Volume 642, October 2020
|Number of page(s)||9|
|Section||Stellar structure and evolution|
|Published online||23 October 2020|
New insights on the massive interacting binary UU Cassiopeiae
Universidad de Concepción, Departamento de Astronomía, Casilla 160-C, Concepción, Chile
2 Astronomical Observatory Belgrade, Volgina 7, 11060 Belgrade, Serbia
3 Astronomical Institute of the Academy of Sciences of the Czech Republic, Boční II 1401/1, 141 00 Praha 4, Czech Republic
4 Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
5 Konkoly Thege Astronomical Institute, Research Center for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
6 Astronomical Institute of Charles University, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
7 Institute of Astronomy and NAO, Bulgarian Academy of Sciences, Bulgaria
Accepted: 29 August 2020
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 Po = 8.d519296(8). In addition, we find a long cycle of length T ∼ 270 d in the Ic-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 = 0.3 mag 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 Tc = 22 700 K. We find a system seen at an angle of 74° with a stellar separation of 52 R⊙, a temperature for the hotter star of Th = 30 200 K and, for the hotter and cooler stars, respectively, stellar masses of 17.4 and 9 M⊙, radii of 7.0 and 16.9 R⊙, and surface gravities log g = 3.98 and 2.94. We find an accretion disk surrounding the more massive star that has a radius of 21 R⊙ and a vertical thickness at its outer edge of 6.5 R⊙; 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.
Key words: binaries: eclipsing / binaries: spectroscopic / stars: evolution / stars: massive / accretion, accretion disks
© ESO 2020
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