Adaptive Optics Produces Ultrasharp Images Of Sunspot

This image, spanning an area more than three times wider than Earth,was made possible by the Dunn's recently completed AO76 advancedadaptive optics image correction system and a new high-resolution CCDcamera.

The Dunn is the nation's premier high-resolution solar telescope.The Association of Universities for Research in Astronomy operates theDunn as part of the National Solar Observatory under a cooperativeagreement with the NSF.

This ultrasharp image of sunspot AR 10810 shows several objects ofcurrent scientific interest. G-band bright points, which indicate thepresence of small-scale magnetic flux tubes, are seen near the sunspotand between several granules (columns of hot gas circulating upward).

The dark cores of penumbral fibrils and bright penumbral grains areseen as well in the sunspot penumbra (the fluted structures radiatingoutward from the spot). These features hold the key to understandingthe magnetic structure of sunspots and can only be seen in ultrahigh-resolution images such as this one. Magnetism in solar activity isthe "dark energy problem" being tackled in solar physics today.

Normally such features are beyond the grasp of ground-based solartelescopes because of blurring by Earth's turbulent atmosphere. TheDunn's AO76 system compensates for much of that blurring by reshaping adeformable mirror 130 times a second to match changes in the atmosphereand refocuses incoming light. This allows the Dunn to operate at itsdiffraction limit (theoretical best) of 0.14 arc-second resolution,rather than the 1.0 to 0.5 arc-second resolution normally allowed byEarth's atmosphere.

The Dunn has two high-order adaptive optics benches, the onlytelescope in the world with two systems, which enhances instrumentsetup and operations.

This image was built from a series of 80 images, each 1/100th of asecond long (10 ms), taken over a period of 3 seconds by ahigh-resolution Dalsa 4M30 CCD camera in its first observing run afterbeing added to the Dunn. Speckle imaging reconstruction then compilesthe 80 images and greatly reduces residual seeing aberrations.

The camera is part of the equipment suite for the Dunn'sDiffraction-Limited Spectropolarimeter, which is designed to analyzemagnetic field strength and direction inside sunspots.

The Dunn and its new systems are available for the world solar physics community to use.