A Comparison between Lucky Imaging and Speckle Stabilization for Astronomical Imaging

Abstract

ABSTRACTThe new technique of speckle stabilization has great potential to provide optical imaging data at the highest angular resolutions from the ground. While speckle stabilization was initially conceived for integral field spectroscopic analyses, the technique shares many similarities with speckle imaging (specifically, shift-and-add and lucky imaging). Therefore, it is worth comparing the two for imaging applications. We have modeled observations on a 2.5 m class telescope to assess the strengths and weaknesses of the two techniques. While the differences are relatively minor, we find that speckle stabilization is a viable competitor to current lucky imaging systems. Specifically, we find that speckle stabilization is 3.35 times more efficient (where efficiency is defined as signal-to-noise ratio [S/N] per observing interval) than shift-and-add and is able to detect targets 1.42 mag fainter when using a standard system. If we employ a high-speed shutter to compare with lucky imaging at 1% image selection, speckle stabilization is 1.28 times more efficient and 0.31 mag more sensitive. However, when we incorporate potential modifications to lucky imaging systems, we find that the advantages are significantly mitigated—and even reversed—in the 1% frame-selection cases. In particular, we find that in the limiting case of optimal lucky imaging, that is, zero read noise and photon counting, we find lucky imaging is 1.80 times more efficient and 0.96 mag more sensitive than speckle stabilization. For the cases in between, we find that there is a gradation in advantages to the different techniques, depending on target magnitude, fraction of frames used, and system modifications. Overall, however, we find that the real strength of lucky imaging is in observations of the brightest targets at all frame-selection levels and in observations of faint targets at the 1% level. For targets in the middle, we find that speckle stabilization regularly achieves higher S/N.