New insights on the massive interacting binary UU Cassiopeiae

We present the results of the study of the close binary UU Cassiopeiae based on previously published multi wavelength photometric and spectroscopic data. Based on eclipse timings of the last 117 years, we find an improved orbital period of $\rm P_{o} = 8.519296(8)$ d. In addition, we find a long cycle of length $T$ $\sim$ 270 d in the $I_c$-band data. There is no evidence for orbital period change during the last century, suggesting that the rate of mass loss from the system or mass exchange between the stars should be small. Sporadic and rapid brightness drops of up to $\Delta$$V$ = 0.3 mag are detected during the whole 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 cool star temperature from previous spectroscopic work; $q$= 0.52 and $T_c$= 22 700 K. We find a system seen at angle 74 degrees with a stellar separation of 52 ${\rm R_{\odot}}$, a temperature for the hotter star $T_h$= 30 200 $K$ and stellar masses 17.4 and 9 ${\rm M_{\odot}}$ , radii 7.0 and 16.9 ${\rm R_{\odot}}$ and surface gravities log g = 3.98 and 2.94, for the hotter and cooler star, respectively. We find an accretion disk surrounding the more massive star, with a radius of 21 ${\rm R_{\odot}}$ and vertical thickness in its outer edge of 6.5 ${\rm R_{\odot}}$, mostly occulting 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 one in the opposite side of the disk. Changes are observed in parameters of the disk and spots in different datasets.