scholarly journals A ROSAT survey of hot DA white dwarfs in non-interacting binary systems

1994 ◽  
Vol 270 (3) ◽  
pp. 499-515 ◽  
Author(s):  
M. A. Barstow ◽  
J. B. Holberg ◽  
T. A. Fleming ◽  
M. C. Marsh ◽  
D. Koester ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Binary Systems

scholarly journals The Search for Close Binary Evolved Stars

1989 ◽  
Vol 114 ◽  
pp. 408-412
Author(s):  
Rex A. Saffer ◽  
James Liebert
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Close Binary ◽  
Brown Dwarf ◽  
Null Results ◽  
Spectroscopic Observations ◽  
Evolved Stars ◽  
Short Period

AbstractWe report on a search for short-period binary systems composed of pairs of evolved stars. The search is being carried out concurrently with a program to characterize the kinematical properties of two different samples of stars. Each sample has produced one close binary candidate for which further spectroscopic observations are planned. We also recapitulate the discovery of a close detached binary system composed of two cool DA white dwarfs, and we discuss the null results of Hα observations of the suspected white dwarf/brown dwarf system G 29–38.

Accretion-Induced Collapse of Old White Dwarfs

1987 ◽  
Vol 93 ◽  
pp. 665-669
Author(s):  
J. Isern ◽  
R. Canal ◽  
M. Hernanz ◽  
J. Labay
Keyword(s):  
Neutron Stars ◽  
Gravitational Collapse ◽  
White Dwarfs ◽  
Binary Systems ◽  
Observational Evidence ◽  
Dynamical Instability ◽  
Thermonuclear Explosion

AbstractThere is observational evidence of the presence of young neutron stars in old binary systems. A likely explanation is that those neutron stars were produced in the collapse of old CO white dwarfs. We show how mass accretion on initially solid white dwarfs can leave central solid cores when dynamical instability sets in and we study the different effects of the existence of such cores on the outcome of the competition between thermonuclear explosion and gravitational collapse.

scholarly journals Nucleosynthesis During Nova Explosions and Grain Formations in Ejected Envelopes

1979 ◽  
Vol 53 ◽  
pp. 533-533
Author(s):  
Masayuki Y. Fujimoto
Keyword(s):  
General Theory ◽  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Thermal Emission ◽  
Finite Amplitude ◽  
Close Binary ◽  
Close Binary Systems

Recent observations have revealed the existence of infrared brightening in some nova explosions, and its absence in others. These infrared excesses are ascribed to thermal emission from grains which are considered to consist of graphite. Such nova explosions are widely accepted to be triggered by hydrogen shell-flashes on the surface of white dwarfs which accrete matter in close binary systems. As for the hydrogen shell-flash, recently, a general theory applicable even to the case of finite amplitude has been developed. According to this theory, the progress of a shell-flash is determined only by the mass of the white dwarf MWD and the mass of the accreted hydrogen-rich envelope ΔMH.

scholarly journals m = 1 Oscillations of Accretion Disks in Close Binary Systems

1997 ◽  
Vol 163 ◽  
pp. 777-778
Author(s):  
Atsuo T. Okazaki
Keyword(s):  
Accretion Disks ◽  
Fundamental Mode ◽  
White Dwarfs ◽  
Binary Systems ◽  
Close Binary ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Close Binary Systems

AbstractWe examine the two-dimensional structure of m = 1 modes in disks around white dwarfs in close binary systems. We find that the odd modes (warping modes) as well as even modes (eccentric modes) are confined to the outermost part of the disk. The period of the fundamental mode is of a few percent of the binary period, and is insensitive to the parity of the mode. These modes naturally explain the superhump periods of SU UMa stars.

scholarly journals White Dwarfs in Cataclysmic Binaries

1979 ◽  
Vol 53 ◽  
pp. 417-425 ◽  
Author(s):  
Brian Warner
Keyword(s):  
Direct Measurement ◽  
White Dwarf ◽  
Proper Motion ◽  
White Dwarfs ◽  
Binary Systems ◽  
Fundamental Property ◽  
Wide Binary ◽  
Trigonometric Parallax ◽  
Select Group ◽  
Cataclysmic Binaries

For isolated stars, identification as a white dwarf may be effected in several ways. The fundamental property of abnormally low luminosity can be detected through direct measurement of trigonometric parallax or indirectly through large proper motion (accompanied by appropriate photometric properties). The presence of greatly pressure broadened absorption lines is another unambiguous criterion. Rapid light oscillations of the kind reviewed by Robinson are another hallmark of a select group of white dwarfs. Any or all of these criteria may be used to classify a star as a white dwarf and in general can be applied to members of wide binary systems.

scholarly journals Gaia white dwarfs within 40 pc II: the volume-limited Northern hemisphere sample

2020 ◽  
Vol 499 (2) ◽  
pp. 1890-1908 ◽  
Author(s):  
Jack McCleery ◽  
Pier-Emmanuel Tremblay ◽  
Nicola Pietro Gentile Fusillo ◽  
Mark A Hollands ◽  
Boris T Gänsicke ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Mass Range ◽  
Wide Binary ◽  
William Herschel ◽  
Initial Selection ◽  
Gaia Dr2 ◽  
Kinematic Properties

ABSTRACT We present an overview of the sample of Northern hemisphere white dwarfs within 40 pc of the Sun detected from Gaia Data Release 2 (DR2). We find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from Gaia DR2 and followed up recently with the William Herschel Telescope and Gran Telescopio Canarias. Three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection in the Gaia DR2 Hertzsprung–Russell diagram. Atmospheric parameters are calculated from Gaia and Pan-STARRS photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20 pc sample. Local white dwarfs are overwhelmingly consistent with Galactic disc kinematics, with only four halo candidates. We find that DAZ white dwarfs are significantly less massive than the overall DA population ($\overline{M}_\mathrm{DAZ}$ = 0.59 M⊙, $\overline{M}_\mathrm{DA}$ = 0.66 M⊙). It may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. We detect a sequence of crystallized white dwarfs in the mass range from 0.6 $\lesssim M/\mbox{$\mathrm{M}_\odot $}\ \lesssim$ 1.0 and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallization alone. We also detect 26 double degenerates and white dwarf components in 56 wide binary systems.

scholarly journals Finding binaries from phase modulation of pulsating stars with Kepler – VI. Orbits for 10 new binaries with mischaracterized primaries

2020 ◽  
Vol 493 (4) ◽  
pp. 5382-5388
Author(s):  
Simon J Murphy ◽  
Nicholas H Barbara ◽  
Daniel Hey ◽  
Timothy R Bedding ◽  
Ben D Fulcher
Keyword(s):  
Phase Modulation ◽  
White Dwarfs ◽  
Binary Systems ◽  
Main Sequence ◽  
Classification Algorithm ◽  
Orbital Parameters ◽  
Pulsating Stars ◽  
Stellar Properties ◽  
Scuti Stars ◽  
Δ Scuti Stars

ABSTRACT Measuring phase modulation in pulsating stars has proven to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables, known as δ Scuti stars consists of particularly good targets for this, and the Kepler sample of these has been almost fully exploited. However, some Keplerδ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new δ Scuti pulsators among tens of thousands of F-type stars, which we then searched for phase modulation attributable to binarity. We discovered 10 new binary systems and calculated their orbital parameters, which we compared with those of binaries previously discovered in the same way. The results suggest that some of the new companions may be white dwarfs.

scholarly journals White Dwarf Pulsations

1980 ◽  
Vol 5 ◽  
pp. 469-472
Author(s):  
W. Dziembowski
Keyword(s):  
Effective Temperature ◽  
High Speed ◽  
White Dwarfs ◽  
Binary Systems ◽  
Early Suggestion ◽  
Nonradial Oscillation ◽  
High Speed Photometry ◽  
Long Time ◽  
Nuclear Burning ◽  
Radial Pulsations

It has been known for a long time that white dwarfs are pulsationally unstable if nuclear burning takes place in their envelopes. Perturbation of energy generation rate promotes pulsational instability and this effect is frequently referred to as ε-mechanism. In recent years, with the advent of high-speed photometry, many rapidly varying white dwarfs have been discovered. However, periods of variability were found to be significantly longer than the periods of radial pulsations which were the only type of oscillations considered before the discovery. Furthermore, the case of ε-mechanism as being responsible for the observed variability has never been made strong for any of the observed objects.Variable white dwarfs are found among: Io single DA-type objects in the effective temperature range 10000-15000K; 2o members of close, usually but not always, cataclysmic binary systems. Although, following an early suggestion by Warner and Robinson (1972), the excitation of nonradial oscillation is postulated in both cases, the two types represent very different physical situations and they will be discussed here separately.

scholarly journals Accretion induced collapse of white dwarfs in binary systems and their observational properties

2009 ◽  
Vol 172 ◽  
pp. 012037 ◽  
Author(s):  
D T Wickramasinghe ◽  
Jarrod R Hurley ◽  
Lilia Ferrario ◽  
Christopher A Tout ◽  
Paul D Kiel
Keyword(s):  
White Dwarfs ◽  
Binary Systems

scholarly journals Optical detection of the rapidly spinning white dwarf in V1460 Her

2021 ◽  
Author(s):  
Ingrid Pelisoli ◽  
R T Marsh ◽  
R P Ashley ◽  
Pasi Hakala ◽  
A Aungwerojwit ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Binary Systems ◽  
Hubble Space Telescope ◽  
Cataclysmic Variable ◽  
Optical Photometry ◽  
Arrival Times ◽  
Precise Ephemeris ◽  
History Of

Abstract Accreting magnetic white dwarfs offer an opportunity to understand the interplay between spin-up and spin-down torques in binary systems. Monitoring of the white dwarf spin may reveal whether the white dwarf spin is currently in a state of near-equilibrium, or of uni-directional evolution towards longer or shorter periods, reflecting the recent history of the system and providing constraints for evolutionary models. This makes the monitoring of the spin history of magnetic white dwarfs of high interest. In this paper we report the results of a campaign of follow-up optical photometry to detect and track the 39 sec white dwarf spin pulses recently discovered in Hubble Space Telescope data of the cataclysmic variable V1460 Her. We find the spin pulsations to be present in g-band photometry at a typical amplitude of 0.4 per cent. Under favourable observing conditions, the spin signal is detectable using 2-meter class telescopes. We measured pulse-arrival times for all our observations, which allowed us to derive a precise ephemeris for the white dwarf spin. We have also derived an orbital modulation correction that can be applied to the measurements. With our limited baseline of just over four years, we detect no evidence yet for spin-up or spin-down of the white dwarf, obtaining a lower limit of $|P/\dot{P}| > 4\times 10^{7}$ years, which is already 4 to 8 times longer than the timescales measured in two other cataclysmic variable systems containing rapidly rotating white dwarfs, AE Aqr and AR Sco.

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