Primary calibration

To build the lightcurves, we used for each supernova a hundred images. The observations were spread out over 2 even 3 years. We thus have a broad choice for the image which will be used as photometric reference.

The goal of this stage is to choose an image whose calibration is well-known. For the observations of research to the CFHT and with the CTIO, standard stars were observed every night.

The choice of the image of science is done according to several criteria:

• The atmospheric absorption, measured by an instrument dedicated or comparison with nominal zero points of the instrument

• The variation of time compared to the standard star observations, the same night.

In practice, we could for all supernovæ followed out of I to find an image taken with more few tens of minutes before or after our observations for an almost null absorption.