2.6. Physical methods

2.6.1. Expansion photosphere model (EPM) for Type II supernovae

This is a variant of the Baade-Wesselink method. If a supernova is a black body emitter one can calculate source brightness from temperature; the distance can then be estimated by comparing source brightness with the observed flux. In SNeII atmosphere the flux is diluted due to electron scattering opacity. If this greyness is calculated source brightness can be inferred. Schmidt, Kirshner & Eastman (1992) developed this approach and obtained the distances to SNeII in agreement with those from the ladder. The point is that EPM gives absolute distance without zero point calibrations. The Hubble constant they obtained is 73 ± 9 (Schmidt et al. 1994).

A possible source of systematic errors is in the estimation of the temperature from the spectrum or colour. The SNeII physics also might not be uniform, as we see occasional large scatters in a cross-correlation analysis.