Shadow Imaging of Transiting Objects

The light curves of transiting exoplanets are rich in information. If we assume a physical model for an exoplanet---usually, a spherical body in a Keplerian orbit about a host star---we may then infer the parameters of this model, including physical properties of the planet, its orbit, and the host star, from the light curve. However, anomalous transit-like events, such as those observed in star KIC 8462852 (Boyajian et al. 2016), resist this type of analysis, because their physical cause, and consequently the appropriate model, is not apparent. Here, we present a novel approach to modeling the shape of a transiting object from its light curve alone, in which we assume no physical model for the object. We instead model the object as a grid of pixels which transits the star; each pixel has an opacity, ranging from transparent to opaque, which we infer directly from the light curve. Our analysis reveals three interesting degeneracies inherent to the transit problem, in which markedly different transiting shapes can produce identical light curves. By understanding and accounting for these degeneracies, we are able to recover informative shadow images of transiting objects.

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