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Infrared Variability from Circumbinary Disc Temperature Modulations

The temperature of a circumbinary disc edge should undulate due to variations in illumination as a function of binary orbital phase. We explore circumbinary disc temperature variations as a source of broad-band infrared light curve variability. Approximating the wall of a circumbinary disc edge as a wide optically thick cylinder with surface temperature dependent on its illumination, we find that a binary comprised of 1 M$_\odot$ and 0.5 M$_\odot$ pre-main sequence stars in a $\sim$15.5 day period, would exhibit the largest amplitude variations of $\sim$9% at 3.77 and 4.68 μm as seen by a distant observer. The amplitude of variations and shape of the light curve is sensitive to the luminosity and mass ratios of the stars in the binary, the radius of the circumbinary disc clearing, the binary separation, and the orbital inclination. The light curve variations are smooth and very red with a non-sinusoidal shape for most of the parameter space explored. Possible morphologies include a single peak with a flat region, two peaks of different heights or a single dip.