The Effects of Sunspots on Spectral Line Shapes in the Visible

Abstract

We present a comparative spectral analysis to explore the ability of a cooler Sun model to accurately capture the spectral line shape changes caused by Sunspots. In the search for small Earth-like planets, the effects of stellar surface activity can overwhelm the $\sim$10 cm/s planetary RV signal. This necessitates the development of new stellar modeling methods and a greater understanding of the impact of surface activity on stellar spectra. Some attempts to model out noise from Sunspot activity, in particular, have used a sum of a stellar model with a model of a cooler, but otherwise identical star. From our analysis, we find that a cooler effective temperature alone cannot capture the numerous spectral line shape variations seen in a Sunspot observation. The cooler temperature of a Sunspot not only deepens the cores of atomic lines, it also increases and strengthens molecular lines that are not fully represented in our line list. Furthermore, our LTE models and a comparison cool star also fail at capturing line strengthening, broadening, blending, and splitting induced by the magnetic field in the Sunspot.