Formation of the Ca II K line

Background

The Ca II K line is one of the strongest lines in the solar spectrum. Its complex profiles, in particular close to the line core, are a reflection of the highly dynamic conditions of the solar chromosphere. The combination of gradients in temperature, density, and velocity leads to the peculiar line profiles that are observed. Learning how the physical quantities of the atmosphere affect spectral properties is therefore essential to understand observations. Bjørgen et al. (2018) comprehensively studied the formation of Ca II H & K using 3D simulations. The aim of this project is to instead use simplified 1D models of the atmosphere to get intuition into how the spectra react to simple changes in the model atmosphere, in a similar vein to how Carlsson et al. (2015) studied the Mg II k line in solar plage.

Goal

The goal of the project is to better understand how changes in the solar atmosphere affect the shape of the Ca II K line.

Method

1. A sequence of simplified one-dimensional "toy model" atmospheres based on the FALC model will be built by modifying parameters such as temperature, velocity, and density in simple ways. Variations should be realistic and similar to the conditions found in and around solar spicules.
2. Use the [RH 1.5D](https://rh15d.readthedocs.io/en/latest/) code to synthesize Ca II K profiles from a series of 1D models. If necessary, generate more 1D models.
3. Analyse the resulting spectra and find out major trends. Make use of tools such as "line formation diagrams" (or "formation breakdown figures").