scholarly journals Time Dependence in Accretion Onto Magnetic White Dwarfs

1983 ◽  
Vol 72 ◽  
pp. 199-205
Author(s):  
Steven H. Langer ◽  
G. Chanmugam ◽  
G. Shaviv
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Orbital Period ◽  
White Dwarf ◽  
Velocity Structure ◽  
Theoretical Models ◽  
Cataclysmic Variable ◽  
X Rays ◽  
Accretion Flow ◽  
The Magnetic Field

In this talk, we consider cataclysmic variable systems containing a white dwarf with a strong magnetic field. These include systems like AM Her (see, e.g., Chiappetti, Tanzi, and Treves 1981) in which the white dwarf rotates at the orbital period and systems such as AE Aquari in which the white dwarf rotates much faster than synchronously (see Patterson et al. 1980). The magnetic field in all of these systems is strong enough to disrupt the accretion disk at a point far above the surface of the white dwarf and may prevent the formation of a disk altogether. We will present theoretical models for the temperature, density, and velocity structure of the accretion flow in the region near the surface of the white dwarf where the kinetic energy of the flow is thermalized and radiated in the form of X-rays and ultraviolet radiation. This information is required to calculate accurate model spectra, and the results also have immediate consequences for the interpretation of observations.

On the Statistics of AM Herculis Binaries

1995 ◽  
Vol 12 (2) ◽  
pp. 165-169 ◽  
Author(s):  
Kinwah Wu ◽  
Dayal T. Wickramasinghe ◽  
Jianke Li
Keyword(s):  
Magnetic Field ◽  
Orbital Period ◽  
High Field ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Cataclysmic Variable ◽  
The Difference ◽  
The Magnetic Field ◽  
Very High

AbstractThe magnetic field and orbital period distributions of AM Herculis binaries are investigated. Our study shows that (i) there is a significant lack of very-high-field magnetic white dwarfs in binaries when compared with isolated white dwarfs, and (ii) the difference between the period distributions of AM Herculis binaries and other cataclysmic variable subclasses is statistically significant. These results imply that the evolution and the birth of AM Herculis binaries are different from those of other cataclysmic variables.

scholarly journals The EUV Excess in Magnetic Cataclysmic Variables

1996 ◽  
Vol 152 ◽  
pp. 325-329
Author(s):  
John K. Warren ◽  
Koji Mukai
Keyword(s):  
Magnetic Field ◽  
Orbital Period ◽  
White Dwarf ◽  
Preliminary Analysis ◽  
Cataclysmic Variables ◽  
X Rays ◽  
System Parameters ◽  
Magnetic Capture ◽  
Magnetic Cataclysmic Variables ◽  
Capture Radius

We present preliminary analysis of EUVE pointed data of 8 magnetic cataclysmic variables. Blackbody temperatures, luminosities, and interstellar columns have been better constrained. Using these luminosities we look for correlations between the EUV excess (over optical and hard X-rays) and various system parameters. While it appears there is no correlation between the EUV excess and the system inclination and orbital period, correlations are suggested between the EUV excess and the longitude of the accretion spot, the colatitude of the accretion spot, the white dwarf magnetic field, and the magnetic capture radius.

scholarly journals The Magnetic Field of the Intermediate Polar RE 0751+14

1996 ◽  
Vol 158 ◽  
pp. 183-183
Author(s):  
H. Väth
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
Accretion Rate ◽  
Shock Structure ◽  
Light Curves ◽  
X Rays ◽  
Strong Magnetic Fields ◽  
X Ray ◽  
Spin Period ◽  
The Magnetic Field

Piirola, Hakala & Coyne (1993) modeled the optical/IR light curve of RE 0751+14 assuming a uniform shock structure and neglecting the hard X-ray emission. In this paper, we model the light curves at optical/IR and hard X-ray wavelengths and include the effects of the shock structure.We base our model on accretion onto a white dwarf with a displaced magnetic dipole for a range of likely white dwarf masses. We find that the observed intensity variations of X-rays and in the I band over one spin period largely determine the position of the emission regions. Furthermore, the observed maximum X-ray flux constrains the specific accretion rate. We deduce that the magnetic field at the pole is likely to be in the range 9 .. .21 MG, which is consistent with the estimates of Piirola et al. (1993). It had been proposed previously that there must exist asynchronous rotators with sufficiently strong magnetic fields such that the binaries will evolve into AM Her binaries (Chanmugam & Ray 1984; King, Frank & Ritter 1985). With this deduced high magnetic field RE 0751+14 is the most likely example of such a system known to date.

The Magnetic Field of 1H1752+08

1995 ◽  
Vol 12 (1) ◽  
pp. 66-70
Author(s):  
Lilia Ferrario ◽  
Dayal T. Wickramasinghe ◽  
Jeremy Bailey ◽  
David Buckley
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Line Intensity ◽  
White Dwarf ◽  
Field Structure ◽  
Cataclysmic Variable ◽  
Magnetic Field Structure ◽  
Low Field ◽  
The Mean ◽  
The Magnetic Field

AbstractWe present spectropolarimetric observations of the eclipsing cataclysmic variable 1H1752+08. Modelling of the line intensity and polarisation spectra of 1H1752+08 shows that the magnetic field structure of the white dwarf is off-centre and the mean photospheric field strength is about 7 MG, the lowest measured in a cataclysmic variable (CV). We argue that 1H1752+08 is most probably a low-field AM Herculis system.

scholarly journals Three-dimensional simulations of accretion flow in the progenitor of Tycho’s supernova

2020 ◽  
Vol 501 (1) ◽  
pp. 664-675
Author(s):  
Li Xue ◽  
Cheng-Liang Jiao ◽  
Yuan Li
Keyword(s):  
Magnetic Field ◽  
Orbital Period ◽  
Equatorial Plane ◽  
Three Dimensional ◽  
Polar Wind ◽  
Accretion Flow ◽  
Energy Equipartition ◽  
The Magnetic Field ◽  
Tycho’S Snr ◽  
Three Dimensional Simulations

ABSTRACT We run 3D numerical simulations for the accretion flow around the white dwarf (WD) in the progenitor system of Tycho’s supernova (SN). The mass of the WD, mass of the companion star, and the orbital period are set to be 1M⊙, 1.6M⊙, and 0.794 d, respectively, based on theoretical and observational researches of Tycho’s SN remnant (SNR). We find that when the magnetic field in the accreted material is negligible, outflowing wind is concentrated near the equatorial plane. When the magnetic field has energy equipartition with internal energy, polar wind is comparable with the equatorial wind. A carefully chosen magnetic field between the above two cases ($B=5.44\times 10^3 \rm {G}$) can roughly reproduce the latitude-dependent wind required to form the peculiar periphery of Tycho’s SNR. Including a reasonable amount of viscosity in the calculation does not change our conclusion.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

scholarly journals The effects of magnetic field strength on the properties of wind generated from hot accretion flow

2018 ◽  
Vol 615 ◽  
pp. A35 ◽  
Author(s):  
De-Fu Bu ◽  
Amin Mosallanezhad
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Pressure Gradient ◽  
Magnetic Field Strength ◽  
Magnetic Pressure ◽  
Gas Pressure ◽  
Accretion Flow ◽  
Accretion Flows ◽  
Black Hole Accretion ◽  
The Magnetic Field

Context. Observations indicate that wind can be generated in hot accretion flow. Wind generated from weakly magnetized accretion flow has been studied. However, the properties of wind generated from strongly magnetized hot accretion flow have not been studied. Aims. In this paper, we study the properties of wind generated from both weakly and strongly magnetized accretion flow. We focus on how the magnetic field strength affects the wind properties. Methods. We solve steady-state two-dimensional magnetohydrodynamic equations of black hole accretion in the presence of a largescale magnetic field. We assume self-similarity in radial direction. The magnetic field is assumed to be evenly symmetric with the equatorial plane. Results. We find that wind exists in both weakly and strongly magnetized accretion flows. When the magnetic field is weak (magnetic pressure is more than two orders of magnitude smaller than gas pressure), wind is driven by gas pressure gradient and centrifugal forces. When the magnetic field is strong (magnetic pressure is slightly smaller than gas pressure), wind is driven by gas pressure gradient and magnetic pressure gradient forces. The power of wind in the strongly magnetized case is just slightly larger than that in the weakly magnetized case. The power of wind lies in a range PW ~ 10−4–10−3 Ṁinc2, with Ṁin and c being mass inflow rate and speed of light, respectively. The possible role of wind in active galactic nuclei feedback is briefly discussed.

scholarly journals The Intermediate Polars

1983 ◽  
Vol 72 ◽  
pp. 155-172
Author(s):  
Brian Warner
Keyword(s):  
Magnetic Fields ◽  
White Dwarf ◽  
Variable Star ◽  
Theoretical Models ◽  
Cataclysmic Variable ◽  
General Role ◽  
X Ray ◽  
Low Mass ◽  
Intermediate Polars ◽  
X Ray Binaries

Until 1976, cataclysmic variable star research proceeded with few requirements for the inclusion of magnetic fields in theoretical models. Although models for low-mass X-ray binaries stressed the importance of magnetic fields (Lamb et at. 1973) and there was an increasing number of known magnetic single white dwarfs (Angel 1977), and a magnetised white dwarf had been one of the models proposed to explain the rapid oscillations in DQ Her (Herbst et al. 1974, Katz 1975), there was no anticipation of the more general role that magnetic fields now seem destined to play. The two major reviews of the time (Robinson 1976, Warner 1976) scarcely considered the presence of magnetic fields.

scholarly journals The Chandrasekhar Mass of A Gravitating Electron Crystal

1994 ◽  
Vol 147 ◽  
pp. 565-570
Author(s):  
D. Engelhardt ◽  
I. Bues
Keyword(s):  
Magnetic Field ◽  
Density Matrix ◽  
White Dwarf ◽  
Matrix Formalism ◽  
Plasma Zone ◽  
Isothermal Model ◽  
Fermi Function ◽  
Density Matrix Formalism ◽  
The Magnetic Field ◽  
Electron Crystal

AbstractThe internal structure of a white dwarf may be changed by a strong magnetic field. A local model of the electrons is constructed within a thermal density matrix formalism, essentially a Heisenberg magnetism model. This results in a matrix Fermi function which is used to construct an isothermal model of the electron crystal. The central density of the crystal is 108kg/m3 independent of the magnetic field within the plasma and therefore lower than the relativistic density, whereas this density is constant until the Fermi momentum x f = 0.3 * me * c. Chandrasekhar masses up to 1.44 * 1.4M0 are possible for polarizations of the plasma zone lower than 0.5, if the temperature is close to the Curie point, whereas the crystal itself destabilizes the white dwarf dependent on temperature.

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