Sky demonstration of potential for ground layer adaptive optics correction

Observations have been made at the Steward Observatory 1.55 m telescope of a four-star asterism in the constellation Serpens Cauda, using a Shack-Hartmann wavefront sensor. The stars are all within a 2 arcminute field, and range in apparent brightness from m_v of 9.4 to 10.6. The instrument placed a 5 × 5 array of square subaperture across the pupil of the telescope, and had sufficient field of view to allow wavefront data to be recorded from all four stars simultaneously. Snapshots at 1/30 s exposure time were recorded, with no temporal coherence between exposures. We have reconstructed the first 20 Zernike modes from the slope data for each star. In a preliminary analysis, we show that the wavefront aberration in each star can be roughly halved by substracting the average of the wavefronts from the other three stars. The averages represent estimates of the aberration introduced by the lowest few hundred meters of the atmosphere, so the result provides an early indication of the potential for image sharpening by compensation of boundary layer turbulence.