An Automatic Image Reduction Pipeline for the Advanced Camera for Surveys

We have written an automatic image processing pipeline for the Advanced Camera for Surveys (ACS) Guaranteed Time Observation (GTO) program. The pipeline, known as Apsis, supports the different cameras available on the ACS instrument and is written in Python with a flexible object-oriented design that simplifies the incorporation of new pipeline modules. The processing steps include empirical determination of image offsets and rotation, cosmic ray rejection, image combination using the drizzle routine called via the STScI Pyraf package, object detection and photometry using SExtractor, and photometric redshift estimation in the event of multiple bandpasses. The products are encapsulated in XML markup for automated ingestion into the ACS Team archive.