THE SKICAT SYSTEM FOR PROCESSING AND ANALYZING DIGITAL IMAGING SKY SURVEYS

We describe the design and implementation of a software system for pro ducing, managing, and analyzing catalogs from the digital scans of the Second Palomar Observatory Sky Survey. The system (SKICAT) integrates new and existing packages for performing the full sequence of tasks f rom raw pixel processing, to object classification, to the matching of multiple, overlapping Schmidt plates and CCD calibration frames. We d escribe the relevant details of constructing SKICAT plate, CCD, matche d, and object catalogs. Plate and CCD catalogs are generated from imag es, while the latter are derived from existing catalogs. A pair of pro grams complete the majority of plate and CCD processing in an automate d, pipeline fashion, with the user required to execute a minimal numbe r of pre- and post-processing procedures. We apply a modified version of FOCAS for the detection and photometry, and new software for matchi ng catalogs on an object-by-object basis. SKICAT employs modern machin e-learning techniques, such as decision trees, to perform automatic st ar-galaxy-artifact classification with a >90% accuracy down to similar to 1 mag above the plate detection limit. The system also provides a variety of tools for interactively querying and analyzing the resultin g object catalogs.