2. The data
Our optical catalog was originally built as part of a program of identification of faint IRAS sources on Schmidt plates (Bertin et al. 1997) near both ecliptic poles. The 7 selected fields are characterized by a very low infrared cirrus emission, which ensures that the interstellar extinction is negligible in the visible. Their coordinates are given in Table 1 . To each field corresponds one plate in the blue photographic passband, and one in the red. Northern plates were taken in France at the CERGA 0.9m Schmidt telescope, while southern ones are copies from the ESO and SERC surveys.
Table 1. Schmidt fields
© European Southern Observatory (ESO) 1997