$\star$ Observations

All the observations former to spring 2001 were carried out by members of our group. Work consisted in mainly managing, throughout the nights of observations, the time of telescope according to the weather and the visibility of the fields in order to maximize time to pass to observe the fields. The time of observation was then granted per night. An unfavourable weather for the references or the images of research could then put in danger all the continuation of the chain (the spectroscopy, then the follow-up), and thus, a whole research campaign.

The installation since 1st six-month period 2001 of a system of observation in mode `` tail '' with the CFHT, in which the observations are carried out either by the instigators of the projects but by observers attached to the CFHT, made it possible to return to us less dependent on the weather. In this new fashion, the observations are granted either per nights but per duration. The observations are carried out according to the priorities of each program (forced atmospheric conditions, of seeing or forced temporal as in our case). The observations can thus be carried out over longer periods thus minimizing the impact of the bad weather, mutualized in this mode. It is in mode `` tail '' that all our observations were carried out with the CFHT since then.