  There is growing observational evidence for some kind of interaction between
stars and close-in extrasolar giant planets. Shkolnik et al. reported
variability in the chromospheric Ca H and K lines of HD 179949 and upsilon And
that seemed to be phased with the planet's orbital period, instead of the
stellar rotational period. However, the observations also indicate that the
chromospheric light curves do not repeat exactly, which may be expected for a
planet plowing through a variable stellar magnetic field. Using the complex
solar magnetic field (modeled with the Potential Field Source Surface
technique) as a guide, we simulate the shapes of light curves that would arise
from planet-star interactions that are channeled along magnetic field lines. We
also study the orbit-to-orbit variability of these light curves and how they
vary from solar minimum (i.e., a more or less axisymmetric stretched dipole) to
solar maximum (a superposition of many higher multipole moments) fields.
Considering more complex magnetic fields introduces new difficulties in the
interpretation of observations, but it may also lead to valuable new
diagnostics of exoplanet magnetospheres.
