Measurement of astronomical seeing using long exposure solar images

Abstract

We extend our modified parameter search method (Sridharan, Dashora, and Venkatakrishnan, Solar Phys.222, 35, 2004) of estimating the Fried parameter (r0) from long exposure images to the images obtained from the Hα-telescope installed at Merak, a cold desert on the Himalayas, with a modified criterion – the contrast ratio of the observed and the deconvolved images – to identify the true r0. We validated our new method by applying it to the solar granulation data and found that it is as accurate as our modified parameter search method. The median seeing at Hα – estimated from the data spanning over 5 months – is ≈ 2 arc-sec and it corresponds to a median r0 of 6 cm. About 30% of the estimated values are above r0=7 cm. The diurnal variation of the seeing is consistent with that expected for a lake-shore site. The significance of our method – extracting the underlying seeing from a single long exposure solar image – lies in the fact that it can be easily adopted to monitor seeing with small Hα-telescopes that are coveted and eagerly possessed by many solar observatories for patrolling solar flares and filament eruptions.