Associations of WFPC2 Exposures

Unlike NICMOS and STIS, where a dataset might be constituted of a set of exposures, the WFPC2 data set’s structure was thought to be a repository of all the files belonging to a single exposure. Lacking higher level of abstraction, there is no simple way of tracing back which observation strategy (e.g., cosmic ray rejection, dithering) a WFPC2 PI decided to employ. Building associations of WFPC2 exposures can therefore be considered an important step towards a comprehensive description of the HST archive contents. ST-ECF has started a project to build such associations and to store them into a database. Knowing what are the shifts among the exposures belonging to an association will allow the ST-ECF Archive to provide its users not only with on-thefly recalibrated exposures, but also with cosmic ray-rejected and resolution-enhanced mosaics of WFPC2 images.