Two decades of optical timing of the shortest-period binary star system HM Cancri
| Autor: | 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 |
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| Rok vydání: | 2022 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science FOS: Physical sciences Astronomy and Astrophysics General Relativity and Quantum Cosmology (gr-qc) Astrophysics - High Energy Astrophysical Phenomena Solar and Stellar Astrophysics (astro-ph.SR) General Relativity and Quantum Cosmology |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 518:5123-5139 |
| ISSN: | 1365-2966 0035-8711 |
| DOI: | 10.1093/mnras/stac3385 |
| Popis: | 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 to be a double degenerate binary undergoing mass transfer, an early surprise was that its orbital frequency, $f_0$, is currently increasing as the result of gravitational wave radiation. This is unusual since it was expected that the mass donor was degenerate and would expand on mass loss, leading to a decreasing $f_0$. We exploit two decades of high-speed photometry to precisely quantify the trajectory of HM Cancri, allowing us to find that $\ddot f_0$ is negative, where $\ddot f_0~=~(-5.38\pm2.10)\times10^{-27}$ Hz s$^{-2}$. Coupled with our positive frequency derivative, we show that mass transfer is counteracting gravitational-wave dominated orbital decay and that HM Cancri will turn around within $2100\pm800\,$yrs from now. We present Hubble Space Telescope ultra-violet spectra which display Lyman-$\alpha$ absorption, indicative of the presence of hydrogen accreted from the donor star. We use these pieces of information to explore a grid of permitted donor and accretor masses with the Modules for Experiments in Stellar Astrophysics suite, finding models in good accordance with many of the observed properties for a cool and initially hydrogen-rich extremely-low-mass white dwarf ($\approx0.17\,$M$_\odot$) coupled with a high accretor mass white dwarf ($\approx 1.0\,$M$_\odot$). Our measurements and models affirm that HM~Cancri is still one of the brightest verification binaries for the Laser Interferometer Space Antenna spacecraft. Comment: 12 pages (+5 pages appendix), 9 figures, 6 tables. Accepted for publication in MNRAS |
| Databáze: | OpenAIRE |
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