The Peak Brightness of SN1974G in NGC4414 and the Hubble Constant

Abstract

The light curve of the Type Ia supernova SN1974G (in NGC4414) is important because the Hubble Space Telescope has measured the distance to the host galaxy by means of Cepheid variables and thus the Hubble Constant can be derived. Light curves from the secondary literature are inadequate since the majority of data is misreported, the majority of the published data is overlooked, and the majority of all data is unpublished, while comparison star sequences have offsets of over half a magnitude. I have recovered and validated all data, remeasured the comparison stars, and performed light curve template fits. I find the observed peak B and V magnitudes to be $12.48 \pm 0.05$ and $12.30 \pm 0.05$, with a decline rate of $\Delta m_{15} = 1.11 \pm 0.06$. For $E(B-V) = 0.16 \pm 0.07$, the unabsorbed peak magnitudes are $B = 11.82 \pm 0.29$ and $V = 11.80 \pm 0.22$. With the distance modulus to NGC4414 as $\mu = 31.41 \pm 0.23$, I find $H_{0} = 55 \pm 8 km \cdot s^{-1} \cdot Mpc^{-1}$.