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The solar and stellar irradiance variations occur at all measured timescales and wavelengths. The variations on timescales longer than a day are attributed to the emergence and evolution of surface magnetic features. The photospheric magnetic features such as spots and faculae cause variations in broadband photometric passbands and spectral lines. The chromospheric counterparts of these photospheric features cause variations in strong spectral lines like Ca II H & K, which are one of the most widely used stellar magnetic activity proxies. I will present a physics-based model to calculate Ca II H & K emissions and its application to understand the various sources of stellar Ca II emissions as well as to identify biases in solar-stellar comparison studies. I will also talk about our ongoing efforts to understand how stellar magnetic activity signals manifest in astrometry and radial velocity.
Colloquium Committee