The Dwarf Nova EX Hydrae

1974 ◽  
Vol 2 (5) ◽  
pp. 271-274 ◽  
Author(s):  
R. D. Watson ◽  
P. T. Rayner
Keyword(s):  
Binary System ◽  
Time Resolution ◽  
White Dwarf ◽  
Roche Lobe ◽  
Dwarf Star ◽  
Dwarf Nova ◽  
Photoelectric Time

The object EX Hya is a dwarf nova with a binary period of 98.3 min (Mumford 1964, 1967). Warner (1972, 1973a) has observed two complete cycles of this star with a photoelectric time resolution of 5 sec. These observations suggested that EX Hya can be understood in terms of the model proposed by Warner and Nather (1971) in their discussion of U Gem. In this model, a white dwarf primary of a semi-detached binary system is surrounded by a disk of gas formed from matter transfered from the secondary, which is a cool dwarf star filling its Roche lobe.

scholarly journals Superoutbursts and Superhumps of SU UMa Stars

1988 ◽  
Vol 108 ◽  
pp. 238-239
Author(s):  
Yoji Osaki ◽  
Masahito Hirose
Keyword(s):  
Accretion Disk ◽  
Orbital Period ◽  
White Dwarf ◽  
Binary Systems ◽  
Roche Lobe ◽  
Light Curves ◽  
Close Binary ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
Close Binary Systems

SU UMa stars are one of subclasses of dwarf novae. Dwarf novae are semi-detached close binary systems in which a Roche-lobe filling red dwarf secondary loses matter and the white dwarf primary accretes it through the accretion disk. The main characteristics of SU UMa subclass is that they show two kinds of outbursts: normal outbursts and superoutbursts. In addition to the more frequent narrow outbursts of normal dwarf nova, SU UMa stars exhibit “superoutbursts”, in which stars reach about 1 magnitude brighter and stay longer than in normal outburst. Careful photometric studies during superoutburst have almost always revealed the “superhumps”: periodic humps in light curves with a period very close to the orbital period of the system. However, the most curious of all is that this superhump period is not exactly equal to the orbital period, but it is always longer by a few percent than the orbital period.

scholarly journals Search for short-time periodic variations among WR+C binaries

1995 ◽  
Vol 163 ◽  
pp. 562-564
Author(s):  
S.V. Marchenko ◽  
I.I. Antokhin ◽  
J.-F. Bertrand ◽  
R. Lamontagne ◽  
A.F.J. Moffat ◽  
...  
Keyword(s):  
Binary System ◽  
Time Resolution ◽  
Roche Lobe ◽  
Secondary Component ◽  
Rapid Phase ◽  
New Born ◽  
Short Time ◽  
Time Periodic

During the 1992–1993 observing season, WR3, 6, 16, 40, 66, 82 and 134 were monitored in fast photometry mode with time-resolution 0.005—0.01 s. Only WR6 reveals a possible period of P = 0.11 s (semi-amplitude A = 0.025 mag), which is close to the derived equilibrium period of a new-born pulsar in a binary system after the rapid phase of Roche Lobe Over-Flow from the original secondary component.

scholarly journals A Wave Model for Dwarf Novae

1980 ◽  
Vol 58 ◽  
pp. 643-648
Author(s):  
Warren M. Sparks ◽  
G. Siegfried Kutter
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Wave Model ◽  
Mathematical Representation ◽  
Coherent Oscillation ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
Nova Outburst

AbstractThe rapid coherent oscillation during a dwarf nova outburst is attributed to an accretion-driven wave going around the white dwarf component of the binary system. The increase and decrease in the period of this oscillation is due to the change in the velocity of the wave as it is first being driven and then damped. Qualitatively, a large number of observations can be explained with such a model. The beginnings of a mathematical representation of this model are developed.

scholarly journals Recurrence of Nova Explosions

1979 ◽  
Vol 53 ◽  
pp. 525-525 ◽  
Author(s):  
Kyoji Nariai ◽  
Ken’ichi Nomoto
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Close Binary System ◽  
Roche Lobe ◽  
Close Binary ◽  
Ignition Point ◽  
Almost All

It has been shown by many computations that a nova explosion is triggered by mass accretion onto a white dwarf in a close binary system. Such nova explosions will recur many times in the following way. When a certain amount of hydrogen-rich gas has been accreted on the white dwarf, a hydrogen-shell flash is ignited. Then the hydrogen-rich envelope expands greatly, which, in some cases, grows into a nova explosion. Almost all envelope mass is ejected into space or at least overflows its Roche lobe. After that the mass of the envelope increases again by accretion and the shell flash is ignited again. The period of such recurrence is given by τrec = ΔMH/(dM/dt), where dM/dt and ΔMH are the rate of accretion and the mass contained in the hydrogen-rich envelope at the ignition point.

scholarly journals Optical Frequencies in V471 TAU

1989 ◽  
Vol 114 ◽  
pp. 293-295
Author(s):  
D. E. Winget ◽  
C. F. Claver
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Mean Amplitude ◽  
Dwarf Star ◽  
Pulsed Light ◽  
Eclipsing Binary ◽  
X Ray ◽  
Significant Power ◽  
Hyades Cluster ◽  
S Period

V471 Tau is a spectroscopic and eclipsing binary system located in the Hyades cluster. The binary consists of a K2V and a hot DA white dwarf star (Nelson and Young 1970). Soft x-ray observations reveal strong modulation at periods of 554.7 ± 0.3s and 277.5 ± 0.1s (Jensen 1985, Jensnen et al. 1986).Robinson et al. (1988) reported the detection of the 555 s period in the optical. This period was about a factor of 20 reduced in mean amplitude in their data relative to the soft x-ray amplitude. They also found that it varied in amplitude from run to run by more than a factor of 2.5, dropping below detectability on several runs. They found some evidence for the 277.5 s period in several runs, but never at high enough amplitude to measure reliably. In addition, they noted that several of their runs had statistically significant power at other frequencies, but noted that in their six runs none of the additional frequencies repeated themselves. Robinson et al. also used observations near the eclipse of the white dwarf to demonstrate that most of the pulsed light is coming from the white dwarf.

scholarly journals Modelling quantum aspects of disruption of a white dwarf star by a black hole

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tomasz Karpiuk ◽  
Marek Nikołajuk ◽  
Mariusz Gajda ◽  
Mirosław Brewczyk
Keyword(s):  
Black Hole ◽  
Binary System ◽  
Accretion Disk ◽  
White Dwarf ◽  
Gamma Ray ◽  
Quantum Turbulence ◽  
Nonlinear Effects ◽  
Quantized Vortices ◽  
Dwarf Star ◽  
Quantum Hydrodynamic Equations

AbstractWe study the final stages of the evolution of a binary system consisted of a black hole and a white dwarf star. We implement the quantum hydrodynamic equations and carry out numerical simulations. As a model of a white dwarf star we consider a zero temperature droplet of attractively interacting degenerate atomic bosons and spin-polarized atomic fermions. Such mixtures are investigated experimentally nowadays. We find that the white dwarf star is stripped off its mass while passing the periastron. Due to nonlinear effects, the accretion disk originated from the white dwarf becomes fragmented and the onset of a quantum turbulence with giant quantized vortices present in the bosonic component of the accretion disk is observed. The binary system ends its life in a spectacular way, revealing quantum features underlying the white dwarf star’s structure. We find a charged mass, falling onto a black hole, could be responsible for recently discovered ultraluminous X-ray bursts. The simulations show that final passage of a white dwarf near a black hole can cause a gamma-ray burst.

scholarly journals Roche Tomography of the Cool Star in IP Peg

1996 ◽  
Vol 158 ◽  
pp. 21-24
Author(s):  
R. G. M. Rutten ◽  
V. S. Dhillon
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
System Parameters ◽  
Dwarf Nova ◽  
Preliminary Results ◽  
Cool Star

AbstractWe analyse orbitally-resolved spectra of the Na I doublet in the dwarf nova IP Peg, using the newly developed technique of Roche tomography. We show that Roche tomography can be successfully employed to image the secondary stars in CVs, and that it also serves as an independent aid for determining binary system parameters. Our preliminary results suggest that the mass of the white-dwarf primary is 1.2 M⊙, significantly higher than previous estimates.

scholarly journals Collapse of Accreting White Dwarf to Form a Neutron Star

1979 ◽  
Vol 53 ◽  
pp. 56-60 ◽  
Author(s):  
Ken’ichi Nomoto ◽  
Shigeki Miyaji ◽  
Daiichiro Sugimoto ◽  
Koichi Yokoi
Keyword(s):  
Neutron Star ◽  
Binary System ◽  
Mass Exchange ◽  
White Dwarf ◽  
Mass Range ◽  
Close Binary System ◽  
Roche Lobe ◽  
Close Binary ◽  
Primary Star ◽  
Companion Star

AbstractIn a close binary system with a primary star in the mass range 8-12 M⊙, the primary star leaves a white dwarf composed of 16O, 20Ne, and 24Mg as a result of mass exchange. When the companion star, fills its Roche lobe, overflowing matter accretes onto the white dwarf. We have computed the evolution of such an accreting O-Ne-Mg white dwarf and found that electron captures on 24Mg and 20Ne trigger the collapse when the mass reaches 1.38 M⊙. As a result of the collapse, oxygen begins to deflagrate but the effects of electron captures dominate over the oxygen deflagration. The white dwarf collapses to form a neutron star.

Aspects of the Collapse of Compact Objects

1980 ◽  
Vol 4 (1) ◽  
pp. 49-50
Author(s):  
R. A. Gingold ◽  
J. J. Monaghan
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
White Dwarf ◽  
Compact Objects ◽  
Dwarf Star

Misner Thorne and Wheeler (1973), (page 629) suggested that a freshly formed White Dwarf star of several solar masses would, if slowly — rotating, collapse to form a neutron star pancake which would become unstable and eventually produce several, possibly colliding, neutron stars.

Jupiter-sized planet found orbiting tiny white dwarf star

Physics World ◽  
2021 ◽  
Vol 33 (11) ◽  
pp. 7i-7i
Author(s):  
Hamish Johnston
Keyword(s):  
White Dwarf ◽  
Dwarf Star
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