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

Recent work on a unified model of accretion flows and X-ray emission in low mass X-ray binaries is summarized. In this model, a weakly magnetic neutron star accretes gas simultaneously from a Keplerian disk and a corona above the inner part of the disk. P...

Theory and Modelling Research in the LHEA - Research Topics. Low Mass X-ray Binaries -- Accretion Disk Corona Radiative Transfer � Synthetic X-ray Spectra ...

Unstable thermonuclear ignition of accreted fuel on neu- tron stars (NSs) in low -mass X-ray binaries (LMXBs) is triggered once a critical column density is ...

Models are presented for the 6-7 keV iron line emission from low-mass X-ray binaries. A simplified model for an accretion disk corona is used to examine the dependence of the observable line properties, line width and mean energy, on the radial distance of the emission region from the X-ray source, and on the fraction of the X-rays ...

Millisecond pulsars are believed to descend from low-mass X-ray binaries. Observable parameters of binary millisecond pulsars, e.g. mass of the pulsar, mass of the companion, spin period of the pulsar, orbital period, orbital eccentricity, etc., are used to probe the past accretion history of the millisecond ...

We calculate the accretion disc temperature profiles, disc luminosities and boundary layer luminosities for rapidly rotating neutron stars considering the full effect of general relativity. We compare the theoretical values of these quantities with their values inferred from EXOSAT data for four low mass X-ray ...

We suggest a possible explanation for the high frequency quasi-periodic oscillations (QPOs) in black hole (BH) low-mass X-ray binaries. By solving the perturbation general relativistic magnetohydrodynamic equations, we find two stable modes of the Alfven wave in the accretion disks with toroidal magnetic fields. We suggest that these ...

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

The illumination of companion stars in very low mass X-ray binaries by various kinds of radiation from the neighborhood of the neutron star after accretion has terminated or during accretion is considered. If a neutron star's spun-up period approaches 0.001 s, pulsar kHz radiation can ...

Among the newly discovered classes of X-ray sources which have attracted wide attention are close binary systems in which mass is transferred via Roche lobe overflow from a low mass donor star to its neutron star companion. Many of these sources exhibit i...

1. Neutron Star Low Mass. X-ray Binaries. (NSLMXBs) seen by. INTEGRAL: high energy behaviour. Neutron Star Low Mass. X-ray Binaries. (NSLMXBs) seen by ...

By means of the accretion induced magnetic field evolution model of neutron star in low mass X-ray binary, the star spin frequency evolution has been studied, and we find that the star spin frequency is almost independent of the mass accretion rate, initial magnetic field and initial period, ...

Exosat observations are used to compare the spectral properties of the persistent emission from a number of X-ray burst sources, high-luminosity low-mass X-ray binaries (LMXRB) and galactic black hole candidates with various models for X-ray emission from an accretion disk surrounding a compact object in a binary ...

Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719-1438, a 5.7 ms pulsar, was detected in a recent survey with the Parkes 64�m radio telescope. We show ...

HETE J1900.1-2455 is a highly peculiar accreting millisecond pulsar, as its pulses disappeared soon after the discovery of the source. Therefore, it can be viewed as a prototype of a system in between pulsating and non pulsating low mass X-ray binaries. We propose to observe it for the first time with XMM-Newton, ...

This dissertation presents research on two low mass X-ray binaries. The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy with the ACS/SBC on the Hubble Space Telescope and ...

We report on a Chandra Director's Discretionary Time observation of the globular cluster Terzan 5, carried out �7 weeks after the cessation of the 2010 outburst of the newly discovered transiently accreting 11-Hz X-ray pulsar. We detect a thermal spectrum that can be fitted with a neutron star atmosphere model with a temperature for an observer at infinity of kT?� 100 eV ...

Context: .V617 Sgr is a V Sagittae star - a group of binaries thought to be the galactic counterparts of the Compact Binary Supersoft X-ray Sources - CBSS. Aims: .To check this hypothesis, we measured the time derivative of its orbital period. Methods: .Observed timings of eclipse minima spanning over 30 000 orbital cycles are presented. Results: .We found ...

The well-studied X-ray/optical/radio supernova remnant (SNR) DDB 1-15 (CXOM31 J004327.8+411829; r3-63) in M31 has been investigated with archival XMM-Newton and Chandra observations. The timing data from XMM-Newton reveal a power density spectrum (PDS) characteristic of accreting compact objects in X-ray binaries (XRBs). The PDS shows features typical of ...

In this paper, we investigate the relationship between the maximal luminosity of X-ray outburst and the orbital period in transient low mass X-ray binaries (or soft X-ray transients) observed by the Rossi X-ray Timing Explorer (RXTE) in the past decade. We find that the maximal luminosity (3-200 keV) in Eddington units generally ...

We propose to capitalise on the extensive set of scientific and calibration observations of the remarkable globular cluster 47 Tuc. The chief goals are: 1 to address key questions about the binaries found in this massive cluster, including studies of cataclysmic variables CVs, low-mass X-ray binaries LMXBs, millisecond pulsars MSPs and ...

There exists a group of persistently faint galactic X-ray sources that, based on characteristics such as location in the galaxy, high Lx/Lopt, association with X-ray bursts, absence of X-ray pulsations and similar characteristics are thought to be low-mass X-ray binaries, but about which very little is known. We propose to observe a sample of them with RXTE in modes and with ...

The eclipsing low-mass X-ray binary 4U 1822-371 is the ideal system in which to observe hot accretion and the effects of strong irradiation. Its orbital period is 5.57~hr and its orbital inclination is high enough that flux from the neutron star is blocked by the edge-on accretion disk in the system. Because the ...

Context. Low mass X-ray binaries are found to have very low frequency breaks in their power density spectra. The power density spectra below these breaks are nearly in white noise structure and at higher frequencies approximately follow the P? ? ?-1.3 law. Aims: To determine whether high mass X-ray binary power ...

We propose a physical model of the Cygnus X-2 like Z-track sources: GX 340+0, GX 5-1 and Cygnus X-2 based on the results of applying a particular emission model for low mass X-ray binaries to high quality Rossi-XTE data on the sources. In this emission model the Comptonizing Accretion Disk Corona is very extended, ...

The relation between mass accretion rate and the X-ray properties of neutron-star low-mass X-ray binaries (NS-LMXBs) remains poorly understood. One of the major questions is whether differences in accretion rate alone are enough to account for the various (Z and atoll) sub-classes. Here I report on observations of ...

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 ...

It has been reported that the observed distribution of Algol binaries contains more systems with large mass ratios than can be produced by conservative evolution. We developed a code of non-conservative evolution in which during a short, violent phase of Roche lobe overflow, the gainer can be incapable of accreting all matter transferred by the donor. ...

In an observation of 4U 0918-549 obtained during AO5 we detected a kHz quasi-periodic oscillation (kHz QPO) with a large fractional rms amplitude. KHz QPOs with fractional rms amplitudes up to 20% are exclusively found in low-luminosity LMXBs. Moreover, the frequencies of kHz QPOs in low-luminosity LMXBs are high, enabling to constrain the hard EOS of neutron star matter. Detailed studies of these ...

Type Ia supernovae (SNe Ia) play an important role in the study of cosmic evolution, especially in cosmology. There are several progenitor models for SNe Ia proposed in the past years. By considering the effect of accretion disk instability on the evolution of white dwarf (WD) binaries, we performed detailed binary evolution ...

We have investigated the influence of X-ray irradiation on the vertical structure of the outer accretion disk in low-mass X-ray binaries by performing a self-consistent calculation of the vertical structure and X-ray radiation transfer in the disk. Penetrating deep into the disk, the field of scattered X-ray photons with energy E ? 10 keV exerts a ...

Rapidly rotating stars are readily produced in binary systems. An accreting star in a binary system can be spun up by mass accretion and quickly approach the break-up limit. Mergers between two stars in a binary are expected to result in massive, fast rotating stars. These rapid rotators may ...

An evolutionary link between Low Mass X-ray Binaries (LMXBs) and Low Mass Binary Pulsars (LMBPs) has long been proposed. Before the launch of RXTE, the critical missing piece of evidence was the detection of coherent millisecond pulsations from LMXBs that would confirm ...

Neutron star configurations are considered as thermodynamical systems for which a phase diagram in the angular velocity ( ? ) - baryon number (N) plane is obtained with a dividing line Ncrit(?) for quark core configurations. Trajectories of neutron star evolution in this diagram are studied for different scenarios defined by the external torque acting on the star due to radiation and/or mass ...

Context. The number of strong iron K? line detections in Seyfert AGN is clearly growing in the Chandra, XMM-Newton and Suzaku era. The iron emission lines are broad, some are relativistically blurred. These relativistic disk lines have also been observed for galactic black hole X-ray binaries. Thermal components found in hard spectra were interpreted as an indication for a ...

We report results on three low-mass X-ray binaries (LMXB) in the LMC, obtained with EXOSAT, IUE and ground-based (ESO) telescopes: LMC X-2 which appears to be �Sco X-1�-like, LHG 83 and LHG 87. The latter are two weaker sources first detected in the course of the HEAO-B LMC survey. They have faint optical counterparts of which LHG 87 was only recently ...

The magnetic field and spin frequency of neutron star in low mass X-ray binaries have been studied through considering the accretion induced evolution process and it is obtained that the magnetic field of X-ray neutron star is proportionally related to the accretion luminosity Moreover the ...

We propose 4 observations of one high inclination black hole low mass X-ray binary (LMXB) at different stages of its outburst. We will investigate the presence of X-ray narrow absorption/emission features in the XMM spectra, which are a signature of a disc wind, and their relation to the accreting regime. Such ...

Observations of neutron stars in low mass X-ray binaries give us an opportunity to probe nuclear physics of both proton rich and neutron rich nuclei. I will describe how observations of Type I X-ray bursts and cooling of neutron stars after long accretion outbursts constrain the physics of the neutron star ocean ...

Model continuum spectra of the accretion disk in the black hole binary A0620-00 are calculated assuming it has a standard alpha-disk structure. The optical and X-ray fluxes obtained are in very good agreement with the observations, provided the mass transfer rate is about 5 x 10 to the -8th solar masses/yr during outburst and less than 10 to the -11th ...

In millisecond pulsars the existence of the Coriolis force allows the development of the so-called Rossby oscillations (r-modes) which are know to be unstable to emission of gravitational waves. These instabilities are mainly damped by the viscosity of the star or by the existence of a strong magnetic field. A fraction of the observed millisecond pulsars are known to be inside ...

Quiescent X-ray emission from the neutron star low-mass X-ray binaries is seen to be variable on timescales as short as hundreds of seconds and as long as years. Yet, this variability is not understood. Our recent studies of the systems Cen X-4 and Aql X-1 have shown that the thermal component is variable. This poses a serious problem for using thermal ...

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

The present conference considers topics in the fields of rotation-powered pulsars, the relationship of pulsars to SNRs, accretion-powered pulsars, neutron-star formation in theoretical SNs, neutrol stellar evolution, neutron star physics, and other manifestations of neutron stars and their place in neutron star evolution. Attention is given to the relation between radio ...

Variability on a variety of timescales is a commonly observed feature of astronomical systems ranging from compact binaries to active galactic nuclei. In some cases, such as those involving the x-ray emissions of certain black-hole candidates and the Z-sources among low-mass x-ray binaries, quasi-periodic oscillations are observed to ...

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 ...

We suggest that a high proportion of brown dwarf (BD) stars are formed by gravitational fragmentation of massive extended discs around Sun-like primary stars. We argue that such discs should arise frequently, but should be observed infrequently, precisely because they fragment rapidly. By performing an ensemble of radiation-hydrodynamic simulations, we show that such discs typically fragment ...

The variability of neutron star and black hole X-ray sources has several dimensions, because of the roles played by different important time-scales. The variations on time scales of hours, weeks, and months, ranging from 50% to orders of magnitude, arise out of changes in the flow in the disk. The most important driving forces for those changes are probably various possible instabilities in the ...

I show that the assumption that the acceleration and collimation mechanisms of jets are the same in all the classes of astrophysical objects which are observed to produce jets, can lead to interesting conclusions. Jets have now been observed in: active galactic nuclei, young stellar objects, massive x-ray binaries, low mass x-ray ...

The pulsing X-ray source 4U 1626-67 is an accreting neutron star in a binary system with a very low mass companion. The source was observed by Exosat continuously for 23 hr on March 30-31, 1986 UT. It is found that, if the orbital inclination angle equals 90 deg, the optical companion star has a mass of less than ...

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 ...

We have carried out a deep X-ray and optical survey with Chandra and HST of low-extinction regions in the Galactic bulge. Here we present the results of a search for low-luminosity (LX lsim 1034 erg s-1) accreting binaries among the Chandra sources in the region closest to the Galactic center, at an angular offset of 1fdg4, that we have named the Limiting ...

I provide a review of observations in the optical, UV (HST), and EUV (EUVE and Chandra LETG) of the rapid periodic oscillations of nonmagnetic, disk-accreting, high mass-accretion rate cataclysmic variables (CVs), with particular emphasis on the dwarf nova SS Cyg in outburst. In addition, I drawn attention to a correlation, valid over nearly six orders of ...

We present optical spectra in the range 4600-8600� for three low-mass X-ray binaries which have been suggested to belong to the class of ultra-compact X-ray binaries based on their X-ray spectra. Our spectra show no evidence for hydrogen or helium emission lines, as are seen in classical X-ray binaries. The ...

We suggest that low-mass hydrogen-burning stars like the Sun should sometimes form with massive extended discs, and we show, by means of radiation hydrodynamic simulations, that the outer parts of such discs (R >~ 100au) are likely to fragment on a dynamical time-scale (103 to 104yr), forming low-mass companions: principally brown dwarfs (BDs), but also very ...

We discuss the formation, evolution and observational parameters of the population of short-period (&? 10 hr) low-mass black-hole binaries (LMBHB). Their evolution is determined by the orbital angular momentum loss and/or nuclear evolution of the donors. All observed semidetached LMBHB are observed as soft X-ray transients (SXTs). The absence of ...

... Understanding of accretion disks, accretion flows, X-ray induced winds, compact obect evolution are all in a primitive state. ...

Material falling (accreting) onto a black hole in a binary system, or at the center of a galaxy, forms an accretion disk about the event horizon, with the inner ...

The Chandrasekhar limit is of key importance for the evolution of white dwarfs in binary systems and for the formation of neutron stars and black holes in binaries. Mass transfer can drive a white dwarf in a binary over the Chandrasekhar limit, which may lead to a Type Ia supernova (in case of a CO white dwarf) or an ...

the process in a flyby for Comet West-Kohoutek-Ikemura in June 2000. Since one of the goals of spacecraft

Binary Black Holes, Accretion Disks and Relativistic. Jets: Photocenters of Nearby AGN and Quasars. Principal Investigator: Ann E. Wehrle (Interferometry ...

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

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 ...

Binary radio pulsars are generally believed to have been spun up to millisecond periods (i.e. recycling) via mass accretion from their donor stars, and they are the descendants of neutron star low-mass X-ray binaries. However, some studies indicate that the formation of pulsars from the ...

It is generally assumed that the magnetic fields of millisecond pulsars (MSPs) are �108 G. We argue that this may not be true and the fields may be appreciably greater. We present six evidences for this: (1) The �108G field estimate is based on magnetic dipole emission losses which is shown to be questionable; (2) The MSPs in low mass X-ray ...

The possible origin of two low-mass hyper-iron-poor (HIP) stars, HE0107-5240 and HE1327-2326 are investigated. The three scenarios tested are as follows. (i) The star forms metal free (Population III) and accretes metals throughout its lifetime. (ii) A Population III binary star system forms, and the lower mass star ...

Low-Mass X-ray binaries (LMXBs) are known to have soft and hard states, like Black Hole Binaries (BHBs). Since LMXBs are similar to BHBs in many respects, comparison between them will help us to understand their accretion mechanisms. With this in mind, we analyzed archival Suzaku data of the recurrent transient ...

Context. Most of the spectra of neutron star low-mass X-ray binaries (NS LMXBs), whether they are persistent or transient, are characterized by the presence of a strong thermal Comptonization bump, which is thought to originate in the transition layer (TL) between the accretion disk and the NS surface. The observable quantities that ...

I review the available RXTE data of the two low-mass X-ray binaries (LMXBs) and atoll sources 4U 1608-52 and 4U 1636-53. I summarize the properties of the quasi-periodic oscillations at kilohertz frequencies (kHz QPOs) observed in their X-ray flux, and how do they relate to other properties of the sources, e.g., X-ray flux, inferred mass ...

We present an extensive study of accretion onto neutron stars in which the velocity of the neutron star and structure of the surrounding medium is such that the Bondi-Hoyle accretion exceeds 10{sup 4} {ital M}{sub {circle_dot}} yr{sup 1}. Two types of initial conditions are considered for a range of entropies and chemical compositions: an atmosphere in ...

Thermal conduction between a cool accretion disk and a hot inner corona can result in either evaporation of the disk or condensation of the hot corona. At low mass accretion rates, evaporation dominates and can completely remove the inner disk. At higher mass accretion rates, condensation ...

It has recently been suggested that the maximum observed quasi-periodic oscillation (QPO) frequencies, ?max, for several low-mass X-ray binaries, particularly 4U 1820-30, correspond to the orbital frequency at the inner-most stable orbit of the accretion disk. This would imply that the neutron stars in these systems have masses> ? 2 ...

Low-mass X-ray binaries (LMXBs) are systems in which a low-mass companion transfers mass via Roche-lobe overflow onto a black hole (BH) or a weakly magnetized neutron star (NS). It is believed that both the solid surface and the magnetic field of an NS can affect the accretion flow and show some observable effects. Using the disk ...

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 paper investigates the onset of dynamical mass transfer instabilities due to angular momentum flows in close low-mass binaries. Allowance is made for the finite growth time of the instability. The results are applied to the formation of single millisecond pulsars in the galactic disk and it is found that mass transfer from a white dwarf onto a neutron ...

In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. While the generic spin-down age may give realistic estimates for normal pulsars, it can fail for pulsars with very short periods. Details of the spin-up process during the low ...

Binary evolution predicts a population of helium core (M < 0.5 M sun) white dwarfs (WDs) that are slowly accreting hydrogen-rich material from low-mass main-sequence or brown dwarf donors with orbital periods less than 4 hr. Four binaries are presently known in the Milky Way that will reach such a ...

The ultracompact low-mass X-ray binary X1916-053, which is composed of a neutron star and a semidegenerate white dwarf, exhibits periodic X-ray dips of variable width and depth. We have developed a new method to parameterize this dipping behavior to systematically study its variations. This can help in further understanding binary and ...

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. ...

Based on the results of applying the extended ADC emission model for low mass X-ray binaries to three Z-track sources: GX 340+0, GX 5-1 and Cyg X-2, we propose an explanation of the Cygnus X-2 like Z-track sources. The Normal Branch is dominated by the increasing radiation pressure of the neutron star caused by a mass ...

The formation of low mass X-ray binaries containing a neutron star as the compact X-ray source is discussed. The problem presented by the standard mechanism and concerning the disruption of the binary system is investigated. Two solutions are possible: ei...

We examine a variety of X-ray and optical data for evidence of evolution in the accretion structure of the dipping, eclipsing, bursting low-mass X-ray binary (LMXB) EXO 0748-676. Our results are divided into three main sections. New ASCA and archival EXOSAT data reveal behavior related to the source brightness state. An anomalous dip ...

The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a ...

The mass function and statistics of binaries provide important diagnostics of the star formation process. Despite this importance, the mass function at low masses remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a ...

We have obtained high-resolution (approximately 1") deep x-ray images of the globular cluster 47Tucanae (NGC 104) with the Chandra X-ray Observatory to study the population of compact binaries in the high stellar density core. A 70-kilosecond exposure of the cluster reveals a centrally concentrated population of faint (Lx approximately 10(30-33) ergs per second) x-ray sources, ...

We report the discovery of a young, 0farcs16 binary, 2M2234+4041AB, found as the result of a Keck laser guide star adaptive optics imaging survey of young field ultracool dwarfs. Spatially resolved near-infrared photometry and spectroscopy indicate that the luminosity and temperature ratios of the system are near unity. From optical and near-infrared spectroscopy, we determine ...

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 ...

High-resolution spectra of low mass X-ray dipping sources would reveal the strong absorption line structures, which could be used for a better understanding of the accretion disk structure. Here, we present a detailed spectral study and X-ray dust scattering halo results of the ``Big Dipper'' 4U 1624-490, based on our Chandra HETGS ...

The most luminous stellar X-ray sources are interacting binaries in which matter from a 'normal' star is transferred to either a neutron star (NS) or black hole. Two groups of X-ray binaries are generally distinguished base the nature of the mass donating star, the high mass X-ray binaries and the low ...

The whole BeppoSAX archive was screened for observations of Neutron Star (NS) Low-Mass X-ray Binaries, in order to characterise the X-ray properties of this class of sources when observed in a Low Hard State (LHS). A total of 12 sources in the sample exhibited LHS spectra; half of the objects showed a "canonical" LHS spectrum, in which two separate ...

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 diluted blackbody. ...

We study the kilohertz quasi-periodic oscillations (kHz QPOs) and the band-limited noise (BLN) in the 0.5-16 Hz range observed simultaneously on the horizontal branch (HB) and on the upper normal branch (NB) of the brightest neutron star low-mass X-ray binary Scorpius X-1 with observations performed with the Rossi X-Ray Timing Explorer. We find that the ...

X-ray bursters form a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion ...

We have completed the analysis of the Chandra Bulge Latitude Survey (BLS), a close-tiled mosaic of 36 ACIS-I fields obtained with Chandra in cycles 7 - 9 and covering (l, b) +/-0.3, +/-1.4deg. With 15ksec exposures per field, some 2500 sources are detected, with luminosities Lx(0.3-8keV) > 10^32 erg/s. This survey maps the latitude distribution of the galactic center region (GCR) sources for ...

Astrophysics papers are presented, covering topics such as UV stellar spectra, far-UV spectra from Voyager 1 and 2, stellar winds in A-type supergiants, calibrated IUE low-resolution spectra of G-type stars, searches for linear polarization and optical flashes in gamma-ray sources, binary evolution, a spectral investigation of eclipsing binaries, the ...

An analysis of the multiplicity of 14 sources driving giant Herbig-Haro flows has revealed an observed binary frequency between 79% and 86%, of which half are higher order multiples. These sources represent the hitherto youngest sample of stars examined for binarity. I postulate that the dynamical decay of triple or multiple systems leads to strong outflow activity. It is well ...

In this article we consider the formation and evolution of black holes, especially those in binary stars where radiation from the matter falling on them can be seen. We consider a number of effects introduced by some of us, which are not traditionally included in binary evolution of massive stars. These are (i) hypercritical accretion, ...

We explore the dynamics of the r-modes in accreting neutron stars in two ways. First, we explore how dissipation in the magnetoviscous boundary layer (MVBL) at the crust-core interface governs the damping of r-mode perturbations in the fluid interior. Two models are considered: one assuming an ordinary-fluid interior, the other taking the core to consist of superfluid ...

A number of neutron star low-mass X-ray binaries (LMXBs) have recently been discovered to show broad, asymmetric Fe K emission lines in their X-ray spectra. These lines are generally thought to be the most prominent part of a reflection spectrum, originating in the inner part of the accretion disk where strong relativistic effects can ...

We explore the dynamics of the r-modes in accreting neutron stars in two ways. First, we explore how dissipation in the magneto-viscous boundary layer (MVBL) at the crust-core interface governs the damping of r-mode perturbations in the fluid interior. Two models are considered: one assuming an ordinary-fluid interior, the other taking the core to consist of superfluid ...

The observations and progress in the theoretical understanding of X-ray burst sources are reviewed. Of about 150 known low mass X-ray binary systems, X-ray bursts have been observed from about 50 sources. X-ray bursts exhibit a wide variety of profiles; rise times vary from less than a second to about 10 s and decay times are in the ...

Recent observational and theoretical investigations in astrophysics and cosmology are discussed in a collection of review essays. Topics addressed include the early universe, superstring theory, quantum gravity, gravitational radiation, the cosmic microwave background, the age of the universe, accretion disks in AGN, superconducting cosmic strings, nascent elliptical galaxies, ...

We present stellar explosion simulations of low mass evolved and high mass polytrope Population III stars. The lower mass evolved single and binary models of 10 and 16 Msolar are presented in a separate work in these proceedings (Lawlor 2005). It is found that the accreted model retains a larger mass and has a ...

In Fall 2009, we conducted a large, multi-wavelength time-series photometric monitoring campaign of about a one square degree region of the Orion Nebula cluster (ONC). Our program produced light curves for 2000 Orion young stellar objects (YSOs), with data often in at least four bands (I, J, [3.6] and [4.5]). While our primary goal was to use these data to investigate the structure of the inner ...

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, such as a planet, brown dwarf, or low-mass star, is engulfed by ...

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, such as a planet, brown dwarf, or low-mass star, is engulfed by ...

Apr 12, 2011 ... The orbital inclination of the system, in degrees. Inclination_Flag. An uncertainty flag for the orbital inclination. Inclination_Error ...

The hard component is assumed to be from low mass X-ray binaries (LMXBs), but the origin of the very soft component is mysterious. ...

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 of energy generation ...

The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based

Aug 4, 2011 ... Propagating fluctuations in the mass accretion rate of a precessing flow as a power spectral model for black hole binaries ...

... Title : Evidence for Residual Material in Accretion Disk Gaps: CO Fundamental Emission from the T Tauri Spectroscopic Binary DQ Tauri. ...

We analyze radial velocity observations of the 12 extremely low-mass (ELM), with <=0.25 M sun, white dwarfs (WDs) in the MMT Hypervelocity Star Survey. Eleven of the twelve WDs are binaries with orbital periods shorter than 14 hr; the one non-variable WD is possibly a pole-on system among our non-kinematically selected targets. Our sample is unique: it ...

We analyze radial velocity observations of the 12 extremely low-mass (ELM), with {<=}0.25 M{sub sun}, white dwarfs (WDs) in the MMT Hypervelocity Star Survey. Eleven of the twelve WDs are binaries with orbital periods shorter than 14 hr; the one non-variable WD is possibly a pole-on system among our non-kinematically selected targets. Our sample is ...

In this work, we study the timing and spectral evolution of the transient low mass X-ray binary IGR J17091-3624 during its recent outburst. We present the results obtained from the observations with two instruments, Rossi X-ray Timing Explorer (RXTE)/ proportional counter array (PCA) and SWIFT/X-ray telescope (XRT), between 03 February ...

Neutron stars are the densest objects known in the Universe. Being the final product of stellar evolution, their internal composition and structure is rather poorly constrained by measurements. It is the purpose of this paper to put some constrains on the mass and moment of inertia of neutron stars based on the interpretation of kHz quasi-periodic oscillations observed in low ...

We present near-infrared (NIR) broadband (0.80-2.42 {mu}m) spectroscopy of two low-mass X-ray binaries: V404 Cyg and Cen X-4. One important parameter required in the determination of the mass of the compact objects in these systems is the binary inclination. We can determine the inclination by modeling the ellipsoidal modulations of ...

We argue that brown dwarfs (BDs) and planemos form by the same mechanisms as low-mass hydrogen-burning stars, but that as one moves to lower and lower masses, an increasing fraction of these objects is formed by fragmentation of the outer parts (R ? 100 AU) of protostellar accretion discs around more massive primary protostars, which in turn formed in their own ...

Type I X-ray bursts from low-mass X-ray binaries result from a thermonuclear runaway in the material accreted onto the neutron star. Although typical recurrence times are a few hours, consistent with theoretical ignition model predictions, there are also observations of bursts occurring as promptly as 10 minutes or less after the ...

Holmberg IX X-1 is an archetypal ultraluminous X-ray source (ULX). Here we study the properties of the optical counterpart and of its stellar environment using optical data from SUBARU/Faint Object Camera and Spectrograph, GEMINI/GMOS-N and Hubble Space Telescope (HST)/Advanced Camera for Surveys, as well as simultaneous Chandra X-ray data. The V ~ 22.6 spectroscopically identified optical ...

Type I X-ray bursts from low-mass X-ray binaries result from a thermonuclear runaway in the material accreted onto the neutron star. Although typical recurrence times are a few hours, consistent with theoretical ignition model predictions, there are also observations of bursts occurring as promptly as 10 minutes or less after the ...

We give an improved estimate of the detectability of gravitational waves from magnetically confined mountains on accreting neutron stars. The improved estimate includes the following effects for the first time: three-dimensional hydromagnetic (`fast') relaxation, three-dimensional resistive (`slow') relaxation, realistic accreted masses Ma <~ 2 � ...

Jun 19, 2006 ... Long Term Intensity Variations in X-ray Binaries ... has led to a number of new insights into accretion onto magnetized neutron stars. ...

neutron stars would have important implications for nuclear and particle physics. While many of these objects are in binary systems ( X-ray binaries ), where ...

Recent detections of massive black holes (BHs), with masses of roughly 10^6-10 9 [Special characters omitted.] , in both our own Milky Way and in other galaxies suggest that central galactic BHs are common. In this work, we attempt to shed some light on the relatively new population of local intermediate-mass BHs (10^3 -10^6 [Special characters omitted.] ) that reside at the low-mass end of the ...

Sep 5, 2011 ... The Wide Brown Dwarf Binary Oph 1622-2405 and Discovery of a Wide, Low-Mass Binary in Ophiuchus (Oph 1632 2402): A New Class of Young ...

A (1 + 0.4) solar mass close binary system consisting of a compact primary and a red dwarf secondary

There are a number of binaries, fairly wide and with one or even two evolved giant components, that do not agree very well with conventional stellar evolution: the secondaries are substantially larger (oversized) than they should be because their masses a...

There are two modes of gas streams in close binary systems: geometrically thick for low mass transfer rate or geometrically thin for higher mass transfer. Geometrical thickness of the streams is not proportional to the amount of transferred mass. The limit between the two possibilities is discussed.

We report the discovery of two eclipsing binaries with a brown dwarf (<0.07Msolar) and a 0.15Msolar late main sequence star companion in close orbits around sdB stars.

We investigate the thermonuclear bursting behaviour of IGR J17473-2721, an X-ray transient that in 2008 underwent a 6-month long outburst, starting (unusually) with an X-ray burst. We detected a total of 57 thermonuclear bursts throughout the outburst with AGILE, Swift, Rossi X-ray Timing Explorer (RXTE) and the INTErnational Gamma-Ray Astrophysics Laboratory(INTEGRAL). The wide range of inferred ...

Aims: We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1-10 Myr) clusters ? Ori and ? Ori. Methods: We observed 98 and 49 low-mass (0.2-1.0 M?) stars in ? Ori and ? Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the ...

It is commonly accepted that jets have not been observed in cataclysmic variables (CVs) so far. This absence was recently explained by their low mass transfer rates compared with objects with jets. A mass accretion limit for jets in CVs was proposed to be M~10-7 to 10-6 Msolar yr-1. There was, however, a report of evidence of jets in ...

A two dimensional numerical model forming two spiral shock fronts in accretion flow in close binary star system is presented. The position of these shocks is discussed. In the model, the position of the second shock front depends on the relation between t...

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...

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...

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...

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...

We propose a simple model explaining two outstanding astrophysical problems related to compact objects: (1) that of stars such as G87-7 (alias EG 50) that constitute a class of relatively low-mass white dwarfs which nevertheless fall away from the C/O composition and (2) that of GRB 110328A/Swift J164449.3+57345 which showed spectacularly long-lived strong X-ray flaring, ...

Ten percent of our Galaxy's luminous (LX>~1036 ergs-1 ) clusters contribute a much smaller fraction of normal stars to the Galaxy. X-ray bursts have been observed from nearly all of them, indicating that these sources are low-mass X-ray binary (LMXB) systems containing a neutron star and a companion star from which matter is being transferred. The understanding of LMXB ...

Binary Oph1622-2405 and Discovery of A Wide, Low Mass Binary in Ophiuchus (Oph1623- 2402): A New Class need LGS AO! #12;2 Young Binary Brown dwarfs in Ophiuchus Imaged with Keck LGS AO & Gemini �Oph 11AB bound binary known. �Oph 16AB has sep=212 AU and 100 and 73 ...

The Low Mass X-ray Binary (LMXB) X1832-330 in NGC 6652 is one of about 10 bright X-ray sources to have been discovered in Globular Clusters. We report on a serendipitous ASCA observation of this Globular Cluster LMXB, during which a Type I burst was detec...

The Low Mass X-ray Binary (LMXB) X1832-330 in NGC 6652 is one of about 10 bright X-ray sources to have been discovered in Globular Clusters. We report on a serendipitous ASCA observation of this Globular Cluster LMXB, during which a Type I burst was detec...

Photometric observations of two newly-discovered low-mass eclipsing binaries: ASAS J045304-0700.4 (ASAS-04) and ASAS J082552-1622.8 (ASAS-08). V and I band curves were obtained in January 2008 with the 1.0-m Elizabeth telescope and its STE4 camera at the South African Astronomical Observatory (SAAO). (4 data files).

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 ...

We will present the results from common proper motion searches for wide low-mass stellar and sub-stellar companions to known tight binary systems. Observations were made with the 4m telescope at KPNO and the 31" NURO telescope at Lowell Observatory. The binary systems observed at KPNO are spectroscopic binaries, ...

I review the present status of the pulsation studies of close binary systems, focusing on pulsating gainers of semi-detached Algol type eclipsing binaries. I discuss the advantages of pulsation studies of eclipsing binaries, influence of the activity cycles of a mass-losing star on mass transfer and accretion rate ...

There's a simple reason why a curious neutron star in the M15 globular star cluster has shown two faces over the years, beaming an X-ray portrait as perplexing as Mona Lisa's smile. The reason: That's not one star system, but two. Scientists at NASA Goddard Space Flight Center in Greenbelt, Md., capitalized on the exquisite resolution afforded by the Chandra X-ray Observatory to find a second ...

Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass star...

My talk will focus on the early evolution of low mass objects. I will discuss the main uncertainties on current evolutionary models and the effects of rotation, magnetic field and early accretion history on young object's structure. I will also present possible solutions to the well known spread in HRD observed in star formation ...

The regulation of angular momentum is one of the key processes for our understanding of stellar evolution. In contrast to solar-mass stars, very low mass (VLM) objects and brown dwarfs are believed to be fully convective. This may lead to major differences of rotation and activity, since fully convective objects may not host a solar-type dynamo. Here, we ...

We report a detailed spectral analysis of the population of low-mass X-ray binaries (LMXBs) detected in the elliptical galaxy NGC 4278 with Chandra. Seven luminous sources were studied individually, four in globular clusters (GCs) and three in the stellar field. The range of (0.3-8 keV) L X for these sources is ~(3-8) � 1038 erg s-1, suggesting that they may be black hole ...

Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular orbit (ISCO). Therefore an inferred disc ...

We present the results of a study with the Swift Burst Alert Telescope in the 14-195 keV range of the long-term variability of five low-mass X-ray binaries with reported or suspected superorbital periods - 4U 1636-536, 4U 1820-303, 4U 1916-053, Cyg X-2 and Sco X-1. No significant persistent periodic modulation was detected around the previously reported ...

We have combined ground-based optical and near-infrared data with Spitzer Space Telescope mid-infrared data for five black hole (BH) soft X-ray transients (SXTs) in order to determine the levels of near- and mid-infrared emission from sources other than the secondary star. Mid-infrared emission from an accretion disk, circumbinary dust, and/or a jet could act as sources of ...

A number of studies have revealed variability from neutron star low-mass X-ray binaries during quiescence. Such variability is not well characterized, or understood, but may be a common property that has been missed due to lack of multiple observations. One such source where variability has been observed is Aql X-1. Here, we analyse 14 Chandra and ...

We ascribe the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the pseudo-Newtonian Keplerian frequency and the apogee and perigee precession frequency of the same matter in the inner disk, and ascribe 15-60 ,Hz QPO (HBO) to the apogee (or perigee) precession and its second ...

Photometric observations with the CTIO 1.5-m telescope were made in 1977 August of the optical candidate for the x-ray pulsar 4U 1626-67. Whereas the average B magnitude was consistent with the June observations by McClintock, the (B - V) and (U - B) colors were significantly different. The B magnitude is also probably variable on short time scales (approx. 1 to 10 minutes). Analysis of approx. 1 ...

Relativistic spectral lines from the accretion disc of a neutron star low-mass X-ray binary can be modelled to infer the disc inner edge radius. A small value of this radius tentatively implies that the disc terminates either at the neutron star hard surface, or at the innermost stable circular orbit (ISCO). Therefore an inferred disc ...

The primary optical caustic surface behind a Kerr black hole is a four-cusped tube displaced from the line of sight. We derive the caustic surface in the nearly asymptotic region far from the black hole through a Taylor expansion of the lightlike geodesics up to and including fourth-order terms in m/b and a/b, where m is the black hole mass, a the spin, and b the impact parameter. The ...

We present a comprehensive spectral analysis of the high-mass X-ray binary (HMXB) pulsar Centaurus X-3 with the Suzaku observatory covering nearly one orbital period. The light curve shows the presence of extended dips which are rarely seen in HMXBs. These dips are seen up to as high as ~40 keV. The pulsar spectra during the eclipse, out-of-eclipse, and dips are found to be ...

We report on an analysis of Rossi X-Ray Timing Explorer data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities, the source switched between two types of Z source behavior ...

We report on an analysis of Rossi X-Ray Timing Explorer data of the transient neutron star low-mass X-ray binary (NS-LMXB) XTE J1701-462, obtained during its 2006-2007 outburst. The X-ray properties of the source changed between those of various types of NS-LMXB subclasses. At high luminosities, the source switched between two types of Z source behavior ...

4U 1822-37 is a low mass X-ray binary (LMXB) system with an accretion disc corona. It is one of the very few LMXBs that shows narrow X-ray eclipses and small amplitude pulsations of the neutron star. The X-ray eclipse is an excellent reference for measurement of orbital evolution of the binary, ...

The neutron star low-mass X-ray binary EXO 0748-676 started a transition from outburst to quiescence in August 2008, after more than 24 years of continuous accretion. The return of the source to quiescence has been monitored extensively by several X-ray observatories. Here, we report on four XMM-Newton observations elapsing a period of ...

Our 5 ks Chandra ACIS-S observation of the globular cluster NGC 6652 detected seven X-ray sources, three of which were previously unidentified. This cluster hosts a well-known bright low-mass X-ray binary, source A (or XB 1832�330). Source B shows unusual rapid flaring variability, with an average LX (0.5-10 keV) ~2 � 1034 erg s�1, but with ...

We have analyzed Rossi X-Ray Timing Explorer pointed observations of the outbursts of black hole and neutron star soft X-ray transients in which an initial low/hard state, or ``island'' state, followed by a transition to a softer state was observed. In three sources-the black hole transient XTE J1550-564, the neutron star transient Aquila X-1, and the quasi-persistent neutron star ...

The close surroundings of young low mass stars hold a multitude of physical phenomena related to star formation. This thesis presents a set of works on theoretical, experimental, and observational issues connected with these phenomena. After a description of the properties of T Tauri, FU Orionis and Ae/Be Herbig stars, with a particular emphasis on their ...

We report the discovery of burst oscillations at the spin frequency in ten thermonuclear bursts from the accreting millisecond X-ray pulsar (AMXP) IGR J17511-3057. The burst oscillation properties are, like those from the persistent AMXPs SAX J1808.4-3658 and XTE J1814-338, anomalous compared to burst oscillations from intermittent pulsars or non-pulsing ...

An issue of fundamental importance in understanding the galaxy-black hole connection is the duty cycle of accretion. If black holes are indeed ubiquitous in galactic nuclei, little is known about the frequency and intensity of their activity, the more so at the low-mass/low-luminosity end. I will present new results from AMUSE-Virgo, a Chandra survey of (formally) inactive ...

Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in "dipping" low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that ...

Context. The burst-only source Swift J1749.4-2807 was discovered in a high X-ray-active state, during an INTEGRAL observations of the Galactic bulge on 2010 April 10. Pulsations at 518 Hz were discovered in the RXTE data, confirming previous suggestions of possible associations between burst-only sources and accreting millisecond X-ray pulsars. The subsequent discovery of ...

A program of precise eclipsing binary photometry with the NASA Kepler Observatory is now in progress. Our goal is to search for variations in minimum light timing for intermediate mass eclipsing binaries. Such periodic variations will reveal the reflex motion caused by any distant, low mass object that orbits the ...

Low-mass X-ray binaries (LMXBs) have been studied in the Galaxy since the beginning of X-ray astronomy. A lot has been learned about these bright X-ray sources, but significant questions are still open. These questions are related to the origin and evolution of LMXBs-dynamical evolution in globular clusters (GC) or evolution of native field ...

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 in the rapid-spin ...

A method is proposed for restoring the structure of the accretion disk in a binary system from analysis of eclipse curves. Application of the method to the x-ray binary HZ Herculis yields the distribution of brightness and color temperatures over the optical accretion disk associated with the neutron star. The ...

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 hydrostatic object up to ...

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 ...