Fizeau Mask Interferometry of Solar Features Using the Multi-application Solar Telescope at the Udaipur Solar Observatory

Efforts are made to demonstrate high-resolution observations of the solar atmosphere using spatial interferometry. Covering the telescope pupil with a Fizeau mask consisting of two small circular apertures separated by a vector distance known as the baseline is the first step towards interferometric imaging. A mask with two circular holes of diameter 7 cm each and separated by a distance of 19 cm is placed in the pupil plane of the Multi-application solar telescope at Udaipur solar observatory. The fringe pattern observed in the image plane signifies the presence of solar structures with sizes smaller than the fringe period. The study is extended with baselines of 29 cm and 38 cm. It is observed that an increase in the baseline causes a reduction in the fringe period and the fringe contrast. Observations are carried out in two spectral lines/bands, centered at 656.3 nm and 861.0 nm using filters of bandwidth 1 nm and 330 nm, respectively. The effect of bandwidth on the fringe visibility is also discussed based on the bandwidth decorrelation function.