AAS 195th Meeting, January 2000
Session 87. Ground-Based Observatories and Techniques
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

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[87.09] Optimal Slit Size Study for the NOAO Next Generation Optical Spectrograph

R.J. Parks (North Park University), S.C. Barden (National Optical Astronomy Observatories)

NOAO is currently conceptualizing a wide-field, imaging spectrograph for their 4-meter telescopes. Implementation of new technologies will enhance its performance. Design goals include: 1) up to 40 arc-minute diameter field of view; 2) 45% peak system efficiency (telescope, instrument, and detector); 3) spectral resolving powers from 2000 to 10000; 4) multi-slit, long-slit, and lenslet IFU capability; 5) operational range from 365 nm to 1700 nm with either CCD or IR detectors.

To optimize the signal to noise performance for the Next Generation Optical Spectrograph (NGOS), it is important to understand the effect of slit size with respect to the target image. We present the results of such a study in our poster.

A Moffat profile was assumed for unresolved, seeing limited images while exponential disk and De Vaucouleurs profiles were used to represent resolved sources (galaxies). The signal to noise ratio was computed assuming an optimal extraction algorithm for a range of target brightness to sky background ratios. A slit width 1.4 times the full width at half maximum of the seeing profile is the optimal slit for unresolved targets that are at or fainter than the background sky. Smaller slits reject too much of the target light while larger slits let in too much background. We will also show the optimal slit size for resolved objects; the effect of displacement of the slit with respect to the target centroid; and a comparison between rectangular slits and circular apertures.

The implication for NGOS is that the optimal slit should be 1.4 arc-seconds for use in median seeing conditions at the Mayall 4-meter telescope on Kitt Peak.

This research is supported by the Kitt Peak National Observatory site program of the Research Experiences for Undergraduates program, funded by the National Science Foundation.

The author(s) of this abstract have provided an email address for comments about the abstract: barden@noao.edu

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