Cool Stars 14 - Submitted Abstract # 144
This version created on 05 October 2006

Can star spots mimic the long term sinusoidal radial velocity
variations observed in red giants?


Saskia Hekker, Leiden Observatory
Ignas Snellen, Leiden Observatory
Andreas Quirrenbach, Landessternwarte Heidelberg, Leiden Observatory
Sabine Reffert, Landessternwarte Heidelberg
Conny Aerts, Instituut voor Sterrenkunde KUL, University of Nijmegen

We have been monitoring radial velocity variations of 180  red giants
with a typical precision of 5 to 8 m/s for several years.  35 of these
stars show sinusoidal radial velocity variations with typical periods
of a few hundred days and amplitudes between 50  and 500  m/s.  The
photometric variability of these stars as observed by Hipparcos is
smaller than 0.06 mag.  We investigate whether these radial velocity
variations can be explained by the presence of star spots.  Therefore
we model circular spots on a slowly rotating star and investigate the
resultant variations in radial velocity and luminosity.  Preliminary
results show that the spot model can cause changes in the radial
velocity and luminosity comparable to the observed data.  In these
cases, in order to determine whether the radial velocity variations
are intrinsic to the star or caused by a companion, line profile
variations need to be investigated.  If the skewness of the line
profile changes with a frequency comparable to that of the radial
velocity variations, the latter are most likely intrinsic to the star.

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