Recovering facular areas through Doppler imaging

¹ The Research Council of Norway, PO Box 2700 St. Hanshaugen, 0131 Oslo, Norway
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: vaarum@aip.de
³ Institute of Theoretical Astrophysics, PO Box 1029 Blindern, 0315 Oslo, Norway

Received: 7 June 2004
Accepted: 1 February 2005

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 simulated 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 unrealistic. 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.