The principle of this new strategy of observation is to observe the same fields with regular interval. It makes it possible in particular to carry out research and the photometric follow-up on the same images with the same instrument.
The method of research remains the same one, the supernovæ are detected on subtractions of images. This method enables us to have quickly references much major, the images being used for research are used thereafter to build the reference.
The research carried out at the time of spring 2002, was made in the same fields as for the marketing year 2001. We thus had one year old major references for research (approximately 6 hours for 2 fields).
In this mode, thanks to the repeated observations we have the beginning of the lightcurve of all the detected objects, it is thus thus possible to select the objects whose lightcurve resembles that of a supernova and to select those in the phase which interests us, in fact the phase of rise of the lightcurve.
The candidates are always selected according to the preceding criteria (signal on noise, rate of increase in light...) but one asks to have coincidences with the preceding observations. The signal on noise from now on considered is the signal on noise cumulated (quadratically) of all detections of the same object on the successive subtractions.
Figure 7.25 presents a supernova discovered at the time of slipping research carried out at the CFHT lasting spring 2002. The lightcurve was built progressively with the observations. This supernova was observed spectroscopiquement in April 2002 by Keck, its redshift is 0.28.
This first slipping research carried out with the CFHT with the CFH12K made it possible to test natural size this new strategy.
This method for summer has installation successfully within the framework of CFHT Legacy Survey (CFHTLS), broad survey carried out with the new MegaCam camera assembled on the CFHT and covering a square degree on the sky. One of the objectives of this great survey is the search and the follow-up for supernovæ of the Ia type in order to measure the cosmological parameters. In particular, the observation of a hundred supernovæ per annum for shifts towards the red ranging between 0.2 and 1 will make it possible to measure the equation of state of black energy.
The observations started in March 2003, and allowed, during the period going until September 2003, to discover and follow more than one score of supernovæ of the Ia type.
This project should in the 5 years come to be able to discover and follow more than 500 supernovæ using a single instrument.