scholarly journals Properties of white dwarf in the binary system AR Scorpii and its observed features

2021 ◽  
Vol 36 (13) ◽  
pp. 2150096
Author(s):  
K. K. Singh ◽  
P. J. Meintjes ◽  
K. K. Yadav
Keyword(s):  
Magnetic Field ◽  
Binary System ◽  
White Dwarf ◽  
Main Sequence ◽  
Thermal Emission ◽  
Beat Frequency ◽  
Milky Way Galaxy ◽  
Surface Magnetic Field ◽  
Cool Star ◽  
Wave Emission

The binary system AR Scorpii hosts an M-type main sequence cool star orbiting around a magnetic white dwarf in the Milky Way Galaxy. The broadband non-thermal emission over radio, optical and X-ray wavebands observed from AR Scorpii indicates strong modulations on the spin frequency of the white dwarf as well as the spin-orbit beat frequency of the system. Therefore, AR Scorpii is also referred to as a white dwarf pulsar wherein a fast spinning white dwarf star plays very crucial role in the broadband non-thermal emission. Several interpretations for the observed features of AR Scorpii appear in the literature without firm conclusions. In this paper, we investigate connection between some of the important physical properties like spin-down power, surface magnetic field, equation of state, temperature and gravity associated with the white dwarf in the binary system AR Scorpii and its observational characteristics. We explore the plausible effects of white dwarf surface magnetic field on the absence of substantial accretion in this binary system and also discuss the gravitational wave emission due to magnetic deformation mechanism.

scholarly journals A new weak-field magnetic DA white dwarf in the local 20 pc volume

2019 ◽  
Vol 628 ◽  
pp. A1 ◽  
Author(s):  
J. D. Landstreet ◽  
S. Bagnulo
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Field Component ◽  
Main Sequence ◽  
Mean Field ◽  
Weak Field ◽  
Line Of Sight ◽  
Limited Sample ◽  
Field Decay ◽  
The Magnetic Field

We report the discovery of a new magnetic DA white dwarf (WD), WD 0011 − 721, which is located within the very important 20 pc volume-limited sample of the closest WDs to the Sun. This star has a mean field modulus ⟨|B|⟩ of 343 kG, and from the polarisation signal we deduce a line-of-sight field component of 75 kG. The magnetic field is sufficiently weak to have escaped detection in classification spectra. We then present a preliminary exploration of the data concerning the frequency of such fields among WDs with hydrogen-rich atmospheres (DA stars). We find that 20 ± 5% of the DA WDs in this volume have magnetic fields, mostly weaker than 1 MG. Unlike the slow field decay found among the magnetic Bp stars of the upper main sequence, the WDs in this sample show no evidence of magnetic field or flux changes over several Gyr.

scholarly journals Close binary evolution

2017 ◽  
Vol 609 ◽  
pp. A3 ◽  
Author(s):  
H. F. Song ◽  
G. Meynet ◽  
A. Maeder ◽  
S. Ekström ◽  
P. Eggenberger ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Binary System ◽  
Magnetic Fields ◽  
Close Binary System ◽  
Momentum Transport ◽  
Close Binary ◽  
Surface Magnetic Field ◽  
Angular Momentum Transport ◽  
Magnetic Braking

Context. Massive stars with solar metallicity lose important amounts of rotational angular momentum through their winds. When a magnetic field is present at the surface of a star, efficient angular momentum losses can still be achieved even when the mass-loss rate is very modest, at lower metallicities, or for lower-initial-mass stars. In a close binary system, the effect of wind magnetic braking also interacts with the influence of tides, resulting in a complex evolution of rotation. Aims. We study the interactions between the process of wind magnetic braking and tides in close binary systems. Methods. We discuss the evolution of a 10 M⊙ star in a close binary system with a 7 M⊙ companion using the Geneva stellar evolution code. The initial orbital period is 1.2 days. The 10 M⊙ star has a surface magnetic field of 1 kG. Various initial rotations are considered. We use two different approaches for the internal angular momentum transport. In one of them, angular momentum is transported by shear and meridional currents. In the other, a strong internal magnetic field imposes nearly perfect solid-body rotation. The evolution of the primary is computed until the first mass-transfer episode occurs. The cases of different values for the magnetic fields and for various orbital periods and mass ratios are briefly discussed. Results. We show that, independently of the initial rotation rate of the primary and the efficiency of the internal angular momentum transport, the surface rotation of the primary will converge, in a time that is short with respect to the main-sequence lifetime, towards a slowly evolving velocity that is different from the synchronization velocity. This “equilibrium angular velocity” is always inferior to the angular orbital velocity. In a given close binary system at this equilibrium stage, the difference between the spin and the orbital angular velocities becomes larger when the mass losses and/or the surface magnetic field increase. The treatment of the internal angular momentum transport has a strong impact on the evolutionary tracks in the Hertzsprung-Russell Diagram as well as on the changes of the surface abundances resulting from rotational mixing. Our modelling suggests that the presence of an undetected close companion might explain rapidly rotating stars with strong surface magnetic fields, having ages well above the magnetic braking timescale. Our models predict that the rotation of most stars of this type increases as a function of time, except for a first initial phase in spin-down systems. The measure of their surface abundances, together, when possible, with their mass-luminosity ratio, provide interesting constraints on the transport efficiencies of angular momentum and chemical species. Conclusions. Close binaries, when studied at phases predating any mass transfer, are key objects to probe the physics of rotation and magnetic fields in stars.

scholarly journals Magnetars and white dwarf pulsars

2016 ◽  
Vol 25 (09) ◽  
pp. 1641025 ◽  
Author(s):  
Ronaldo V. Lobato ◽  
Manuel Malheiro ◽  
Jaziel G. Coelho
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Neutron Stars ◽  
White Dwarf ◽  
Alternative Model ◽  
Gamma Ray ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Rotation Periods ◽  
Strong Surface

The anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are a class of pulsars understood as neutron stars (NSs) with super strong surface magnetic fields, namely [Formula: see text][Formula: see text]G, and for that reason are known as magnetars. However, in the last years, some SGRs/AXPs with low surface magnetic fields [Formula: see text]–[Formula: see text][Formula: see text]G have been detected, challenging the magnetar description. Moreover, some fast and very magnetic white dwarfs (WDs) have also been observed, and at least one showed X-ray energy emission as an ordinary pulsar. Following this fact, an alternative model based on WDs pulsars has been proposed to explain this special class of pulsars. In this model, AXPs and SGRs as dense and magnetized WDs can have surface magnetic field [Formula: see text]–[Formula: see text] G and rotate very fast with frequencies [Formula: see text][Formula: see text]rad/s, consistent with the observed rotation periods [Formula: see text]–12)[Formula: see text]s.

scholarly journals SIMILARITIES OF SGRs WITH LOW MAGNETIC FIELD AND WHITE DWARF PULSARS

2012 ◽  
Vol 18 ◽  
pp. 96-100 ◽  
Author(s):  
J. G. COELHO ◽  
M. MALHEIRO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Dwarf ◽  
Alternative Explanation ◽  
Gamma Ray ◽  
Strong Magnetic Fields ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Astrophysical Objects ◽  
Low Magnetic Field

Some of the most interesting types of astrophysical objects that have been intensively studied in the recent years are the Anomalous X-ray Pulsars (AXPs) and Soft Gamma-ray Repeaters (SGRs) seen usually as neutron stars pulsars with super strong magnetic fields. However, in the last two years two SGRs with low magnetic fields have been detected. Moreover, fast and very magnetic white dwarf pulsars have also been observed in the last years. Based on these new pulsar discoveries, white dwarf pulsars have been proposed as an alternative explanation to the observational features of SGRs and AXPs. Here we present several properties of these SGRs/AXPs as WD pulsar, in particular the surface magnetic field and the magnetic dipole momentum.

scholarly journals Cyclotron Emission from the Shock-Heated Region of AM Herculis

1979 ◽  
Vol 53 ◽  
pp. 341-342 ◽  
Author(s):  
G. Chanmugam
Keyword(s):  
Magnetic Field ◽  
Strong Magnetic Field ◽  
White Dwarf ◽  
Main Sequence ◽  
X Rays ◽  
Heated Region ◽  
Magnetic Pole ◽  
Uv Emission ◽  
Cyclotron Emission

There has been considerable interest recently in the AM Herculis binaries, which are believed to contain a strongly magnetic white dwarf accreting matter from a lower-main-sequence companion (Tapia 1977, Chanmugam and Wagner 1977, Stockman et al. 1977). Models for these systems feature an accretion column above a magnetic pole of the white dwarf. A shock-heated region, with a temperature kT ≈ 20 keV (Raymond et al. 1979) and a height h – 106cm (Masters 1978), believed to be formed in AM Her just above the magnetic pole is likely to be responsible for the emission of the hard X-rays observed (Swank et al. 1977). It has been further suggested that this region should emit optically thick cyclotron emission in the ultraviolet because of the presence of the strong magnetic field ~ 108 gauss (Masters 1978, Lamb and Masters 1979). Such UV emission has not been observed (Raymond et al. 1979).

scholarly journals Abundance and Magnetic Field Geometries of Helium-Strong and Helium-Weak Stars

1988 ◽  
Vol 132 ◽  
pp. 309-312
Author(s):  
David A. Bohlender ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Hot Stars ◽  
Surface Magnetic Field ◽  
Peculiar Stars ◽  
Ap Stars

The helium-weak and helium-strong stars are main sequence stars with anomalously weak and strong helium lines for their spectral types respectively. Many members of the two classes have strong, globally ordered magnetic fields (Thompson and Landstreet 1985; Bohlender et al. 1987) and are currently thought to represent high temperature extensions of the Ap stars. In collaboration with C. T. Bolton (U. of Toronto), we have obtained high S/N phase resolved spectra of several stars using the coudé reticon detector at CFHT. One of the principle goals of this work is to determine abundance and surface magnetic field geometries of several helium peculiar stars with large, well-determined effective fields. We employ a line synthesis program (Landstreet 1987) that incorporates the effects of surface magnetic fields and non-uniform abundances on the observed line profiles of a star. Since these stars are rapid rotators the surface magnetic field strength must be inferred from differential magnetic intensification of lines with different magnetic sensitivities. Of the few lines with suitable strengths in these hot stars we have decided that the Si III multiplet 2 lines are best suited for this aspect of our investigation. We have also modelled the unblended He I line λ4437, ignoring magnetic effects for the time being. Individual results are discussed below.

scholarly journals NGC 6611 601: A hot pre-main sequence spectroscopic binary containing a centrifugal magnetosphere host star

2021 ◽  
Author(s):  
M E Shultz ◽  
E Alecian ◽  
V Petit ◽  
S Bagnulo ◽  
T Böhm ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Magnetic Star ◽  
Be Stars ◽  
Strong Emission ◽  
Surface Magnetic Field ◽  
Spectroscopic Binary ◽  
Be Star ◽  
Hα Emission ◽  
Strong Surface

Abstract W 601 (NGC 6611 601) is one of the handful of known magnetic Herbig Ae/Be stars. We report the analysis of a large dataset of high-resolution spectropolarimetry. The star is a previously unreported spectroscopic binary, consisting of 2 B2 stars with a mass ratio of 1.8, masses of 12 M⊙ and 6.2 M⊙, in an eccentric 110-day orbit. The magnetic field belongs to the secondary, W 601 B. The Hα emission is consistent with an origin in W 601 B’s centrifugal magnetosphere; the star is therefore not a classical Herbig Be star in the sense that its emission is not formed in an accretion disk. However, the low value of log g = 3.8 determined via spectroscopic analysis, and the star’s membership in the young NGC 6611 cluster, are most consistent with it being on the pre-main sequence. The rotational period inferred from the variability of the Hα line and the longitudinal magnetic field 〈Bz〉 is 1.13 d. Modelling of Stokes V and 〈Bz〉 indicates a surface dipolar magnetic field Bd between 6 and 11 kG. With its strong emission, rapid rotation, and strong surface magnetic field, W 601 B is likely a precursor to Hα-bright magnetic B-type stars such as σ Ori E. By contrast, the primary is an apparently non-magnetic (Bd < 300 G) pre-main sequence early B-type star. In accordance with expectations from magnetic braking, the non-magnetic primary is apparently more rapidly rotating than the magnetic star.

scholarly journals Magnetic field in a young circumbinary disk

2018 ◽  
Vol 616 ◽  
pp. A56 ◽  
Author(s):  
F. O. Alves ◽  
J. M. Girart ◽  
M. Padovani ◽  
D. Galli ◽  
G. A. P. Franco ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Binary System ◽  
Thermal Emission ◽  
The Other ◽  
Toroidal Magnetic Field ◽  
Continuum Emission ◽  
Disk Model ◽  
Radiation Fields ◽  
Other Hand ◽  
The Magnetic Field

Context. Polarized continuum emission at millimeter-to-submillimeter wavelengths is usually attributed to thermal emission from dust grains aligned through radiative torques with the magnetic field. However, recent theoretical work has shown that under specific conditions polarization may arise from self-scattering of thermal emission and by radiation fields from a nearby stellar object. Aims. We use multi-frequency polarization observations of a circumbinary disk to investigate how the polarization properties change at distinct frequency bands. Our goal is to discern the main mechanism responsible for the polarization through comparison between our observations and model predictions for each of the proposed mechanisms. Methods. We used the Atacama Large Millimeter/submillimeter Array to perform full polarization observations at 97.5 GHz (Band 3), 233 GHz (Band 6) and 343.5 GHz (Band 7). The ALMA data have a mean spatial resolution of 28 AU. The target is the Class I object BHB07-11, which is the youngest object in the Barnard 59 protocluster. Complementary Karl G. Jansky Very Large Array observations at 34.5 GHz were also performed and revealed a binary system at centimetric continuum emission within the disk. Results. We detect an extended and structured polarization pattern that is remarkably consistent between the three bands. The distribution of polarized intensity resembles a horseshoe shape with polarization angles following this morphology. From the spectral index between Bands 3 and 7, we derived a dust opacity index β ~ 1 consistent with maximum grain sizes larger than expected to produce self-scattering polarization in each band. The polarization morphology and the polarization levels do not match predictions from self-scattering. On the other hand, marginal correspondence is seen between our maps and predictions from a radiation field model assuming the brightest binary component as main radiation source. Previous molecular line data from BHB07-11 indicates disk rotation. We used the DustPol module of the ARTIST radiative transfer tool to produce synthetic polarization maps from a rotating magnetized disk model assuming combined poloidal and toroidal magnetic field components. The magnetic field vectors (i.e., the polarization vectors rotated by 90°) are better represented by a model with poloidal magnetic field strength about three times the toroidal one. Conclusions. The similarity of our polarization patterns among the three bands provides a strong evidence against self-scattering and radiation fields. On the other hand, our data are reasonably well reproduced by a model of disk with toroidal magnetic field components slightly smaller than poloidal ones. The residual is likely to be due to the internal twisting of the magnetic field due to the binary system dynamics, which is not considered in our model.

scholarly journals Secondary Components of Binary Pulsars & Magnetic Field Decay in Neutron Stars

1987 ◽  
Vol 125 ◽  
pp. 407-407
Author(s):  
Shrinivas R. Kulkarni
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Field Strength ◽  
Neutron Stars ◽  
White Dwarf ◽  
Optical Counterpart ◽  
Surface Magnetic Field ◽  
Binary Pulsars ◽  
Field Decay

We report the discovery of white dwarf secondaries in 0655+64 and 0820+02 systems. In the 2303+46 system, we do not find any optical counterpart suggesting that the companion is another neutron star. The existence of a cool and therefore old white dwarf in the 0655+64 system implies that the surface magnetic field of neutron stars stops decaying beyond some value(s) of field strength.

scholarly journals Discovery of a Sirius-like binary system with a very strongly magnetic white dwarf

2020 ◽  
Vol 634 ◽  
pp. L10 ◽  
Author(s):  
John D. Landstreet ◽  
Stefano Bagnulo
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
White Dwarfs ◽  
Optical Spectrum ◽  
Binary Systems ◽  
Main Sequence ◽  
High Mass ◽  
Wide Binary ◽  
Linear Polarisation ◽  
The Continuum

Non-interacting binary systems containing a magnetic white dwarf and a main-sequence star are considered extremely rare, perhaps non-existent. In the course of a search of magnetic fields in high-mass white dwarfs we have discovered a Sirius-like wide binary system composed of a main-sequence G0 star and an M ∼ 1.1 M⊙ white dwarf with a huge (hundreds of MG) magnetic field. This star, WDS J03038+0608B, shows a circular polarisation amplitude of 5% in the continuum, with no evidence of variability on a 1 d timescale, little or no linear polarisation in the blue part of the spectrum, and about 2% linear polarisation in the red part of the optical spectrum. A search in the literature reveals the existence of four more binary systems that include a magnetic white dwarf and a non-degenerate companion; three such systems passed unremarked in previous studies. We estimate that up to a few percent of magnetic white dwarfs may be found to occur in wide binary pairs. However, at least four of the five known binary systems with a magnetic white dwarf are too widely separated to be expected to evolve into systems experiencing Roche-lobe overflow, and cannot be considered as progenitors of magnetic cataclysmic variable (AM Her and DQ Her) systems.

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