AAS 201st Meeting, January, 2003
Session 123. Supernovae and Other Distance Indicators
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[123.03] Color-Magnitude Intercept Calibrations (CMAGIC) for Type Ia Supernovae

L. Wang, G. Goldhaber, G. Aldering, S. Perlmutter (Lawrence Berkeley National Laboratory)

We show empirically that fits to the color-magnitude relation of Type Ia supernovae after optical maximum can provide accurate calibrations of extragalactic distance scales. In particular, uniform linear relations between B magnitude and B-V, B-R, and B-I colors, universal to SN~Ia during much of the first month past maximum, can be found. These linear relations can provide robust estimates of distance scales, in particular, by using the magnitudes when the supernova reaches a given color. After corrections of light curve shapes and rejecting a few obvious outliers, the dispersions of the magnitudes taken at the intercept of the linear color-magnitude relation are found to be around 0m.08 for the sub-sample of supernovae with Bmax-Vmax < 0m.05, and around 0m.11 for the sub-sample with Bmax-Vmax < 0m.2. This small dispersion is consistent with being mostly due to observational errors. The method presented here and the conventional light curve fitting methods can be combined to further improve statistical dispersions of distance estimates. It can also be combined with the magnitude at maximum to deduce dust extinction. The slopes of the color-magnitude relation may also be used to identify intrinsically different SN Ia systems. The method provides a tool that is fundamental to using SN Ia to estimate cosmological parameters such as the Hubble constant and the mass and dark energy content of the universe.

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