K-CORRECTIONS FOR TYPE-IA SUPERNOVAE

The usefulness of Type Ia supernovae as distance indicators is a matter of current study and discussion. The available data suggest that the intrinsic dispersion in the absolute B magnitudes of SNe Ia at maximum light is less than 0.4 mag. Hence, SNe Ia offer considerable potential for cosmological studies out to redshifts of z approximately 0.1 or greater. At these distances, however, the effects of the redshift on the observed magnitudes are not negligible and must be taken into account in order to compare the magnitudes and light curves of objects of different redshifts. In this paper we make use of the best spectra available for Type Ia supernovae in order to calculate the effect of the redshift on the observed B and V magnitudes. We present K terms in the redshift range z=0.005-0.50 from a collection of spectra of SNe 1990N, 1991T, and 1992A covering from day - 14 to day + 76, counted from the time of maximum light in the blue band. The K terms calculated for the V band from the different spectra show a well-defined trend as a function of time. In the B band the K terms show some scatter before maximum light due to the spectroscopic differences displayed by the three SNe selected. These spectral differences tend to disappear for later epochs and, consequently the K term curves in the B band after maximum light are much tighter. Our calculations enable us to interpolate K terms for SNe Ia at maximum light, which should prove useful to study the Hubble diagram for these objects.