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 A Beat Phenomenon in Dwarf Nova Eruptions

1977 ◽  
Vol 42 ◽  
pp. 227-233
Author(s):  
N. Vogt
Keyword(s):  
Mass Transfer ◽  
Orbital Period ◽  
Transfer Rate ◽  
Convection Zone ◽  
Mass Transfer Rate ◽  
Accretion Disc ◽  
Light Curves ◽  
Dwarf Nova ◽  
Beat Phenomenon ◽  
Photoelectric Observations

Photoelectric observations of the dwarf nova VW Hyi, obtained at the end of the December 1975 supermaximum, are presented. After decline from the outburst, the superhump period (0ḍ07622) combines with the orbital period (0ḍ07427) to a beat phenomenon: the O-C’s and the light curves of the orbital hump vary systematically with the phase of the beat period for at least one week after recovery from the supermaximum. It is suggested that the red secondary component, which rotates non-synchroneously with the superhump period, expands slightly at the beginning of a supermaximum and is heated up asymmetrically, probably due to instabilities in its convection zone. In addition, the increased mass transfer rate may trigger the long eruption in the accretion disc while short eruptions originate in the disc without participation of the secondary.

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 FS Aur as a Permanent Superhump System

2004 ◽  
Vol 194 ◽  
pp. 169-171
Author(s):  
Gaghik H. Tovmassian ◽  
Sergei V. Zharikov
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Variable Mass ◽  
Accretion Disc ◽  
Light Curves ◽  
Cataclysmic Variable ◽  
Short Period ◽  
Photometric Period ◽  
Low Amplitude

AbstractWe discovered that the short period cataclysmic variable FS Aur at some epochs shows a photometric period close to the orbital. It exceeds the orbital period by ∽2%, which is a sign of the presence of a permanent superhump in the system. Superhumps tend to appear near short, low amplitude outbursts. We assume that FS Aur possesses a large thermally stable accretion disc and that the outburst may be due to the variable mass transfer rate. This, however, does not alter our previous explanation of yet another, 2.4 times longer than orbital, photometric period of FS Aur, found earlier, and persistently observed in its light curves.

scholarly journals Irregular X-ray Variation of LMC X-3

1995 ◽  
Vol 151 ◽  
pp. 336-337
Author(s):  
H.C. Pan ◽  
G.K. Skinner ◽  
R.A. Sunyaev ◽  
N.L. Alexandrovich
Keyword(s):  
Mass Transfer ◽  
Energy Range ◽  
Spectral Resolution ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Space Station ◽  
Large Magellanic Cloud ◽  
Accretion Disc ◽  
X Ray ◽  
Coded Mask

LMC X-3 is an X-ray binary in the Large Magellanic Cloud. It was discovered by UHURU and observations with various satellites showed that the X-ray source was variable by a factor of up to 100 (e.g. Traves et al. 1988). Using the GINGA and HEAO-1 observations, Cowley et al. (1991) found a strong ∼ 198 (or possibly ∼ 99) day modulation in the X-ray luminosities of LMC X-3. They suggested that this modulation may be due to an accretion disc precession, or periodic variations in the mass transfer rate, or a combination of both.We observed LMC X-3 with the TTM in 1988-1990. The present paper gives some results from the analysis of the data obtained.The TTM is a coded mask telescope on board the MIR space station. It is capable of producing images in the energy range 2-30 keV with a spectral resolution of about 18% at 6 keV (Brinkman et al. 1985).

scholarly journals Hot Spots Drift in Synchronous and Asynchronous Polars: Results of Three-Dimensional Numerical Simulation

Galaxies ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 110
Author(s):  
Dmitry Bisikalo ◽  
Andrey Sobolev ◽  
Andrey Zhilkin
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Temperature Distribution ◽  
Hot Spots ◽  
Transfer Rate ◽  
Hot Spot ◽  
Mass Transfer Rate ◽  
Three Dimensional ◽  
Jet Trajectory ◽  
Dominant Influence

In this paper, the characteristics of hot spots on an accretor surface are investigated for two types of polars: the eclipsing synchronous polar V808 Aur and the non-eclipsing asynchronous polar CD Ind in configuration of an offset and non-offset magnetic dipole. The drift of hot spots is analyzed based on the results of numerical calculations and maps of the temperature distribution over the accretor surface. It is shown that a noticeable displacement of the spots is determined by the ratio of ballistic and magnetic parts of the jet trajectory. In the synchronous polar, the dominant influence on the drift of hot spots is exerted by variations in the mass transfer rate, which entail a change in the ballistic part of the trajectory. It was found that when the mass transfer rate changes within the range of 10−10M⊙/year to 10−7M⊙/year, the displacement of the hot spot in latitude and longitude can reach 30∘. In the asynchronous polar, a change in the position of hot spots is mainly defined by the properties of the white dwarf magnetosphere, and the displacement of hot spots in latitude and longitude can reach 20∘.

scholarly journals A Model for WZ Sge with “Standard” Values of α

1997 ◽  
Vol 163 ◽  
pp. 279-282 ◽  
Author(s):  
J.M. Hameury ◽  
J.M. Huré ◽  
J.P. Lasota
Keyword(s):  
Mass Transfer ◽  
Thermal Equilibrium ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Accretion Disc ◽  
Recurrence Time ◽  
Equilibrium Curve ◽  
Standard Values ◽  
Inner Parts ◽  
Standard Disc

AbstractWe present a model for the dwarf nova WZ Sge which does not imply an unusually – and unexplained – low value of the viscosity during low states. We propose that the inner parts of the accretion disc are disrupted by either a magnetic field or evaporation, so that the disc is stable (or very close to being stable) in quiescence, as the mass transfer rate is very low, and the disc can sit on the cool, lower branch of the thermal equilibrium curve. Outbursts are triggered by an increase of mass transfer, causing a standard disc instability, and are strongly enhanced by illumination effects. Both the recurrence time, and the characteristics of the light curve in outburst can be accounted for.

scholarly journals Nova Outbursts and the Secular Evolution of Cataclysmic Variables

1996 ◽  
Vol 158 ◽  
pp. 447-448
Author(s):  
K. Schenker ◽  
U. Kolb ◽  
H. Ritter
Keyword(s):  
Mass Transfer ◽  
Angular Momentum ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Secular Evolution ◽  
Term Evolution ◽  
Angular Momentum Loss ◽  
The Mean ◽  
Nova Outbursts

AbstractWe present calculations of the long-term evolution of CVs which include the influence of nova outbursts. In particular we investigate the consequences of the discontinuous mass loss due to recurring outburst events and the effects of frictional angular momentum loss (FAML), i.e. the interaction of the expanding nova envelope with the secondary. We show that a description assuming continuous mass loss – averaged over a complete nova cycle – is applicable for determining the mean mass transfer rate and the secular evolution both with and without FAML. Between two subsequent outbursts, deviations from the mean evolution depend on the strength of FAML and on the mass ejected during the outburst. Formally FAML is a consequential angular momentum loss [1] and therefore increases the mean mass transfer rate by pushing the systems closer to mass transfer instability. Depending on the actual strenghth of FAML the long-term evolution of CVs could be significantly different from the standard model predictions.

scholarly journals VY Sculptoris stars are Magnetic Cataclysmic Variables

2004 ◽  
Vol 190 ◽  
pp. 46-52 ◽  
Author(s):  
Jean-Pierre Lasota ◽  
Jean-Marie Hameury
Keyword(s):  
Mass Transfer ◽  
Transfer Rate ◽  
Magnetic Moments ◽  
Mass Transfer Rate ◽  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Intermediate States ◽  
Intermediate Polars ◽  
Magnetic Cataclysmic Variables ◽  
Evolutionary Aspects

AbstractWe show that VY Scl stars must be magnetized in order to account for the absence of outbursts during their low and intermediate states. Absence of outbursts during low states requires only rather low magnetic moments but in systems in which the drops and rises of luminosity are slower than it takes for the accretion disc to adjust viscously to the variation in mass-transfer rate preventing outbursts require magnetic moments of Intermediate Polars. We discuss some evolutionary aspects of this conclusion.

scholarly journals Effective Growth Rate of White Dwarf Mass in Nova Outbursts

1990 ◽  
Vol 122 ◽  
pp. 390-391
Author(s):  
Mariko Kato ◽  
Izumi Hachisu
Keyword(s):  
Mass Transfer ◽  
Growth Rate ◽  
Mass Loss ◽  
White Dwarf ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Net Growth Rate ◽  
Chandrasekhar Limit ◽  
Nova Outbursts ◽  
Effective Growth

AbstractWe have obtained the effective growth rate of white dwarf masses which are suffering mass loss during both hydrogen and helium nova outbursts. If the mass transfer rate from the companion is smaller than 10−7 M⊙/yr, the net growth rate is reduced to less than one tenth of the mass transfer rate from the companion star. It is suggested that the white dwarf mass is hard to grow to the Chandrasekhar mass unless its initial mass is very close to the Chandrasekhar limit.

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