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

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 ...

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

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 ...

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 ...

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...

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 ...

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 ...

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 ...

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

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). ...

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 ...

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 ...

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. ...

A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed

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 ...

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 ...

. 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 ...

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...

A range of important astrophysical systems consist of a strongly magnetic star accreting material from a surrounding disc. These include young stars in T Tauri systems, magnetic neutron stars in X-ray binaries and strongly magnetic white dwarfs in some cataclysmic variables. In all these ...

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 ...

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 ...

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 ...

UV spectra of the magnetic accretor AO Psc show absorption features for half the binary orbit. The absorption is unlike the wind-formed features often seen in similar stars. Instead, we attribute it to a fraction of the stream that overflows the impact with the accretion disk. Rapid velocity variations can be explained by changes in the trajectory of the ...

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 magnetic cataclysmic variables (CVs) the primary is a highly magnetized white dwarf (WD) whose field controls the accretion flow close to the WD, leading to a shock and accretion column that radiate chiefly in X-rays. We present preliminary results from a 500 ks Chandra HETG observation of ...

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 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 ...

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 ...

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 ...

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 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 ...

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 report on the discovery of variable circular polarization in the SW Sex star LS Pegasi. The observed modulation has an amplitude of ~0.3 % and a period of 29.6 minutes, which we assume as the spin period of the magnetic white dwarf. We also detected periodic flaring in the blue wing of Hbeta, with a period of 33.5 minutes. The difference between both ...

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 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 ...

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 ...

data yield the accretion disk thickness, diameter, electron density, and magnetic field. Introduction. The structure of AGN accretion disks on sub-parsec ...

... 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.

Ways of determining the nature of the companion to the pulsar PSR 1913+16 from observations of the pulsar's orbit and the slow rate of the orbit's precession are discussed. Geometric constraints require that the companion be a black hole, a neutron star, a white dwarf, or a helium-main sequence star. A uniform, geometrically thin slab was used to approximate the post-shock ...

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 dwarf can be propelled to larger ...

A theory of polarization of X rays emitted by magnetized neutron stars, white dwarfs and black hole accretion disks is presented and predictions are compared with polarimetric data. Polarization occurs in accreting neutron stars and white dwarfs in binary systems as plasma travels along ...

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 ...

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 they were not detected as hard X-ray sources. Two of the HEAO-1 ...

The stellar origin of gamma-ray bursts can be explained by the rapid release of energy in a highly collimated, extremely relativistic jet. This in turn appears to require a rapidly spinning highly magnetised stellar core that collapses into a magnetic neutron star or a black hole within a relatively massive envelope. We hypothesize a binary star model that ends with the ...

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 ...

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...

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, ...

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, ...

Jan 22, 2011 ... Title: The Production of Jets From Magnetized Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, D. ...

Jan 22, 2011 ... Title: The Production of Jets From Magnetic Accretion Disks: Simulation of the Blandford-Payne Mechanism. Authors: Meier, David L. ...

of a collimated jet ejected from the center of the accretion disk. The jet velocity is a strong function of the strength of the initial magnetic field: ...

V1432 Aquilae (=RX J1940.2-1025) is the X-ray bright, eclipsing magnetic cataclysmic variable {approx} 37 minutes away from the Seyfert galaxy, NGC 6814. Due to a 0.3% difference between the orbital (12116.3 s) and the spin (12150 s) periods, the accretion geometry changes over the {approx}50 day beat period. Here we report the results of an RXTE campaign ...

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 most energetic phenomena in the universe are systems powered by gravity through accretion. For compact stars such as white dwarfs, neutron stars, and especially black holes, the energy released per unit mass accreted can significantly exceed that released by nuclear reactions. Over the last half century a growing body of ...

Time-resolved spectropolarimetry and spectrophotometry of the recently discovered magnetic binary CW 1103+254 reveal Zeeman-split Balmer polarization and absorption features corresponding to a mean photospheric field on the white dwarf primary of strength B = (19 +- 2) x 10/sup 6/ gauss. The orbital inclination i = 69/sup 0/ and latitude of the ...

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the ``smoking gun'' signature of magnetically-driven viscosity in accretion disks. ...

X-ray light curves from XMM-Newton combined with optical data from the satellite and ground-based observers provide distinctive shapes and periodicities that give information on the correct classification of cataclysmic variables. Our recent data on three SDSS sources with strong helium emission are used to identify a highly magnetic system (a polar), the spin of the ...

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 ...

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 by the body of the ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and ...

We present the first results of a global axisymmetric simulation of accretion on to rotating magnetized stars from a turbulent accretion disc, where the turbulence is driven by the magnetorotational instability (MRI). We observed that the angular momentum is transported outwards by the magnetic stress and ...

Geometrically thin, optically thick, turbulent accretion disks are believed to surround many stars. Some of them are the compact components of close binaries, while the others are throught to be T Tauri stars. These accretion disks must be magnetized obje...

How do accretion disks launch winds and jets? From the Fundamental Accretion and Ejection Astrophysics Astro2010. White Paper, Miller et al. ...

Accretion Disk Coronae were first suggested to explain the incomplete eclipses and shallow profiles observed from some Low Mass X-ray Binaries (White and ...

Spectroscopic and photometric observations of the DQ Herculis binary 1H0542-407 are reported, and models are derived based on these and earlier observations. The system consists of a high-mass, about 1.3 solar mass white dwarf with a spin period of 1911 sec in a 5.7-h orbital period with about a 0.6 solar mass M0 dwarf secondary. The system is viewed at low inclination, so ...

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 (1999) for the ...

We present the first detailed extreme photometric observations of a magnetic cataclysmic variable. Our two Extreme Ultraviolet Explorer (EUVE) observations of the AM Her star RE 1149 + 28 were obtained about 1 yr apart and show light-curve variations on orbital to yearly timescales, as well as long-term mean flux level changes of a factor of 2. The photometric data show a ...

We consider the consequences of magnetic buoyancy and the magnetic shearing instability (MSI) on the

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...

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 abundances of the DAZs with information on the ...

SW Sextantis stars are fundamental to understanding how cataclysmic variables evolve. Their maverick behavior and unexplained accumulation in the orbital period range 3-4 h, about to enter the ``period gap'' where mass transfer is predicted to cease until a period of 2 h is reached, challenge the current evolution theory. To characterize these systems better, we need to determine the nature of the ...

We report the discovery of the ninth pre-polar consisting of a late-type ZAMS secondary and a magnetic white dwarf. The white dwarf accretes at an extreme low rate, dot{M} � 10-14 M_&sun; yr-1, from the wind of the companion donor star. The source was found in our systematic search for WD/MS binaries within ...

290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...

Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...

Sep 4, 1998 ... In the case of a HMXB with a large ( $\\mathrel{\\hbox{\\rlap{\\hbox{\\lower4pt\\ ) magnetic field the accretion disk cannot extend all the way down to ...

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 ...

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 ...

Context: The majority of cataclysmic variables observed in the hard X-ray energy band are intermediate polars where the magnetic field is strong enough to channel the accreting matter to the magnetic poles of the white dwarf. A shock above the stellar surface heats the gas to fairly high temperatures (10-100 keV). ...

For a non-magnetized white dwarf the accretion disk extends all the way to the surface, where matter impacts and spreads as new matter continuously piles up behind it. Using the RIEMANN code we have simulated the boundary layer on an axisymmetric grid to see how its structure depends on magneto-rotational instabilities (MRI) and ...

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 ...

Context. The energy balance of cataclysmic variables with strong magnetic fields is a central subject in understanding accretion processes on magnetic white dwarfs. With XMM-Newton, we perform a spectroscopic and photometric study of soft X-ray selected polars during their high states of ...

Polarization of starlight carries important information on the physical processes and the radiation mechanisms in the source of emission. These include scattering by free electrons in the hot circumstellar plasma, and cyclotron emission by mildly relativistic electrons in accretion shocks on highly magnetic white dwarf stars. We review ...

In this letter we show that the observed gamma -ray luminosity can be produced by an accretion disc around a non-magnetic neutron star or low mass black hole in which the dominant dissipative process in the disc is due to magnetic fields. The shearing mot...

The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such a star, in which upward diffusion of photons is balanced by their downw...

With the discovery that Alfven waves can be strongly unstable in a magnetized accretion disk, it can be expected to explain the turbulence necessary to drive accretion in these disks. The instability of non-axisymmetric Alfven waves is studied using analy...

MAGNETOHYDRODYNAMIC SIMULATIONS OF ACCRETION ONTO A STAR IN THE `` PROPELLER '' REGIME M. M ABSTRACT This work investigates spherical accretion onto a rotating magnetized star in the `` propeller-called `` propeller '' stage of evolution (Davidson & Ostriker 1973; Illarionov & Sunyaev 1975). The propeller stage

This presentation describes the behavior of matter in environments with extreme magnetic and gravitational fields, explains the instability/stability of accretion disks in certain systems, and discusses how emergent radiation affects accretion flow. Magne...

We use 3D numerical simulations to study MHD flows in close binary system SS Cyg. This star belongs to the class of the semi-detached binaries where the secondary star (donor) fills its Roche lobe and loses mass through the inner Lagrangian point L1. The matter accretes to the magnetized primary star - the white dwarf (accretor). To ...

Astro2010 Science White Paper (GCT). Fundamental Accretion and Ejection Astrophysics. J. Miller, M. Nowak, P. Nandra, N. Brandt, G. Matt, M. Cappi, ...

Series of photometric CCD observations of the asynchronous polar BY Cam in a low accretion state (R = 14m 16m) were made on the K-380 telescope at the Crimean Astrophysical Observatory (CrAO) over 100 hours in the course of 31 nights during 2004 2005. A period of P 1 = 0.137120�0.000002 days was found for the variations in the brightness, along with less significant periods ...

We report on XMM-Newton and accompanying phase-resolved optical observations of HS0922+1333, one out of nine pre-polars. It shows X-ray and UV variability correlated with the visibility of the main accretion spot. The spectral X-ray properties reveal a low temperature thermal plasma of ~1 keV with FX more than one order of magnitude below the cyclotron flux. The UV data ...

The advent of the grating spectrometers onboard Chandra and XMM-Newton opened up a new era in plasma diagnostics of compact binaries. High resolution spectroscopy using these spectrometers is of particular use in investigating accretion plasmas in cataclysmic variables (CVs) because they show a wealth of emission lines owing to their optically thin thermal nature. In this ...

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 ...

Abstract. The accretion process onto a magnetized isolated neutron star, which captures material from the interstellar medium, is discussed. The evolutionary track of such a star can be presented as a sequence of four states: ejector, supersonic propeller, subsonic propeller, andsteady accretor. Ishowthatsubsonic propeller ? accretor transition does not ...

The AM Her systems are widely believed to be mass transfer binaries containing a white dwarf primary accreting from a red dwarf secondary. The magnetic field of the white dwarf is so strong that it prevents the formation of an accretion disk and funnels the accretion flow ...

Spherical (nonrotating) accretion flows with small-scale magnetic fields have been investigated using three-dimensional, time-dependent MHD simulations. These simulations have been designed to model high-resolution (quasi-) steady accretion flows in a wedge computational domain that represents a small fraction of the full spherical ...

Highly nonstationary accretion onto a magnetized neutron star from a surrounding accretion disc is considered. Nonstationary accretion has been considered before in terms of droplets or rain or as a necessary consequence of instabilities in the accretion column flow. Here, the extreme of very ...

We study the accretion process in the region of the Preston-Poisson space-time describing a Schwarzschild black hole perturbed by an asymptotically uniform magnetic field and axisymmetric tidal structures. We find that the accretion disk shrinks and the marginally stable orbit shifts toward the black hole with the perturbation. The ...

We present the results of a uniform analysis of all the ASCA X-ray observations of non-magnetic cataclysmic variables. The collection includes 13 objects. We believe that the ASCA spectra of 8 of these objects are presented here for the first time. After experimenting with a variety of models, we find that 2-temperature, thermal plasma models (by Mewe, Kaastra, & Liedahl, ...

T Tauri stars (TTS) are low-mass pre-main-sequence stars that are accreting mass from the surrounding disc. The hotspots detected in some of them are probably heated by the release of gravitational energy in the accretion of the disc material on to the star. In this work we study the UV spectrum of the hotspot detected in DI Cep to constrain the physical ...

We calculate the advection/diffusion of the large-scale magnetic field threading an advection-dominated accretion flow (ADAF) and find that the magnetic field can be dragged inward by the accretion flow efficiently if the magnetic Prandtl number \\mathscr{P}_m=\\eta /\

High-speed optical photometry of the X-ray source 2A 0311--227 shows a light curve modulated with the 81 minute orbital period, with superposed large-amplitude flaring. The light curve, combined with Tapia's polarimetry, suggests that this system is similar to AN UMa in that it contains a white dwarf with an accreting magnetic ...

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 of the ...

THE PRODUCTION OF JETS FROM MAGNETIC ACCRETION DISKS: SIMUI,ATION OF THE BLANDFORD-PAYNE MECHANISM. D. L. Meier, D. G. Payne, K. R. Lind ...

velocities and to magnetic #12;eld decay. 2 The Ejector, Propeller and Accretion Phases Over the stellar challenge. In Section 2 we trace the evolution of a neutron star in the Ejector, Propeller and Accretion close to their mass shedding threshold, a limit sensitive to the equation of state for nuclear matter

ries containing weakly magnetized neutron stars, and to recently suggested models of accretion-powered emission from anomalous X-ray pulsars. ...

The study of magnetized plasmas in astrophysics is complicated by a number of factors, not the least of which is that in considering magnetic fields in stars or accretion disks, we are considering plasmas with densities well above those we can study in th...

Values for the maximum frequency up to which cyclotron radiation in the accretion columns of magnetic degenerate stars is self-absorbed are presented and the results applied to the Am Herculis binaries and Hercules X-1.

Time-resolved spectroscopy covering half an orbit and one eclipse during an outburst of the dwarf nova IP Peg are presented and compared with quiescent data. The outburst spectra show strong Balmer and He II 4686 A emission lines that are atypical of outbursting dwarf novae. Double-peaked velocity profiles and rotational distortions during eclipse show that the lines arise primarily in a Keplerian ...

The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For finds the source to be a factor > 103 fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ksec exposure with the EPIC cameras, suggesting that the accretion rate either decreased, or stopped altogether. However a 1.1 ksec burst ...

The XMM-Newton pointing toward the magnetic cataclysmic variable UZ For finds the source to be a factor of greater than 103 fainter than previous EXOSAT and ROSAT observations. The source was not detected for the majority of a 22 ks exposure with the European Photon Imaging Cameras, suggesting that the accretion rate either decreased or stopped altogether. ...

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 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 ...

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 ...

Students will use static electricity and magnetism to illustrate the accretion of chondritic material into larger bodies like planets and asteroids ...

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 ...

In AE Aqr, magnetic fields transfer energy and angular momentum from a rapidly-spinning white dwarf to material in the gas stream from the companion star, with the effect of spinning down the white dwarf while flinging the gas stream material out of the binary system. This magnetic propeller produces a host of ...

Accretion disks are invoked to explain a host of astrophysical phenomena, from protostellar objects to AGN. And yet the mechanism allowing accretion disks to operate are completely unknown. This proposal seeks to observe the smoking gun signature of magnetically--driven viscosity in accretion disks. ...

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 ...

The optical counterpart of the 555-s X-ray periodicity from V471 Tau has been detected based on high-speed photometry acquired using the 0.76 and 0.92 m McDonald Observatory telescopes. The fractional semiamplitude of the periodicity in the Johnson U band is found to vary from 9.7 x 10 to the -4th to less than 3.8 x 10 to the -4th. It is suggested that the observed periodicity could be caused ...

The origin of the hard X-ray spectrum emitted by Gamma-Cas remains a puzzle. Both a white dwarf accreting from the Be star circumstellar disc or magnetic interaction between the photosphere and the disc can explain the unusually hard X-ray emission. The recent discovery of several new G-Cas analogs offers new opportunities to address ...

We report on the discovery by the Hamburg Quasar Survey of a magnetic CV with a pure cyclotron emission line spectrum. With a photometric and spectroscopic period of 167.6 min it is located in the CV period gap. From 91 spectra taken over 1.2 orbital periods we identify the n = 2 and 3 cyclotron harmonics of the main accretion pole with 60 MG as well as ...

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 ...

Magnetic fields are present in a wide variety of stars throughout the HR diagram and play a role at basically all evolutionary stages, from very-low-mass dwarfs to very massive stars, and from young star-forming molecular clouds and protostellar accretion discs to evolved giants/supergiants and magnetic white ...

Magnetic fields are present in a wide variety of stars throughout the HR diagram and play a role at basically all evolutionary stages, from very-low-mass dwarfs to very massive stars, and from young star-forming molecular clouds and protostellar accretion discs to evolved giants/supergiants and magnetic white ...

The accretion of matter on to intermediate polar white dwarfs (IPWDs) seems to provide attractive conditions for acceleration of particles to high energies in a strongly magnetized turbulent region at the accretion disc inner radius. We consider possible acceleration of electrons and hadrons in such region and ...

V1432 Aquilae (=RX J1940.2-1025) is the X-ray-bright, eclipsing magnetic cataclysmic variable ~37' away from the Seyfert galaxy NGC 6814. Because of a 0.3% difference between the orbital (12,116.3 s) and the spin (12,150 s) periods, the accretion geometry changes over the ~50 day beat period. Here we report the results of a Rossi X-Ray Timing Explorer ...

lent dynamo to maintain and amplify any magnetic seed field. ... with studying a magnetic dynamo, afact that is not commonly recognized in the literature. ...

A theory for the formation and propagation of nonrelativistic jets and winds from magnetized accretion disks is derived from the equation of ideal magnetohydrodynamics. The theory allows the self consistent determination of the jet's axial velocity, radiu...

... Title : Implications of Fine-Scale Magnetics for the Structure and Evolution of Slowly Accreted Oceanic Crust. Descriptive Note : Final rept. ...

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 ...

Accretion discs are composed of ionized gas in motion around a central object. Sometimes, the disc is the source of powerful bipolar jets along its rotation axis. Theoretical models invoke the existence of a bipolar magnetic field crossing the disc and require two conditions to produce powerful jets: field lines need to be bent enough at the disc surface ...

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 ...

An accumulation of multi-epoch, high-resolution optical spectra reveal that the nearby star G77-50 is a very cool DAZ white dwarf externally polluted by Mg, Fe, Al, Ca and possibly Na, Cr, Mn. The metallic and hydrogen absorption features all exhibit multiple components consistent with Zeeman splitting in a B? 120 kG magnetic field. Ultraviolet through ...

We present an analysis of ULTRACAM light curves of the magnetic cataclysmic variable HU Aquarii which were taken at the VLT in May 2005. Since the light curves were serendipitously obtained during a low state, they allowed us to determine the binary and the stellar parameters with high accuracy. The light curve was decomposed into the components originating from the ...

The stability of magnetic fields within the accretion disks is examined, including the effects of magnetic buoyancy. Rayleigh-Taylor, and Kelvin-Helmholtz instabilities. The purpose of the study is to examine the efficacy of turbulent accretion (..cap alpha..-) disk models which depend upon ...

Accreting neutron stars can produce jets only if they are weakly magnetized (B ~ 108 G). On the other hand, neutron stars are compact objects born with strong surface magnetic fields (B ~ 1012 G). In this work we study the conditions for jet formation in a binary system formed by a neutron star and a massive donor star once the ...

Polarimetric observations of V1500 Cygni, the remnant of Nova Cygni 1975, reveal periodic variations of optical circular polarization with semi-amplitudes of about + or - 1.5 pct. Measured over a six-month baseline, the period of variation, 0.137154 + or - 0.000004 days, is 1.8 percent shorter than the stable photometric period, 0.1396129 days, obtained by Patterson (1979), and refined by Kaluzny ...

We discuss the effect of the Poynting flux on a magnetically dominated thin accretion disk, which is simplified to a two-dimensional disk on the equatorial plane. It is shown in the relativistic formulation that the Poynting flux caused by a rotating magnetic field with Keplerian angular velocity can balance the energy and angular ...

Millisecond pulsars, both during and after accretion, stand a class apart from the general pulsar population due to the much weaker field strength at their surface. The prevailing view is that accretion of matter on to a neutron star causes a decay of its magnetic field strength, as viewed by an external observer. In this paper we ...

The transport of angular momentum in the outward direction is the fundamental requirement for accretion to proceed in an accretion disk. This objective can be achieved if the accretion flow is turbulent. Instabilities are one of the sources for the turbulence. We study a differentially rotating compressive flow in the presence of ...

Alpha models of astrophysical accretion disks assume an ad hoc viscous stress which scales locally as the total pressure. It is shown here that, if turbulent magnetic Maxwell stresses are the source of this viscosity in quasi-stellar object accretion disk models, then the stress cannot follow the assumed alpha-law in the radiation ...

Arguments are presented which suggest that accretion disks around black holes and neutron stars may self-generate ordered magnetic fields, from currents associated with orbital motion of the disk material. This leads one to expect electromagnetic extraction of the rotational energy of the disk, and it is proposed that such a magnetic ...

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 ...

Recent observational data has shown that the Algol-type binary system RS Vul possesses an accretion disk tilted out of the orbital plane. Magnetic effects in the surface of the donor star could produce a nontrivial effect in the flow of the accretion stream as it travels through the L1 Lagrange point. Such a deflection could introduce ...

A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without magnetic a field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge ...

The highest efficiency of converting rest mass into energy by accreting matter into a Kerr black hole is approximately 31% (Thorne 1974). We propose a new process in which periods of accretion from a thin disk, and the associated spin-up of the black hole, alternate with the periods of no accretion and magnetic ...

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. ...

We discuss the dynamics of the accretion flow onto a black hole driven by Poynting flux in a simplified model of a two-dimensional accretion disk. In this simplified model, the condition of the stationary accretion flow is found to impose a nontrivial constraint on the magnetic field configuration. The effect of ...

A linear theory is developed for thermal convective instability in radiating gas dominated by radiation pressure. Analysis demonstrates how the magnetic field and differential rotation will affect the onset of thermal convection in the interior of a black hole accretion disk.

This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigen fre...

We consider the structure and emission spectra of nonthermal accretion disks around both strongly and weakly magnetized neutron stars. Such disks may be dissipating their gravitational binding energy and transferring their angular momentum via semicontinu...