Viscous effects on the interaction between the coplanar decretion disc and the neutron star in Be/X-ray binaries

Okazaki, Atsuo T.; Bate, Matthew R.; Ogilvie, Gordon I.; Pringle, J. E.

doi:10.1046/j.1365-8711.2002.05960.x

Cited by 193 publications

(298 citation statements)

References 27 publications

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“…Since the resonant torque prevents disk material from drifting outwards, the disk density increases faster in systems where the distance between the two components of the binary is shorter. This is the same argument used by Okazaki et al (2002), which predicts that the disks in BeXBs should be more dense than in classical, isolated Be stars. This correlation provides further evidence for the truncation of the disk in BeXB systems.…”

Section: Disk Growth Ratessupporting

confidence: 68%

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Long-term optical variability of high-mass X-ray binaries

Reig

Nersesian

Zezas

et al. 2016

A&A

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Context. High-mass X-ray binaries are bright X-ray sources. The high-energy emission is caused by the accretion of matter from the massive companion onto a neutron star. The accreting material comes from either the strong stellar wind in binaries with supergiant companions or the cirscumstellar disk in Be/X-ray binaries. In either case, the Hα line stands out as the main source of information about the state of the accreting material. Aims. We present the results of our monitoring program to study the long-term variability of the Hα line in high-mass X-ray binaries. Our aim is to characterise the optical variability timescales and study the interaction between the neutron star and the accreting material. Methods. We fitted the Hα line with Gaussian profiles and obtained the line parameters and equivalent width. The peak separation in split profiles was used to determine the disk velocity law and estimate the disk radius. The relative intensity of the two peaks (V/R ratio) allowed us to investigate the distribution of gas particles in the disk. The equivalent width was used to characterise the degree of variability of the systems. We also studied the variability of the Hα line in correlation with the X-ray activity. Results. Our results can be summarised as follows: i) we find that Be/X-ray binaries with narrow orbits are more variable than systems with long orbital periods; ii) we show that a Keplerian distribution of gas particles provides a good description of the disks in Be/X-ray binaries, as it does in classical Be stars; iii) a decrease in the Hα equivalent width is generally observed after major X-ray outbursts; iv) we confirm that the Hα equivalent width correlates with disk radius; v) while systems with supergiant companions display multistructured profiles, most of the Be/X-ray binaries show, at some epoch, double-peak asymmetric profiles, which indicates that density inhomogeneities is a common property in the disk of Be/X-ray binaries; vi) the profile variability (V/R ratio) timescales are shorter and the Hα equivalent widths are smaller in Be/X-ray binaries than in isolated Be stars; and vii) we provide new evidence that the disk in Be/X-ray binaries is, on average, denser than in classical Be stars. Conclusions. We carried out the most complete optical spectroscopic study of the global properties of high-mass X-ray binaries with the analysis of more than 1100 spectra from 20 sources. Our results provide further evidence for the truncation of the disk in Be/X-ray binaries. We conclude that the interaction between the compact object and the Be-type star works in two directions: the massive companion provides the source of matter for accretion, affecting the surroundings of the compact object, and the continuous revolution of the neutron star around the optical counterpart also produces the truncation of the Be star's equatorial disk.

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Section: Disk Growth Ratessupporting

confidence: 68%

“…As the equatorial disk is more exposed to the action of the neutron star, we would expect to see different properties in the disks of isolated Be stars compared to those of BeXBs. The most important difference is the truncation of the disk (Reig et al 1997b;Okazaki 2001;Okazaki et al 2002;Reig 2011).…”

Section: Discussionmentioning

confidence: 99%

Long-term optical variability of high-mass X-ray binaries

Reig

Nersesian

Zezas

et al. 2016

A&A

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“…Okazaki et al (2002) showed that truncation does not mean that the disc is really broken at some distance smaller than the orbital separation (see also Reig et al 1997). Rather, beyond the truncation point the density drops much more rapidly with increasing distance from the primary Be star, i.e.…”

Section: Corotating Structure At Steady Statementioning

confidence: 99%

“…The new results on the azimuthal structure of the disc and how it is affected by the values of the parameters confirm the conclusions of Paper I, but they are more accurate and allow for better distinction of the differences between binary systems of different parameters. Three-dimensional smoothed particle hydrodynamics (SPH) simulations were performed for binary systems in which the Be disc is formed by uniform ejection of matter along the equator (Okazaki et al 2002). The mass injection rate is constant and the same in all simulations, Minj = 10 −7 M⊙/yr.…”

Section: Corotating Structure At Steady Statementioning

confidence: 99%

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Be discs in coplanar circular binaries: Phase-locked variations of emission lines

Panoglou

Faes

Carciofi

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The first results of radiative transfer calculations on decretion discs of binary Be stars are presented. A smoothed particle hydrodynamics code computes the structure of Be discs in coplanar circular binary systems for a range of orbital and disc parameters. The resulting disc configuration consists of two spiral arms, and can be given as input into a Monte Carlo code, which calculates the radiative transfer along the line of sight for various observational coordinates. Making use of the property of steady disc structure in coplanar circular binaries, observables are computed as functions of the orbital phase. Orbital-phase series of line profiles are given for selected parameter sets under various viewing angles, to allow comparison with observations. Flat-topped profiles with and without superimposed multiple structures are reproduced, showing, for example, that triple-peaked profiles do not have to be necessarily associated with warped discs and misaligned binaries. It is demonstrated that binary tidal effects give rise to phase-locked variability of the violet-to-red (V/R) ratio of hydrogen emission lines. The V/R ratio exhibits two maxima per cycle; in certain cases those maxima are equal, leading to a clear new V/R cycle every half orbital period. This study opens a way in identifying binaries and in constraining the parameters of binary systems that exhibit phase-locked variations induced by tidal interaction with a companion star.

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Effects of local thermodynamics and of stellar mass ratio on accretion disc stability in close binaries

Lanzafame¹

2009

Astron Nachr

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Inflow kinematics at the inner Lagrangian point L1, gas compressibility, and physical turbulent viscosity play a fundamental role on accretion disc dynamics and structure in a close binary (CB). Physical viscosity supports the accretion disc development inside the primary gravitational potential well, developing the gas radial transport, converting mechanical energy into heat. The Stellar-Mass-Ratio (SMR) between the compact primary and the secondary star (M1/M2) is also effective, not only in the location of the inner Lagrangian point, but also in the angular kinematics of the mass transfer and in the geometry of the gravitational potential wells. In this work we pay attention in particular to the role of the SMR, evaluating boundaries, separating theoretical domains in compressibility-viscosity graphs where physical conditions allow a well-bound disc development, as a function of mass transfer kinematic conditions. In such domains, the lower is the gas compressibility (the higher the polytropic index γ), the higher is the physical viscosity (α) requested. In this work, we show how the boundaries of such domains vary as a function of M1/M2. Conclusions as far as dwarf novae outbursts are concerned, induced by mass transfer rate variations, are also reported. The smaller M1/M2, the shorter the duration of the active-to-quiet and vice-versa transitional phases. Time-scales are of the order of outburst duration of SU Uma, OY Car, Z Cha and SS Cyg-like objects. Moreover, conclusions as far as active-quiet-active phenomena in a CB, according to viscous-thermal instabilities, in accordance to such domains, are also reported.

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Viscous effects on the interaction between the coplanar decretion disc and the neutron star in Be/X-ray binaries

Cited by 193 publications

References 27 publications

Long-term optical variability of high-mass X-ray binaries

Long-term optical variability of high-mass X-ray binaries

Be discs in coplanar circular binaries: Phase-locked variations of emission lines

Effects of local thermodynamics and of stellar mass ratio on accretion disc stability in close binaries

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