摘要：We typically measure the radii of transiting exoplanets from the transit depth, which are given by the ratio of cross-sectional areas of the planet and star. However, if a star has dark starspots (or bright regions) distributed throughoutthe transit chord, the transit depth will be biased toward smaller (larger) values, and thus the inferred planet radiuswill be smaller (larger) if these are unaccounted for. We reparameterize the transit light curve to account for “self-contamination” by photospheric inhomogeneities by splitting the parameter R p /R å into two parameters: one for theradius ratio, which controls the duration of ingress and egress, and another which measures the possiblycontaminated transit depth. We show that this is equivalent to the formulation for contamination by a second star(with positive or negative flux), and that it is sensitive to time-steady inhomogeneity of the stellar photosphere. Weuse synthetic light curves of spotted stars at high signal-to-noise to show that the radius recovered frommeasurement of the ingress/egress duration can recover the true radii of planets transiting spotted stars withaxisymmetric spot distributions if the limb-darkening parameters are precisely known. We fit time-averaged highsignal-to-noise transit light curves from Kepler and Spitzer of 10 planets to measure the planet radii and search forevidence of spot distributions. We find that this sample has a range of measured depths and ingress durations thatare self-consistent, providing no strong evidence for contamination by spots. However, there is suggestive evidencefor occultation of starspots on Kepler-17, and that relatively bright regions are occulted by the planets of Kepler-412 and HD 80606. Future observations with the James Webb Space Telescope may enable this technique to yieldaccurate planetary radii in the presence of stellar inhomogeneities.
关键词：eclipses;planets and satellites: fundamental parameters;stars: activity;stars: magnetic field;starspots
