The $I$-band Hubble Diagram for Type~Ia Supernovae

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Session 33 -- Supernovae
Oral presentation, Monday, 9, 1995, 2:00pm - 3:30pm

[33.08] The $I$-band Hubble Diagram for Type~Ia Supernovae

M.M.Phillips, M.Hamuy, R.A.Schommer, N.B.Suntzeff (CTIO/NOAO), J.Maza (U.Chile), R.Avil\'{e}s (CTIO/NOAO)

The Cal\'{a}n/Tololo supernova search resulted in the discovery of 30 type~Ia supernovae (SNe~Ia) during the period 1990-1993. In this paper, we report $I$-band photometry obtained at CTIO for 16 of these events. The $I$-band light curves of SNe~Ia are potentially important for cosmological studies since 1) the effect of dust extinction is a factor of 2 less (in magnitudes) than in blue light, and 2) the intrinsic dispersion in absolute luminosity is apparently also significantly smaller than in the $B$ or $V$ bands. Recent studies have indicated that the $I$-band light curves of SNe~Ia are characterized by a secondary maximum which occurs $\sim$23~days after the primary peak, similar to what has been observed in the $J$, $H$, and $K$ bands. Nevertheless, observations of events covering a range of initial decline rates (in $B$) suggest that there is considerable diversity in the detailed shapes of the $I$ light curves. This is confirmed by the data for the Cal\'{a}n/Tololo supernovae found before primary maximum. In order to derive peak magnitudes for events discovered after maximum, it is therefore necessary to fit the data using several different ``templates'' representative of the range of observed $I$-band light curve shapes. Using this technique, we have produced an $I$-band Hubble diagram for the Cal\'{a}n/Tololo SNe~Ia. The $I$-band light curve for SN~1972E is also presented which, combined with the Cepheid distance for its host galaxy (NGC~5253), provides a new and independent estimate of the Hubble constant.

Partial support for this research was provided by grant 92/0312 from Fondo Nacional de Ciencias y Tecnolog\'{i}a (FONDECYT--Chile).

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