Time-resolved Doppler images of the rapidly rotating, but long-period
(25 days), giant KU Pegasi show several cool low-to-medium latitude
spots as well as an asymmetric polar feature. The average spot
temperature is about 700K below the photospheric temperature of
4700K.
KU Peg is one of the most massive, and currently the most
evolved, late-type star with a Doppler image. We obtained two
independent images from two consecutive stellar rotations covering 50
nights with a total of 43 spectra. From a cross-correlation analysis
of the two maps, we detect systematic longitudinal and latitudinal
shifts that we tentatively interpret as latitude-dependent
differential rotation and local meridional flows, respectively.
The
differential-rotation pattern is more complex than on the Sun, but on
average in the sense that the poles rotate slower than the stellar
equator, i.e. in the same direction and also of the same order than
on the Sun. The latitudinal shifts are of the order of 0.4 degr per
day towards the stellar pole and occur at longitudes of around 40 degr
and 330 degr. The residual Halpha profiles show a stationary emission
component at rest wavelength and a blue-shifted absorption. The latter
suggests an outward pointed velocity field with a flow velocity of
approximately 35 km/s.
(paper by Weber and Strassmeier in press A&A 2001)
