..802S Cepheid Calibration of the Peak Brightness of Type Ia Supernovae. IX. SN 1989B in NGC 3627 A. SAHA National Optical Astronomy Observatories, 950 North Cherry Avenue, Tucson, AZ 85726 ALLAN SANDAGE The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 G. A. TAMMANN AND LUKAS LABHARDT Astronomisches Institut der Universitat Basel, Venusstrasse 7, CH-4102 Binningen, Switzerland AND F. D. MACCHETTO AND N. PANAGIA Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 Received 1999 January 12; accepted 1999 April 26 ABSTRACT Repeated imaging observations have been made of NGC 3627 with the Hubble Space Telescope in 1997-1998 over an interval of 58 days. Images were obtained on 12 epochs in the F555W band and on five epochs in the F814W band. The galaxy hosted the prototypical, "Branch normal," type Ia supernova SN 1989B. A total of 83 variables have been found, of which 68 are definite Cepheid variables with periods ranging from 75 to 3.85 days. The dereddened distance modulus is determined to be (m - M)_0_ = 30.22+/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose reddening and error parameters are secure. The photometric data of Wells and coworkers combined with the Cepheid data for NGC 3627 give M_B_(max)=-19.36+/-0.18 and M_V_(max)=-19.34+/-0.16 for SN 1989B. The previous six calibrations in this program combined with two additional calibrations determined by others gives the mean absolute magnitudes at maximum of <M_B_> = -19.48+/-0.07 and <M_V_> = -19.48+/-0.07 for "Branch normal" SNe Ia at this interim stage in the calibration program. Using the argument by Wells et al. that SN 1989B here is virtually identical in decay rate and colors at maximum with SN 1980N in NGC 1316 in the Fornax cluster, and that such identity means nearly identical absolute magnitude, it follows that the difference in the distance modulus of NGC 3627 and NGC 1316 is 1.6210.03 mag. Thus the NGC 3627 modulus implies that (m - M)_0_ = 31.84 for NGC 1316. The second-parameter correlations of M(max) of blue SNe Ia with decay rate, color at maximum, and Hubble type are reinvestigated. The dependence of <M(max)> on decay rate is nonlinear, showing a minimum for decay rates between 1.0< {DELTA}m_15_ < 1.6. Magnitudes corrected for decay rate show no dependence on Hubble type, but a dependence on color remains. Correcting both the fiducial sample of 34 SNe Ia with decay-rate data and the current eight calibrating SNe Ia for the correlation with decay rate as well as color gives H_0_ = 60+/-2(internal)km s^-1^ Mpc^-1^, in both B and V. The same value to within 4% is obtained if only the SNe Ia in spirals (without second-parameter corrections) are considered. The correlation of SNe Ia color at maximum with M(max) cannot be due to internal absorption, because the slope coefficients in B, V, and I with the change in magnitude are far from or even opposite to the canonical reddening values. The color effect must be intrinsic to the supernova physics. "Absorption" corrections of distant blue SNe Ia will lead to incorrect values of H_0_. The Cepheid distances used in this series are insensitive to metallicity differences. The zero point of the P-L relation is based on an assumed LMC modulus of (m - M)_0_ = 18.50. Because this may have to be increased by 0.06-0.08 mag, all distances in this paper will follow, and H_0_ will decrease by 3%-4%. Subject headings: Cepheids-distance scale-galaxies: individual (NGC 3627)- supernovae: individual (SN 1989B)
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