AAS 197, January 2001
Session 12. Hubble Space Telescope: Instruments and Data Reduction
Display, Monday, January 8, 2001, 9:30am-7:00pm, Exhibit Hall

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[12.02] Space Telescope Imaging Spectrograph: 2-Dimensional Scattered Light Correction Algorithm

D. Lindler (ACC, Inc.), C. Bowers (NASA/GSFC)

The Space Telescope Imaging Spectrograph (STIS) has four ultraviolet echelle spectrographic modes all subject to scattered light. The current pipeline reduction routine, CALSTIS, uses a one-dimensional algorithm to estimate the in-order scattered light from the background observed between the spectral orders. Using this algorithm, the error in the cores of saturated interstellar lines can be nearly 10% of the continuum level at 1200 Angstroms.

We describe a new iterative algorithm which is applicable to other echelle spectrographs. The algorithm uses a two-dimensional model of the scattered light including the telescope point spread function, the echelle grating scatter, the cross-disperser grating scatter, and the detector and STIS point spread functions. This new algorithm reduces the errors found in the current STIS pipeline reduction algorithm by at least a factor of ten.

The algorithm has been implemented by the Space Telescope Science Institute as an IRAF task and is currently available for download by the astronomical community (see 2000AAS...1971203, ``Performance of a New Algorithm to Remove Scattered Light from STIS Echelle Spectra," also at this meeting).

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