Abstract
EX Dra is a long-period eclipsing dwarf nova with \(\sim2\mbox{--}3\) mag amplitude outbursts. This star has been monitored photometrically from November, 2009 to March, 2016 and 29 new mid-eclipse times were obtained. By using new data together with the published data, the best fit to the \(O-C\) curve indicate that the orbital period of EX Dra have an upward parabolic change while undergoing double-cyclic variations with the periods of 21.4 and 3.99 years, respectively. The upward parabolic change reveals a long-term increase at a rate of \(\dot{P}= {+7.46}\times10^{-11}~\mbox{s}\,\mbox{s}^{-1}\). The evolutionary theory of cataclysmic variables (CVs) predicts that, as a CV evolves, the orbital period should be decreasing rather than increasing. Secular increase can be explained as the mass transfer between the secondary and primary or may be just an observed part of a longer cyclic change. Most plausible explanation for the double-cyclic variations is a pair of light travel-time effect via the presence of two companions. Their masses are determined to be \(M_{A}\sin i'_{A}=29.3(\pm0.6) M_{Jup}\) and \(M_{B}\sin i'_{B}=50.8(\pm0.2) M_{Jup}\). When the two companions are coplanar to the orbital plane of the central eclipsing pair, their masses would match to brown dwarfs.
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Acknowledgements
This work is supported by the Chinese Natural Science Foundation (Grant No. 11325315, 11133007, 11573063 and 11611530685), the Strategic Priority Research Program “The Emergence of Cosmological Structure” of the Chinese Academy of Sciences (Grant No. XDB09010202) and the Science Foundation of Yunnan Province (Grant No. 2012HC011). This study is also supported by the Russian Foundation for Basic Research (project No. 17-52-53200). New CCD photometric observations of EX Dra were obtained with the 60 cm and the 2.4 m telescopes at the Yunnan Observatories, the 85 cm telescope in Xinglong Observation base in China and 50 cm and 60 cm telescopes of Sternberg Astronomical Institute Crimean Station. Finally, we thank the anonymous referee for those helpful comments and suggestions.
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Han, Zt., Qian, Sb., Voloshina, I. et al. Double cyclic variations in orbital period of the eclipsing cataclysmic variable EX Dra. Astrophys Space Sci 362, 109 (2017). https://doi.org/10.1007/s10509-017-3091-2
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DOI: https://doi.org/10.1007/s10509-017-3091-2