The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was
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accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...
NASA Website
Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,
Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...
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...
National Technical Information Service (NTIS)
Magnetic compact objects (neutron stars or white dwarfs) are currently thought to be present in many
The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was to bring together workers on accretion disks in the western Gulf region (Texas and Louisiana). Part 2 presents the workshop program, a list of poster pres...
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 ...
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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 ...
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have been. : size and distribution of such flux tubes. We then apply the model to identified using numerical, nonlinear hydrodynamic techniques, accretion ...
290 Stepinski:On Maonetic Dynamos in Thin Accretion Disks Around Stars pressure is smaller than gas pressure, otherwise the assumption of a thin disk ...
Dec 19, 1999 ... Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. ...
accreting star. Roughly half the known X�ray novae contain BH candidates and the rest contain NSs. X of the accreting star. As discussed in the Introduction, the accretion rate in a typical X�ray nova spans a wide in which the compact accreting ...
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 ...
NASA Astrophysics Data System (ADS)
The collapse of massive molecular clumps can produce high mass stars, but the evolution is not simply a scaled-up version of low mass star formation. Outflows and radiative effects strongly hinder the formation of massive stars via accretion. A necessary condition for accretion growth of a ...
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...
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, ...
Jan 14, 2011 ... Thus a "funnel point" is created for significant mass to flow out toward the compact star for accretion. In the case of Roche-lobe overflow, ...
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 ...
stars via accretion. A necessary condition for accretion growth of a hy- ... via accretion for stars more massive than 1 M@. 1. Introduction ...
We discuss the consequences of the accretion of dark matter (DM) particles on compact stars such as white dwarfs and neutron stars. We show that in large regions of the DM parameter space, these objects are sensitive probes of the presence of DM and can be used to set constraints both on the DM density and on the ...
the mass transfer rate from the secondary star) can be determined. The visible disk maps of dwarf novae Pegasi IP Peg is a dwarf nova consisting of a mass-donating, M-dwarf secondary star and an accretion diskChapter 1 Introduction 1.1 Compact Binary Systems Compact binaries are binary ...
The origin of ultra-compact binaries composed of a neutron star and a low-mass (about 0.06 solar mass) white dwarf is considered. Taking account of the systemic losses of mass and angular momentum, it was found that a serious difficulty exists in the scenarios which involve tidal captures of a normal star (a main sequence ...
Radiation spectra modelling of accretion flows in close binary systems is considered. The modern state of such modelling is reviewed. The review is mainly based on the works, performed by the author with collaborators, where the basic parameters of compact stars are obtained from radiation spectra. For a start, the physical processes ...
A model for disk accretion by a rotating magnetic neutron star is proposed which includes a detailed
Bright pulsating X-ray sources (X-ray pulsars, AM Her stars,...) have been identified as strongly magnetized compact objects accreting matter from a binary companion. We give here a summary of some of the work which has been recently done to try to unders...
We have computed the ejection of a massive envelope by a star during a type II supernova explosion in the presence of a compact remnant (a neutron star or black hole). This problem is of interest because of the possible presence of a compact remnant following the SN 1987A explosion. The computations demonstrate ...
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.
Accretion from a disk onto a collapsed, relativistic star--a neutron star or black hole--is the mechanism widely believed to be responsible for the emission from compact X-ray binaries. Because of the extreme spatial resolution required, is not yet possib...
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 ...
Compact star clusters found in the centers of galaxies tend to be dense, massive, and comprised of multiple generations of stars. The formation of such clusters may be linked to the formation of supermassive black holes in galaxy nuclei. X-rays provide one means of detecting a supermassive black hole associated with a nuclear cluster. ...
We consider a model in which massive stars form in a self-gravitating accretion disk around an active galactic nucleus (AGN). These stars may evolve and collapse to form compact objects on a time scale shorter than the accretion time, thus producing an important family of sources for LISA. ...
The gravitational accretion of gas onto a compact star moving supersonically through a uniform ambient medium is dynamically unstable in the restricted case of two-dimensional planar geometry (a cylindrical star). Numerical simulations in 3D (e.g., the series of papers by Ruffert) show some hint of instability, but ...
We study the standing dissipative and non-dissipative shocks and the isentropic compression waves systematically in the thin, rotating, adiabatic astrophysical flows, such as accretion or winds, near the black holes and the neutron stars. The flow is assu...
Jul 15, 2004 ... "X-Ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338", ... ``Bounds on Compactness for LMXB Neutron Stars from X-ray Burst ...
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 ...
Matter swirls around the compact object in the accretion disk like water going down the drain. Because a black hole is invisible and a neutron star is so ...
We study the evolution of the rotation frequency for accreting compact stars. The discontinuous change of the moment of inertia of a rapidly rotating star due to the possible quark core appearance entails a characteristic change in the spin evolution. Numerical solutions have been performed using a model equation ...
We consider roughly 106 to 107 solar mass black holes (MBHs) in galactic nuclei. As such objects grow by accretion, some fraction of the accreted mass is in the form of compact stars. If the approach to coalescence proceeds gradually, many orbital revolutions will occur, and substantial amounts of gravitational ...
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 ...
A one-zone model is developed for analysis of properties of nuclear shell flashes on accreting degenerate dwarfs and neutron stars. The model provides a description of a steady-state nuclear burning and a linear stability analysis with a small number of algebraic equations. Time evolution of the accreted layer is described with two ...
Accreting neutron stars provide the bulk of high luminosity X-ray sources. Decade long studies of low-mass X-ray binaries have provided a wealth of information about the various nature of X-ray emissions and proposed emission sites include the neutron star surface, an immediate boundary layer, the inner disk region, a possible ...
We show that a moderately massive disk (10/sup -5/--10/sup -2/ M/sub sun/) can cause the Lense-Thirring precession of the compact object (neutron star or black hole) at its center. The inner regions of the disk (r< or approx. =10/sup 8/ cm) align with the equator of an will precess at the same rate as the compact object. We propose ...
formation of massive stars via accretion. A necessary condition for accre- ... constraints on the accretion rate necessary to produce high mass stars and ...
Possible mechanisms of ..gamma..-ray emission from a neutron star during the accretion of matter onto its surface are discussed. The proposed mechanism of the creation of ..pi../sup 0/ mesons in the collisions of nuclei led to considerable strengthening of the expected ..gamma..-ray emission. Measurement of the spectrum of hard ..gamma.. radiation in the ...
Equations for the degree of linear polarization of stellar radiation are derived under general assumptions regarding the surface-brightness distribution. The polarization is evaluated for the cases of accretion by a compact star with a strong magnetic field, the optical component of a binary system containing an x-ray source, and ...
Numerical studies of the early evolution of star clusters have traditionally been based on full hydrodynamic treatments or a purely gravitational N-body approach . I will discuss recent work that pushes the N-body techniques toward a more realistic gas treatment. In particular I will focus on the behavior of very young clusters as they accrete gas, ...
With IXO, spectroscopy of accretion onto black holes will finally rival optical and IR spectroscopy of accreting young stars. ...
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 frequencies and eigenfunctions of the modes for different values of the mass and ...
accretion? " What is the structure of the inner disk? " How do accretion disks drive jets? ... IXO will reveal the physics of disk accretion, and low L_X ...
The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) ...
PubMed
The detection of fast quasi-periodic variability from accreting black holes and neutron stars has been used to constrain their masses, radii, and spins. If the observed oscillations are linear modes in the accretion disks, then bounds can be placed on the properties of the central objects by assuming that these modes are locally ...
Observations of T Tauri stars and young brown dwarfs suggest that the accretion rates of their disks
Low mass X-ray binaries (LMXBs) are interacting systems in which a neutron star or black hole accretes material from a donor star via an accretion disk. LMXBs provide excellent environments for studying the evolution of compact objects, disk accretion dynamics, and physics ...
About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In ...
It is stated that the detection of a number of soft gamma -ray bursts by Vela satellites has generated great interest in their possible source. The possibility is considered that the bursts may originate from transient episodes of accretion on to compact galactic objects, such as white dwarfs, neutron stars, or black holes. ...
During the past 8 years, extended temporal and broadband spectroscopic studies carried out by x-ray astronomical satellites have led to the identification of specific compact x-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique ...
Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion discs that power active galactic ...
SW Sextantis stars are a relatively large group of cataclysmic variables (CVs) which plays a fundamental role in our understanding of CV structure and evolution. 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 ...
Several neutron stars associated with the accretion-powered long-period X-ray pulsars are observed to experience rapid spin-down years-long trends. Modeling of these trends in terms of the canonical spin-down scenario for accretionpowered compact stars in close binaries suggests that the surface field of these ...
We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent ...
Galactic accreting compact objects, such as stellar-mass black holes and neutron stars, can give us a unique perspective into the behavior of matter in extreme conditions. However, the exact nature of accretion onto these objects is not yet well understood. X-ray studies provide us with a means to observe the ...
Galactic accreting compact objects, such as stellar-mass black holes and neutron stars can give us a unique perspective into the behavior of matter in extreme conditions. However, the exact nature of accretion onto these objects is not yet well understood. X-ray studies provide us with a means to observe the ...
This volume presents 41 articles by distinguished Chinese and Western scientists on topics such as pulsars, neutron stars, supernova explosions, neutrino processes, cataclysmic binaries and other phenomena. As a record of progress in the field, this book is an indispensable guide and reference for professionals and students in astrophysics. Topics considered include pulsars; ...
We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star ...
Over the past decade our understanding of accreting neutron stars has been revolutionized. Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast, coherent X-ray intensity oscillations (hereafter, ``burst oscillations'') during thermonuclear X-ray bursts from 13 low mass X-ray binaries (LMXBs). Although many of ...
Detection of gravitational waves from accreting neutron stars (NSs) in our Galaxy, due to ellipticity or internal oscillation, would be a breakthrough in our understanding of compact objects and explain the absence of NSs rotating near the break-up limit. Direct detection, however, poses a formidable challenge. Using the current data ...
Very-long-baseline interferometry observations have revealed a bright, compact radio component near the center of the expanding shell of supernova 1986J. The component, not present in earlier images, has an inverted radio spectrum different from that of the shell. Such an inversion has not been seen in the spectrum of any other supernova. The new component is likely radio ...
V1408 Aql (= 4U 1957+115) is a low-mass X-ray binary with an orbital period of nearly 9.3 hr, whose compact star is a black hole candidate. The system shows a large-amplitude orbital photometric modulation at optical wavelengths. We have obtained new optical photometry of V1408 Aql from which we derive the orbital light curve and an improved orbital ...
Although massive stars play a critical role in the production of turbulent energy in the ISM, in the
... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...
In the ``competitive accretion" picture, the high-mass end of the stellar initial mass function (IMF) results from continuing accretion onto the central star from a gas reservoir. Most simulations to date have been conducted assuming formation in a cluster gravitational potential. In this contribution we report a set of numerical ...
Systematic multi-wavelength studies of neutron stars (NSs) have shown a jet and disk-jet coupling phenomenology which resembles, although with some important differences, that observed in black holes; ultra-relativistic transient ejection, steady compact jets, accretion-ejection cycles are indeed observed in NSs. I will review our ...
... wTTS). This term defines PMS stars without obvious signs for disk accretion, while young stars, in which accretion from ...
DTIC Science & Technology
They could see details as fine as the neutron star's accretion disk, a ring of gas swirling around and flowing onto the neutron star, as the disk buckled ...
Symbiotic stars (SSs) and Cataclysmic Variables (CVs) are two families of binary systems which occasionally vary in brightness because of accretion from the secondary star. High frequency oscillations, also known as flickering, are thought to occur because of turbulence in the accretion disk especially in and near ...
Recent infrared observations of the Galactic Center have permitted the estimation of orbital parameters for the 8 O stars closest to the compact, nonthermal radio source, Sgr A*. The emission of Sgr A* is thought to be due to the accretion of gas down the potential well of a {approx} 3 x 10{sup 6} solar mass black hole at the dynamical ...
It is shown that Cyg X-3 can be interpreted by means of the standard model'' for galactic x-ray sources in terms of mass loss from a large companion star and accretion on to a compact object. In the standard model'' assumed the x rays originate from a compact object ...
Matter accretion onto compact stars has been considered as a likely process of x-ray emission from stellar x-ray sources. The accreting matter forms a circumstellar envelope that absorbs a part of x rays emitted from the central star. The ionization equilibrium due to the ...
We interpret the recently observed super-long cosmic gamma-ray burst GRB 110328A in the model of collapsing galactic nucleus. The neutron stars and stellar-mass black holes can form evolutionary a compact self-gravitating subsystem in galactic center. Merges of these star remnants during the avalanche contraction and collapse of the ...
The energy release due to neutralino WIMP self-annihilation in the thermalization volume inside a compact object is shown to be comparable to the energy needed to create a long-lived lump of strange quark matter, or strangelet, for WIMP masses above a few GeV. Since strange matter is the most stable state of matter, accretion of self-annihilating dark ...
We use direct N-body simulations of gas embedded star clusters to study the importance of stellar collisions for the formation and mass accretion history of high-mass stars. Our clusters start in virial equilibrium as a mix of gas and protostars. Protostars then accrete matter using different mass ...
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 ...
It has long been believed that the optical and infrared (OIR) fluxes of compact accreting sources will not generally show fast, stochastic variability. This is because reprocessing of high energy photons is thought to be the primer driver of the OIR fluxes. In recent work, we have found fast (sub-second) optical variations in accreting ...
Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M? is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas distribution to ...
There is currently no accepted theoretical framework for the formation of the most massive stars, and the manner in which protostars continue to accrete and grow in mass beyond �10 M&sun; is still a controversial topic. In this study we use several prescriptions of stellar accretion and a description of the Galactic gas ...
At a distance of about only 100pc, Mira AB is the nearest symbiotic system containing an Asymptotic Giant Branch (AGB) star (Mira A), and a compact accreting companion (Mira B) at about 0.5" from Mira A. Symbiotic systems are interacting binaries with a key evolutionary importance as potential progenitors of a fraction of asymmetric ...
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 -1/) leads to the initiation of the carbon ...
do not have accretion disks. Optical spectra are the only way that we can .... inner accretion disks) confirms the asymmetrical distribution of such stars ...
I review the X-ray observations of galactic accreting black holes and neutron stars and interpretations of these in terms of solutions of the accretion flow equations. PMID:12804240
Nov 6, 2000 ... "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two ...
Spectra of the spreading layers on the neutron star surface are calculated on the basis of the Inogamov-Sunyaev model taking into account general relativity correction to the surface gravity and considering various chemical composition of the accreting matter. Local (at a given latitude) spectra are similar to the X-ray burst spectra and are described by a ...
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 ...
... accreting young star that ... 4. TITLE AND SUBTITLE An X-Ray Outburst From the Rapidly Accreting Young Star That Illuminates McNeil's Nebula 5a. ...
We discuss the development of a relativistic hydrodynamic code for describing the evolution of astrophysical systems in three spatial dimensions. The application of this code to several test problems is presented. Preliminary results from the simulation of the dynamics of accreting binary white dwarf and neutron star systems are discussed. 14 refs., 4 ...
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In the early 1990's, isolated thermally-emitting neutron stars accreting from the interstellar medium were predicted to show up in their thousands in the ROSAT soft X-ray all-sky survey. The glut of sources would provide unprecedented opportunities for probing the equation of state of ultra-dense matter. Only seven objects have been firmly identified to ...
Globular clusters (GCs) with their ages of the order of several billion years contain many final products of evolution of stars such as: neutron stars, white dwarfs and probably also black holes. These compact objects can be at present responsible for the acceleration of particles to relativistic energies. Therefore, ?-ray emission is ...
We propose that the intermediate luminosity optical transient NGC 300 OT2008-1 was powered by a mass transfer episode from an extreme asymptotic giant branch star to a main sequence (MS) companion. We find a remarkable similarity in the shapes of the light curves of the several months long NGC 300 OT2008-1 outburst, of the three-month long 2002 enigmatic outburst of the B ...
A model of the X-ray radiation emitted from the accretion column of a compact object in AM Herculis binaries, using Monte Carlo methods is presented. The accretion column in the model has cylindrical symmetry. Above a shocked region in the column there is...
X-ray flashes from accreting neutron stars are considered. A number of possible explanations for the phenomenon are reviewed. A physical picture is drawn, and numerical models are discussed. 3 figures. (RWR)
Jan 22, 2010 ... Many astrophysical objects, including neutron stars and accretion disks, are powered by a combination of very strong magnetic fields and ...
CAN MASSIVE STARS BE FORMED BY ACCRETION? Harold W. Yorke. Jet Propulsion Laboratory, California Insitute of Technology, Pasadena, CA email: Harold. ...
... Accession Number : ADA426581. Title : An X-Ray Outburst from the Rapidly Accreting Young Star that Illuminates McNeil's Nebula. ...
Primordial stars formed in the early universe are thought to be hosted by compact dark matter (DM) halos. If DM consists of weakly interacting massive particles (WIMPs), such stars may be powered by DM annihilation during the early phases of their evolution. We study the pre-main-sequence evolution of the primordial ...
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 ...
We present a full general relativistic numerical code for estimating the energy-momentum deposition rate (EMDR) from neutrino pair annihilation (?). The source of the neutrinos is assumed to be a neutrino-cooled accretion disc around neutron and quark stars. We calculate the neutrino trajectories by using a ray-tracing algorithm with the general ...
During the past three years a study has been made of a class of variable x-ray sources in our Galaxy which radiate up to a million times more powerfully than the Sun. The energy supply which powers these luminous sources of x rays is considered. It is argued that this arises from matter transferred from one star to a compact companion in a close ...
We briefly summarise the observational properties of ultra-compact binaries called AM CVn stars. We analyse their outbursts originating from the thermal-viscous instability in helium accretion disc. We present our preliminary results in applying the model of Dwarf Novae outbursts to helium discs. We can calculate models of outbursts of ...
Spectrophotometry of the proposed optical counterpart of the hard X-ray source GX 1+4 is presented. The spectrum is that of a symbiotic star which is an M giant with a variable blue continuum and a rich emission line spectrum including H I, He I, Fe II, (Fe VII), and probably (Fe X). An explanation in terms of a compact object ...
The improved sensitivity of the XMM-Newton satellite is quickly expanding our knowledge of X-ray emission mechanisms and physical conditions in and around compact objects. Thanks to the large collecting power and high energy resolution of the EPIC and RGS instruments, detailed X-ray spectral analysis can be performed in the 0.2 to 12 keV energy range. In this short review, I ...
Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 ...
Symbiotic stars, in which material from a red-giant donor accretes onto or interacts with a compact companion, provide astrophysics with fascinating (relatively) nearby laboratories displaying phenomena such as astrophysical jets, shocks, accretion disks and colliding winds. Here we request a modest allotment of ...
Accretion-powered millisecond pulsars (AMPs) are very interesting astrophysical objects. Mat-ter from accretion disk is captured by star's magnetic field and falls along the field lines, creating "hotspots" near magnetic poles of the star. Typical spectrum of an AMP contains a disk emis-sion, blackbody emission of ...
X-ray line emission with several-keV of photon energy was observed from photoionized accreting clouds, for example CYGNUS X-3 and VELA X-1, those are exposed by hard x-ray continuum from the compact objects, such as neutron stars, black holes, or white dwarfs, although accreting clouds are thermally cold. The x-ray ...
LS I +61 303 is a puzzling Be/X-ray binary with variable gamma-ray emission at up TeV energies. The nature of the compact object and the origin of the high-energy emission are unclear. One family of models invokes particle acceleration in shocks from the collision between the B-star wind and a relativistic pulsar wind, while another centers on a ...
The Kepler observatory was designed to discover transits by Earth-like planets orbiting Sun-like stars. Its first major discoveries, however, are hot objects in close orbits around main-sequence stars. These are likely to be white-dwarf remnants of stars that have transferred mass to the present-day main sequence ...
I present H- and K-band light curves of the dwarf nova cataclysmic variable (CV), IP Peg, and the novalike CV, RW Tri, and an H-band light curve of the novalike CV, SW Sex. All three systems showed contributions from the late-type secondary star and the accretion disk, including a primary eclipse of the accretion disk by the secondary ...
Suggestive evidence has accumulated that intermediate mass black holes (IMBHs) exist in some globular clusters. Some stars will inevitably wander sufficiently close to the hole to suffer a tidal disruption. IMBHs can disrupt not only solar-type stars but also compact white dwarf stars. We investigate the fate of ...
While it is well known that neutrinos are emitted from standard core collapse protoneutron star supernovae, less attention has been focused on neutrinos from accretion disks. These disks occur in some supernovae (i.e. collapsars) as well as in compact object mergers, and they emit neutrinos with similar properties to those from ...
We propose to use the IRAC and MIPS camera arrays on Spitzer to establish the mid-infrared spectral energy distribution and search for evidence for jet emission contributions at Spitzer wavelengths for three Z sources: GX 349+2, GX 17+2, and Cyg X-2. These neutron star X-ray binaries are the brightest X-ray sources in the Galaxy and also the most radio bright of their class. ...
Type I X-ray bursts are very common in neutron star X-ray binaries. We have carried out a global linear stability analysis of the accumulating fuel on the surface of a compact star and the underlying crust to identify the conditions under which thermonuclear bursts are triggered. Our analysis, which improves on previous calculations, ...
We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars, and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model that includes planet migration and disk evolution, and subsequent evolution yield consistent ...
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 ...
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 magnetic field lines formed ...
Although neutral hydrogen high velocity clouds (HVCs) have been known to exist for over 40 years, surprisingly little is known about their physical properties such as distance, mass and size. Whether HVCs reside in the Galactic halo or in the larger scale Local Group medium has long been a matter of debate and studies of compact HVCs are likely to provide us with a piece of ...
The discovery of hundreds of young, bright stars within a parsec from the massive black hole at the center of the Galaxy presents a challenge to star formation theories. The requisite Roche densities for gravitational collapse of gas clouds are most naturally achieved in accretion disks. The water maser sources in Keplerian rotation in ...
Stars with masses in the range 1-8 solar masses (M(\\circ)) live ordinary lives for approximately 10(9)-10(10) years, but die extraordinary deaths. First, during their death throes as asymptotic giant branch (AGB) stars they eject, over 10(4)-10(5) years, half or more of their mass in slowly expanding, spherical winds, and then, in a short (a few 100-1,000 ...
Turbulence is ubiquitous in astrophysics, ranging from cosmology, interstellar medium to stars, supernovae, accretion disks, etc. ...
A large number of neutron stars (NSs), approximately 10(exp 9), populate the Galaxy, but only a tiny
The central compact objects are a newly emerging class of young neutron stars near the centre of supernova remnants. From X-ray timing and spectral measurements, their magnetic fields are determined to be �1010-1011 G, which is significantly lower than that found on most pulsars. Using the latest electrical and thermal conductivity calculations, we solve ...
The origin of large scale magnetic fields in astrophysical rotators, and the conversion of gravitational energy into radiation near stars and compact objects via accretion have been subjects of active research for a half century. Magnetohydrodynamic turbulence makes both problems highly nonlinear, so both subjects have benefitted from ...
Perhpas the most extreme examples of ``Active OB stars" are the subset of high-mass X-ray binaries - consisting of an OB star plus compact companion - that have recently been observed by Fermi and ground-based Cerenkov telescopes like HESS to be sources of very high energy (VHE; up to 30 TeV!) ?-rays. This paper focuses on the ...
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 ...
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 ...
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 accretion ...
... codes for the prediction of ice accretion on aeroplanes ... NUMERICAL ANALYSIS, ICE, AVIATION SAFETY, COMPACT DISKS, ICE FORECASTING ...
Quasar Jets and Accretion Disks. Questions: " Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? ...
Once quantum mechanical effects are included, the hypotheses underlying the positive mass theorem of classical general relativity fail. As an example of the peculiarities attendant upon this observation, a wormhole mouth embedded in a region of high mass density might accrete mass, giving the other mouth a net [ital negative] mass of unusual gravitational properties. The ...
We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters the accretion rate, diffusion coefficient, ...
Observational evidence suggests a link between long duration gamma ray bursts (LGRBs) and Type Ic supernovae. Here, we propose a potential mechanism for Type Ic supernovae in LGRB progenitors powered solely by accretion energy. We present spherically-symmetric hydrodynamic simulations of the long-term accretion of a rotating gamma-ray burst progenitor ...
This thesis examines aspects of subsonic reactive flows in stars. Highlighted are fluid flows in which the velocity of the fluid is much less than the local sound speed of the fluid, and where the thermodynamic conditions of the fluid are conducive to nuclear reactions. Reactive flows of this nature are capable of generating self-sustained flame fronts, also known as ...
The extent to which the continuum spectral energy distributions of T Tauri stars from 0.2 to 10 microns can be explained by a simple model consisting of an active PMS star and active accretion disk is considered. The disk contributes both an IR excess due to accretion energy dissipation and stellar light ...
Recent data on low-mass X-ray binaries (LMXBs) and msec pulsars (MSPs) pose a challenge to evolutionary which neglect the effects of disk and companion irradiation. Here we discuss the main features of a radiation-driven (RD) evolutionary model that may be applicable to several LMXBs. According to this model, irradiation from the accreting compact ...
Accreting black holes and neutron stars in their hard (low) state show not only very similar X/?-ray spectra but also that the behavior of their light curves is quite similar which can be quantified as having similar power-density spectra and Fourier-frequency-dependent time/phase lags. Taken together this argues for a common mechanism of the X/?-ray ...
Compact object mergers have long been speculated to be a possible site of r-process nucleosynthesis. While most attention has been focused on the cold decompression of neutron star matter ejected from the merger, other sites within the merger likely contribute to its nucleosynthetic output. Here we consider hot outflows from the ...
Recent studies of galaxies ~2-3Gyr after the Big Bang have revealed large, rotating disks, similar to those of galaxies today. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation indicates that gas accretion is likely to be the dominant mode by which galaxies grow, because major mergers of galaxies would ...
Recent studies of galaxies approximately 2-3 Gyr after the Big Bang have revealed large, rotating disks, similar to those of galaxies today. The existence of well-ordered rotation in galaxies during this peak epoch of cosmic star formation indicates that gas accretion is likely to be the dominant mode by which galaxies grow, because major mergers of ...
The accretion disk around a compact object is a nonlinear general relativistic system involving magnetohydrodynamics. Naturally, the question arises whether such a system is chaotic (deterministic) or stochastic (random) which might be related to the associated transport properties whose origin is still not confirmed. Earlier, the black hole system GRS ...
Current published results suggest that the maximum and the minimum kHz QPO frequencies are flux-dependent for individual sources when missionlong observations are plotted together, i.e., the maximum frequency decreases with increasing flux while the minimum frequency increases with increasing flux. A confirmation of the flux-dependences would 1) prove that the radiation force of the X-ray flux ...
HD 15137 is an intriguing runaway O-type binary system that offers a rare opportunity to explore the mechanism by which it was ejected from the open cluster of its birth. Here, we present recent blue optical spectra of HD 15137 and derive a new orbital solution for the spectroscopic binary and physical parameters of the O star primary. We also present the first XMM-Newton ...
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 ...
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 ...
Recently, three variable stars have been identified as likely accreting binary systems with ultra-short orbital periods of 10 minutes or less. This makes them the closest binaries known as well as strong sources of gravitational wave emission. These objects have thus been identified as crucial calibration sources for the LISA mission. V407 Vul diplays a ...
We present X-ray observations of the transient accretion-powered millisecond pulsar IGR J00291+5934 during quiescence. IGR J00291+5934 is the first source among accretion-powered millisecond pulsars to show signs of a thermal component in its quiescent spectrum. Fitting this component with a neutron star atmosphere or a blackbody model ...
We provide a brief review of the physical processes behind the radiative driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and accretion of a fraction of the stellar wind by a compact object, typically a neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we describe a ...
Recent Kepler observations revealed an abundance of 'hot' Earth-size to Neptune-size planets in the inner 0.02-0.2 au from their parent stars. We propose that at least some of these smaller planets are the remnants of massive giant planets that migrated inwards quicker than they could contract. We show that such disruptions occur if the young giant planet embryo is initially ...
During mass exchange in binary systems the star which is receiving mass increases its volume. This effect is estimated by evolutionary calculations for different (constant) accretion rates. It is shown the chance that the two stars do not come in contact ...
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...
Dec 31, 2008 ... The line widths are influenced by rotation of the star via the Doppler effect. Since the spin rates of many of these accreting neutron stars ...
APOD: 1999 December 19 Accretion Disk Binary System Explanation: Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems. ...
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 authors develop the ...
