stars via accretion. A necessary condition for accretion growth of a hy- ... via accretion for stars more massive than 1 M@. 1. Introduction ...

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

formation of massive stars via accretion. A necessary condition for accre- ... constraints on the accretion rate necessary to produce high mass stars and ...

With IXO, spectroscopy of accretion onto black holes will finally rival optical and IR spectroscopy of accreting young stars. ...

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

The purpose of the two-day Workshop on Physics of Accretion Disks Around Compact and Young Stars was

accretion disks in the western Gulf region (Texas and Louisiana). Accretion ... protostellar disks are believed to be accretion disks associated with young, ...

Although massive stars play a critical role in the production of turbulent energy in the ISM, in the

... wTTS). This term defines PMS stars without obvious signs for disk accretion, while young stars, in which accretion from ...

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 ...

Nov 9, 2003 ... Consequently accretion disks have fundamental roles in the formation of planets, stars and compact objects, and are the engines driving the ...

Radial oscillations resulting from axisymmetric perturbations in viscous accretion disks surrounding

Nuclear reactions in the hot accretion plasma surrounding a collapsed star are a source of neutrons,

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 ...

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 ...

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...

... accreting young star that ... 4. TITLE AND SUBTITLE An X-Ray Outburst From the Rapidly Accreting Young Star That Illuminates McNeil's Nebula 5a. ...

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. ...

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 ...

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 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...

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 ...

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 ...

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 primary ...

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 ...

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 ...

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 ...

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

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 ...

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 ...

have been. : size and distribution of such flux tubes. We then apply the model to identified using numerical, nonlinear hydrodynamic techniques, accretion ...

... 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. ...

A star acquires much of its mass by accreting material from a disk. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative ...

Spherically symmetric, time-dependent accretion of an ionized hydrogen plasma onto a neutron star is

Mar 16, 2006 ... Accretion Promotion a change of an employee to a higher grade when the employee assumes higher graded duties and responsibilities (and ...

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

Feb 23, 2004 ... "Accretion disks are known to flow around many objects in the universe ... Under normal conditions, accretion disks appear far too minute to ...

Dec 19, 1999 ... Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. ...

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 ...

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 ...

High resolution infrared spectroscopy is a very valuable tool for the study of the formation of low mass and very low mass stars. At the stage in which these objects are already visible, they still undergo strong mass accretion and mass loss processes. Many of the features observed on these stars can be explained by the magnetospheric ...

The shape of the Alfven surface separating the magnetosphere of a neutron star from the stream of accreting plasma and the velocity and scattering optical depth of the gas layer flowing along the Alfven surface are calculated. Calculations are made both for spherically symmetrical fall of the gas and for disk accretion. It is shown ...

An initial study of the evolution of a neutron star in a close-binary orbit of high eccentricity discloses a special class of systems that will never achieve a state of pure, steady accretion: the neutron star will continually oscillate between an accreting state and a propeller state. This may be what is happening ...

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...

The report deals with the question of whether mass accretion on a star can cause pulsational instability by itself. The principal result is a formula for the effect of accretion on the growth (or decay) rate of a radial pulsation mode. Application of this...

The present study of hypercritical accretion flows onto neutron stars considers steady-state, spherically symmetric flows whose accretion rate range is characterized by the carrying away of gravitational-accretion energy by neutrinos. The models used encompass pair production, radiation diffusion, and general ...

Herbig Ae/Be stars(HAeBes) are young stellar objects of spectral class F2 through B0, with the central star often surrounded by a circumstellar disk of gas and dust. They are the higher mass analogs to T Tauri stars. The interaction between the star and the disk is not well understood, nor is the disk structure. ...

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 ...

The current status of the physics of accretion disks in close binary stars is reviewed, with an emphasis on the hydrodynamic overreflection instability, which is a factor leading to the accretion disk turbulence. The estimated turbulent viscosity coefficients are in good agreement with observations and explain the high angular momentum ...

Although the powering mechanism for quasars is now widely recognized to be the accretion of matter in a geometrically thin disk, the transport of matter to the inner region of the disk where luminosity is emitted remains an unsolved question. Miralda-Escud� & Kollmeier (2005) proposed a model whereby quasars are fuelled when stars are captured by the ...

Degenerate secondary stars, optically thin accretion disks, and starspots and stellar activity are discussed via a brief romp through the pages of some recent astrophysical literature.

The X-ray luminosity of black holes is produced through the accretion of material from their companion stars. Depending on the mass of the donor star, accretion of the material falling onto the black hole through the inner Lagrange point of the system or ...

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

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...

The IUE was used to study processes connected with accretion disk structure and stability, wind accretion and wind-wind collisions, contact systems, and stellar activity in close binary stars. Time dependent phenomena already known from optical studies ap...

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

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 a magnetic field. Initially soft photons are heated as they are compressed between the accr...

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 accr...

In this note, we confront the results of a spectroscopic analysis giving s-process element abundances in a sample of barium stars with theoretical predictions from the wind accretion scenario of Boffin & Jorissen (1988). This comparison is done in the overabundance-orbitaql period plane.

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.

We compare observed and simulated images of the accretion flows associated with high mass star formation in the regions G10.6--0.4 and DR21. We describe, as a result of the comparison, the temperature, density, and velocity fields. Our results indicate th...

X-ray bursters are considered to be neutron stars with a weak magnetic field that are undergoing disk-type accretion. If the field is weak enough, the disk will reach to the neutron star surface; next to the surface, a narrow boundary layer will develop, girdling the star. Using available formulations for ...

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 ...

thermonuclear flashes on accreting neutron stars are compared. ... An ignition mechanism of the bursts is proposed in terms of elemental mixing and ...

Mar 1, 2011 ... thermonuclear flashes on accreting neutron stars are compared. ... An ignition mechanism of the bursts is proposed in terms of elemental ...

X-ray emitting MHD accretion shocks in classical T Tauri stars. Case for moderate to high plasma-? values

Jul 2, 2003 ... Caption for Animation 1: ACCRETION SPINS PULSAR TO MILLISECOND RANGE. If a pulsar -- a dense star with strong gravitational attraction -- is ...

A semi-analytical scheme for augmenting existing evolutionary tracks of pre-main sequence protostars

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

A grid of numerical models is used here to study how accretion flows are affected by star formation. The observables associated with these models are investigated, presenting their X-ray surface brightness profiles. An X-ray diagnostic is searched for that, in the absence of spatially resolved X-ray spectral data, can be an unambiguous indicator for ...

It is shown here that the behavior of nuclear burning on accreting neutron stars depends on the mass

... the hard X-ray Galactic continuum could be the superposition of unresolved point sources such as accreting neutron stars or black holes. ...

... the hard X-ray Galactic continuum could be the superposition of unresolved point sources such as accreting neutron stars or black holes. ...

The current generation of gamma-ray telescopes (SIGMA, GRO) provides a new opportunity for observing

Neutron Stars, Pulsars, Millisecond Pulsars, and Gravitational Radiation: GLOSSARY. Accretion disk: The flattened, pancake-like structure formed by matter ...

Abstracts of individual items from the workshop were prepared separately for the data base. (ERA citation 08:044825)

A model of a thin polytropic disk accretion onto a polytropic star through a polytropic boundary layer is analyzed and a one-parameter series of models is calculated with the stellar angular velocity varying from small to somewhat supercritical values along the series. It is demonstrated that there is no limit to the amount of mass that can be ...

of these phenomena, the one supported by the data is the following. Accreting black holes and neutron stars are observed to launch relativistic puffs of plasma:...

Mass accretion onto (proto-)stars at high accretion rates \\dot{M}_* > 10^{-4} M_{&sun;} yr^{-1} is expected in massive star formation. We study the evolution of massive protostars at such high rates by numerically solving the stellar structure equations. In this paper, we examine the evolution via disk ...

... from a bipolar jet that has formed near the point where material streaming from star 2 interacts with the accretion disk around star 1 (Harmanec et al. ...

Feb 23, 2004 ... The gas spirals toward the neutron star like water going down a drain, forming what scientists call an accretion disk. ...

Star clusters/ULX associations? Survival or dispersion of protoclusters. What is the mass of the accreting BHs in ULXs? From: luminosity. X-ray colors ...

Oct 29, 2010 ... Stars formed, planetary systems around stars formed from within these ... Kepler is observing accretion disks with a combined photometric ...

We present archival and recent IUE high dispersion spectra of late B stars which reveal the presence

M stars as targets for terrestrial exoplanet searches and biosignature detection. [Astrobiology. 2007] Review M stars as targets for terrestrial exoplanet searches and...