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Dynamical tides in compact white dwarf binaries: tidal synchronization and dissipation

Fuller, Jim and Lai, Dong (2012) Dynamical tides in compact white dwarf binaries: tidal synchronization and dissipation. Monthly Notices of the Royal Astronomical Society, 421 (1). pp. 426-445. ISSN 0035-8711. doi:10.1111/j.1365-2966.2011.20320.x.

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In compact white dwarf (WD) binary systems (with periods ranging from minutes to hours), dynamical tides involving the excitation and dissipation of gravity waves play a dominant role in determining the physical conditions (such as rotation rate and temperature) of the WDs prior to mass transfer or binary merger. We calculate the amplitude of the tidally excited gravity waves as a function of the tidal forcing frequency ω = 2(Ω−Ω_s) (where Ω is the orbital frequency and Ω_s is the spin frequency) for several realistic carbon–oxygen WD models, under the assumption that the outgoing propagating waves are efficiently dissipated in the outer layer of the star by non-linear effects or radiative damping. Unlike main-sequence stars with distinct radiative and convection zones, the mechanism of wave excitation in WDs is more complex due to the sharp features associated with composition changes inside the WD. In our WD models, the gravity waves are launched just below the helium–carbon boundary and propagate outwards. We find that the tidal torque on the WD and the related tidal energy transfer rate, Ė_(tide), depend on ω in an erratic way, with Ė_(tide) varying by orders of magnitude over small frequency ranges. On average, Ė_(tide) scales approximately as Ω^5ω^5 for a large range of tidal frequencies. We also study the effects of dynamical tides on the long-term evolution of WD binaries prior to mass transfer or merger. Above a critical orbital frequency Ω_c, corresponding to an orbital period of the order of 1h (depending on WD models), dynamical tides efficiently drive Ω_s towards Ω, although a small, almost constant degree of synchronization (Ω−Ω_s∼ constant) is maintained even at the smallest binary periods. While the orbital decay is always dominated by gravitational radiation, the tidal energy transfer can induce a significant phase error in the low-frequency gravitational waveforms, detectable by the planned Laser Interferometer Space Antenna project. Tidal dissipation may also lead to significant heating of the WD envelope and brightening of the system long before binary merger.

Item Type:Article
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URLURL TypeDescription Paper
Fuller, Jim0000-0002-4544-0750
Lai, Dong0000-0002-1934-6250
Additional Information:© 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS. Accepted 2011 December 2. Received 2011 December 1; in original form 2011 August 24. We thank Gilles Fontaine (University of Montreal) for providing the WD models used in this paper and for valuable advice on these models. DL thanks Lars Bildsten and Gordon Ogilvie for useful discussions, and acknowledges the hospitality of the Kavli Institute for Theoretical Physics at UCSB (funded by the NSF through Grant PHY05–51164) where part of the work was carried out during the spring of 2010. This work has been supported in part by NSF grant AST-1008245.
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Subject Keywords:hydrodynamics, waves, binaries: close, stars: kinematics and dynamics, white dwarfs
Issue or Number:1
Record Number:CaltechAUTHORS:20190425-152213253
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Official Citation:Jim Fuller, Dong Lai, Dynamical tides in compact white dwarf binaries: tidal synchronization and dissipation, Monthly Notices of the Royal Astronomical Society, Volume 421, Issue 1, 21 March 2012, Pages 426–445,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:94993
Deposited By: George Porter
Deposited On:25 Apr 2019 22:58
Last Modified:16 Nov 2021 17:09

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