An 8.8 Minute Orbital Period Eclipsing Detached Double White Dwarf Binary

Creators: Burdge, Kevin B.; Coughlin, Michael W.; Fuller, Jim; Kaplan, David L.; Kulkarni, S. R.; Marsh, Thomas R.; Bellm, Eric C.; Dekany, Richard G.; Duev, Dmitry A.; Graham, Matthew J.; Mahabal, Ashish A.; Masci, Frank J.; Laher, Russ R.; Riddle, Reed; Soumagnac, Maayane T.; Prince, Thomas A.

Abstract

We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf binary with an orbital period of just 8.8 minutes, the second known eclipsing binary with an orbital period of less than 10 minutes. The system likely consists of two low-mass white dwarfs and will merge in approximately 400,000 yr to form either an isolated hot subdwarf or an R Coronae Borealis star. Like its 6.91 minute counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the strongest gravitational-wave sources detectable by the space-based gravitational-wave detector the Laser Space Interferometer Antenna (LISA) because its gravitational-wave frequency falls near the peak of LISA's sensitivity. Based on its estimated distance of d = 2425⁺¹⁰⁸₋₁₁₄ pc, LISA should detect the source within its first few months of operation and achieve a signal-to-noise ratio of 63 ± 7 after 4 yr. We find component masses of M_A = 0.323^(+0.065)_(-0.047) and M_B = 0.335^(+0.052)_(-0.054) M_⊙ , radii of R_A = 0.0298^(+0.0013)_(-0.0012) and R_B = 0.0275^(+0.0012)_(-0.0013) R_⊙, and effective temperatures of T_A = 26, 300⁺¹⁷⁰⁰₋₉₀₀ and T_B = 19, 200⁺¹⁵⁰⁰₋₉₀₀ K. We determine all of these properties and the distance to this system using only photometric measurements, demonstrating a feasible way to estimate parameters for the large population of optically faint (r > 21 m_(AB)) gravitational-wave sources that the Vera Rubin Observatory and LISA should identify.

Additional Information

© 2020 The American Astronomical Society. Received 2020 October 20; revised 2020 November 13; accepted 2020 November 13; published 2020 December 9. K.B.B. thanks the National Aeronautics and Space Administration and the Heising-Simons Foundation for supporting his research. K.B.B. also wishes to thank Andrew Tisdale for his generous contribution to this research effort. M.W.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. J.F. acknowledges support from an Innovator Grant from the Rose Hills Foundation and the Sloan Foundation through grant FG-2018-10515. T.R.M. was supported by the UK's Science and Technology Facilities Council through grant ST/T000406/1. We wish to thank the referee of this work for their excellent suggestions, which have considerably enhanced the quality of the work. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF is supported by the National Science Foundation under grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron and Humboldt University, Los Alamos National Laboratories, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratories. Operations are conducted by the COO, IPAC, and UW. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The ZTF forced-photometry service was funded under Heising-Simons Foundation grant 12540303 (PI: Graham). Facilities: PO:1.2 m (ZTF) - , Hale (CHIMERA) - , Keck:I (LRIS) - , Swift (XRT and UVOT). - Software: Aplpy (Robitaille & Bressert 2012), Astropy (Astropy Collaboration et al. 2013), CUVARBASE (https://github.com/johnh2o2/cuvarbase), LCURVE (Copperwheat et al. 2010), Lpipe (Perley 2019), Multinest (Feroz et al. 2009), Numpy (van der Walt et al. 2011).

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