scholarly journals Comparisons of MHD propeller model with observations of cataclysmic variable AE Aqr

2019 ◽  
Vol 487 (2) ◽  
pp. 1754-1763 ◽  
Author(s):  
A A Blinova ◽  
M M Romanova ◽  
G V Ustyugova ◽  
A V Koldoba ◽  
R V E Lovelace
Keyword(s):  
Magnetic Field ◽  
Time Scale ◽  
Accretion Rate ◽  
Light Curves ◽  
Short Time Scale ◽  
Mhd Simulations ◽  
Representative Model ◽  
Polar Type ◽  
Short Time ◽  
The Magnetic Field

ABSTRACT We have developed a numerical magnetohydrodynamic (MHD) model of the propeller candidate star AE Aqr using axisymmetric MHD simulations. We suggest that AE Aqr is an intermediate polar-type star, where the magnetic field is relatively weak and an accretion disc may form around the white dwarf. The star is in the propeller regime, and many of its observational properties are determined by the disc–magnetosphere interaction. Comparisons of the characteristics of the observed versus modelled AE Aqr star show that the model can explain many observational properties of AE Aqr. In a representative model, the magnetic field of the star is B ≈ 3.3 × 105 G and the time-averaged accretion rate in the disc is 5.5 × 1016 g s−1. Most of this matter is ejected into conically shaped winds. The numerical model explains the rapid spin-down of AE Aqr through the outflow of angular momentum from the surface of the star to the wind, corona, and disc. The energy budget in the outflows, 9 × 1033 erg s−1, is sufficient for explaining the observed flaring radiation in different wavebands. The time-scale of ejections into the wind matches the short time-scale variability in the light curves of AE Aqr.

scholarly journals Observations of the Two-Level Structure of Sunspot Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 231-234
Author(s):  
H. I. Abdussamatov
Keyword(s):  
Magnetic Field ◽  
Fine Structure ◽  
Level Structure ◽  
Field Structure ◽  
Short Time Scale ◽  
Sunspot Umbra ◽  
Magnetic Field Structure ◽  
Spectroscopic Information ◽  
Short Time ◽  
The Magnetic Field

Inhomogeneity of magnetic field structure, ‘granulation’ in sunspot umbrae and fine structure of the Evershed motions lead to the conclusion that the sunspot umbra is composed of magnetic ropes (or plaits) with dimensions near the limit of resolution. Progress in the study of these ropes is closely connected with the possibility of obtaining extensive spectroscopic information about some selected regions on the solar disc. It is extremely interesting to obtain a picture of short-time-scale variations of the magnetic field strength and the radial velocity field in connection with the transfer of energy from the photosphere to the upper layers of the solar atmosphere (chromosphere, corona).

scholarly journals New CCD Observations of Eclipsing Binary VW Cephei

1998 ◽  
Vol 11 (1) ◽  
pp. 394-394
Author(s):  
Adbdulrahman Ali S. Malawi
Keyword(s):  
Time Scale ◽  
Light Curves ◽  
Short Time Scale ◽  
Eclipsing Binary ◽  
Photometric Elements ◽  
Ccd Observations ◽  
Short Time

New CCD observations of the eclipsing binary VW Cephei were made on the 9th and 10th of October 1996 and on the 11th of Nov. 1996. The light curves and short time-scale variations are discussed. Photometric elements were determined from analyses of the light curves. These new solutions are also discussed.

scholarly journals Short time-scale fluctuations in the difference light curves of QSO 0957+561A,B: microlensing or noise?

2001 ◽  
Vol 322 (2) ◽  
pp. 397-410 ◽  
Author(s):  
R. Gil-Merino ◽  
L. J. Goicoechea ◽  
M. Serra-Ricart ◽  
A. Oscoz ◽  
D. Alcalde ◽  
...  
Keyword(s):  
Time Scale ◽  
Light Curves ◽  
Short Time Scale ◽  
The Difference ◽  
Short Time

scholarly journals Detection of small-size planetary candidates with CoRoT data

2010 ◽  
Vol 6 (S276) ◽  
pp. 523-524
Author(s):  
Aldo S. Bonomo ◽  
Pierre-Yves Chabaud ◽  
Magali Deleuil ◽  
Claire Moutou ◽  
Pascal Bordé
Keyword(s):  
Time Scale ◽  
Detection Threshold ◽  
Space Mission ◽  
Light Curves ◽  
Short Time Scale ◽  
Blind Test ◽  
Short Period ◽  
Short Time ◽  
Rocky Planets

AbstractWith the discovery of CoRoT-7b, the first transiting super-Earth, the CoRoT space mission has shown the capability to detect short-period rocky planets around solar-like stars. By performing a blind test with real CoRoT light curves, we want to establish the detection threshold of small-size planets in CoRoT data. We investigate the main obstacles to the detection of transiting super-Earths in CoRoT data, notably the presence of short-time scale variability and hot pixels.

scholarly journals The endgame of gas giant formation: accretion luminosity and contraction post-runaway

2019 ◽  
Vol 490 (3) ◽  
pp. 4334-4343 ◽  
Author(s):  
Sivan Ginzburg ◽  
Eugene Chiang
Keyword(s):  
Time Scale ◽  
Accretion Rate ◽  
High Viscosity ◽  
Giant Planets ◽  
Short Time Scale ◽  
Low Viscosity ◽  
Running Away ◽  
Accretion Rates ◽  
Gas Accretion ◽  
Short Time

ABSTRACT Giant planets are thought to form by runaway gas accretion on to solid cores. Growth must eventually stop running away, ostensibly because planets open gaps (annular cavities) in their surrounding discs. Typical models stop runaway by artificially capping the accretion rate and lowering it to zero over an arbitrarily short time-scale. In reality, post-runaway accretion persists as long as the disc remains. During this final and possibly longest phase of formation, when the planet is still emerging from the disc, its mass can more than double, and its radius contracts by orders of magnitude. By drawing from the theory of how gaps clear, we find that post-runaway accretion luminosities diverge depending on disc viscosity: luminosities fall in low-viscosity discs but continue to rise past runaway in high-viscosity discs. This divergence amounts to a factor of 102 by the time the disc disperses. Irrespective of the specifics of how planets interact with discs, the observed luminosity and age of an accreting planet can be used to calculate its instantaneous mass, radius, and accretion rate. We perform this exercise for the planet candidates embedded within the discs orbiting PDS 70, HD 163296, and MWC 758, inferring masses of 1–10 MJ, accretion rates of 0.1–10 MJ Myr−1, and radii of 1–10 RJ. Our radii are computed self-consistently from the planet’s concurrent contraction and accretion and do not necessarily equal the value of 2RJ commonly assumed; in particular, the radius depends on the envelope opacity as R ∝ κ0.5.

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.

scholarly journals Origin of Blazar Activity

1999 ◽  
Vol 194 ◽  
pp. 256-268
Author(s):  
M. M. Romanova
Keyword(s):  
Magnetic Field ◽  
Black Hole ◽  
Energy Spectrum ◽  
Magnetic Fields ◽  
Time Scale ◽  
High Frequency ◽  
Short Time Scale ◽  
Poynting Flux ◽  
Electron Positron ◽  
Short Time

Models of Blazars based on the propagation of finite discontinuities or fronts in the Poynting flux jet from the innermost regions of an accretion disk around a black hole are discussed. Such fronts may be responsible for short time–scale (from less than hours to days) flares in different wavebands from high frequency radioband to TeV, with delay in low radio frequencies as a result of synchrotron self-absorption. The cases of magnetic fields of one and opposite polarities across the front are investigated. We find that annihilation of magnetic field in the front leads to higher energy spectrum of leptons and possibility of strong TeV flares. Electron–positron pairs form in most cases as a result of interaction between numerous synchrotron photons and SSC photons, and constitute the majority species, compared with the ions at subparsec scales. Frequent weak outbursts may be responsible for flickering core radiation in all wavebands, while the stronger outbursts may be observed as short time–scale flares.

SIMULATIONS OF DYNAMICS AND EMISSION FROM MAGNETIZED GRB AFTERGLOWS

2010 ◽  
Vol 19 (06) ◽  
pp. 985-990 ◽  
Author(s):  
PETAR MIMICA ◽  
DIMITRIOS GIANNIOS ◽  
MIGUEL ANGEL ALOY
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Light Curves ◽  
Reverse Shock ◽  
Ultrahigh Resolution ◽  
Mhd Simulations ◽  
The Magnetic Field ◽  
Early Phases

The role of magnetic fields in the GRB flow is still controversial. The afterglow emission, particularly the early phases, may provide a probe into the magnetization of the outflow. Using ultrahigh resolution relativistic MHD simulations, the interaction between radially expanding magnetized ejecta with the interstellar medium is studied. We explore the effect of the magnetic field strength of the ejecta on the afterglow structure, particularly regarding the presence and strength of a reverse shock. We compute synthetic afterglow light curves to quantify the effect of the magnetization of the flow on observed radiation.

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