Faint source detection in ISOCAM images

We present a tool adapted to the detection of faint mid-infrared sources wi thin ISOCAM mosaics. This tool is based on a wavelet analysis which allows us to discriminate sources from cosmic ray impacts at the very limit of the instrument. four orders of magnitudes below IRAS. It is called PRETI for P attern REcognition Technique fur ISOCAM data, because glitches with transie nt behaviors are isolated in the wavelet space, i.e. frequency space, where they present peculiar signatures in the form of patterns automatically ide ntified and then reconstructed. We have tested PRETI with Monte-Carlo simul ations of fake ISOCAM data. These simulations allowed us to define the frac tion of remaining false sources due to cosmic rays, the sensitivity and com pleteness limits as well as the photometric accuracy as a function of the o bservation parameters. Although the main scientific applications of this technique have appeared o r will appear in separated papers, we present here an application to the IS OCAM-Hubble Deep Field image. This work completes and confirms the results already published (Aussel et al. 1999).