Type II Supernovae as Standardized Candles

Abstract

We present evidence for a correlation between expansion velocities of the ejecta of Type II plateau supernovae and their bolometric luminosities during the plateau phase. This correlation permits one to standardize the candles and decrease the scatter in the Hubble diagram from ~1 mag to levels of 0.4 and 0.3 mag in the V and I bands, respectively. When we restrict the sample to the eight objects that are well in the Hubble flow (cz>3000 km s-1), the scatter drops even further, to only 0.2 mag (or 9% in distance), which is comparable to the precision yielded by Type Ia supernovae and is far better than the ``expanding photosphere method'' applied to Type II supernovae. Using SN 1987A to calibrate the Hubble diagrams, we get H0=55+/-12.