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SEEING, POSITIONING, AND ATMOSPHERIC LOSSES

The fiber diameter for the red cable corresponds to 2 arc-seconds on the sky while the blue fibers subtend 3 arc-seconds. Seeing losses should be minimal when the seeing FWHM is on the order of one-half of the fiber aperture. If the FWHM of the seeing profile is equal to the diameter of the fiber aperture, then the seeing losses will be about 50%. Throughput will degrade rapidly as the seeing increases beyond the size of the fiber.

Positional errors in fiber placement onto point sources can also lead to throughput losses.

Note that the WIYN does not have an atmospheric dispersion compensator for the Hydra field. Wide band spectral observations that extend into the blue may be compromised for observations made at airmasses of 1.5 or larger.

The following references provide estimates of fiber losses due to seeing, positional error, and atmospheric dispersion.

Donnelly, R.H., Brodie, J.P., Bixler, J.V., and Hailey, C.J. (1989), P.A.S.P. 101:1046.
Brodie, J.P., Lampton, M., and Bowyer, S. (1988), A.J. 96:2005.



Sam Barden
Tue Aug 29 16:45:05 MST 1995