Measurements of atmospheric turbulence parameters at Vainu Bappu Observatory using short-exposure CCD images

Abstract

We report the atmospheric turbulence parameters namely, atmospheric seeing, the tilt-anisoplanatic angle (${\theta }_0$) and the coherence time (${\tau }_0$), measured under various sky conditions, at Vainu Bappu Observatory in Kavalur. Bursts of short exposure images of selected stars were recorded with a high-speed, frame-transfer CCD mounted on the Cassegrain focus of a newly commissioned 1.3 m telescope. The estimated median seeing is $\approx 1.85^{\prime \prime }$ at wavelength of $\sim 600$ nm, the image motion correlation between different pairs of stars is $\sim 44\%$ for ${\theta }_0\approx 36^{\prime \prime }$ and mean ${\tau }_0$ is $\approx 2.4$ ms. This work was motivated by the design considerations and expected the performance of an adaptive optics system that is currently being planned for the telescope.