A Reanalysis of the Photometry of the Prototype Type Ia Supernovae: SN1937C

Previous abstract Next abstract

Session 72 -- High Z Line Measurements; Gravitational Microlensing: Distance Determination
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[72.15] A Reanalysis of the Photometry of the Prototype Type Ia Supernovae: SN1937C

M.J. Pierce (NOAO/KPNO), G.H. Jacoby (NOAO/KPNO), E. Carder (NOAO/KPNO)

The historical type Ia supernova (SN Ia) SN 1937C plays a central role in the extragalactic distance scale controversy and the value of the Hubble Constant. The event was monitored extensively by Baade \& Zwicky (1938) and it remains one of the best observed SN Ia events to date. It is one of only two SN Ia events in parent galaxies near enough for Cepheid searches with currently available technology. Sandage et al. (1993) recently reported a Cepheid distance modulus of $m - M = 28.4 \pm 0.09$ to IC 4182, the host galaxy of SN 1937. This distance sets the absolute luminosity for SN Ia events. When compared with photometry of more distant SN Ia, this luminosity leads to $H_\circ \sim 50$ km s$^{-1}$ Mpc$^{-1}$ (e.g. Sandage \& Tammann 1993), a value in contrast with estimates obtained from other methods (e.g. Jacoby et al. 1992). Subsequent analysis since 1938 has been limited to fitting the published data with template light curves (Leibundgut et al. 1991) and zero point adjustments from modern photometry of nearby comparison stars (Schaefer 1993).

We have obtained the original photographic films of SN 1937C taken by Baade \& Zwicky, including a series in V that was never published. The region on each film surrounding the supernova (including the comparison stars) was scanned with a PDS microdensitometer. We then compared the integrated photographic density of the standards to their known B and V magnitudes (via Schaefer's CCD photometry) to obtain a transformation curve. The photographic density of the supernova then yields B and V magnitudes through the transformation curve with a precision of 3 - 5\%. We present an analysis of the light curve based on these data, including a discussion of the rate of decline and the implications to the determination of the Hubble Constant using type Ia supernovae.

At the conclusion of our study, we will make available tapes of the digitized images so that other investigators can examine our results.

Friday program listing