The peak brightness of SN 1937C in IC 4182 and the Hubble constant: Comments on Pierce & Jacoby [AJ, 110, 2885 (1995)]

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The peak brightness of SN 1937C in IC 4182 is important as a calibrator of type Ia supernovae absolute magnitudes. Recently, Pierce & Jacoby [AJ, 110, 2885 (1995)] have remeasured some original plates with a scanning microdensitometer and have deduced a peak magnitude and decline rate. Unfortunately, a technical error (relating to day/night vision and the appropriate color correction term) has introduced a large and variable systematic error into all their photovisual magnitudes. In addition, their early remeasured photographic magnitudes are ∼0.25 mag fainter than those measured by all eight independent observers as well as ∼0.20 mag fainter than the original measurements of the same plates by Baade and Zwicky. Finally, Pierce and Jacoby deduced the peak magnitude with only 13% of the available data. In this paper, I present an improved analysis using the latest magnitude estimates, analysis techniques, and calibrations. I find the peak B magnitude to be 8.71±0.16 at JD2428769.7, while the peak V magnitude was 8.75±0.10. The decline in the B light curve over the first 15 days after maximum was 1.07±0.11 mag. This leads to a Hubble constant of 57±4 km s-1 Mpc-1. © 1996 American Astronomical Society.

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Astronomical Journal

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