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21.2 Structure of calstis

Calstis consists of a series of individual modules which:

Figure 21.1: Basic 2-D Image Reduction (First Step in Subsequent Flowcharts)

The calibration beyond the basic 2-D image processing depends upon whether the data are obtained in imaging or spectroscopic mode, as illustrated in Figure 21.2. The primary operations are geometric correction and photometric calibration, and a summation of multiple MAMA exposures if NRPTEXP > 1. The output is a geometrically rectified image with header keywords that specify the photometric calibration. When geometric correction is not applied, the output will be photometrically calibrated flatfielded data with suffix _crj, _flt, or _sfl.

Figure 21.2: Schematic of calstis for Secondary Image Processing

For spectroscopic exposures, calstis will process the associated wavelength calibration (wavecal) exposure to determine the zero point offset of the wavelength and spatial scales in the science image, thereby correcting for the lack of repeatability of the mode select mechanism (MSM) or for thermal drift. The accompanying wavecal observations are stored in the rootname_wav.fits file.

Figure 21.3: Schematic of calstis for Contemporaneous Wavecals

Two-dimensional spectral processing produces a flux-calibrated, rectified spectroscopic image with distance along the slit running linearly along the y axis and dispersion running linearly along the x axis.

One-dimensional spectral extraction produces a one-dimensional spectrum of flux versus wavelength (rootname_x1d.fits), uninterpolated in wavelength space, but integrated across an extraction aperture in the spatial direction. This extraction is currently performed only for echelle short slit -observations in the pipeline. Future enhancements will perform the extraction for point sources in all first-order modes as well.

Figure 21.4: Schematic of calstis for Spectroscopic Data



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