An IRAF program called SLITLESS has been written to allow the quick extraction of a spectrum from a direct image and slitless grating pair. It is primarily aimed at quick reduction of STIS parallel data where the direct image is taken with the 50 CLEAR aperture and the spectrum image with the G750L grating and no slit. SLITLESS displays the direct image, then simply by selecting an object on that image, the matching spectrum can be extracted. SLITLESS extracts the appropriate region of the grating image and determines the wavelength range of the extracted spectrum. The properties of some STIS gratings (also NICMOS grisms) are pre-defined in an ASCII table read by SLITLESS. Program parameters allow the user to fine tune the extraction process, such as the extent of the object and the number and size of the background spectrum apertures, or these can be altered interactively. The data quality for the spectrum image is also used to exclude bad points from the extracted spectra. When used in its non-interactive mode, SLITLESS automatically extracts a given number of rows from the grating image and determines the level of the spectral background using regions of the grating image that are near the spectrum. For interactive extraction, SLITLESS assists the user by marking the appropriate part of the grating image and displaying the extraction profile, the background sky(s) and finally the extracted spectrum. SLITLESS displays the extracted, background subtracted spectrum, produces a text file listing the extracted spectrum (and background) and can optionally produce a FITS image of the background subtracted spectrum.
The program can be downloaded and will soon be available in the STSDAS contrib package.
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09 Dec 97