Characterizing image quality of solar ultraviolet imaging telescope on board Aditya L1- mission and long- term study of the sun

Abstract

Spatially resolved solar near ultraviolet (NUV, 200-400 nm) observation is important to understand the coupling between different layers of solar atmosphere and its impact on Earth’s climate. Again, solar features in NUV regime are crucial in budgeting long-term variation of solar irradiance and probing solar magnetic cycle. Contextually, Solar Ultraviolet Imaging Telescope (SUIT), on-board upcoming ADITYA-L1 mission, attempts full-disc solar imaging with 1.4" resolution in NUV through 11 filters. Thesis starts with optimization of SUIT optics incorporating design requirements,

constraints to generate an off-axis Ritchey-Chretien configuration. Ghost flux mini- mization produces tilted filter configuration. Afterwards, fabrication, alignment and

thermal tolerances are derived constraining image quality. Scattering caused by op- tical surface micro-roughness and particulate contamination is analysed producing

requirements on surface polish and assembly environment. SUIT baffles are designed to restrict scatter from entrance aperture. A flat-field model is developed using light emitting diodes. Also, a plan for SUIT optical alignment is rendered. Having relevance to SUIT observation, digitized Ca ii K and Hα spectroheliograms from Kodaikanal Solar Observatory (KoSO) are analysed. Plages are detected through an automated method from Ca ii K series (1907-2007). Carrington maps are generated and correlated with modern magnetic maps for overlapping times confirming locational correspondence between plages and magnetic patches. The Ca ii K series is also used in automated detection of supergranules, which represents solar magneto-convection. Time evolution of their morphological parameters near and away from active region depict contrasting correlations with sunspot cycle hinting different dynamos involved. Full disc KoSO Hα images are calibrated for the period 1914-2007 and Carrington maps are generated. A semi-automated technique is developed to detect filaments from Carrington maps. Time-latitude distribution of filaments reveals polar rush and its role in polar field reversal. Prominences are detected through an automated method

for 10 solar cycles from a combined dataset with a major share from KoSO Ca ii K disc- blocked series (1906-2002). Results illustrate nonlinear profile of poleward migration

for all cycles and may provide constraints in deriving solar meridional flow rate. Thus this long-term study can complement SUIT data pipeline with relevant algorithms and build confidence for future cycle predictions.