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

## TL;DR

This study measures atmospheric turbulence parameters at Vainu Bappu Observatory using high-speed CCD imaging to inform adaptive optics system design, providing median seeing, tilt-anisoplanatic angle, and coherence time data.

## Contribution

First detailed measurement of atmospheric turbulence parameters at Vainu Bappu Observatory using short-exposure CCD images for adaptive optics planning.

## Key findings

- Median seeing of approximately 1.85 arcseconds at 600 nm
- Tilt-anisoplanatic angle of about 36 arcseconds with 44% correlation
- Mean coherence time around 2.4 milliseconds

## 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.