The IDL package `dbase' is used to convert the FITS source lists to IDL databases. ASTROLIB routines are used to read the binary table columns into structure fields, which are then built into the database. This process is automatically repeated for each source list, concatenating the 4 CCDs into one database and then sorting it by Right Ascension.
The databse contains only selected fields from the initial FITS source list, as can be seen in Appendix 4, which contains a typical .dbd file ( i.e. the file describing the database format) for a single band source list. RA and DEC are stored in decimal hours and degrees respectively.
Magnitudes are computed from the fluxes given in the FITS files by reading the exposure time t and band name from the FITS header and using the following zero--points (obtained from [3]):
where S is the Core flux for that object (hence the magnitude is sometimes referred to as Core magnitude.
For a given field, these database files can be found in:
/data/cass010a/xmmssc/public_html/field/dbase/
and are called wfci, wfcz, wfcr, wfcg, wfcu depending on the band.
The `dbase' package then provides powerful and fast routines for extracting information and comparing entries between databases.
