... unique opportunities to study the details of the accretion flow in the cases of normal white dwarfs with accretion disks and magnetic white dwarfs. ...

The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass ...

... CVs) in which a white dwarf (WD) accretes matter from a main-sequence star (the secondary) filling its Roche lobe by means of an accretion disk. ...

Properties of the neutrinos emitted during an accretion of white dwarf matter by a primordial black hole are considered. The possibility of detecting these neutrinos and their oscillations is discussed.

We consider time-dependent accretion onto magnetized white dwarfs. A detailed description of a numerical method of solution to the hydrodynamical equations is given. The postshock flow is cooled by optically thin bremsstrahlung and is thermally unstable. As a result the shock height undergoes periodic oscillations. We consider the ...

Understanding boundary layer heating is crucial in determining the thermal structure of the accreted envelope of a prenova white dwarf. The matched asymptotic expansion method was used to solve consistently for the structure of accretion disks transferring matter onto rotating white ...

In this review I describe the basic properties of white dwarfs and their pulsations. I then discuss some of the areas in which the pulsations can provide meaningful results, such as internal chemical profiles, possible emission of ``exotic'' particles, planet detection, crystallization, convection, accretion, and cosmochronology.

If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae an...

Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many

... Abstract : The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. ...

of the secondary star and accretion of nova abundance-enriched matter back to the white dwarf via the accretion of a nova remnant-like nebula around EY Cyg. Subject Headings: Stars: cataclysmic variables, white dwarfs, related either to donor star contamination by nova ...

Over the past few years, we have been investigating the effects of accretion onto massive white dwarfs and its implications for their growth in mass toward the Chandrasekhar limit, in attempts to identify a possible relationship between SN I and novae. In our studies we have considered accretion at various mass ...

WZ Sge provides us with an excellent test for numerical codes trying to reproduce the heating and cooling of a white dwarf due to accreted material. This is because of both the many observed quantities of this binary and its long quiescent state. However, a large discrepancy appears between the observed white ...

Accretion onto and nova events on the surface of a degenerate cold one-solar-mass iron white dwarf are investigated. It is found that, during accretion, hydrogen diffuses deeper into the core than its CNO catalysts, suggesting that the thermonuclear runaway occurs not at the innermost radius achieved by the ...

The growth of a carbon-oxygen white dwarf is investigated within the framework of the general shell-flash theory of accreting white dwarfs. Account is taken of the envelope restructing in response to the shell flash and to possible mass loss from the white ...

Recent discovery of an unexpectedly large number of low-mass binary pulsars (LMBPs) in globular clusters has instigated active discussions on the evolutionary origin of binary pulsars. Prompted by the possibility that at least some of LMBPs originate from accretion-induced collapse (AIC) of white dwarfs, a reexamination is conducted as ...

The main physical phenomena which occur on accretion disks, are discussed. A numerical simulation of a three dimensional accretion disk model around a white dwarf in a binary system composed of two equal mass stars is developed. The smoothed particle hydr...

It is proposed a new mechanism for high energy gamma ray burst in Supernova type I (SNI) explosion. Presupernova is assumed to be a binary system comprised of a red giant and a white dwarf with a wind accretion. The accretion flow terminates by the accret...

We examine the role of the accretion disk in the steady-burning white dwarf model for supersoft sources. The accretion luminosity of the disk is quite small compared to the nuclear burning luminosity of the central source. Thus, in contrast to standard ac...

Accreting white dwarfs in cataclysmic variables (CVs) have also recently been shown to exhibit non-radial pulsations similar to their non-interacting counterparts; GW Librae was the first accreting pulsator discovered in 1998 (Warner & van Zyl 1998; van Zyl et al. 2000, 2004). When the orbital period of a CV is ...

Our past HST studies of the temperatures of 9 accreting, pulsating white dwarfs in cataclysmic variables show that 3 are in the normal instability strip for single white dwarfs, but the other 6 are much hotter {15,000-16,500K}. This dual strip has been proposed to be due to mass differences in ...

The history and properties of white dwarfs (Bessel's conclusion that Sirius and Procyon have invisible companions, Clark's discovery of Sirius B, Adams and Russell's study of white dwarf spectra, Chandrasekhar's explanation of white dwarf ...

DQ Herculis (Nova Herculis 1934) is a deeply eclipsing cataclysmic variable containing a magnetic white dwarf primary. The accretion disk is thought to block our line of sight to the white dwarf at all orbital phases due to its extreme inclination angle. ...

The AM Her systems are widely believed to be cataclysmic variable systems in which the white dwarf has a magnetic field strong enough to lock the white dwarf to the companion star. The magnetic field channels the accretion flow to the magnetic polar caps ...

WZ Sge provides us with an excellent test for numerical codes trying to reproduce the heating and cooling of a white dwarf due to accreted material. This is because of both the many observed quantities of this binary and its long quiescent state. However, a large discrepancy appears between the observed white ...

Papers are presented concerning present knowledge on degenerate stars, including white dwarfs and variable degenerates. Specific topics include the masses of DB degenerate dwarfs, the evolution of degenerate components of close binary systems, the collapse of accreting white ...

We use the data base of spectroscopically identified white dwarfs to isolate a sample of cool degenerates with trace metals. The spatial distribution and space velocity components of the white dwarfs projected onto and perpendicular to the galactic plane are compared with the distribution of local interstellar ...

The hydrostatic evolution of a carbon-oxygen white dwarf (COWD) experiencing accretion of matter from its companion, a second COWD, is calculated for accretion rates ranging from 10 to the -8th to 10 to the -5th solar masses per year. It is shown that, for accretion rates less than (3.3 + or - ...

The hydrostatic evolution of a carbon-oxygen white dwarf (COWD) experiencing accretion of matter from its companion, a second COWD, is calculated for accretion rates ranging from 10 to the -8th to 10 to the -5th solar masses per year. It is shown that, for accretion rates less than (3.3 + or - ...

May 2, 2007 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...

Evidence is mounting that cataclysmic variables are weak sources of synchrotron emission. If true, it demonstrates that accretion powered interacting binaries produce such emission whether their primaries are white dwarfs, neutron stars, or black holes.

In analogy the soft component probably originates from an accretion-heated surface region around the white dwarfs magnetic pole(s). ...

Comets Clash at Heart of Helix Nebula. 02.12.07 ... thought that perhaps the white dwarf was accreting matter onto itself from a hidden companion star. ...

Jan 2, 2003 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...

this vein, V2301 Oph is particularly interesting because it is an ... The BL Hyi data are published in The Astrophysical Journal and the V2301 Oph data ...

Dec 7, 2001 ... Cataclysmic Variables (CVs) are close binary systems in which a white dwarf is accreting material from a more or less normal star. ...

Accreting high magnetic field neutron stars are observed as X-ray pulsars. ... An examination of a power spectrum of the pulsed emission shows that the peak ...

Important aspects of the theory of accretion are reviewed and the theory of the spherical accretion of a polytropic gas is presented. The effect of the termination of the flow at the surface of a neutron star or white dwarf is studied with consideration given to the interaction with a magnetic field anchored to the ...

Accreting white dwarfs have recently been shown to exhibit non-radial pulsations similar to their non-interacting counterparts. This allows us to probe the interior of the accreting white dwarf using seismology, and may be the only way to determine masses for non-eclipsing ...

The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass ...

The primary white dwarf of the cataclysmic variable SDSS J074531.92+453829.6 was discovered to exhibit non-radial pulsations in 2006 January. This accreting white dwarf underwent its first recorded dwarf nova outburst in 2006 October, during which its brightness increased ...

Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the ...

The observations of WZ Sge provide us with the best test for computational codes trying to calculate the accretion process onto a white dwarf. We find that the accreted material on WZ Sge cannot spread over the whole star at least on a time scale of ten y...

Mar 1, 2010 ... Chandra has also revealed unexpected parallels between accretion onto pre-main sequence stars, white dwarfs, neutron stars, stellar-mass and ...

Observations of novae and theoretical results, in which the authors studied the nova outburst by radially accreting H-rich matter onto an He white dwarf, have convinced them that realistic nova models must be based on accretion that includes the angular momentum of the accreting matter. In the ...

Observational and theoretical studies of the outbursts of classical novae have provided critical insights into a broad range of astrophysical phenomena. Thermonuclear runaways (TNRs) in accreted hydrogen-rich envelopes on the white dwarf (WD) components o...

If the accreting white dwarf increases its mass to the Chandrasekhar mass, it will either explode as a Type I supernova or collapse to form a neutron star. In fact, there is a good agreement between the exploding white dwarf model for Type I supernovae and observations. We describe various ...

It is demonstrated that existing theories of mixing in accreting white dwarfs encounter difficulties when confronted with observations of enrichments in nova ejecta. Arguments are presented, based on the Ekman spin-up process, which suggest that angular momentum transport from the accreted material to the ...

Although CI Cam, which showed an outburst in April 1998, has been regarded as a soft X-ray transient (SXT) harboring a black hole, it has some characteristics that can hardly be reconciled with the SXT picture. In this paper, we propose a white dwarf as the central accreting star in CI Cam.

opportunity to study rapid variations in stars that are very compact, like white dwarfs and neutron stars exotic neutron stars. How does accretion occur in binary stars? Two stars in orbit around each other up like compact stars (black holes, neutron stars or white dwarfs) and are ...

Simple theories of the accretion phase and expansion phase of hydrogen shell flashes on accreting white dwarfs are used to find the conditions under which classical novae occur. Particular attention is paid to the possibility that the CNO abundances in the accreted envelope are greatly enhanced ...

The rate of accretion of the interstellar medium onto a star is discussed. It is shown that this is a complex, fractionated process. The relative abundances of heavy elements accreting onto the star are very different from the abundances in the ambient medium. These accretion rates are important in determining the abundances on the ...

The magnetospheres of accreting compact stars (neutron stars and white dwarfs) are examined. It is assumed that the compact star possesses a multipole magnetic field. The shape of the magnetosphere for the two-dimensional analog of spherically symmetric accretion and the magnetic-field configuration for the case of ...

The time scales of a few representative elements diffusion in hydrogen- and helium-rich white-dwarf envelopes are presented. The dependences on depth, the stellar mass, and effective temperature are investigated. It is shown that diffusion processes are sufficiently rapid that the observed monoelemental character of white-dwarf spectra can be explained. ...

We present the results of a multicomponent synthetic spectral analysis of Hubble Space Telescope (HST) STIS spectra of the ultrashort-period dwarf novae VY Aqr and WX Ceti during their deep quiescence following their last superoutburst. The white dwarf in these extremely low accretion rate systems dominates the ...

The outbursts of dwarf novae are suggested as being due to the liberation of energy in the accretion disk surrounding the white dwarf component following unstable mass outflow by the red companion. The periodicities observed in dwarf novae near maximum light are shown to be consistent ...

The nova outburst phenomenon is presently studied in light of the results of numerical calculations for the accretion of H-rich material onto 1-solar mass C/O white dwarfs, with arrival angular momentums of the order of 10-100 percent of the Keplerian values. The range of models investigated lies between the two limiting cases of ...

A critical condition is obtained for which carbon deflagration induces collapse of an accreting C + O white dwarf, not explosion. If the carbon deflagration is initiated at central density as high as 10/sup 10/ g cm/sup -3/ and if the propagation of the deflagration wave is slower than approx. 0.15 upsilon/sub s/ (upsilon/sub s/ is the ...

The main aim in the current survey is to suggest models of the development of structures, such as vortices and spirals, in accretion white dwarf's binaries. On the base of hydrodynamical analytical considerations it is applied numerical methods and simulations. It is suggested in the theoretical model the perturbation's parameters of ...

Using newly determined parallaxes for dwarf novae, we have derived outburst accretion rates for VY Aqr, RU Peg, and T Leo, and for T Leo during quiescence. The two short-period dwarf novae, VY Aqr and T Leo, show good agreement with optically thick steady-state accretion disks in outburst, whereas RU Peg shows a ...

Effects of a new triple-? reaction rate on the ignition of carbon-oxygen white dwarfs accreting helium in a binary systems have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type la supernova. We examine the cases of different accretion rates of helium and ...

Elements heavier than hydrogen or helium that are present in the atmospheres of white dwarfs with effective temperatures lower than 25,000 K, are believed to be the result of accretion. By measuring the abundances of these elements and by assuming a steady-state accretion, we can derive the composition of the ...

The effects of a new triple-? reaction rate on the ignition of carbon-oxygen white dwarfs accreting helium in a binary system have been investigated. The ignition points determine the properties of a thermonuclear explosion of a Type Ia supernova. We examine the cases of different accretion rates of helium and ...

We compare Smoothed Particle Hydrodynamic simulations of retrogradely precessing accretion disks that have a white dwarf primary and a main sequence secondary with observational data and with theory on retrograde precession via tidal torques like those by the Moon and the Sun on the Earth [1, 2]. Assuming the primary does not ...

We discuss the properties of HD49798/RXJ0648.0-4418 the only known X-ray binary composed by a hot sub-dwarf and an X-ray pulsar. We recently found evidence that the pulsations are due to a very massive (1.28 Msolar), fast rotating (13 s) white dwarf. The future evolution of this post common envelope binary will involve a new phase of ...

The long-term evolution of massive (M>1.1 M/sub sun/) accreting white dwarfs in close binary systems is discussed in the context of several astrophysical problems. The evolution of massive white dwarfs was followed with model calculations. The models have /sup 12/C--/sup 16/O cores and ...

A steady-state model of the accretion disk around a white dwarf, including the boundary layer and the hot spot, has been constructed. Calculated distributions of radiation are compared with soft X-ray, ultraviolet, visual, and infrared observations of SS Cyg during outburst as well as with ultraviolet measurements of V 603 Aql and RR ...

Diffuse Galactic 1.809 MeV line emission, produced by the decay of the radionuclide Al-26 is modeled for nova distributions. Two distinct nova contributions were investigated: accreting carbon-oxygen white dwarfs and accreting oxygen-neon-magnesium white dwarfs. It is ...

White dwarfs may offer new insights into how common extrasolar minor bodies such as asteroids are. One quarter of all white dwarfs appear to have heavy elements such as Ca, Mg, Si, and Fe in their atmospheres, despite the fact that the extreme gravity of these stars causes heavy elements to sink through their ...

The authors point out that the hard (?3 keV) X-ray light-curves of accreting magnetic white dwarfs can be understood as due solely to occultations of the emission region by the white-dwarf body. The prevalence of quasi-sinusoidal hard X-ray light-curves amongst the intermediate polars probably implies that the ...

. We have analysed all available rosat pspc observations of non-magnetic cataclysmic variables. The VY Scl and non-SU UMa systems have harder X-ray spectra than the SU UMa and UX UMa systems. The old nova RR Pic has a very soft X-ray spectrum and might not be an ordinary nonmagnetic cataclysmic variable. There appears to be no clear correlation of the X-ray temperature, the emission measure, or ...

We investigate the role of the accretion rate in determining the outcome of the accretion of hydrogen-rich material onto a 1.25 M/sub sun/ C/O white dwarf. It is found that there is an upper limit to the mass accretion rate that leads to a nova outburst. The upper limit is between 10/sup -8/ ...

We find a dimming during optical quiescence of the cataclysmic variable WZ Sge by about half a magnitude between superoutbursts. We connect the dimming with the development of a cavity in the inner part of the accretion disk. We suggest that, when the cavity is big enough, accretion of material is governed by the magnetic field of the ...

In a close binary system or in a dense cloud, gas may be accreted onto a carbon-oxygen white dwarf and will be processed into helium by hydrogen burning in an accreted envelope. As a result, a helium zone grows in mass, and a helium shell flash takes place just as in cores of red giant stars. Properties of such ...

We suggest that the electric fields of stellar atmospheres play an essential role in the accretion and mass ejection processes, especially of He-rich stars. The static configuration implies an electric field that is strong enough to push protons outward, but sufficiently weak to enable as many electrons as protons to escape. This process can stop hydrogen ...

By applying an analytical solution to the envelope, hydrogen shell flashes on accreting white dwarfs are computed semianlytically from their ignition to their final stage. When the mass of the white dwarf, M, and the mass of the hydrogen-rich envelope, ..delta..M/sub 1/, are specified, their ...

The observations of WZ Sge provide us with the best test for computational codes trying to calculate the accretion process onto a white dwarf. We find that the accreted material on WZ Sge cannot spread over the whole star at least on a time scale of ten years. Numerical models which include the angular momentum of ...

The observations of WZ Sge provide us with the best test for computational codes trying to calculate the accretion process onto a white dwarf. We find that the accreted material on WZ Sge cannot spread over the whole star at least on a time scale of ten years. Numerical models which include the angular momentum of ...

Approximately half the luminosity of a typical cataclysmic variable may emerge as an optically thick component peaking in the EUV. Observations of this component are important for understanding the energetics and accretion rates of CV's in general, as well as for understanding the physics of the accretion process. The nature of the turbulent ...

We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. From the best-fit model solutions to the combined HST +FUSE ...

It has been clear for many years now that the process of accretion on to a compact object is largely dominated by magnetic fields. The magnetic field channels the accretion flow onto strongly magnetized stars such as magnetic white dwarfs (cataclysmic variables), and neutron stars (accreting ...

Infrared studies have revealed debris likely related to planet formation in orbit around {approx}30% of youthful, intermediate mass, main-sequence stars. We present evidence, based on atmospheric pollution by various elements heavier than helium, that a comparable fraction of the white dwarf descendants of such main-sequence stars are orbited by planetary ...

Emission-line profiles of several cataclysmic variables have been observed through eclipse, and they do not show strong evidence for the rotational signature that is characteristic of an accretion disk. The lines appear to be formed in material that has some rotation with respect to the white dwarf, but that also has a substantial ...

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, show evidence for ongoing accretion of material onto their surfaces. Some DAZs are known to have unresolved M dwarf companions, which could account for the observed accretion through a stellar wind. I combine observed Ca ...

Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks

Recent results are presented and discussed regarding the EUV and X-ray emission of nonmagnetic cataclysmic variables. Emphasis is given to high accretion rate systems (novalike variables and dwarf novae in outburst), and to a number of apparent discrepancies between observations and the theory of the boundary layer between the ...

We present an abundance analysis of a sample of 33 hydrogen-rich (DA) white dwarfs. We have used archival high-resolution spectra to measure abundances of calcium, magnesium and iron in a set of 30 objects. In addition, we present preliminary calcium abundances in three new white dwarfs based on low-dispersion ...

There are 9 dwarf novae (DN) among the 43 cataclysmic variables (accreting white dwarfs in close binary systems) that were detected during the HEAO-1 all-sky X-ray survey (1977-1979). On the other hand, there are roughly one hundred dwarf novae that are closer and/or optically brighter and yet ...

A long-standing and unverified prediction of binary star evolution theory is the existence of a population of white dwarfs accreting from substellar donor stars. Such systems ought to be common, but the difficulty of finding them, combined with the challenge of detecting the donor against the light from accretion, ...

Astrophysical jets seem to occur in nearly all types of accreting objects, from supermassive black holes to young stellar objects. On the basis of x-ray binaries, a unified scenario describing the disc/jet coupling has evolved and been extended to many accreting objects. The only major exceptions are thought to be cataclysmic variables: ...

We have computed three evolutionary sequences which treat the accretion of hydrogen-rich material onto 1.38 M/sub sun/ white dwarfs. In each of these sequences the accreting matter had only a solar composition of the CNO nuclei (Z = 0.015). In the first sequence we utilized an accretion rate of ...

The prime scientific objectives of the Rossi X-Ray Timing Explorer (RXTE) were the study of astrophysical compact objects: black holes (galactic and extragalactic), many types of neutron stars, and accreting white dwarfs. RXTE was successful in achieving ...

The photospheres of 25000 K helium white dwarfs should not produce X-rays, while an accretion-powered source should emit much of its emergy in the ROSAT ...

We describe a mechanism that promises to explain how nova outbursts take place on white dwarf of 1 Msub solar or less and for accretion rates of 4 x 10/sup -10/ Msub solar yr/sup -1/ or greater. 7 refs.

We describe a mechanism that promises to explain how nova outbursts take place on white dwarf of 1 solar mass or less, and for accretion rates of 4 x 10 sup -10 solar mass/year or greater. 7 refs. (ERA citation 13:007924)

Over the past few years, we have been investigating the effects of accretion onto massive white dwarfs and its implications for their growth in mass toward the Chandrasekhar limit, in attempts to identify a possible relationship between SN I and novae. In...

Two rather disjoint scenarios for Type I supernovae are presented. One is based upon mass accretion by a white dwarf in a binary system. The second involves a star having some 8 to 10 times the mass of the sun which may or may not be a solitary star. Desp...

) #12;Type Ia Supernovae Theory Thermonuclear explosion of MCh white dwarf � Accretes from companion at high front Pressure is continuous across the front Density drops in the ash region. � Thermal diffusion of surface area are generated.ash fuel ash

The blackbody integrated fluxes emitted from and real photospheric composite colors of disks surrounding white dwarfs and neutron stars are calculated, taking into account the exchange of radiation among different parts of the disk.

We describe briefly the properties of the recently completed Southern African Large Telescope (SALT), along with its first light imager SALTICAM. Using this instrument, we present 4.3 h of high-speed unfiltered photometric observations of the eclipsing polar SDSS J015543.40+002807.2 with time-resolution as short as 112 ms, the highest-quality observations of this kind of any polar to date. The ...

Many researchers have proposed that the Type I supernova (SNI) explosion originates in a white dwarf (WD) star that is undergoing mass accretion from a companion star in a close binary orbit. Previous hydrodynamic computations by others have described the...

We plan to continue our research on the only system of a white dwarf with a M star ... black hole accretion mechanisms, and the presence of supernovae, ... them may teach us about the evolution and survival of planetary systems. ...

We received Type A and B funding under the NASA Astrophysics Data Program for the analysis and interpretation of hard x-ray data obtained by the Rossi X-ray Timing Explorer and other NASA sponsored missions for Intermediate Polars (IPS) and Polars. For so...

The model involves a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay...

We have searched for evidence for dust and gas disks at a sample of hot DA white dwarfs 20000 Kaccreting metals from surrounding material derived from disrupted ...

a white dwarf (no hydrogen) accrets material from a companion star (possibly another white dwarf- combination (z 1100), the photons decouple from the baryons and start to free stream, whereas the pressure% up to one micron, and HgCdTe detectors covering the near- infrared region. The nine ...

We have searched for evidence for dust and gas disks at a sample of hot DA white dwarfs 20000 Kaccreting metals from surrounding material derived from disrupted ...

The contents include: Star deaths and the formation of compact objects; White dwarfs; Rotation and magnetic fields; Cold equation of state above neutron drip; Pulsars; Accretion onto black holes; Supermassive stars and black holes; Appendices; and Indexes. This book discusses one aspect, compact objects, of astronomy and provides ...

More than 100 hot white DA white dwarfs have been observed by the FUSE mission, exceeding by more than a factor 4 the numbers of stars observed at high spectral resolution by IUE and HST together. Thus far, this resource has not been fully exploited, with, mostly, papers published on single or small numbers of objects. We now present a ...

The question of the nature of the ultraviolet and X-ray radiation field of cataclysmic binaries is addressed. The spectrum and luminosity of this radiation are important in determining the mass transfer rate and energy budget of the system and in studies of the ejecta surrounding novae. In many systems, the soft X-ray luminosity is approx.10/sup 2/--10/sup 4/ times weaker than predicted by simple ...

We are attempting to model the nova outburst by spherically accreting H-rich material onto a 1 M/sub sun/ He white dwarf at a rate of 10/sup -8/ M/sub sun/ yr/sup -1/. The star accretes for 5848 years, when the nuclear reactions run away near the base of the accreted envelope. The ...

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix ...

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix ...

We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find ...

The necessary conditions for the production of strong thermonuclear runaways in the hibernation scenario are identified and explored. It is found that a reduction in the accretion rate by a factor of about 100, for a period longer than a few thousand years, is generally sufficient to ensure nova-type outbursts, even in the presence of rather high preoutburst ...

We study the power spectra of the variability of seven intermediate polars containing magnetized asynchronous accreting white dwarfs, XSS J00564+4548, IGR J00234+6141, DO Dra, V1223 Sgr, IGR J15094-6649, IGR J16500-3307 and IGR J17195-4100, in the optical band and demonstrate that their variability can be well described by a model ...

We have carried out a combined Hubble Space Telescope and FUSE FUV spectroscopic analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS Cygni's accurate HST FGS parallax giving d = ...

Context: X-ray spectra of dwarf novae in quiescence observed by Chandra and XMM-Newton provide new information on the boundary layers of their accreting white dwarfs. Aims: Comparison of observations and models allows us to extract estimates for the thermal conductivity in the accretion layer ...

Hydrodynamic studies have been performed of accretion onto 1.00 Msun, 1.25 Msun, and 1.35 Msun oxygen-neon-magnesium (ONeMg) white dwarfs at a rate of 1017 g s-1. The material from the companion star is expected to be of solar composition but is assumed to be mixed with material from the underlying white ...

In the last two years a hand-full of white dwarfs (WDs) with circumstellar debris disks have been discovered. The debris disks are either left over from the late stages of stellar evolution or are the result of tidally disrupted asteroids or comets, and are thus signposts of planetary systems. Our team has been investigating the properties of these debris ...

This thesis examines aspects of subsonic reactive flows in stars. Highlighted are fluid flows in which the velocity of the fluid is much less than the local sound speed of the fluid, and where the thermodynamic conditions of the fluid are conducive to nuclear reactions. Reactive flows of this nature are capable of generating self-sustained flame fronts, also known as deflagration waves. An ...

The evolution of the magnetic field of an accreting magnetic white dwarf with an initially dipolar field at the surface has been studied for non-spherical accretion under simplifying assumptions. Accretion on to the polar regions tends to advect the field toward the stellar equator which is ...

A quarter of DA white dwarfs are metal polluted, yet elements heavier than helium sink down through the stellar atmosphere on time-scales of days. Hence, these white dwarfs must be the currently accreting material containing heavy elements. Here we consider whether the scattering of comets or ...

An XMM-Newton observation performed in May 2008 has confirmed that the 13 seconds pulsations in the X-ray binary HD49798/RX J0648.0-4418 are due to a rapidly rotating white dwarf. From the pulse time delays induced by the 1.55 days orbital motion, and the system's inclination, constrained by the duration of the X-ray eclipse discovered in this observation, ...

White dwarfs inspiralling into black holes of mass MBH >~ 105 Msolar are detectable sources of gravitational waves in the Laser Interferometer Space Antenna (LISA) band. In many of these events, the white dwarf begins to lose mass during the main observational phase of the inspiral. The mass-loss starts gently ...

White dwarfs inspiraling into black holes of mass MBH � 105 are bright sources of gravita-tional waves in the LISA band. In many of these events, the white dwarf begins to lose mass during the main observational phase of the inspiral. The mass loss starts gently and can last for thousands of orbits. The ...

Suggestive evidence has accumulated that intermediate mass black holes (IMBHs) exist in some globular clusters. Some stars will inevitably wander sufficiently close to the hole to suffer a tidal disruption. IMBHs can disrupt not only solar-type stars but also compact white dwarf stars. We investigate the fate of white ...

The dwarf nova VSX J0747+0650 has pulsations at 238.2 s and 684.2 s (found only two years after its superoutburst), and is therefore a CV/ZZ star. Our observations of the accreting white dwarf SDSS0919+08 show that it occasionally has a brightness modulation at 214 s in addition to the known one near 260 s, ...

There is wide agreement that type Ia supernovae (used as standard candles for cosmology) are associated with the thermonuclear explosions of white dwarf stars. The nuclear runaway that leads to the explosion could start in a white dwarf gradually accumulating matter from a companion star until it reaches the ...

A nova outburst is one consequence of the accretion of hydrogen rich material onto a white dwarf in a close binary system. The strong electron degeneracy of a massive white dwarf drives the temperatures in the nuclear burning region to values exceeding 108K under all circumstances. As a result, ...

SW Sextantis stars are a relatively large group of cataclysmic variables whose properties contradict all predictions made by the current CV evolution theories. Very little is known about the properties of their accreting white dwarfs and their donor stars, as the stellar components are usually outshone by an extremely bright ...

We compute that extrasolar minor planets can retain much of their internal H_2O during their host star's red giant evolution. The eventual accretion of a water-rich body or bodies onto a helium white dwarf might supply an observable amount of atmospheric hydrogen, as seems likely for GD 362. More generally, if hydrogen pollution in ...

We compute that extrasolar minor planets can retain much of their internal H2O during their host star's red giant evolution. The eventual accretion of a water-rich body or bodies onto a helium white dwarf might supply an observable amount of atmospheric hydrogen, as seems likely for GD 362. More generally, if hydrogen pollution in ...

We compute that extrasolar minor planets can retain much of their internal H{sub 2}O during their host star's red giant evolution. The eventual accretion of a water-rich body or bodies onto a helium white dwarf might supply an observable amount of atmospheric hydrogen, as seems likely for GD 362. More generally, if hydrogen ...

We obtained Hubble Space Telescope far-ultraviolet spectra of the Z Cam-type dwarf nova RX And during the early rise to outburst and the decline from the same outburst. The spectral wavelength range covered was 1149-1435 �. The rise spectrum is dominated by strong, very broad absorption lines, while the decline spectrum has strong, narrower absorption with weak to moderately ...

Properties of white dwarfs which are accreting hydrogen-rich matter at rates in the range 1.5 x 10/sup -9/ to 2.5 x 10/sup -7/ M/sub sun/ yr/sup -1/ are investigated in several approximations. Steady-burning models, in which matter is processed through nuclear-burning shells as rapidly as it is accreted, provide a ...

We have analyzed the Far Ultraviolet Spectrocopic Explorer (FUSE) spectra of two U Gem-Type dwarf novae, SS Aur and RU Peg, observed 28 days and 60 days (respectively) after their last outburst. In both systems the FUSE spectra (905 - 1182 A) reveal evidence of the underlying accreting white dwarf exposed in the ...

We have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10-11 - 10-8M? yr-1. These ...

The true nature of Mira's companion star "Mira B" has intrigued and troubled investigators for the past 30 years. In the FUV spectral region, which is free of contamination from Mira A, the nature of the line spectrum and continuum energy distribution provide important clues. We have analyzed numerous IUE archival spectra of Mira B, in the wavelength range shorter than 2600 �, with high gravity ...

Pycnonuclear fusion processes take place at extreme density conditions of ?>10^10 g/cm^3, anticipated for the core of white dwarfs or the crust of neutron stars. A formalism was developed for predicting pycnonuclear reaction rates for neutron rich nuclei in the carbon to magnesium range. The reaction rates have been used to simulate pycnonuclear burning ...

We present the results of a multicomponent synthetic spectral analysis of the archival far ultraviolet spectra of several key nova-like variables including members of the SW Sex, RW Tri, UX UMa, and VY Scl subclasses: KR Aur, RW Tri, V825 Her, V795 Her, BP Lyn, V425 Cas, and HL Aqr. Accretion rates as well as the possible flux contribution of the accreting ...

Studies have shown that alpha-induced nuclear reactions in the hot CNO cycles and on the waiting points of the rp-process play a principal role in energy production and nucleosynthesis on the surface of mass-accreting white dwarfs and neutron stars. This paper will present recent measurements at Notre Dame on the rate of 15O(?,?) and ...

We present the results of a synthetic spectral analysis of HST STIS spectra of five long-period dwarf novae obtained during their quiescence to determine the properties of their white dwarfs, which are little known for systems above the CV period gap. The five systems, TU Men, BD Pav, SS Aur, TT Crt, and V442 Cen, were observed as part ...

2S 0918-549 is a low-mass X-ray binary (LMXB) with a low optical to X-ray flux ratio. Probably it is an ultracompact binary with an orbital period shorter than 60 min. Such binaries cannot harbor hydrogen rich donor stars. As with other (sometimes confirmed) ultracompact LMXBs, 2S 0918-549 is observed to have a high neon-to-oxygen abundance ratio (Juett et al. 2001, ApJ, 560, L59) which has been ...

Recently, it has become observationally evident that during a dwarf nova (DN) outburst, a significant portion of the gravitational energy accreted onto the white dwarf (WD) may not be radiated away instantly from a narrow boundary layer as predicted by the standard disk theory. Instead, it may be stored in the WD ...

The physical processes generating nova eruptions are reviewed, along with the effects on nova eruptions of binary-system parameters such as the chemical composition or mass of the white dwarf and the mass accretion rate. Also considered are the possible metamorphosis from dwarf to classical novae and back again, ...

The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. We used ultraviolet data from Galaxy Evolution Explorer and ground-based optical photometry and spectroscopy to follow GW Lib for three ye...

Disk accretion onto a magnetized spinning neutron star or a white dwarf will not be possible if the radius of the magnetosphere exceeds the corotation radius. A dead disk serving as a reservoir of material will then form around the star. Such a disk could retard the spin of the star; it might produce a transient x-ray source of a flare ...

Symbiotic stars appear almost certainly to be interacting binaries with a cool giant losing mass from its wind or by Roche lobe overflow to a much more compact companion. The latter is thought to be usually a white dwarf, but may sometimes be a main sequence star and perhaps even a neutron star. Symbiotic stars go through activity phases, which are thought ...

AG Dra is a symbiotic variable bearing a number of similarities to the suspected emitting components in RS Oph among which are an irradiated red giant mass donor, metal poor, similarly long orbital periods, a hot accreting white dwarf irradiating an optically thick bright accretion disk. Both objects have been ...

A model for the 0.3-1.2 Hz optical quasi-periodic oscillations (QPOs) observed in a number of AM Her-type binary systems has been developed. It is suggested that the observed optical modulation is the result of shock oscillations induced by nonsteady accretion flows. It is shown that time-dependent models of radiative shock waves in nonsteady accretion ...

The interaction between two stars in a binary system can lead to the dynamically stable accretion of H- or He-rich matter onto a degenerate white dwarf (WD). The accreted material constitutes a fresh thermonuclear fuel source that, when ignited, yields a wide variety of observable consequences. In this ...

We study simultaneous X-ray and optical observations of three intermediate polars, EX Hya, V1223 Sgr and TV Col, with the aim of understanding the propagation of matter in their accretion flows. We show that in all cases the power spectra of the flux variability of binary systems in X-ray and optical bands are similar to each other, and the majority of X-ray and optical fluxes ...

We present phase-resolved infrared and optical spectrophotometry of the intermediate polar EX Hya supplemented by archival ultraviolet data. The spin-modulated emission from the accretion funnel and the emission from the accretion disk or ring contain substantial optically thin components. The white dwarf dominates ...

The accretion-induced collapse (AIC) of a white dwarf (WD) may lead to the formation of a protoneutron star and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in Type Ia supernovae. ...

The carbon deflagration models in accreting C+O white dwarfs are presented as a plausible model for Type I supernovae. The evolution of the white dwarf is calculated from the beginning of accretion. The relatively rapid accretion studied here (M> or ...

We argue that the quiescent value of the viscosity parameter of the accretion disc in WZ Sge may be ?cold ~ 0.01, in agreement with estimates of ?cold for other dwarf novae. Assuming the white dwarf in WZ Sge to be magnetic, we show that, in quiescence, material close to the white ...

The spin behaviour of a strongly magnetic star accreting from an internally disrupted disc is considered. The torques are calculated due to the interaction of the star with the disc and the accretion flow, together with the modified structure of the disc. The torques depend on the spin period of the star, and a stable equilibrium period can be found at ...

VW Vulpecula and X Leo are two U Geminorum type dwarf novae, the latter with a newly found orbital period (0.16870+/-0.00007 days). The inclination angle of VW Vul is known to be 44+/-12 deg, the mass of the white dwarf is 0.24+/-0.06 Msun, a secondary mass of 0.14+/-0.01 Msun and the system appears to have an outburst period of 14-24 ...

The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, ...

We present ISOCAM 7 and 15 ?m observations of 12 nearby white dwarfs, 6 of which have been found to have metals such as Ca, Mg and Fe in their photospheres. Our purpose was to search for an excess of infrared emission above the stellar photospheres. We find that none of the white dwarfs other than G29-38 shows a ...

The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, ...

We have carried out a combined Hubble Space Telescope (HST/GHRS) and Far Ultraviolet Spectroscopic Explorer (FUSE) analysis of the prototype dwarf nova SS Cygni during quiescence. The FUSE and HST spectra were obtained at comparable times after outburst and have matching flux levels where the two spectra overlap. In our synthetic spectral analysis, we have used SS ...

Using Chandra HETG data we present light curves for individual spectral lines of Mg XI and Mg XII for EX Hydrae, an intermediate-polar type cataclysmic variable. The Mg XI light curve, folded on the white dwarf spin period, shows two spikes that are not seen in the Mg XII or broad-band light curves. Occultation of the accretion column ...

We report the results of XMM-Newton observations of HD 49798/RX J0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P = 13.2 s) and has a dynamically measured mass of 1.28 � 0.05 M sun. Its X-ray emission consists of ...

A model involving binary mass transfer and accretion onto main sequence stars is developed to explain the brightest known stars in external galaxies, the Hubble-Sandage variables. The similarity in spectral properties between the Hubble-Sandage variables and cataclysmic variables and the extreme disparity in their luminosities are presented as evidence for the essential ...

We present a spectral analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of the eclipsing double-line spectroscopic binary EM Cygni (EM Cyg), a Z Cam DN system. The FUSE spectrum, obtained in quiescence, consists of four individual exposures (orbits): two exposures, at orbital phases {phi} {approx} 0.65 and {phi} {approx} 0.90, have a lower flux; and two exposures, at orbital ...

In a dwarf nova, the accretion disk around the white dwarf is a source of ultraviolet, optical, and infrared photons, but is never hot enough to emit X-rays. Observed X-rays instead originate from the boundary layer between the disk and the white dwarf. As the disk switches ...

In a dwarf nova, the accretion disk around the white dwarf is a source of ultraviolet, optical, and infrared photons, but is never hot enough to emit X-rays. Observed X-rays instead originate from the boundary layer between the disk and the white dwarf. As the disk switches ...

We present the results of a multi-component synthetic spectral analysis of the archival far ultraviolet spectra of several key nova-like variables including members of the SW Sex, RW Tri, UX UMa and VY Scl subclasses: KR Aur, V795 Her, BP Lyn, V825 Her, HL Aqr, RW Tri and V425 Cas. Accretion rates as well as the flux contribution of the accreting ...

We study accretion-induced collapse of magnetized white dwarfs as an origin of millisecond pulsars. We apply magnetized accretion disk models to the precollapse accreting magnetic white dwarfs and calculate the white ...

The results of a spectroscopic monitoring are presented of the object C-1 in the Draco dwarf galaxy during 1987-90. It is shown that C-1 is not a planetary nebula in the process of formation but instead a symbiotic binary, composed of a carbon giant, of unusual blue colors, and of a very hot compact companion, possibly an accreting ...

High speed photometric observations of the dwarf nova VSX J074727.6 + 065050 made in December 2009 during quiescence show an orbital modulation at P orb =85.6 min. They also show that the star is a member of the relatively rare CV/ZZ group, i.e. the accreting white dwarf primary has non-radial pulsations. The two ...

We report the detection of a new point source of soft X-rays (H0405--08) consistent with the position of the nearby triple star system 40 Eridani. The source, which has a temperature near 10/sup 7/ K, has a flux of 3 x 10/sup -11/ ergs cm/sup -2/ s/sup -1/ at Earth, implying a luminosity of 9( +- 3) x 10/sup 28/ ergs s/sup -1/ at the distance of 40 Eridani. We discuss whether the likely source of ...

Spitzer Space Telescope IRAC 3-8 ?m and AKARI IRC 2-4 ?m photometry are reported for 10 white dwarfs with photospheric heavy elements; nine relatively cool stars with photospheric calcium and one hotter star with a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest excess emissions are identified at HE ...

Heavy elements detected in the atmospheres of hot white dwarfs are commonly explained in terms of a diffusion model involving an equilibrium between radiative forces and gravity. In spite of the declining relative importance of radiative accelerations at lower effective temperatures, an increasing number of cooler DA white ...

White dwarfs are basically divided into two spectral classes, the hydrogen-rich DAs and the helium-rich non-DAs. However, between 28 000 and 45 000 K not a single non-DA star exists, although there are many helium-rich stars above and below this ``DB gap''. Currently, the only scenario to explain this gap is the assumption that every non-DA must contain or ...

We present Hubble Space Telescope GHRS G160M spectra of the white dwarf in VW Hydri, exposed during quiescence, one month after the end of a normal dwarf nova outburst. Our spectra reveal strong photospheric Si II 1260 Angstroms, 1265 Angstroms absorption features, and a previously unidentified broad feature centered around 1250 ...

The origin of ultra-compact binaries composed of a neutron star and a low-mass (about 0.06 solar mass) white dwarf is considered. Taking account of the systemic losses of mass and angular momentum, it was found that a serious difficulty exists in the scenarios which involve tidal captures of a normal star (a main sequence star or a red giant) by a neutron ...

Peculiar type I supernovae (SN Ip's) may result from explosive helium burning in low-mass He or He-C-O white dwarfs. Incomplete He burning would concurrently explain the relatively low expansion velocities and luminosities observed in SN Ip's. The disparities between SN Ip and SN I spectra may be attributable to the distinctive reaction ...

Nova explosions are caused by the explosive burning of hydrogen in the envelope of accreting white dwarfs. During the thermonuclear runaway some radioactive isotopes are synthesized, which emit ? -rays when they decay. The ? -ray signatures of a nova explosion still remain undetected, because even the best instruments like SPI onboard ...

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are ...

In some luminous supersoft X-ray sources, hydrogen accretes onto the surface of a white dwarf at rates more-or-less compatible with steady nuclear burning. The white dwarfs in these systems therefore have a good chance to grow in mass. Here we review what is known about the rate of Type la ...

High-temperature degenerate cores (about 100 million K) are susceptible to thermonuclear runaway at the 'ignition line' where nuclear-energy generation rates are equal to neutrino energy-loss rates. In contrast, low-temperature white dwarfs (about 1 million K) do not necessarily suffer thermal runaway at the ignition line because the nuclear rates are ...

Type Ia supernovae are thought to result from thermonuclear explosions of carbon-oxygen white dwarf stars. This model generally explains the observed properties with certain exceptions, like sub-luminous supernovae. Here we discuss the possibility of sub-Chandrasekhar WDs detonating due to the build up of a layer of helium on the C-O WD by ...

Accretion in astrophysical objects and the energetic phenomena it triggers are discussed in reviews and reports of recent theoretical and observational investigations. Topics examined include fly's-eye observations of ultrahigh-energy (UHE) gamma rays, recent results from the IMB detector, the theoretical implications of UHE detections of binary X-ray sources, Cyg X-3 as a ...

We present simultaneous EUV and infrared (J, K) observations of the polar HU Aquarii obtained during 1998 August when the star was in a high mass accretion state. EUV and IR light curves and EUV spectra are presented and compared with previous observations. The accretion region on the white dwarf has increased in ...

We study the stability of disc accretion in the recurrent nova RS Ophiuchi. We construct a one-dimensional time-dependent model of the binary-disc system, which includes viscous heating and radiative cooling and a self-consistent treatment of the binary potential. We find that the extended accretion disc in this system is always unstable to the ...

We present an analysis of high-dispersion and high signal-to-noise ratio spectra of the DAZ white dwarf GALEX J1931+0117. The spectra obtained with the VLT-Kueyen/UV-Visual Echelle Spectrograph show several well-resolved Si II spectral lines enabling a study of pressure effects on line profiles. We observed large Stark shifts in silicon lines in agreement ...

We review recent X-ray observations of potential type Ia supernova progenitors: white dwarfs in ``single degenerate systems'' that are undergoing hydrogen shell burning. Grating spectra prove to be very different from each other, and basically fall into two classes: in some systems we observe X-ray emission in a wind, or diffuse circumstellar material, ...

The Kepler observatory was designed to discover transits by Earth-like planets orbiting Sun-like stars. Its first major discoveries, however, are hot objects in close orbits around main-sequence stars. These are likely to be white-dwarf remnants of stars that have transferred mass to the present-day main sequence stars. These particular main-sequence stars are among the Kepler ...

The presence of elements heavier than helium in white dwarf atmospheres is often a signpost for the existence of rocky objects that currently or previously orbited these stars. We have measured the abundances of various elements in the hydrogen-atmosphere white dwarfs G149-28 and NLTT 43806. In comparison with ...

We review recent X-ray observations of potential type Ia supernova progenitors: white dwarfs in "single degenerate systems" that are undergoing hydrogen shell burning. Grating spectra prove to be very different from each other, and basically fall into two classes: in some systems we observe X-ray emission in a wind, or diffuse circumstellar material, while ...

White dwarfs typically have masses in a narrow range centered at about 0.6 solar mass (M(o)). Only a few ultramassive white dwarfs (mass > 1.2 M(o)) are known. Those in binary systems are of particular interest, because a small amount of accreted mass could drive them above the Chandrasekhar ...

The consequences of accretion of hydrogen rich material onto ONeMg white dwarfs with masses of 1.0, 1.25, and 1.35 Msolar are examined. Our results demonstrate that novae produce both 22na and 26Al in astrophysically interesting amounts. Hot hydrogen burning on ONeMg white dwarfs can produce as ...

Context: The magnetic fields of the accreting white dwarfs in magnetic cataclysmic variables (mCVs) determine the accretion geometries, the emission properties, and the secular evolution of these objects. Aims: We determine the structure of the surface magnetic fields of the white ...

For a weakly magnetized white dwarf with a thin accretion disk, the matter impacts near the equator and spreads out as new matter continuously piles up behind it. In a scenario proposed and investigated analytically by Piro & Bildsten (2004) for the white dwarf case and Inogamov and Sunyeav ...

Hard and soft X-ray spectra of the AM Herculis star EF Eridani obtained with the Einstein Observatory are found to be fitted by a thermal bremsstrahlung spectrum with kT of about 20 keV, and a blackbody spectrum with kT of between 16 and about 33 eV, respectively. EF Eri is shown to behave almost exactly as predicted by simple theory, with its soft X-ray luminosity not exceeding the hard X-ray ...

We present optical and infrared characterization of the polluted DAZ white dwarf GALEX J193156.8+011745. Imaging and spectroscopy from the ultraviolet to the thermal infrared indicate that this white dwarf hosts excess infrared emission consistent with the presence of an orbiting dusty debris disk. In addition to ...

Type Ia supernovae are exploding stars that are used to measure the accelerated expansion of the Universe and are responsible for most of the iron ever produced. Although there is general agreement that the exploding star is a white dwarf in a binary system, the exact configuration and trigger of the explosion is unclear, which could hamper their use for ...