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

Abstract

We report atmospheric turbulence parameters, namely atmospheric seeing, tilt-anisoplanatic angle (θ0) and coherence time (τ0), 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 ≈ 1.85′′ at wavelength of ∼ 600 nm, the image motion correlation between different pairs of stars is ∼ 44% for θ0 ≈ 36′′ and mean τ0 is ≈ 2.4 ms. This work was motivated by the design considerations and expected performance of an adaptive optics system that is currently being planned for the telescope.