2020A&A...642A.211M

We present the results of our study of the close binary UU Cassiopeiae based on previously published multiwavelength photometric and spectroscopic data. Based on eclipse timings from the last 117 years, we find an improved orbital period of P_o=8.519296(8)^d. In addition, we find a long cycle of length T∼270d in the I_c-band data. There is no evidence for orbital period change over the last century, suggesting that the rate of mass loss from the system or mass exchange between the stars is small. Sporadic and rapid brightness drops of up to ΔV=0.3mag are detected throughout the orbital cycle, and infrared photometry clearly suggests the presence of circumstellar matter. We model the orbital light curve of 11 published datasets, fixing the mass ratio and cooler star temperature from previous spectroscopic work: q=0.52 and T_c=22700K. We find a system seen at an angle of 74° with a stellar separation of 52R_☉, a temperature for the hotter star of T_h=30200K and, for the hotter and cooler stars, respectively, stellar masses of 17.4 and 9M_☉, radii of 7.0 and 16.9R_☉, and surface gravities logg=3.98 and 2.94. We find an accretion disk surrounding the more massive star that has a radius of 21R_☉ and a vertical thickness at its outer edge of 6.5R_☉; the disk nearly occults the hotter star. Two active regions hotter than the surrounding disk are found, one located roughly in the expected position where the stream impacts the disk and the other on the opposite side of the disk. Changes are observed in parameters of the disk and spots in different datasets.