scholarly journals Dwarf nova outbursts in intermediate polars

2017 ◽  
Vol 602 ◽  
pp. A102 ◽  
Author(s):  
J.-M. Hameury ◽  
J.-P. Lasota
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
White Dwarf ◽  
Accretion Disc ◽  
Numerical Code ◽  
Dwarf Nova ◽  
Viscous Instability ◽  
Intermediate Polars ◽  
Nova Outbursts ◽  
The Magnetic Field

Context. The disc instability model (DIM) has been very successful in explaining the dwarf nova outbursts observed in cataclysmic variables. When, as in intermediate polars, the accreting white dwarf is magnetised, the disc is truncated at the magnetospheric radius, but for mass-transfer rates corresponding to the thermal-viscous instability such systems should still exhibit dwarf-nova outbursts. Yet, the majority of intermediate polars, in which the magnetic field is not large enough to completely disrupt the accretion disc, seem to be stable, and the rare observed outbursts, in particular in systems with long orbital periods, are much shorter than normal dwarf-nova outbursts. Aims. We investigate the predictions of the disc instability model for intermediate polars in order to determine which of the observed properties of these systems can be explained by the DIM. Methods. We use our numerical code for the time evolution of accretion discs, modified to include the effects of the magnetic field, with constant or variable mass transfer from the secondary star. Results. We show that intermediate polars have mass transfer low enough and magnetic fields large enough to keep the accretion disc stable on the cold equilibrium branch. We show that the infrequent and short outbursts observed in long-period systems, such as, for example, TV Col, cannot be attributed to the thermal-viscous instability of the accretion disc, but instead have to be triggered by an enhanced mass-transfer from the secondary, or, more likely, by some instability coupling the white dwarf magnetic field with that generated by the magnetorotational instability operating in the accretion disc. Longer outbursts (a few days) could result from the disc instability.

scholarly journals The disappearance and reformation of the accretion disc during a low state of FO Aquarii

2017 ◽  
Vol 606 ◽  
pp. A7 ◽  
Author(s):  
J.-M. Hameury ◽  
J.-P. Lasota
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Hot Spot ◽  
Mass Transfer Rate ◽  
Accretion Disc ◽  
Numerical Code ◽  
Light Sources ◽  
Instability Strip ◽  
Dwarf Nova ◽  
Nova Outbursts

Context. FO Aquarii, an asynchronous magnetic cataclysmic variable (intermediate polar) went into a low state in 2016, from which it slowly and steadily recovered without showing dwarf nova outbursts. This requires explanation since in a low state, the mass-transfer rate is in principle too low for the disc to be fully ionised and the disc should be subject to the standard thermal and viscous instability observed in dwarf novae. Aims. We investigate the conditions under which an accretion disc in an intermediate polar could exhibit a luminosity drop of two magnitudes in the optical band without showing outbursts. Methods. We use our numerical code for the time evolution of accretion discs, including other light sources from the system (primary, secondary, hot spot). Results. We show that although it is marginally possible for the accretion disc in the low state to stay on the hot stable branch, the required mass-transfer rate in the normal state would then have to be extremely high, of the order of 1019 g s-1 or even larger. This would make the system so intrinsically bright that its distance should be much larger than allowed by all estimates. We show that observations of FO Aqr are well accounted for by the same mechanism that we have suggested as explaining the absence of outbursts during low states of VY Scl stars: during the decay, the magnetospheric radius exceeds the circularisation radius, so that the disc disappears before it enters the instability strip for dwarf nova outbursts. Conclusions. Our results are unaffected, and even reinforced, if accretion proceeds both via the accretion disc and directly via the stream during some intermediate stages; the detailed process through which the disc disappears still requires investigation.

scholarly journals Accretion Disc Formation in Intermediate Polars

1996 ◽  
Vol 158 ◽  
pp. 161-164
Author(s):  
G. A. Wynn ◽  
A. R. King
Keyword(s):  
Magnetic Field ◽  
Accretion Disc ◽  
Local Magnetic Field ◽  
Magnetic Systems ◽  
X Ray ◽  
Accretion Flow ◽  
Intermediate Polars ◽  
X Ray Binaries ◽  
The Magnetic Field ◽  
Disc Formation

The large-scale accretion flow in the intermediate polars (IPs) is still a matter of vigorous debate. It is known that the magnetic field of the white dwarf (WD) controls the accretion flow close to the surface, channeling the plasma onto the polecaps and giving rise to X-ray emission modulated at the WD spin period (Pspin). After their discovery it was assumed that IPs were the WD analogues of the pulsing X-ray binaries, where a magnetic neutron star accretes from a disrupted accretion disc. However, a number of authors have pointed out that the criteria for disc formation in IPs are less certain than those for the X-ray binaries.The simplest possible criterion for disc formation in a binary is that the accretion flow should be able to orbit freely about the primary star (see Frank, King & Raine 1991 for a review). In non-magnetic systems this is merely the condition that the minimum approach distance of the free stream (Rmin) should exceed the radius of the primary. The situation in magnetic systems is more complex, as the magnetic field of the primary presents an obstacle to the infalling accretion stream. In many treatments of IPs it is assumed that the plasma stream is able to orbit freely about the WD until the ram pressure of the stream is of the same order as the magnetic pressureρv2~B2/8π, whereρis the stream density,vthe stream velocity andBthe local magnetic field strength. This condition fixes the magnetospheric radius,Rmag, inside which the magnetic field is assumed to thread the stream material and direct the accretion flow along the fieldlines.

scholarly journals Do We See Magnetic Effects in Dwarf Nova Outbursts?

1995 ◽  
Vol 151 ◽  
pp. 285-285
Author(s):  
N. Vogt ◽  
E. Meyer-Hofmeister ◽  
F. Meyer
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Accretion Disk ◽  
White Dwarf ◽  
Magnetic Activity ◽  
Light Curves ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
Cyclic Behaviour ◽  
Nova Outbursts

Many observations indicate that fast rotating late type stars show magnetic activity. We therefore argue that some of the secondary stars in cataclysmic binaries might also have magnetic fields. Such magnetic fields would reach over the accretion disk around the white dwarf primary. We investigate their effect on dwarf nova outbursts. The magnetic field lines will penetrate the disk and remove angular momentum. This shifts the accumulation of mass towards the inner disk, closer to the white dwarf, and therefore leads to a different outburst behaviour, which can be recognized in observed light curves of dwarf novae. If a magnetic field of the order 50 - 100 gauss is acting on the accretion disk, we expect narrower and more frequent outbursts as compared to the non-magnetic case. Outburst records of three dwarf novae above the period gap (P > 3h), whose long-term light curves are well covered, were used to search for traces of magnetic activity. All three cases display a pronounced bimodality in the distribution of their outburst width, i.e. either narrow or wide outbursts occur. We found evidence for a cyclic behaviour in one case, SS Aur: possible “magnetic episodes” repeating every 18 years reveal epochs with abnormally frequent narrow outbursts and nearly or totally missing wide ones. There are also indications for a similar behaviour of SS Cyg with a 7-years cycle, but with less pronounced periodicity. The third case, U Gem, does not show clear evidence of magnetic activity although we found some indications for a transitory oscillation of the width of wide outbursts after 1926, with a period of 13.6 years. The behaviour of SS Aur and SS Cyg resembles the theoretical predictions, there is, however, an important difference: Throughout the entire cycle, marked by the “magnetic episodes”, neither wide nor narrow outbursts alter their mean light curves: magnetic fields seem to affect only the observed proportion in the frequency of both outburst types without altering the light curves of individual outbursts. Remarkably, most of the “anomalous outbursts” (which are characterized by an abnormally slow rising branch to an outburst) occur also at or near the “magnetic episodes”.

scholarly journals The Effect of the Nova Explosion on the Evolution of Cataclysmic Variables

1997 ◽  
Vol 163 ◽  
pp. 771-772
Author(s):  
T. Naylor ◽  
M.W. Somers
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
White Dwarfs ◽  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Surface Layers ◽  
Secondary Star ◽  
Classical Nova ◽  
Nova Outbursts

Classical nova outbursts are thermonuclear explosions on the surfaces of the white dwarfs in cataclysmic variables. The explosion heats the surface layers of the white dwarf, which are expected to cool on a timescale of a hundred years. The hot white dwarf should have two obvious effects on the system.(1)It will heat the surface of the accretion disc and secondary star, increasing the overall luminosity of the system.(2)By irradiating the surface of the secondary star it may bloat it and drive more mass transfer, thus again increasing the overall luminosity.

scholarly journals On the Influence of Magnetic Field on Accretion Processes in CVs

2015 ◽  
Vol 2 (1) ◽  
pp. 60-65
Author(s):  
D. V. Bisikalo ◽  
A. G. Zhilkin
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
White Dwarf ◽  
Transfer Rate ◽  
Accretion Rate ◽  
Mass Transfer Rate ◽  
Rotation Velocity ◽  
Spin Rotation ◽  
Mhd Simulations ◽  
Intermediate Polars

We consider the influence of such parameters as the value of the proper magnetic field Ba and the spin-rotation velocity of the white dwarf on accretion processes in CVs. The results of 3D MHD simulations have shown that the accretion rate is a non-monotonic function of Ba: with growing Ba it raises in the intermediate polars and decreases in the polars. The maximal accretion rate occurs in the systems, transiting from the stage of intermediate polars to polars; it’s value reaches 60% of the initially set mass transfer rate. We have also shown that the acretion rate decreases with the growing<br />spin-rotation velocity of the white dwarf.

scholarly journals Magnetic Field Evolution in Accreting White Dwarfs

2004 ◽  
Vol 190 ◽  
pp. 58-70
Author(s):  
Andrew Cumming
Keyword(s):  
Magnetic Field ◽  
White Dwarf ◽  
White Dwarfs ◽  
Strong Field ◽  
Weak Field ◽  
Field Structure ◽  
Field Evolution ◽  
Induced Field ◽  
Intermediate Polars ◽  
The Magnetic Field

AbstractI discuss the effect of accretion on the magnetic field of an accreting white dwarf. Whereas the magnetic fields of isolated white dwarfs are not expected to change significantly with time, I show that if an accreting white dwarf increases in mass at a rate > 1–5 × 10−10MΘ yr–1, accretion overcomes ohmic diffusion and has a significant effect on the field structure. I discuss the implications of this result for observed systems. In particular, accretion induced field evolution may provide the missing evolutionary link between the strong field, slowly accreting AM Her systems and the weak field, more rapidly accreting intermediate polars.

Monte Carlo calculation of the energy parameters and spatial distribution of the cathodic arc ions while passing through the macro-particles filters

2018 ◽  
Vol 1 (1) ◽  
pp. 30-34 ◽  
Author(s):  
Alexey Chernogor ◽  
Igor Blinkov ◽  
Alexey Volkhonskiy
Keyword(s):  
Magnetic Field ◽  
Mass Transfer ◽  
Monte Carlo ◽  
Monte Carlo Calculation ◽  
Inhomogeneous Magnetic Field ◽  
Flow Energy ◽  
Wide Range ◽  
Field Concentrator ◽  
Cathodic Arc ◽  
The Magnetic Field

The flow, energy distribution and concentrations profiles of Ti ions in cathodic arc are studied by test particle Monte Carlo simulations with considering the mass transfer through the macro-particles filters with inhomogeneous magnetic field. The loss of ions due to their deposition on filter walls was calculated as a function of electric current and number of turns in the coil. The magnetic field concentrator that arises in the bending region of the filters leads to increase the loss of the ions component of cathodic arc. The ions loss up to 80 % of their energy resulted by the paired elastic collisions which correspond to the experimental results. The ion fluxes arriving at the surface of the substrates during planetary rotating of them opposite the evaporators mounted to each other at an angle of 120° characterized by the wide range of mutual overlapping.

scholarly journals Theory of Dwarf Novae

1976 ◽  
Vol 73 ◽  
pp. 173-192
Author(s):  
G. T. Bath
Keyword(s):  
Mass Transfer ◽  
Steady State ◽  
Recent Work ◽  
Accretion Disc ◽  
Optical Behaviour ◽  
Dwarf Novae ◽  
Physical Processes ◽  
Dwarf Nova ◽  
Theoretical Results

Recent work on the physical processes resulting from mass transfer between the red and blue components of dwarf nova binaries is reviewed. The optical behaviour of the blue component's accretion disc suggests that it may be the infall, accretion energy which is being liberated during outbursts. Theoretical results which suggest that the red component may suffer quasi-periodic mass transfer instabilities are discussed. The resulting accretion disc properties are considered and compared with the observed optical outburst behaviour for the simplest steady state disc models. The complexity of the interaction between the two stellar components in these systems is emphasized.

scholarly journals Classical Novae in the Context of the Evolution of Cataclysmic Binaries

1990 ◽  
Vol 122 ◽  
pp. 313-324
Author(s):  
Hans Ritter
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
White Dwarfs ◽  
Mass Range ◽  
High Mass ◽  
Transfer Rates ◽  
Classical Novae ◽  
Secular Evolution ◽  
Cataclysmic Binaries ◽  
Nova Outbursts

AbstractIn this paper we explore to what extent the TNR model of nova outbursts and our current concepts of the formation and secular evolution of cataclysmic binaries are compatible. Specifically we address the following questions: 1) whether observational selection can explain the high white dwarf masses attributed to novae, 2) whether novae on white dwarfs in the mass range 0.6M⊙ ≲ M ≲ 0.9M⊙ can occur and how much they could contribute to the observed nova frequency, and 3) whether the high mass transfer rates imposed on the white dwarf in systems above the period gap can be accommodated by the TNR model of nova outbursts.

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