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

Non-radial pulsations The surface shape of pulsating stars is periodically distorted in a complex way. The main effect on the spectral line profiles is their differential Doppler shift due to variation of the local velocity with respect to distant observer. The corresponding perturbations in the spectral lines can propagate both from blue to red or from red to blue. This variability strongly depends on the l and m numbers of the dominant pulsation mode excited in the star.