Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...408.1103s&link_type=abstract
Astronomy and Astrophysics, v.408, p.1103-1113 (2003)
Astronomy and Astrophysics
Astrophysics
16
Stars: Activity, Stars: Imaging, Stars: Individual: Hd31993, Stars: Late-Type, Stars: Starspots
Scientific paper
We present two Doppler images from two consecutive stellar rotations of the single K2-giant HD 31993. Each Doppler image is reconstructed from spectra obtained within a single stellar rotation. With its 25-day rotational period and a radius of ~18 solar radii, HD 31993 is considered a very rapidly rotating star and thus allows the application of the Doppler-imaging technique, despite the unusually long period. All maps reveal 7 isolated, predominantly low-latitude spots with a temperature difference, photosphere minus spot, of just ~200 K. No polar spot or high-latitude activity above, say, +60° is seen. A large warm feature is detected at high latitude and is believed to be real. These spots act as tracers for a cross correlation analysis and yield a clear signature of anti-solar differential surface rotation, i.e. the polar regions rotating faster than the equator, with alpha =0.125 +/-0.05 corresponding to a lap time of ~200 days. A detailed parameter study is carried out to verify the reality of the HD 31993 maps.
Kratzwald L.
Strassmeier Klaus G.
Weber Matthias
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