Beyond Circular Eclipsers (BeyonCE) light curve modelling

Abstract

Context. Time series photometry offers astronomers the tools to study time-dependent astrophysical phenomena, from stellar activity to fast radio bursts and exoplanet transits. Transit events, in particular, are focussed primarily on planetary transits and eclipsing binaries with eclipse geometries that can be parameterised with a few variables. However, more complex light curves caused by the substructure within the transiting object would require a customised analysis code. Aims. We present Beyond Circular Eclipsers (BeyonCE), which reduces the parameter space encompassed by the transit of circumsec-ondary disc (CSD) systems with azimuthally symmetric, non-uniform optical-depth profiles. By rejecting disc geometries that are not able to reproduce the measured gradients within their light curves, we can constrain the size and orientation of discs with a complex sub-structure. Methods. We mapped out all the possible geometries of a disc and calculated the gradients for rings crossing the star. We then rejected those configurations where the measured gradient of the light curve is greater than the theoretical gradient from the given disc orientation. Results. We present the fitting code BeyonCE and demonstrate its effectiveness in considerably reducing the parameter space of discs that contain an azimuthally symmetric structure. We used the code to analyse the light curves seen towards J1407 and PDS 110, attributed to CSD transits.