Installation and Field Tests of ChAOS at Apache Point Observatory

M. Chun, F. Shi, M. F. Smutko, V. Scor, W. Wild, J. Larkin, & E. Kibblewhite

(This is a partial "reprint" of a poster presented at the San Antonio meeting of the American Astronomical Society, January, 1996.)

All data was taken on the Apache Point 3.5m telescope.
Gamma Cygni These are broadband visible (lambda <1.0µ) images of Gam Cyg taken on August 31, 1995. "Opened Loop" means that ChAOS was turned off. "Closed Loop" means that ChAOS was turned on. The seeing was estimated to be 1.6 arcsec. With ChAOS, the FWHM is 0.4 arcsec.
Gamma 2 Andromedae These are I-band images of the binary Gam2 And taken on December 3, 1995. Seeing was roughly 0.7 arcsec. With the adaptive optics system, FWHM is 0.3 arcsec. The binary separation is 0.5 arcsec.

ChAOS Mounted on the Apache Point Telescope

Performance Limitations

Although improvements to ChAOS are on going, the major limitation in the performance of ChAOS seems to be high-frequency telescope vibrations. We have filtered opened and closed loop wavefront sensor data (measured slopes) by a modeled system servo response function to examine the nature of the residual phase errors.

These two figures illustrate the spectral power in the telescope jitter. In the upper plot in each figure, we filtered the power spectrum of the mean image motion to estimate the corrections from a tip/tilt mirror driven by a modeled control servo. The integrated power in the unfiltered power spectrum (dotted line) is proportional to the FWHM of an uncorrected image. In the lower plot in each figure, we show the actual closed-loop performance of ChAOS with the tip/tilt and deformable mirror servos on. The actual closed-loop and the modeled closed-loop power spectra are in good agreement.

Click here to download a Postscript version of Figure 1
Click here to download a Postscript version of Figure 2

The third figure displays time sequences of the mean slopes of both opened and closed loop data. The telescope jitter is apparent in both plots and is the dominant feature in the residual slope data. Note also that the amplitude and frequency of the jitter appears time dependent.

Click here to download a Postscript version of Figure 3

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