Two decades of optical timing of the shortest-period binary star system HM Cancri

• DOI: 10.1093/mnras/stac3385
• Publication Date: 2022-11-25T01:34:03Z
• Authors: James Munday; T R Marsh; Mark Hollands; Ingrid Pelisoli; Danny Steeghs; Pasi Hakala; Elmé Breedt; Alex Brown; V S Dhillon; Martin J Dyer; Matthew Green; Paul Kerry; S P Littlefair; Steven G Parsons; Dave Sahman; Sorawit Somjit; Boonchoo Sukaum; James Wild
• Keywords: Orbital period; Mass ratio

ABSTRACT The shortest-period binary star system known to date, RX J0806.3+1527 (HM Cancri), has now been observed in the optical for more than two decades. Although it is thought be a double degenerate undergoing mass transfer, an early surprise was that its orbital frequency, f0, currently increasing as result of gravitational wave radiation. This unusual since expected donor and would expand on loss, leading decreasing f0. We exploit decades high-speed photometry precisely quantify trajectory HM Cancri, allowing us find $\ddot{f}_0$ negative, where $\ddot{f}_0~=~(-5.38\pm 2.10)\times 10^{-27}$ Hz s−2. Coupled with our positive frequency derivative, we show transfer counteracting gravitational-wave dominated decay Cancri will turn around within 2100 ± 800 yr from now. present Hubble Space Telescope ultra-violet spectra which display Lyman-α absorption, indicative presence hydrogen accreted star. use these pieces information explore grid permitted accretor masses Modules Experiments Stellar Astrophysics suite, finding models good accordance many properties cool initially hydrogen-rich extremely low white dwarf (≈0.17 M⊙) coupled high-accretor (≈1.0 M⊙). Our measurements affirm still one brightest verification binaries Laser Interferometer Antenna spacecraft.