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The shortest period detached binary white dwarf system

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Abstract

  • We identify SDSS J010657.39?100003.3 (hereafter J0106?1000) as the shortest period detached binary white dwarf (WD) system currently known. We targeted J0106?1000 as part of our radial velocity programme to search for companions around known extremely low-mass (ELM; ˜0.2 M?) WDs using the 6.5-m Multiple Mirror Telescope. We detect peak-to-peak radial velocity variations of 740 km s?1 with an orbital period of 39.1 min. The mass function and optical photometry rule out a main-sequence star companion. Follow-up high-speed photometric observations obtained at the McDonald 2.1-m telescope reveal ellipsoidal variations from the distorted primary but no eclipses. This is the first example of a tidally distorted WD. Modelling the light curve, we constrain the inclination angle of the system to be 67°± 13°. J0106?1000 contains a pair of WDs (0.17 M? primary 0.43 M? invisible secondary) at a separation of 0.32 R?. The two WDs will merge in 37 Myr and most likely form a core He-burning single subdwarf star. J0106?1000 is the shortest time-scale merger system currently known. The gravitational wave strain from J0106?1000 is at the detection limit of the Laser Interferometer Space Antenna (LISA). However, accurate ephemeris and orbital period measurements may enable LISA to detect J0106?1000 above the Galactic background noise. Based on observations obtained at the Multiple Mirror Telescope (MMT) Observatory, a joint facility of the Smithsonian Institution and the University of Arizona.

Publication Date

  • 2011

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