Abstract By using the Lunar-based Ultraviolet Telescope (LUT) from 2 December to 4 December, 2014, the first near-UV light curve of the well-known Algol-type binary TW Dra is reported, which is analyzed with the 2013 version of W-D code. Our solutions confirmed that TW Dra is a semi-detached binary system where the secondary component fills its Roche lobe. The mass ratio and a high inclination are obtained (q = 0.47, i = 86◦.68 ). Based on 589 available data spanning more than one century, the complex period changes are studied. Secular increase and three cyclical changes are found in the corresponding orbital period analysis. The secular increase changes reveal mass transfer from the secondary component to the primary one at a rate of 6.8 × 10^−7Msun/yr. One large cyclical change of 116.04 yr may be caused by disturbance of visual component ADS9706B orbiting TW Dra (ADS9706A), while other two cyclical changes with shorter periods of 22.47 and 37.27 yrs can be explained as the result of two circum-binary companions are orbiting around TW Dra, where the two companions are in a simple 3 : 5 orbit-rotation resonances. TW Dra itself is a basic binary in a possible sextuple system (1+1)+(1+1)+(1+1), which further suggests that multiplicity may be a fairly common phenomenon in close binary systems.
Keywords stars: binaries: close — stars: binaries: eclipsing — stars: individual (TW Draco)
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