Christoph Keller and Claude Plymate
In the last newsletter (NOAO Newsletter, No. 62), we reported the successful installation of a prototype Shack-Hartmann wavefront sensor with over 300 subapertures. That was the first step in our efforts to implement a low-order adaptive optics system for the infrared at the McMath-Pierce main telescope over the next few years. We have since added a science camera that takes simultaneous images with the wavefront sensor. The measured wavefront can be used to determine the instantaneous point-spread function and deconvolve the simultaneous images acquired by the science camera. The resulting image is a good approximation of what an adaptive optics system with the same wavefront sensor would deliver.
In addition to improvement to the visibility of sunspots and pores (see figure), we were also able to successfully measure the wavefront aberration in the quiet granulation and deconvolve the corresponding images. While the present data set has both images and wavefront measured at the same wavelength, the next step will be the addition of an infrared science camera operating at a longer wavelength than the wavefront sensor, which will remain at 1000 nm.
|Caption: The tremendous improvement of image quality from adaptive optics is illustrated by 100 simultaneous short-exposure images of a small sunspot at 1000 nm and the corresponding wavefront sensor data. The left image corresponds to the average of all 100 images; the center image represents the average after correcting for image motion (which simulates the effect of a correlation tracker); and on the right is the deconvolved image assuming an adaptive mirror that corrects the first 54 Zernike components of the measured wavefront aberration.|