Physics of the Applegate mechanism: Eclipsing time variations from magnetic activity

Völschow, Marcel; Schleicher, Dominik R. G.; Banerjee, Rinti; Schmitt, J. H. M. M.

doi:10.1051/0004-6361/201833506

Cited by 33 publications

(44 citation statements)

References 33 publications

(89 reference statements)

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“…Refinements where later brought by Brinkworth et al (2006) who introduced a treatment based on a finite shell and a core, followed by Völschow et al (2016) who generalised that approach to more realistic density profiles of the companion star. Alternatively, Lanza (2005Lanza ( , 2006 introduced a treatment of the complete continuous redistribution of angular momentum across the entire convective zone of the star, later expanded by Völschow et al (2018). In all these models, the underlying magnetic cycle are imposed as ad hoc assumptions.…”

Section: The Phase-locked Quadrupole Potentialmentioning

confidence: 99%

“…However qualitatively successful, this simulation is restricted in range and cannot assess fully realistic cases due to the overwhelming computing power needed. Most of the aforementioned models (in particular Lanza (2006); Völschow et al (2016Völschow et al ( , 2018; Navarrete, Schleicher, Käpylä, Schober, Völschow & Mennickent (Navarrete et al)) conclude that it is impossible to produce the observed magnitude of orbital period variations with the Applegate mechanism only, except maybe for postcommon-envelope systems with companions slightly below the fully-convective mass limit m c ∼ 0.35M (Lanza 2006;Völschow et al 2018). Interestingly, these might be akin to redback companions.…”

Section: The Phase-locked Quadrupole Potentialmentioning

confidence: 99%

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A spider timing model: accounting for quadrupole deformations and relativity in close pulsar binaries

Voisin

Breton

Summers

2019

Monthly Notices of the Royal Astronomical Society

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Spider millisecond pulsars are, along with some eclipsing post-common envelope systems and cataclysmic variables, part of an expanding category of compact binaries with low-mass companions for which puzzling timing anomalies have been observed. The most prominent type of irregularities seen in them are orbital period variations, a phenomenon which has been proposed to originate from changes in the gravitational quadrupole moment of the companion star. A physically sound modelling of the timing of these systems is key to understanding their structure and evolution. In this paper we argue that a complete timing model must account for relativistic corrections as well as rotationally and tidally induced quadrupole distortions. We solve for the resulting orbital dynamics using perturbation theory and derive the corresponding timing model in the low eccentricity limit. We find that the expected strong quadrupole deformation of the companion star results in an effective minimum orbital eccentricity. It is accompanied by a fast periastron precession which, if not taken into account, averages out any measurement of the said eccentricity. We show that, with our model, detection of both eccentricity and precession is likely to be made in many if not all spider pulsar systems. Combined with optical light curves, this will allow us to measure the apsidal motion constant, connecting the quadrupole deformation to the internal structure, and thus opening a new window into probing the nature of their exotic stellar interiors. Moreover, more accurate timing may eventually lead spider pulsars to be used for high-precision timing experiments such as pulsar timing arrays.

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Section: The Phase-locked Quadrupole Potentialmentioning

confidence: 99%

Section: The Phase-locked Quadrupole Potentialmentioning

confidence: 99%

A spider timing model: accounting for quadrupole deformations and relativity in close pulsar binaries

Voisin

Breton

Summers

2019

Monthly Notices of the Royal Astronomical Society

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“…by stellar magnetic cycles as proposed in Applegate (1992) and later refined by e.g. Lanza & Rodonò (1999); Lanza (2006); Völschow et al (2018);Navarrete et al (2019). If quadrupole-moment changes are responsible for the observed orbital period variations, then it is possible to design a dynamical model of the binary that includes this contribution.…”

Section: Introductionmentioning

confidence: 96%

First measurement of the total gravitational quadrupole moment of a black widow companion

Voisin

Clark

Breton

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present the first measurement of the gravitational quadrupole moment of the companion star of a spider pulsar, namely the black widow PSR J2051−0827. To this end we have re-analysed radio timing data using a new model which is able to account for periastron precession caused by tidal and centrifugal deformations of the star as well as by general relativity. The model allows for a time-varying component of the quadrupole moment, thus self-consistently accounting for the ill-understood orbital period variations observed in these systems. Our analysis results in the first detection of orbital precession in a spider system at ω = −68.6 +0.9 −0.5 deg/yr and the most accurate determination of orbital eccentricity for PSR J2051−0827 with e = (4.2 ± 0.1) × 10 −5 . We show that the variable quadrupole component is about 100 times smaller than the average quadrupole momentQ = −2.2 +0.6 −1 × 10 41 kg m 2 . We discuss how accurate modelling of high precision optical light curves of the companion star will allow its apsidal motion constant to be derived from our results.

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“…In addition to the finite shell model, Lanza & Rodonò (2004) and Lanza (2005) presented a one-dimensional framework based on the angular momentum transport equations, using simplifying assumptions of magneto-hydrodynamical (MHD) turbulence and the mean magnetic field. We have extended this framework in Völschow et al (2018), considering in particular time-dependent hydrodynamic and magnetic fluctuations assuming a magnetic activity cycle, as well as a superposition of different modes. For typical RS Canum Venaticorum (RS CVn) systems, which are detached binaries typically composed of a chromospherically active G or K star, the expected eclipsing time variations are however two orders of magnitude lower than observed.…”

Section: Introductionmentioning

confidence: 99%

“…For typical RS Canum Venaticorum (RS CVn) systems, which are detached binaries typically composed of a chromospherically active G or K star, the expected eclipsing time variations are however two orders of magnitude lower than observed. The most promising Applegate candidates are post-common-envelope binaries with secondary masses of ∼ 0.35 M (Völschow et al 2018), as these produce more energy through nuclear burning and can thus more easily redistribute angular momentum as required by the Applegate mechanism, while simultaneously not being critically affected by the presence of a radiative core.…”

Section: Introductionmentioning

confidence: 99%

Magneto-hydrodynamical origin of eclipsing time variations in post-common-envelope binaries for solar mass secondaries

Navarrete

Schleicher

Käpylä

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Eclipsing time variations have been observed for a wide range of binary systems, including post-common-envelope binaries. A frequently proposed explanation, apart from the possibility of having a third body, is the effect of magnetic activity, which may alter the internal structure of the secondary star, particularly its quadrupole moment, and thereby cause quasi-periodic oscillations. We here present two compressible non-ideal magneto-hydrodynamical (MHD) simulations of the magnetic dynamo in a solar mass star, one of them with three times the solar rotation rate ("slow rotator"), the other one with twenty times the solar rotation rate ("rapid rotator"), to account for the high rotational velocities in close binary systems. For the slow rotator, we find that both the magnetic field and the stellar quadrupole moment change in a quasi-periodic manner, leading to O-C (observed -corrected times of the eclipse) variations of ∼ 0.635 s. For the rapid rotator, the behavior of the magnetic field as well as the quadrupole moment changes become considerably more complex, due to the less coherent dynamo solution. The resulting O-C variations are of the order 23 s.The observed system V471 Tau shows two modes of eclipsing time variations, with amplitudes of 151 s and 20 s, respectively. While our simulations do not fully explain the observations, they provide the first demonstration through 3D MHD simulations of the importance of the MHD dynamo on stellar structure.

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Physics of the Applegate mechanism: Eclipsing time variations from magnetic activity

Cited by 33 publications

References 33 publications

A spider timing model: accounting for quadrupole deformations and relativity in close pulsar binaries

A spider timing model: accounting for quadrupole deformations and relativity in close pulsar binaries

First measurement of the total gravitational quadrupole moment of a black widow companion

Magneto-hydrodynamical origin of eclipsing time variations in post-common-envelope binaries for solar mass secondaries

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