Recovering facular areas through Doppler imaging

Abstract

Similar to the Sun, stellar active regions appear to consist of dark spots in combination with surrounding bright facular regions. The present study uses the Doppler imaging technique to recover the stellar surface structures from simu- lated spectral observations obtained from a given theoretical stellar surface. The objective of the study is to investigate how the recovered surface structure depends on observing parameters such as rotational phase coverage, choice of spectral lines, signal-to-noise ratio, and projected equatorial rotational velocity. The inversions demonstrate that those stellar surface active regions with high temperature contrast in both longitudinal and latitudinal directions can be satisfactorily reproduced using Doppler imaging. Observations must, however, fulfill such strict conditions that a complete reconstruction is somewhat unreal- istic. Nevertheless, in a more realistic example, the hot facular areas result in quite distinct and easily recognizable features on the stellar surface map, even though they are not completely reconstructed.