The receipt

It is thus necessary to measure the flux of a star being able to estimate:

1. bottom present under star in a precise and not biased way.

2. Profile of stars: the PSF.

3. The position of star in the image so as to correctly center the opening or the model of PSF.

Within the limit of small fluxes, the estimate will be made with the technique of flux of PSF. For great fluxes, one will use the flux of opening.

In the case of measurements of flux of the supernovæ, the presence of a nonconstant bottom spatially coming from the galaxy in which the supernova exploded brings an additional difficulty. It is necessary to be able to estimate then to withdraw this contribution. That forces in particular to have image of reference of the galaxy without the supernova taken after the supernova is extinct. In practice, these observations are made at least a year after the observation of the supernovæ.

Let us see henceforth which are the constraints related to the observations.