The carnegie supernova project: analysis of the first sample of low-redshift type-Ia supernovae (original) (raw)
An analysis of the first set of low-redshift (z<0.08) Type Ia supernovae monitored by the Carnegie Supernova Project between 2004 and 2006 is presented. The data consist of well-sampled, high-precision optical (ugriBV ) and near-infrared (NIR; Y JHK s ) light curves in a well-understood photometric system. Methods are described for deriving light-curve parameters, and for building template light curves which are used to fit Type Ia supernova data in the ugriBV Y JH bands. The intrinsic colors at maximum light are calibrated using a subsample of supernovae assumed to have suffered little or no reddening, enabling color excesses to be estimated for the full sample. The optical-NIR color excesses allow the properties of the reddening law in the host galaxies to be studied. A low average value of the total-to-selective absorption coefficient, R V ≈ 1.7, is derived when using the entire sample of supernovae. However, when the two highly reddened supernovae (SN 2005A and SN 2006X) in the sample are excluded, a value R V ≈ 3.2 is obtained, similar to the standard value for the Galaxy. The red colors of these two events are well matched by a model where multiple scattering of photons by circumstellar dust steepens the effective extinction law. The absolute peak magnitudes of the supernovae are studied in all bands using a two-parameter linear fit to the decline 1 This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
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