The WFPC2 Archival Pure Parallels Project

Abstract

We introduce the WFPC2 Archival Pure Parallels Project, in which the methods and procedures described here are used to obtain a near-automatic combination of WFPC2 images obtained as part of the WFPC2 Archival Parallels Program. Several techniques have been developed or refined to ensure proper alignment, registration, and combination of overlapping images that can be obtained at different times and with different orientations. We quantify the success rate and the accuracy of the registration of different types of images, and we develop techniques that are suitable to equalize the sky background without unduly affecting extended emission. About 600 combined images of the 1500 eventually planned have already been publicly released through the STScI Archive. The images released to date are especially suited to the study of star formation in the Magellanic Clouds, the stellar population in the halo of nearby galaxies, and the properties of star-forming galaxies at z~3.