J. Llama, M. Jardine, D. H. Mackay, R. Fares
Planetary transits provide a unique opportunity to investigate the surface
distributions of star spots. Our aim is to determine if, with continuous
observation (such as the data that will be provided by the Kepler mission), we
can in addition measure the rate of drift of the spot belts. We begin by
simulating magnetic cycles suitable for the Sun and more active stars,
incorporating both flux emergence and surface transport. This provides the
radial magnetic field distribution on the stellar surface as a function of
time. We then model the transit of a planet whose orbital axis is misaligned
with the stellar rotation axis. Such a planet could occult spots at a range of
latitudes. This allows us to complete the forward modelling of the shape of the
transit lightcurve. We then attempt the inverse problem of recovering spot
locations from the transit alone. From this we determine if transit lightcurves
can be used to measure spot belt locations as a function of time. We find that
for low-activity stars such as the Sun, the 3.5 year Kepler window is
insufficient to determine this drift rate. For more active stars, it may be
difficult to distinguish subtle differences in the nature of flux emergence,
such as the degree of overlap of the "butterfly wings". The rate and direction
of drift of the spot belts can however be determined for these stars. This
would provide a critical test of dynamo theory.
View original:
http://arxiv.org/abs/1202.3785
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