Previous Article
Next Article
Table of Contents

The Sun at 0.2" Resolution (1Mar95)
(from NOAO HIGHLIGHTS!, NOAO Newsletter No. 41, 1 March 1995)

NSO is in the process of evaluating the optical quality of the McMath/Pierce
Facility at Kitt Peak and the Vacuum Tower Telescope at Sac Peak (see
NOAO Newsletter No. 39) with the aim of improving the image quality.
The images below demonstrate the present image quality at the Sac Peak
telescope. They were taken from a high-resolution time sequence of solar
granulation images recorded over several hours at the VTT/SP on 20 October
1994.  The rms image contrast meter of the correlation tracker was used to
trigger high-speed (8 msec) exposures with the 1024 X 1024 TIJ CCD
camera during moments of excellent seeing.  The correlation tracker
computed image contrast in a 10" X 10" FOV at a 500 Hz rate. We observed
at a wavelength of 500 nm, using an interference filter with 5 nm FWHM.
The camera's field of view was 77", and its resolution was 0.075" per pixel.

                         [Figures not included]

         High resolution images of solar granulation  observed at the
         VTT/SP. The exposure time was 8 msec. The resolution of
         both images is 0.2" and thus close to the diffraction limit of
         the VTT/SP.

The figure is a representative image from the time sequence and
demonstrates the high quality of the recorded images.  This particular
exposure was taken at approximately 11:30 local time.  Shown are two
subframes covering a field of 15" X 15" taken from the full 77" FOV.  The
rms contrast in this image is 6.5%.  In both images, structures with spatial
scales as small as 0.2" are resolved.  This demonstrates that near
diffraction-limited resolution can be achieved at the VTT/SP.  Residual
aberrations still exist, especially at the edge of the mirror (spherical
aberration).  Work is ongoing aimed at removing these aberrations in order
to further enhance the image quality.

Thomas Rimmele

Previous Article
Next Article
Table of Contents