Light-curve analysis of KIC 12557548b: An extrasolar planet with a comet-like tail

Context. An object with a very peculiar light curve was recently discovered using Kepler data. When this object was discovered, it was suggested that this object may be a transiting disintegrating extrasolar planet with a comet-like dusty tail. Aims. We aim to verify this model by modelling the light curve and put constraints on the geometry of the dust region and various dust properties. Methods. We modified the code SHELLSPEC, which is designed for modelling interacting binary stars to calculate the light curves of such planets. Mie absorption and scattering on spherical dust grains with realistic dust opacities, phase functions, and a finite radius of the source of the scattered light are taken into account Results. The light curve is reanalysed using long- and short-cadence Kepler observations from the first 14 quarters. The orbital period of the planet was improved. We prove that the peculiar light curve agrees with the idea of a planet with a comet-like tail. The light curve has a prominent pre-transit brightening and a less prominent post-transit brightening. Both are caused by the forward scattering and are a strong function of the particle size. This feature enabled us to estimate a typical particle size (radius) in the dust tail of about 0.1-1 micron. However, there is an indication that the particle size changes (decreases) along the tail. The dust density in the tail is a steep decreasing function of the distance from the planet, which indicates a significant tail destruction caused by the star-planet interaction. Several possible combinations of other dust properties are tabulated. We reveal interesting periodic long-term evolution of the tail on a time scale of about 1.3 years and also argue that the "planet" does not show a uniform behaviour, but may have at least two constituents. This exoplanet's tail evolution may find an analogy in the comet tail disconnection events caused by the magnetic/coronal activity of the Sun while the light curve with pre-transit brightening is analogous to the light curve of Ïμ Aur and AZ Cas with mid-eclipse brightening and forward scattering playing a significant role in such eclipsing systems.