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

Abstract 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. Here we 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 ∼0.025 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 0.13 s. The observed system V471 Tau shows two modes of eclipsing time variations, with amplitudes of 151 s and 20 s, respectively. However, the current simulations may not capture all relevant effects due to the neglect of the centrifugal force and self-gravity. Considering the model limitations and that the rotation of V471 Tau is still a factor of 2.5 faster than our rapid rotator, it may be conceivable to reach the observed magnitudes.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833506 ◽

2018 ◽

Vol 620 ◽

pp. A42 ◽

Cited By ~ 8

Author(s):

M. Völschow ◽

D. R. G. Schleicher ◽

R. Banerjee ◽

J. H. M. M. Schmitt

Keyword(s):

Binary Systems ◽

Theoretical Work ◽

Magnetic Activity ◽

Close Binary ◽

Magnetic Fluctuations ◽

Common Envelope ◽

Stellar Parameter ◽

Low Mass ◽

Time Variations ◽

Binary Separations

Since its proposal in 1992, the Applegate mechanism has been discussed as a potential intrinsical mechanism to explain transit-timing variations in various types of close binary systems. Most analytical arguments presented so far focused on the energetic feasibility of the mechanism while applying rather crude one- or two-zone prescriptions to describe the exchange of angular momentum within the star. In this paper, we present the most detailed approach to date to describe the physics giving rise to the modulation period from kinetic and magnetic fluctuations. Assuming moderate levels of stellar parameter fluctuations, we find that the resulting binary period variations are one or two orders of magnitude lower than the observed values in RS-CVn like systems, supporting the conclusion of existing theoretical work that the Applegate mechanism may not suffice to produce the observed variations in these systems. The most promising Applegate candidates are low-mass post-common-envelope binaries with binary separations ≲1 R⊙ and secondary masses in the range of 0.30 M⊙ and 0.36 M⊙.

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Stochastic proton heating by kinetic-Alfvén-wave turbulence in moderately high- plasmas

Journal of Plasma Physics ◽

10.1017/s0022377818001277 ◽

2018 ◽

Vol 84 (6) ◽

Cited By ~ 10

Author(s):

Ian W. Hoppock ◽

Benjamin D. G. Chandran ◽

Kristopher G. Klein ◽

Alfred Mallet ◽

Daniel Verscharen

Keyword(s):

Magnetic Field ◽

Heating Rate ◽

Electrostatic Potential ◽

Alfven Wave ◽

Average Magnetic Moment ◽

Kinetic Alfvén Wave ◽

Stochastic Heating ◽

Kinetic Alfven Wave ◽

Time Variations ◽

The Magnetic Field

Stochastic heating refers to an increase in the average magnetic moment of charged particles interacting with electromagnetic fluctuations whose frequencies are smaller than the particles’ cyclotron frequencies. This type of heating arises when the amplitude of the gyroscale fluctuations exceeds a certain threshold, causing particle orbits in the plane perpendicular to the magnetic field to become stochastic rather than nearly periodic. We consider the stochastic heating of protons by Alfvén-wave (AW) and kinetic-Alfvén-wave (KAW) turbulence, which may make an important contribution to the heating of the solar wind. Using phenomenological arguments, we derive the stochastic-proton-heating rate in plasmas in which $\unicode[STIX]{x1D6FD}_{\text{p}}\sim 1$–30, where $\unicode[STIX]{x1D6FD}_{\text{p}}$ is the ratio of the proton pressure to the magnetic pressure. (We do not consider the $\unicode[STIX]{x1D6FD}_{\text{p}}\gtrsim 30$ regime, in which KAWs at the proton gyroscale become non-propagating.) We test our formula for the stochastic-heating rate by numerically tracking test-particle protons interacting with a spectrum of randomly phased AWs and KAWs. Previous studies have demonstrated that at $\unicode[STIX]{x1D6FD}_{\text{p}}\lesssim 1$, particles are energized primarily by time variations in the electrostatic potential and thermal-proton gyro-orbits are stochasticized primarily by gyroscale fluctuations in the electrostatic potential. In contrast, at $\unicode[STIX]{x1D6FD}_{\text{p}}\gtrsim 1$, particles are energized primarily by the solenoidal component of the electric field and thermal-proton gyro-orbits are stochasticized primarily by gyroscale fluctuations in the magnetic field.

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CLOSE BINARY PROGENITORS OF HYPERNOVAE

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512004618 ◽

2012 ◽

Vol 08 ◽

pp. 209-219 ◽

Cited By ~ 2

Author(s):

MAXIM V. BARKOV

Keyword(s):

Magnetic Field ◽

Black Hole ◽

Neutron Star ◽

Binary Systems ◽

Close Binary ◽

Transient Event ◽

Common Envelope ◽

Starting Point ◽

The Common ◽

Rayet Star

In this paper we propose a new plausible mechanism of supernova explosions specific to close binary systems. The starting point is the common envelope phase in the evolution of a binary consisting of a red super giant and a neutron star. As the neutron star spirals towards the center of its companion it spins up via disk accretion. Depending on the specific angular momentum of gas captured by the neutron star via the Bondi-Hoyle mechanism, it may reach millisecond periods either when it is still inside the common envelope or after it has merged with the companion core. The high accretion rate may result in strong differential rotation of the neutron star and generation of a magnetar-strength magnetic field. The magnetar wind can blow away the common envelope if its magnetic field is as strong as 1015 G, and can destroy the entire companion if it is as strong as 1016 G. The total explosion energy can be comparable to the rotational energy of a millisecond pulsar and reach 1052 erg. The result is an unusual type-II supernova with very high luminosity during the plateau phase, followed by a sharp drop in brightness and a steep light-curve tail. The remnant is either a solitary magnetar or a close binary involving a Wolf-Rayet star and a magnetar. When this Wolf-Rayet star explodes this will be a third supernovae explosion in the same binary. A particularly interesting version of the binary progenitor involves merger of a red super giant star with an ultra-compact companion, neutron star or black hole. In the case if a strong magnetic field is not generated on the surface of a neutron star then it will collapse to a black hole. After that we expect the formation of a very long-lived accretion disk around the black hole. The Blandford-Znajek driven jet from this black hole may drive not only hypernovae explosion but produce a bright X-ray transient event on a time scale of 104 s.

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Magnetic geometries of Sun-like stars: exploring the mass-rotation plane

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031068 ◽

2008 ◽

Vol 4 (S259) ◽

pp. 441-442

Author(s):

Pascal Petit ◽

B. Dintrans ◽

M. Aurière ◽

C. Catala ◽

J.-F. Donati ◽

...

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Solar Rotation ◽

Physical Parameters ◽

Solar Mass ◽

Rotation Rates ◽

Large Scale Magnetic Field ◽

First Results ◽

Field Geometry ◽

Rotation Plane

AbstractSun-like stars are able to continuously generate a large-scale magnetic field through the action of a dynamo. Various physical parameters of the star are able to affect the dynamo output, in particular the rotation and mass. Using the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France), it is now possible to measure the large-scale magnetic field of solar analogues (i.e. stars very close to the Sun in the mass-rotation plane, including strict solar twins). From spectropolarimetric time-series, tomographic inversion enables one to reconstruct the field geometry and its progressive distortion under the effect of surface differential rotation. We show the first results obtained on a sample of main-sequence dwarfs, probing masses between 0.7 and 1.4 solar mass and rotation rates between 1 and 3 solar rotation rate.

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Temporal evolution of short-lived penumbral microjets

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038370 ◽

2020 ◽

Vol 642 ◽

pp. A128

Author(s):

A. L. Siu-Tapia ◽

L. R. Bellot Rubio ◽

D. Orozco Suárez ◽

R. Gafeira

Keyword(s):

Magnetic Field ◽

Temporal Evolution ◽

Spectral Characteristics ◽

Field Approximation ◽

Weak Field ◽

Field Vector ◽

Magnetic Field Vector ◽

Maximum Brightness ◽

Time Variations ◽

The Magnetic Field

Context. Penumbral microjets (PMJs) is the name given to elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes, and their origin is presumed to be related to magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere. Methods. We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. By separating the Ca II 854.2 nm line into two different wavelength domains to account for the chromospheric origin of the line core and the photospheric contribution to the wings, we infer the height variation of the magnetic field vector. Results. The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25% of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs. Conclusions. The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs.

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Comparing extrapolations of the coronal magnetic field structure at 2.5R⊙with multi-viewpoint coronagraphic observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834125 ◽

2019 ◽

Vol 627 ◽

pp. A9 ◽

Cited By ~ 1

Author(s):

C. Sasso ◽

R. F. Pinto ◽

V. Andretta ◽

R. A. Howard ◽

A. Vourlidas ◽

...

Keyword(s):

Magnetic Field ◽

Solar Corona ◽

Large Scale ◽

Solar Rotation ◽

Coronal Holes ◽

Coronal Magnetic Field ◽

Central Meridian ◽

Fast Method ◽

The Many ◽

The Magnetic Field

The magnetic field shapes the structure of the solar corona, but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (such as streamers, plumes, and coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify whether this comparison can be a fast method to systematically determine the reliability of the many methods that are available for modeling the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements that are typically obtained in a region close to the central meridian on the solar disk and are then compared with coronagraphic images at the limbs, acquired at least seven days before or after to account for solar rotation. This implicitly assumes that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that observe the Sun from different viewing angles to build Carrington maps that cover the entire corona to reduce the effect of temporal evolution to about five days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to distinguish between different magnetic field extrapolations.

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Zooming in on the Formation of Protoplanetary Disks

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313008107 ◽

2013 ◽

Vol 8 (S299) ◽

pp. 131-135 ◽

Cited By ~ 3

Author(s):

Åke Nordlund ◽

Troels Haugbølle ◽

Michael Küffmeier ◽

Paolo Padoan ◽

Aris Vasileiades

Keyword(s):

Magnetic Field ◽

Energy Efficient ◽

Adaptive Mesh Refinement ◽

Accretion Rate ◽

Magnetic Energy ◽

Protoplanetary Disks ◽

Adaptive Mesh ◽

Gravitational Energy ◽

Solar Mass ◽

The Magnetic Field

AbstractWe use the adaptive mesh refinement code RAMSES to model the formation of protoplanetary disks in realistic star formation environments. The resolution scales over up to 29 powers of two (~ 9 orders of magnitude) covering a range from outer scales of 40 pc to inner scales of 0.015 AU. The accretion rate from a 1.5 solar mass envelope peaks near 10−4 M⊙ about 6 kyr after sink particle formation and then decays approximately exponentially, reaching 10−6 M⊙ in 100 kyr. The models suggest universal scalings of physical properties with radius during the main accretion phase, with kinetic and / or magnetic energy in approximate balance with gravitational energy. Efficient accretion is made possible by the braking action of the magnetic field, which nevertheless allows a near-Keplerian disk to grow to a 100 AU size. The magnetic field strength ranges from more than 10 G at 0.1 AU to less than 1 mG at 100 AU, and drives a time dependent bipolar outflow, with a collimated jet and a broader disk wind.

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Magnetic field vector ambiguity resolution in a quiescent prominence observed on two consecutive days

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935488 ◽

2019 ◽

Vol 629 ◽

pp. A138 ◽

Cited By ~ 1

Author(s):

T. Kalewicz ◽

V. Bommier

Keyword(s):

Magnetic Field ◽

Solar Rotation ◽

Field Vector ◽

Magnetic Field Vector ◽

Stokes Parameters ◽

Absolute Value ◽

The Past ◽

Tenerife Island ◽

The Magnetic Field ◽

European Site

Context. Magnetic field vector measurements are always ambiguous, that is, two or more field vectors are solutions of the observed polarisation. Aims. The aim of the present paper is to solve the ambiguity by comparing the ambiguous field vectors obtained in the same prominence observed on two consecutive days. The effect of the solar rotation is to modify the scattering angle of the prominence radiation, which modifies the symmetry of the ambiguous solutions. This method, which is a kind of tomography, was successfully applied in the past to the average magnetic field vector of 20 prominences observed at the Pic du Midi. The aim of the present paper is to apply this method to a prominence observed with spatial resolution at the THÉMIS telescope (European site at Izaña, Tenerife Island). Methods. The magnetic field vector is measured by interpretation of the Hanle effect observed in the He I D3 5875.6 Å line, within the horizontal field vector hypothesis for simplicity. The ambiguity is first solved by comparing the two pairs of solutions obtained for a “big pixel” determined by averaging the observed Stokes parameters in a large region at the prominence centre. Each pixel is then disambiguated by selecting the closest solution in a propagation from the prominence centre to the prominence boundary. Results. The results previously obtained on averaged prominences are all recovered. The polarity is found to be inverse with a small angle of about −21° between the magnetic field vector and the long axis of the filament. The magnetic field strength of about 6 G is found to slightly increase with height, as previously observed. The new result is the observed decrease with height, of the absolute value of the angle between the magnetic field vector and the long axis of the filament. Conclusions. This result is in excellent agreement with prominence magnetohydrodynamical models.

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On the weak magnetic field of millisecond pulsars: does it decay before accretion?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2701 ◽

2019 ◽

Vol 490 (2) ◽

pp. 2013-2022 ◽

Cited By ~ 3

Author(s):

Marilyn Cruces ◽

Andreas Reisenegger ◽

Thomas M Tauris

Keyword(s):

Magnetic Field ◽

White Dwarf ◽

Binary Systems ◽

Alternative Hypothesis ◽

General Distribution ◽

Ohmic Dissipation ◽

Millisecond Pulsars ◽

Standard Scenario ◽

Field Decay ◽

The Magnetic Field

ABSTRACT Millisecond pulsars (MSPs) are old, fast spinning neutron stars (NSs) thought to have evolved from classical pulsars in binary systems, where the rapid rotation is caused by the accretion of matter and angular momentum from their companion. During this transition between classical and MSPs, there is a magnetic field reduction of ∼4 orders of magnitude, which is not well understood. According to the standard scenario, the magnetic field is reduced as a consequence of accretion, either through ohmic dissipation or through screening by the accreted matter. We explored an alternative hypothesis in which the magnetic field is reduced through ambipolar diffusion before the accretion. This is particularly effective during the long epoch in which the pulsar has cooled, but has not yet started accreting. This makes the final magnetic field dependent on the evolution time of the companion star and thus its initial mass. We use observed binary systems to constrain the time available for the magnetic field decay based on the current pulsar companion: a helium white dwarf, a carbon–oxygen white dwarf, or another NS. Based on a simplified model without baryon pairing, we show that the proposed process agrees with the general distribution of observed magnetic field strengths in binaries, but is not able to explain some mildly recycled pulsars where no significant decay appears to have occurred. We discuss the possibility of other formation channels for these systems and the conditions under which the magnetic field evolution would be set by the NS crust rather than the core.

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The Remarkable Rotational Braking of G5 Giants

Symposium - International Astronomical Union ◽

10.1017/s0074180900030138 ◽

1983 ◽

Vol 102 ◽

pp. 461-466

Author(s):

David F. Gray

Keyword(s):

Magnetic Field ◽

Main Sequence ◽

Driving Forces ◽

Stellar Winds ◽

Main Sequence Stars ◽

Dynamo Mechanism ◽

Slow Progress ◽

Time Variations ◽

The Magnetic Field ◽

Stellar Dynamo

The strong rotational braking seen in the G5 III stage of evolution may be the key to understanding how stellar dynamos work.We are all familiar with the leisurely spin-down seen in cool main-sequence stars like our Sun. The time scales here are ∼ 109 years and the accepted cause is the loss of high angular momentum mass in the form of stellar winds interacting with the stellar magnetic field. The magnetic field is believed to result from the interaction of envelope convection with the rotation of the star through a dynamo mechanism. Our understanding of how a dynamo actually operates, how that operation depends on the driving forces of rotation and convection, what kind of stochastic and secular time variations are to be expected, remains fragmentary even though many inventive minds have contributed. One reason for slow progress is simply that the Sun is almost the only example of a stellar dynamo we have had. But nature has given us another, much more powerful dynamo in the G5 giants, it just took us a little longer to discover it.

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