Searching for Compact Binary Central Stars of Planetary Nebulae with the Zwicky Transient Facility

There are > 3000 planetary nebulae (PNe) in our Galaxy and they have very diverse morphology with approximately 80% not being spherical. It is difficult to be explained with a single-star scenario and it is widely believed that binaries may be responsible for the complex morphologies. There are currently about 100 known PNe with binary central stars and the true binary population may be much larger than that. To reveal the true binary population of the central objects of PNe, we have systematically searched for optical periodic variations of central stars for about 2000 PNe observed with the Zwicky Transient Facility (ZTF). By applying several period searching techniques such as the Lomb-Scargle periodogram and phase dispersion minimisation, we identified numerous new binary candidates and confirmed the binary nature of known systems found by Kepler and Gaia. The periods cover from about an hour to several days indicating that many of them are compact systems. We have also examined the X-ray emission to investigate the nature of the binary objects. By expanding the known binary population, our work will aid in understanding the formation and evolution of PNe, as well as the role of binary systems in shaping the complex morphology.