Basic Principles of Doppler Imaging

The goal of Doppler imaging is to invert line profile variations into 2-D map of stellar surface. Due to Doppler effect arising from the stellar rotation contributions of different surface zones are shifted in wavelength. Surface structures produce perturbations moving across line profiles as the star rotates. The longitude of a starspot can be determined directly from the position of the corresponding distortion in the line profile. The latitude can be inferred from the temporal behaviour of the distortion.

Below I illustrate typical line profile variation produced by different types of structures on the surfaces of rotating stars. I am doing Doppler Imaging analysis of all these different types of starspots.

Temperature Chemical abundance Magnetic field Non-radial pulsation

Temperature spots Active late-type stars have cool, dark spots on their surfaces. Their contribution to the disk-averaged spectrum is smaller than for the unspotted part of the stellar surface. Thus, the signature of cool spot is a bump travelling from blue to red across the stellar spectral line.