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 demonstrated that the ...
Energy Citations Database
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 sound speed), ...
DOE Information Bridge
Carbon-oxygen white dwarfs formed in close binary systems may become unstable by mass accretion. Recent results concerning carbon-oxygen separation at the freezing point during the phase of cooling may have very important consequences for the problem of neutron star formation. The central, high-density regions of ...
The long-term evolution of accreting carbon-oxygen white dwarfs in close binary systems is considered. Depending on the time of onset of mass accretion (for a given stellar mass), thermonuclear ignition happens when the star's center is either in the fluid or in the solid phase. In the last case, burning ...
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 framework for ...
... unique opportunities to study the details of the accretion flow in the cases of normal white dwarfs with accretion disks and magnetic white dwarfs. ...
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The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon-oxygen white dwarf stars that have accreted matter from a companion star, although the nature of this companion ...
PubMed
Type Ia supernovae result when carbon-oxygen white dwarfs in binary systems accrete mass from companion stars, reach a critical mass and explode. The near uniformity of their light curves makes these supernovae good 'standard candles' for measuring cosmic expansion, but a correction must be applied to account for the fact that the ...
Type Ia supernovae result when carbon-oxygen white dwarfs in binary systems accrete mass from companion stars, reach a critical mass, and explode. The near uniformity of their light curves makes these supernovae good standard candles for measuring cosmic expansion, but a correction must be applied to account for the fact that the ...
E-print Network
Recent studies have suggested that the merging of two degenerate dwarfs composed of carbon and oxygen and of total mass larger than the Chandrasekhar limit occurs at a frequency comparable to that of Type I supernovae. The rate at which mass is transferred in the merging process is at present unknown, except that it must be less than some appropriate Eddington limit. It is found that, unless 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. ...
DTIC Science & Technology
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 properties of this ...
Recently, several Type Ib supernovae (SNe; with the prototypical SN 2005E) have been shown to have atypical properties. These SNe are faint (absolute peak magnitude of ~ - 15) and fast SNe that show unique composition. They are inferred to have low ejecta mass (a few tenths of a solar mass) and to be highly enriched in calcium, but poor in silicon elements and nickel. These SNe were therefore ...
NASA Astrophysics Data System (ADS)
We present optical spectra in the range 4600-8600� for three low-mass X-ray binaries which have been suggested to belong to the class of ultra-compact X-ray binaries based on their X-ray spectra. Our spectra show no evidence for hydrogen or helium emission lines, as are seen in classical X-ray binaries. The spectrum of 4U 0614+09 does show emission lines, which we identify with carbon and oxygen ...
We describe a mechanism by which a failed deflagration of a Chandrasekhar-mass carbon-oxygen white dwarf can turn into a successful thermonuclear supernova explosion, without invoking an ad hoc high-density deflagration-detonation transition. Following a pulsating phase, an accretion shock develops above a core of ~1 Msolar composed of ...
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 ac...
National Technical Information Service (NTIS)
The thermonuclear explosion of a carbon-oxygen white dwarf that has accreted mass until it approaches the Chandrasekhar limit is widely accepted to be the correct model for Type Ia supernovae (SN Ia). The basic observational characteristics of these models are in general agreement with the observed composition, light curves, and velocities of the ejecta. ...
Recently several type Ib supernovae (SNe; with the prototypical SN 2005E) have been shown to have atypical properties. These SNe are faint (absolute peak magnitude of ~ -15) and fast SNe that show unique composition. They are inferred to have low ejecta mass (a few tenths of a solar mass) and to be highly enriched in calcium, but poor in silicon elements and nickel. These SNe were therefore ...
How do accretion disks launch winds and jets? From the Fundamental Accretion and Ejection Astrophysics Astro2010. White Paper, Miller et al. ...
Jun 17, 2009 ... The simplest picture of IPs is that they have a partial (and fully Keplerian) accretion disk, truncated by the magnetic field of the white ...
Accretion Disk Coronae were first suggested to explain the incomplete eclipses and shallow profiles observed from some Low Mass X-ray Binaries (White and ...
We analyze the evolution of binary stars to calculate synthetic rates and delay times of the most promising Type Ia Supernovae (SNe Ia) progenitors. We present and discuss evolutionary scenarios in which a white dwarf (WD) reaches the Chandrasekhar mass and potentially explodes in a SNe Ia. We consider Double Degenerate (DDS; merger of two WDs), Single Degenerate (SDS; WD ...
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...
Type Ia Supernovae (SNe Ia) have high and homogeneous luminosities, making them an essential tool for measuring distances on a cosmic scale, useful to gauge the geometry and evolution of the Universe. However, the nature of the progenitor system of these explosions is still uncertain. The consensus view is that SNe Ia originate from an accreting ...
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 present paper the ...
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 star. Spherical ...
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 hydrogen but farther out ...
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 dwarfs. The fraction of ...
Astro2010 Science White Paper (GCT). Fundamental Accretion and Ejection Astrophysics. J. Miller, M. Nowak, P. Nandra, N. Brandt, G. Matt, M. Cappi, ...
Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many
NASA Technical Reports Server (NTRS)
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 ejecta from the accreting ...
Equations of state for dense carbon-oxygen (C-O) binary-ionic mixtures (BIM's) appropriate to the interiors of white dwarfs are investigated through Monte Carlo simulations, by solution of relevant integral equations andvariational calculations in the density-functional formalism. It is thereby shown that the internal energies of the C-O BIM ...
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 disk ...
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 - 1.5) x 10 to the -6th ...
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 close to the ...
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 dwarf's cooling ...
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 dwarf`s cooling curve and ...
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 ...
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 ...
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...
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 the ...
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 X-ray pulsars). ...
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 different initial masses of ...
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 different initial masses ...
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 ...
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 hydrogen. The results are consistent with the ...
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 relative to the Sun. ...
candles, the Type Ia supernovae, for example, may be a consequence of accretion onto a white ... mation about the close-in spatial structure of supernovae. ...
In analogy the soft component probably originates from an accretion-heated surface region around the white dwarfs magnetic pole(s). ...
... Additonal cues such as accretion/deletion of texture (not considered here) are ... a perceptually vivid, illusory white square in a field of black discs. ...
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. ...
May 2, 2007 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...
Jan 2, 2003 ... Results: V407 Vul proposed to be a double degenerate Algol (i.e., non-magnetic white dwarf accreting via direct stream impact). ...
... Abstract : The prototype of accreting, pulsating white dwarfs (GW Lib) underwent a large amplitude dwarf nova outburst in 2007. ...
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 ...
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.
We have posited in another white paper that all of Planetary System Science can be ... containing important clues to planetary formation, the accretion of ...
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 ...
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 dwarf. Estimates are given for the amount of helium ...
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 to whether or not ...
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 ...
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 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/ and 10/sup -9/ M/sub ...
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 accretion rate. Relatively fast ...
... Title : Carbon-Oxygen Complexes as Nuclei for the ... precipitation, Infrared radiation, Oxygen, Carbon, Complex compounds, Absorption ...
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 demonstrate that a spherical accretion onto astrophysical black holes, under the influence of Newtonian or various post-Newtonian pseudo-Schwarzschild gravitational potentials, may constitute a concrete example of classical analogue gravity naturally found in the Universe. We analytically calculate the corresponding analogue Hawking temperature as a function of the minimum ...
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 ...
White Papers (both new and old). Accretion Physics (BH, NS, WD) in outburst ( Miller) ... TOO Observations of nearby SN1a/c (Hughes old white paper) ...
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 radial ...
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 accreting matter from
Sedimentation of the neutron rich isotope 22Ne may be an important source of gravitational energy during the cooling of white dwarf stars. This depends on the diffusion constant for 22Ne in strongly coupled plasma mixtures. We calculate self-diffusion constants D(i) from molecular dynamics simulations of carbon, oxygen, and neon ...
Nucleosynthesis is the study of the nuclear processes responsible for the formation of the elements which constitute the baryonic matter of the Universe. The elements of which the Universe is composed indeed have a quite complicated nucleosynthesis history, which extends from the first three minutes of the Big Bang through to the present. Contemporary nucleosynthesis theory associates the ...
Many hydrogen-deficient stars are characterized by surface abundance patterns that are hard to reconcile with conventional stellar evolution. Instead, it has been suggested that they may represent the result of a merger episode between a helium and a carbon-oxygen white dwarf. In this Letter, we present a nucleosynthesis study of the merger of a 0.4 M sun helium ...
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 cataclysmic variables. Improving our ...
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 white dwarfs ...
We reexamine Eardley's analysis of the death of white holes, which shows that, due to the accretion of ambient matter, a white hole ceases to radiate significantly after a time scale comparable to its mass. While Eardly only vaguely provided the meaning of such a time scale, we give a precise, operational definition for the lifetime of ...
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 white ...
We critically review Eardley's argument which shows that, due to accretion, white holes are eventually converted into black holes-the death of white holes. While Eardley's main conclusions remain unscathed, we question some of the details of his analysis. We argue, together with Lake and Roeder, and Blau, that the death of ...
We show that spherical accretion onto astrophysical black holes can be considered as a natural example of an analogue system. We provide, for the first time, an exact analytical scheme for calculating the analogue Hawking temperature and surface gravity for general relativistic accretion onto astrophysical black holes. Our calculation may bridge the gap ...
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 ...
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 by more than 5 mag. A Hubble Space Telescope (HST) ultraviolet ...
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 envelopes with composition X=0.7, Z=0.03. The ...
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 nuclear-energy generation rate ...
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 across the surface, any ...
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 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 ...
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 then buried. This ...
The utility of Type Ia supernovae, not simply as probes of the distance scale but also as a means of constraining the properties of dark energy, demands a significant improvement in theoretical predictions of their properties in outburst. To this end, we have given substantial effort to quantifying the energetics and nucleosynthesis properties of deflagration fronts in the interiors of the ...
We study a type Ia supernova explosion using three-dimensional numerical simulations based on reactive fluid dynamics. We consider a delayed-detonation model that assumes a deflagration-to-detonation transition. In contrast with the pure deflagration model, the delayed-detonation model releases enough energy to account for a healthy explosion, and does not leave carbon, ...
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 that these solutions ...
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 ...
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 based on fluctuations ...
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 helium shell flashes are ...
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 ...
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 velocity directed ...
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 disks with near- and ...
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 types of evolution of ...
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 in the deeper crust ...
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 new experiments for ...
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 1.7 x 10/sup ...
We study shock-flame interactions on small scales as a possible mechanism for deflagration-to-detonation transition (DDT) in an exploding carbon-oxygen white dwarf. Thermonuclear flames are modeled using reactive Navier-Stokes equations coupled with a 13-species alpha-network. Two-dimensional numerical simulations that resolve carbon and oxygen burning ...
Motivated by the strong discrepancy between the main-sequence turnoff age and the white dwarf cooling age in the metal-rich open cluster NGC 6791, we compute a grid of white dwarf evolutionary sequences that incorporates for the first time the energy released by the processes of {sup 22}Ne sedimentation and of carbon/oxygen phase separation upon ...
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 asteroids from an outer planetary system, ...
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)
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...
gas, quenching SF and BH accretion. " IXO well tuned to follow and confirm/ constrain this process. Hernquist (1989). Springel et al. (2005). Hopkins et al. ...
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 explore the physics of crystallization in the deep interiors of white dwarf (WD) stars using the color-magnitude diagram and luminosity function constructed from proper-motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of WD stars and ...
We determine the phase diagram for dense carbon-oxygen mixtures in white dwarf (WD) star interiors using molecular dynamics simulations involving liquid and solid phases. Our phase diagram agrees well with predictions from Ogata et al. and from Medin and Cumming and gives lower melting temperatures than Segretain et al. Observations of WD crystallization ...
RS Ophiuchi is a recurrent nova system that experiences outbursts every ~20 years, implying accretion at a high rate onto a massive white dwarf. However, previous X-ray observations of the system in quiescence have detected only faint emission that is difficult to reconcile with the high accretion rate (>2 � 10�8 M sun yr�1) ...
include the carbon carbon bond of alkanes(C----C); the carbon oxygen bond of alcohols(C----O); and the carbon oxygen carbon bond present in ethers ...
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 Pic. The results ...
Temporal variations in metal-line strengths in H-atmosphere white dwarfs hold the potential to test the timescales of graviational settling theory. These short timescales, in turn, require that DAZs are currently accreting. Such temporal variations would also indicate that accretion from a circumstellar dust disk can be episodic. We ...
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 structure by equations incorporating quantum mechanics and ...
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 Cygni's accurate HST ...
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 progress is determined uniquely. Structural ...
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 far-UV light. We find that the ...
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 temperature (124,000 ...
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 ...
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 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 with laboratory ...
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 to be sometimes due ...
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 counted among the yellow ...
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 dissertation, we utilize a ...
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 atmospheres on a timescale of weeks to years. ...
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 emission regions occupy a ...
Steady state, spherically symmetric solutions of the cosmic-ray transport equation describing the acceleration of energetic particles in galactic accretion flows onto neutron stars, black holes, white dwarfs, and protostars are studied. The results indicate that astrophysical accretion flows can be partitioned into distinct classes ...
The supercritical wind theory of Papers II and III is applied to winds driven by accretion phenomena. An expression for the total luminosity LT is derived in terms of the accretion rate dotMT and injection radius r?. When applied specifically to accretion disks, the theory becomes the supercritical counterpart to standard subcritical ...
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 final result given the WD mass and composition (usually assumed uniform), the mass ...
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 dwarf spin evolution. If the pulsar magnetic field ...
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 dwarfs, EUV observations of hot white ...
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 unmodulated flux ...
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. Motivated by the need for systematic ...
We apply an eclipse mapping technique using `genetically modified fire-flies' to the eclipse light curves of HU Aqr and EP Dra. The technique makes as few assumptions as possible about the location of accretion stream material, allowing the emission to be located anywhere within the Roche lobe of the white dwarf. We model two consecutive eclipses in the ...
We apply an eclipse mapping technique using `genetically modified fireflies' to the eclipse light curves of HU Aqr and EP Dra. The technique makes as few assumptions as possible about the location of accretion stream material, allowing the emission to be located anywhere within the Roche lobe of the white dwarf. We model two consecutive eclipses in the ...
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 approx. =4 x 10/sup -8/ M/sub sun/ yr/sup ...
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 ...
... HYPERSONIC FLOW, REACTION KINETICS, BOUNDARY LAYER, STAGNATION, BLUNT BODIES, HEAT SHIELDS, CARBON, OXYGEN. ...
... Descriptors : *NUCLEAR SCATTERING, *NUCLEAR STRUCTURE, ELECTRONS, CARBON, OXYGEN, NUCLEAR SHELL MODELS, MOMENTUM ...
Recent discoveries of compact (sizes lsimR sun) debris disks around more than a dozen metal-rich white dwarfs (WDs) suggest that pollution of these stars with metals may be caused by accretion of high-Z material from the disk. But the mechanism responsible for efficient transfer of mass from a particulate disk to the WD atmosphere has not yet been ...
We study the accreting white dwarfs (WDs) and accretion disks in Cataclysmic Variables (CVs) by carrying out a systematic analysis of the FUSE spectra of galactic CVs. Using the codes TLUSTY, SYNSPEC and BINSYSN, we generate synthetic spectra of WDs, and accretion disks, and derive the parameters of the systems: ...
The temperature of a white dwarf (WD) in a cataclysmic variable (CV) can tell you much about the accretion history of the binary system, and hence the evolution of the system. Best seen in the ultraviolet, a white dwarf's temperature is typically measured through modeling of a UV spectrum. This approach has been taken for numerous CVs ...
We have used a model of magnetic accretion to investigate the rotational equilibria of magnetic cataclysmic variables (mCVs). The results of our numerical simulations demonstrate that there is a range of parameter space in the Pspin/Porb versus ?1 plane at which rotational equilibrium occurs. This has allowed us to calculate the theoretical histogram describing the ...
Hydrogen-rich matter has been added to a CO white dwarf of initial mass 0.516 compared with those for a white dwarf of the same initial mass which accretes pure helium at the same rates. For the chosen accretion rates, hydrogen burns in a series of recurrent mild flashes and the ashes of hydrogen burning build up a ...
The accretion of hydrogen-rich matter onto C/O and O/Ne white dwarfs (WDs) in binary systems may lead to unstable thermonuclear ignition of the accreted envelope, triggering a convective thermonuclear runaway and a subsequent classical, recurrent, or symbiotic nova. Prompted by uncertainties in the composition at the base of the ...
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 = 166 pc, a newly ...
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 and reach conclusions on the relevant ...
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 strong emission ...
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 filters ensure
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 minor planets in an ...
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 information of ...
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 accretion ...
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 spectral energy ...
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 helium ...
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 helium ...
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 pollution in helium ...
We analyze the influence of the evolution of light absorption by gray dust in the host galaxies of type Ia supernovae (SN Ia) and the evolution of the mean combined mass of close-binary carbon-oxygen white dwarfs merging due to gravitational waves (SN Ia precursors) on the interpretation of Hubble diagrams for SN Ia. A significant increase in the mean SN ...
Large-scale, three-dimensional numerical simulations of the deflagration stage of a thermonuclear supernova explosion show the formation and evolution of a highly convoluted turbulent flame in the gravitational field of an expanding carbon-oxygen white dwarf. The flame dynamics are dominated by the gravity-induced Rayleigh-Taylor instability that controls ...
We explore the sensitivity of massive stars to neutrino magnetic moments. We find that the additional cooling due to the neutrino magnetic moments brings about qualitative changes to the structure and evolution of stars in the mass window 7 M {sub sun} {approx}< M {approx}< 18 M {sub sun}, rather than simply changing the timescales for the burning. We describe some of the ...
Rates of nuclear fusion reactions in dense matter and their enhancement due to electron screening and internuclear many-body correlation are calculated by explicitly taking into account dielectric functions of relativistic and nonrelativistic electrons, screening potentials based on the Monte Carlo simulations, and interaction free energies in dense electron-screened binary-ionic-mixture fluids. ...
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. ...
Although disk accretion onto compact objects-white dwarfs, neutron stars and black holes-is central to much of high-energy astrophysics, the mechanisms that enable this process have remained observationally difficult to determine. Accretion disks must transfer angular momentum in order for matter to travel radially inward onto 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 accretion ...
We investigate the evolution of a thin viscous disc surrounding a magnetic star, including the spin-down of the star by the magnetic torques it exerts on the disc. The transition from an accreting to a non-accreting state, and the change of the magnetic torque across the corotation radius rc are included in a generic way, the widths of the transition taken ...
The line profiles and relative fluxes of the emission lines in the quiescent spectra of cataclysmic variables contain information about the physical state of the material in the accretion disks around the white dwarfs. Several physical and phenomenological models for the emission line regions are discussed, and the resulting emission line profiles and ...
The Mira AB system is a nearby (~107 pc) example of a wind accreting binary star system. In this class of system, the wind from a mass-losing red giant star (Mira A) is accreted onto a companion (Mira B), as indicated by an accretion shock signature in spectra at ultraviolet and X-ray wavelengths. Using novel imaging techniques, we ...
Cataclysmic variables (CVs) provide a rich laboratory to study the effects of mass transfer and accretion on the properties and evolution of white dwarfs. One interesting aspect is the effect of accretion on the instability strip. So far, there is only one ZZ Cet pulsator known to be a CV - GW Lib. Our UV spectra obtained with HST ...
