World coordinate system keywords for FITS files from Lick Observatory

Abstract

Every bit of metadata added at the time of acquisition increases the value of image data, facilitates automated processing of those data, and decreases the effort required during subsequent data curation activities. In 2002 the FITS community completed a standard for World Coordinate System (WCS) information which describes the celestial coordinates of pixels in astronomical image data. Most of the instruments in use at Lick Observatory and Keck Observatory predate this standard. None of them was designed to produce FITS files with celestial WCS information. We report on the status of WCS keywords in the FITS files of various astronomical detectors at Lick and Keck. These keywords combine the information from sources which include the telescope pointing system, the optics of the telescope and instrument, a description of the pixel layout of the detector focal plane, and the hardware and software mappings between the silicon pixels of the detector and the pixels in the data array of the FITS file. The existing WCS keywords include coordinates which refer to the detector structure itself (for locating defects and artifacts), but not celestial coordinates. We also present proof-of-concept from the first data acquisition system at Lick Observatory which inserts the WCS keywords for a celestial coordinate system.