Site Characterization Using Solar Hα Images

Abstract

A Multi-Application Solar Telescope (MAST) is proposed to be installed at the lake site (Lake Fatehsagar) of Udaipur Solar Observatory (USO) in India. The lake site Observatory of USO is located on a small island in the middle of the lake. To determine the optimum size of the MAST (for use with an adaptive optics system), it was decided to quantify the seeing conditions prevailing at the lake site during the different months of the year. For this purpose, we have used short-exposure (3 ms) high-resolution Hα (6563 A) images (spatial scale of ∼0.55 arc sec per pixel) of the Sun taken in burst mode with the 15-cm refractor Spar telescope located at the lake site of USO. Spectral ratio technique as reported by von der Luhe (1984, J. Opt. Soc. Am.A1, 510) has been used to estimate the Fried’s parameter (r0) at this site, which gives the quantitative measure of astronomical seeing. This study has been carried out daily on an hourly basis during 4:30 – 10:30 UT over the months January – June of the years 2005 and 2006 to understand the diurnal and seasonal variations in r0 at this site. It is noteworthy that the lake was almost dry during the observing period in 2005, while it overflowed during our observations in 2006 because of abundant monsoon rains. The seeing in the presence of water shows improvement in r0 by about 1.0 cm with respect to the previous year’s dry condition and mean r0 varies between 4.0 and 4.5 cm as evident from the data obtained between January and June, 2006.