Construction of the space lightcurves

The construction of the lightcurves is relatively easy when the galaxy is sufficiently distant from its galaxy host so that the bottom is negligible. Three supernovæ of our batch are in this case: 2000fr and 2001gq where the galaxies hosts are sufficiently far away from the supernova and 2001hb. For the latter, a major reference was taken during the summer 2002, the galaxy host is not detectable on the reference however major than the images of follow-up. For these three supernovæ, we will use a aperture photometry in a small ray (3 pixels, is $0.15' '$).

For the three others supernovæ, the galactic bottom does not allow such a simple analysis. The galaxy host remains right with the lower part of the signal of the supernova. In particular, for 2001gn, the signal of the galaxy becomes prevalent for the images at the end of the curves of light.

It was thus necessary to make observations complementary to these three supernovæ to consider the bottom galactic. These observations were made during May 2003. As we saw, camera ACS has photometric performances better than the WFPC2. In particular, in filter F814W, this camera is 5 times more sensitive than the old camera. It was thus decided to make the observations of reference by using this camera.

The appendix B presents the observations of reference for these three supernovæ. It will be noticed that the exposure times are up to 4 times less significant than for the images of follow-up. Qualities and the depths of the images are however much better.

To build the lightcurves, it is necessary to withdraw the galactic bottom of each supernova. For that, the first stage consists in aligning the images of references astrométriquement and photométriquement.