Analysis of the Light Curves of Type I Supernovae
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**Session 29 -- Novae and Supernovae**
*Display presentation, Tuesday, 9:30-6:30, Pauley Room*

## [29.06] Analysis of the Light Curves of Type I Supernovae

*William D. Vacca and Bruno Leibundgut (UC Berkeley)*
The broad-band light curves of supernovae trace the temporal evolution of the
radiative energy emitted by these objects.
The apparent photometric uniformity of Type I supernovae (SNe I)
has led to the adoption of standard templates to describe the light curves of these
objects. Recent observations, however, have indicated that variations in the
light curves of SNe I do occur. In order to investigate the differences in SNe I
light curves, a quantitative description of the shape of the light curve is needed.

We have developed a least-squares fitting scheme for the broad band $UBV$
photometric data in which the observed light curves are approximated by a
combination of a Gaussian curve for the peak and early decline phase
and a line for the decline after $\sim$40 days past maximum. This purely empirical
representation allows us to obtain objective measurements of a set of parameters
describing the light curves of individual supernovae. For example, the fitting
procedure yields the maximum magnitude, the time of maximum, the decline
rates, and the width of the peak. In addition, an estimate of
the observational errors is obtained.

Using this empirical representation, we have fitted
all the photometric (and photographic) data available
for SNe I light curves presented in Leibundgut et al. (1991, A\&AS,
89, 537). We discuss the
decline parameter $\Delta$m$_{15}$, as defined by Phillips (1993, ApJ
Letters, in press), and compare it to other quantities characterizing of the
light curve shapes. We examine the late-time decline rates and
find a wide range of values.

While not based on any particular physical model, the
continuous representation of the data that we have used
provides a convenient and quantitative means of characterizing
SNe I light curves. Possible differences among the light curves of subtypes
of SNe I can be investigated in an objective manner.
Comparisons can be made not only between the light curves of various
supernovae, but also between the light curves exhibited by the
photometric data in different pass bands for a given individual supernova.
This approach is clearly superior to the use of standard templates
to describe SNe I light curves.

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