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

Chemical abundance spots Hot stars often posses inhomogeneous distribution of chemical elements across their surfaces. The lines of spotted elements show large variation during rotation of the star. Typically, elements have an enhanced concentration inside spots and normal abundance outside. The resulting spectral line variation is seen as dips in the line profile, propagating from blue to red.