K. Takats(1), A. Szing(1), J. Vinko(1,2)
(1): Department of Optics & Quantum Electronics, University of Szeged, Hungary
(2): Department of Astronomy, University of Texas at Austin
Type II_P supernovae (SNe) are valuable distance indicators via either the Expanding Photosphere Method (EPM) or the Standard Candle Method (SCM). Both of these methods rely on the empirical determination of the velocity at the photosphere of the expanding ejecta at certain epochs. In addition, direct estimates of the photospheric temperature and the effect of the electron scattering opacity on the fluxes (the dilution factor) are also necessary for EPM.
We compare and discuss different measurement techniques, and explore the possibility of improving the velocity estimates using simple parametrized model spectra. We apply the methods to recent SNe having observational data of good quality. In particular, by using an inverted EPM-analysis, we infer "empirical" dilution factors for SN 2004et that has a reliable, independent distance. This could be an important observational test of the current SNe model atmospheres.
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