Construction of the owners of lightcurve

To evaluate the parameters of the lightcurve, it should be adjusted with a model of lightcurve parameterized. We have points of photometry resulting from observation from different telescopes taken under different conditions.

We saw in the preceding chapter that the majority of the differences are taken into account during the construction of the lightcurve. All the points of photometry are brought in theory to the same photometric unit. However, it can exist significant differences between the filters of the various instruments for the same band of observation. In particular, the filters of observation of the Hubble telescope introduce to significant differences compared to the standard filters Johnson-Cousins.

The standard method to bring photometry in the standard system is to apply filter corrections (see appendix A).

Significant measurement in the case of the photometry of the supernovæ is that in the filter of the reference frame of the supernova. This forces, in practice, to make two successive filter correctionss: the filter correction and the K-correction We thus decided to build what we will call in the continuation effective filters . These effective filters are defined as the band-widths of all the system of observation, will have to be taken into account:

1. Band-widths of the filters $T_f(\lambda)$.

2. Transmission of optics and reflectivity of the mirrors $T_{opt}(\lambda)$.

3. Quantum effectiveness of the CCD considered $Qe(\lambda)$.

4. Transmission of the atmosphere for the data taken on the ground $T_{atm}(\lambda)$.

We also took into account a last effect: absorption by dust of the Milky Way which is discussed in chapter 2 .

The construction of this effective filter will enable us to pass directly from the system of observation to the standard filter in the reference frame of the supernova.