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Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF

El-Badry, Kareem and Conroy, Charlie and Fuller, Jim and Kiman, Rocio and van Roestel, Jan and Rodriguez, Antonio C. and Burdge, Kevin B. (2022) Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF. Monthly Notices of the Royal Astronomical Society, 517 (4). pp. 4916-4939. ISSN 0035-8711. doi:10.1093/mnras/stac2945.

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We constrain the orbital period (Porb) distribution of low-mass detached main-sequence eclipsing binaries (EBs) with light-curves from the Zwicky Transient Facility (ZTF), which provides a well-understood selection function and sensitivity to faint stars. At short periods (Porb ≲ 2 d), binaries are predicted to evolve significantly due to magnetic braking (MB), which shrinks orbits and ultimately brings detached binaries into contact. The period distribution is thus a sensitive probe of MB. We find that the intrinsic period distribution of low-mass (0.1 ≲ M_(1)/M_(⊙) < 0.9) binaries is basically flat (⁠dN/dP_(orb) ∝ P^(0)_(orb)⁠) from P_(orb) = 10 d down to the contact limit. This is strongly inconsistent with predictions of classical MB models based on the Skumanich relation, which are widely used in binary evolution calculations and predict dN/dP_(orb) ∝ P^(7/3)_(orb) at short periods. The observed distributions are best reproduced by models in which the magnetic field saturates at short periods with a MB torque that scales roughly as J˙ ∝ P^(−1)_(orb)⁠, as opposed to J˙ ∝ P^(−3)_(orb) in the standard Skumanich law. We also find no significant difference between the period distributions of binaries containing fully and partially convective stars. Our results confirm that a saturated MB law, which was previously found to describe the spin-down of rapidly rotating isolated M dwarfs, also operates in tidally locked binaries. We advocate using saturated MB models in binary evolution calculations. Our work supports previous suggestions that MB in cataclysmic variables (CVs) is much weaker than assumed in the standard evolutionary model, unless mass transfer leads to significant additional angular momentum loss in CVs.

Item Type:Article
Related URLs:
URLURL TypeDescription
El-Badry, Kareem0000-0002-6871-1752
Conroy, Charlie0000-0002-1590-8551
Fuller, Jim0000-0002-4544-0750
Kiman, Rocio0000-0003-2102-3159
van Roestel, Jan0000-0002-2626-2872
Rodriguez, Antonio C.0000-0003-4189-9668
Burdge, Kevin B.0000-0002-7226-836X
Additional Information:We thank Saul Rappaport, Boris Gaensicke, Tom Marsh, Brian Metzger, Ken Shen, Dave Charbonneau, Mercedes López-Morales, Eliot Quataert, Hans-Walter Rix, Selma de Mink, and E. Sterl Phinney, for helpful discussions. This research was supported in part by the National Science Foundation under Grant No. NSF PHY-1748958. Based on observations obtained with the Samuel Oschin 48-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-1440341 and a collaboration including Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm University, the University of Maryland, the University of Washington, Deutsches Elektronen-Synchrotron, and Humboldt-Universität, Los Alamos National Laboratory, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, and Lawrence Berkeley National Laboratory. Operations are conducted by COO, IPAC, and UW.
Group:Astronomy Department, Zwicky Transient Facility
Funding AgencyGrant Number
ZTF partner institutionsUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20221128-494241100.39
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118077
Deposited By: Research Services Depository
Deposited On:16 Dec 2022 18:33
Last Modified:16 Dec 2022 21:34

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