A study published in The Astronomical Journal recently, made by Dr. HAN Zhongtao, Prof. QIAN Shengbang from Yunnan Observatories of the Chinese Academy of Sciences and Prof. Boonrucksar Soonthornthum from National Astronomical Research Institute of Thailand, discovered and identified an eclipsing Z Cam-type dwarf nova, IPHAS J051814.34+294113.2 (IPHAS J0518). They found that IPHAS J0518 has a bimodal distribution of the outbursts, and revealed that the complex behavior of accretion disk during outburst is a combined effect of the varying disc size and radial temperature gradient.

Dwarf novae are a subtype of cataclysmic variables (CVs), and typically exhibit multiple optical outbursts. Z Cam-type stars are believed to share properties of both thermally unstable dwarf novae and thermally stable nova-like variables. Eclipsing dwarf nova allows to measure accurate parameters of the binary components and their orbital period changes, which are crucial for improving our understanding on CV evolution. Over the years, the number of dwarf novae is growing rapidly due to modern astronomical surveys. Up to now, however, only a few eclipsing Z Cam stars were known. The discovery and study of new eclipsing dwarf novae are hence fundamentally important in testing the theoretical models of the outburst, and could shed new light on our understanding of accretion disk properties.

The long-term light curves of IPHAS J0518 from Transiting Exoplanet Survey Satellite（TESS） and Zwicky Transient Facility（ZTF） telescope show the alternation of long outbursts and short outbursts. Meanwhile, TESS data display two outbursts, as well as the striking eclipsing light curve. Using the generalized Lomb-Scargle method and the weighted wavelet transform, the researchers obtained precise orbital period and the recurrence time of long and short outbursts. By combining the derived outburst parameters and Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) spectra, the researchers discovered and identified IPHAS J0518 to be an eclipsing Z Cam-type dwarf nova. These data are also used to constrain the binary parameters.

Also, researchers analyze the accretion disc eclipse and find that the total disc eclipse is possible during quiescence, whereas during outburst the disc would be only partially obscured. Further studies show that the complex behavior of accretion disk during outburst appears more complicated than the single mechanism driven, and should be a combined effect of the varying disc size and radial temperature gradient.

The discovery of this system is expected to reveal its disk structure and the brightness distribution in the future, and allows to trace the disk evolution with time during outburst.

Contact:

HAN Zhongtao, Yunnan Observatories, CAS

zhongtaohan@ynao.ac.cn