Reduction and calibration of data from the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) has presented new challenges, as well as opportunities, for the pipeline processing systems at the Space Telescope Science Institute (STScI), which have resulted in many features that are new and different from what has been employed for previous Hubble Space Telescope (HST) instruments. The biggest challenge is the need to handle, as a group, multiple exposures associated with a single target. Associated images are required for several reasons, including the need to measure the near-infrared thermal background signal, cosmic-ray rejection via anticoincidence detection, and mosaicing of large angular-sized targets. STScI has taken advantage of the opportunities presented by the creation of a new pipeline system to make other changes and advancements as well. First, all reduction and analysis software for NICMOS is written in the ANSI C language, and uses C-to-IRAF interface libraries to allow access to IRAF data I/O and analysis routines. Second, the run-time file format for all NICMOS data reduction and analysis is FITS format, with extensive use of FITS image and table extensions. Two levels of physical packaging of NICMOS data are employed. Images produced by multiple non-destructive detector readouts during the course of a single exposure are packaged together within one FITS file. Second, error estimate and data quality flag images associated with each science image are also contained within the same FITS file. A third, logical, grouping of images is used to relate multiple observations of a single target. The data reduction and calibration process is divided into two distinct phases. The first phase, accomplished by the program "calnica", is used to perform standard instrumental calibration (e.g. dark current subtraction, flat-fielding) for individual exposures. The second phase, "calnicb", performs background subtraction and image combination for associated observations of a single target. This paper describes in detail the functions of calnica and calnicb.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1997