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Session 26 - Proto Stars to Supernovae.
Oral session, Monday, June 08

[26.07] The Luminous Type Ic SN 1992ar at z=0.145

A. Clocchiatti (Pontificia Universidad Catolica de Chile), M. M. Phillips, N. B. Suntzeff (CTIO), M. Turatto, E. Cappellaro (Osservatorio Astronomico di Padova), M. Hamuy (U. Arizona)

SN 1992ar at z=0.145 was one of the most distant and brightest SNe discovered by the Calán/Tololo Survey. Surprisingly, its spectroscopic type was not Ia but Ic.

This SN illustrates many of the challenges faced by the detailed study of individual SNe at moderately large redshift. These are, among others, the loss of features in the red part of the spectrum due to universal expansion, and K--corrections strongly varying in time which determine the shape of the light curve in the rest frame of the SN. It illustrates, as well, the necessity of spectra with better S/N ratio than typically obtained with 4m class telescopes.

In addition, SN 1992ar exemplifies the problem of contamination faced by the high z Type Ia SNe samples, whose luminosity distances are used to determine the cosmological parameters of the Universe. It proves that there are SNe which are as bright as a Type Ia SN and have a similar light curve near maximum light, but have different intrinsic colors, different color evolution, and do not follow the Light Curve Shape--Luminosity relation used to calibrate the intrinsic luminosity of a Type Ia event.

We discuss the effect that these luminous Type Ic SNe, if not removed from the High--z Type Ia SN samples, would have on the measured cosmological parameters. We also present observational criteria to distinguish the two different SN types when the SiII 6355 line is redshifted out of the sensitivity range of typical CCD detectors.

Program listing for Monday