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symbiotic stars often contain white dwarfs with quasi-steady shell burning on their surfaces. however, in most symbiotics, the origin of this burning is unclear. in symbiotic slow novae, however, it is linked to a past thermonuclear runaway. in 2015 june, the symbiotic slow nova ag peg was seen in only its second optic... | swift observations of the 2015 outburst of ag peg - from slow nova to classical symbiotic outburst |
context. rotation plays a key role in the star-formation process, from pre-stellar cores to pre-main-sequence (pms) objects. understanding the formation of massive stars requires taking into account the accretion of angular momentum during their pms phase.aims: we study the pms evolution of objects destined to become m... | massive star formation by accretion. ii. rotation: how to circumvent the angular momentum barrier? |
we examine the possible role of turbulence in feeding the emission of gamma-ray bursts (grbs). turbulence may develop in a grb jet as the result of hydrodynamic or current-driven instabilities. the jet carries dense radiation and the turbulence cascade can be damped by compton drag, passing kinetic fluid energy to phot... | subphotospheric turbulence as a heating mechanism in gamma-ray bursts |
magneto-gravity-elliptic instability is addressed here considering an unbounded strained vortex (with constant vorticity $2\varomega$ and with ellipticity parameter $\varepsilon$ ) of a perfectly conducting fluid subjected to a uniform axial magnetic field (with alfvén velocity scaled from the basic magnetic field $b)$... | magneto-gravity-elliptic instability |
context. binaries hosting a massive star and a non-accreting pulsar are powerful non-thermal emitters owing to the interaction of the pulsar and the stellar wind. the winds of massive stars are thought to be inhomogeneous, which could have an impact on the non-thermal emission.aims: we study numerically the impact of t... | non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind |
we examine the dependence of the total hydrogen mass m hi in late-type star-forming galaxies on rotation velocity v rot and optical size d 25 or radial scale length r 0 of the disk for two samples of galaxies: (i) isolated galaxies (amiga) and (ii) galaxies with edge-on disks (flat galaxies according to karachentsev et... | hi content in galactic disks: the role of gravitational instability |
we found that the su uma-type dwarf nova ny ser in the period gap [orbital period 0.097558(6) d] showed standstills twice in 2018. this is the first clear demonstration of a standstill occurring between superoutbursts of an su uma-type dwarf nova. there was no sign of superhumps during the standstill, and at least one ... | discovery of standstills in the su uma-type dwarf nova ny serpentis |
recent inspections of local available data suggest that the almost linear relation between the stellar mass of spheroids (msph) and the mass of the super massive black holes (bhs), residing at their centres, shows a break below msph ∼ 1010 m⊙, with a steeper, about quadratic relation at smaller masses. we investigate t... | interpreting the possible break in the black hole-bulge mass relation |
sgr a* is an ideal target to study low-luminosity accreting systems. it has been recently proposed that properties of the accretion flow around sgr a* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the s-cluster. when a star intercepts the accretion disc, the ram and t... | modelling accretion disc and stellar wind interactions: the case of sgr a* |
by performing a global magnetohydrodynamical simulation for the milky way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the galactic centre region. the radial distribution of the rotation... | stochastic non-circular motion and outflows driven by magnetic activity in the galactic bulge region |
using the disc instability model for dwarf novae and soft x-ray transients, we investigate the stability of accretion discs in long-period binary systems. we simulate outbursts resulting from this thermal-viscous instability for two symbiotic systems, rs ophiuchi and z andromedae. the outburst properties deduced from o... | disc instabilities and nova eruptions in symbiotic systems: rs ophiuchi and z andromedae |
asassn-14ko was identified as an abnormal periodic nuclear transient with a potential decreasing period. its outbursts in the optical and uv bands have displayed a consistent and smooth "fast rise and slow decay" pattern since its discovery, which has recently experienced an unexpected alteration in the last two epochs... | dissonance in harmony: the uv/optical periodic outbursts of asassn-14ko exhibit repeated bumps and rebrightenings |
close-in super-earths are the most abundant exoplanets known. it has been hypothesized that they form in the inner regions of protoplanetary discs, out of the dust that may accumulate at the boundary between the inner region susceptible to the magneto-rotational instability (mri) and an mri-dead zone further out. in pa... | mri-active inner regions of protoplanetary discs - ii. dependence on dust, disc, and stellar parameters |
self-gravity plays an important role in the evolution of rotationally supported systems such as protoplanetary discs, accretion discs around black holes, or galactic discs, as it can both feed turbulence and lead to gravitational fragmentation. while such systems can be studied in the shearing box approximation with hi... | gravito-turbulence in local disc simulations with an adaptive moving mesh |
we found an active state lasting for ~200 d in the am cvn star nsv 1440 in 2022. during this state, the object reached a magnitude of 16.5, 2.0-2.5 mag above quiescence, and showed a number of superposed normal outbursts. such an active state was probably brought either by an enhanced mass-transfer from the secondary o... | the 2022 active state of the am cvn star nsv 1440 |
aims: we study the spectral evolution of the h1743-322 during outbursts in the rxte era. we aim to connect the variation of the spectral parameters with the accretion parameters along with the progress of the outbursts. we understand the evolution of the accretion parameters and hence the dynamics of the accretion proc... | spectral and accretion evolution of h1743-322 during outbursts in rxte era |
in currently favoured hierarchical cosmologies, the formation of massive black hole binaries (mbhbs) following galaxy mergers is unavoidable. still, due the complex physics governing the (hydro)dynamics of the post-merger dense environment of stars and gas in galactic nuclei, the final fate of those mbhbs is still uncl... | accretion of clumpy cold gas onto massive black hole binaries: a possible fast route to binary coalescence |
we study the hydrodynamical stability of the laminar flows associated with warped astrophysical discs using numerical simulations of warped shearing boxes. we recover linear growth rates reported previously due to a parametric resonance of inertial waves, and show that the non-linear saturated state can significantly r... | local numerical simulations of warped discs |
the accretion phase of star formation is investigated in magnetically dominated clouds that have an initial subcritical mass-to-flux ratio. we employ non-ideal magnetohydrodynamic simulations that include ambipolar diffusion and ohmic dissipation. during the early prestellar phase, the mass-to-flux ratio rises towards ... | different modes of star formation - ii. gas accretion phase of initially subcritical star-forming clouds |
context. although the disc instability model is widely accepted as the explanation for dwarf nova outbursts, it is still necessary to compare its predictions to observations because many of the constraints on angular momentum transport in accretion discs are derived from the application of this model to real systems.ai... | modelling hystereses observed during dwarf nova outbursts |
massive molecular gas has been discovered in giant elliptical galaxies at the centers of galaxy clusters. to reveal its role in active galactic nucleus (agn) feedback in those galaxies, we construct a semianalytical model of gas circulation. this model especially focuses on the massive molecular gas (interstellar cold ... | massive molecular gas as a fuel tank for active galactic nuclei feedback in central cluster galaxies |
we present a series of simulations in both pure hydrodynamics (hd) and magnetohydrodynamics (mhd) exploring the degree to which alignment of disks subjected to external precessional torques (e.g., as in the “bardeen-petterson” effect) is dependent upon the disk sound speed cs . across the range of sound speeds examined... | sound speed dependence of alignment in accretion disks subjected to lense-thirring torques |
we observed rz lmi, which is renowned for its extremely short (∼19 d) supercycle and is a member of a small, unusual class of cataclysmic variables called er uma-type dwarf novae, in 2013 and 2016. in 2016, the supercycles of this object substantially lengthened in comparison to the previous measurements to 35, 32, and... | rz leonis minoris bridging between er ursae majoris-type dwarf nova and nova-like system |
buoyancy of the fossil magnetic field in the accretion disks of young stars is investigated. it is assumed that the parker instability leads to the formation of slender flux tubes of toroidal magnetic field in the regions of effective magnetic field generation. stationary solution of the induction equation is written i... | magnetic field buoyancy in accretion disks of young stars |
we study the structural evolution of isolated star-forming (sf) galaxies in the illustristng100-1 hydrodynamical simulation, with a focus on investigating the growth of the central core density within 2 kpc (σ*,2 kpc) in relation to total stellar mass (m*) at z < 0.5. first, we show that several observational trends... | the structural evolution of isolated galaxies at low redshift in the illustristng simulation |
the magnetorotational instability (mri) is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. the rate at which mri-driven turbulence transports angular momentum is intimately related to both the strength of the amplitudes of the fluctuations on various scales and the d... | on the anisotropic nature of mri-driven turbulence in astrophysical disks |
we describe a new mechanism that leads to the destabilization of non-axisymmetric waves in astrophysical discs with an imposed radial temperature gradient. this might apply, for example, to the outer parts of protoplanetary discs. we use linear density wave theory to show that non-axisymmetric perturbations generally d... | one-armed spirals in locally isothermal, radially structured self-gravitating discs |
the bright, erratic black hole x-ray binary grs 1915+105 has long been a target for studies of disk instabilities, radio/infrared jets, and accretion disk winds, with implications that often apply to sources that do not exhibit its exotic x-ray variability. with the launch of the neutron star interior composition explo... | a persistent disk wind in grs 1915+105 with nicer |
the low luminosity, x-ray flaring activity, of the sub-class of high-mass x-ray binaries called supergiant fast x-ray transients, has been investigated using xmm-newton public observations, taking advantage of the products made publicly available by the extras project. one of the goals of extras was to extract from the... | supergiant fast x-ray transients uncovered by the extras project: flares reveal the development of magnetospheric instability in accreting neutron stars |
the ionization state of the gas plays a key role in the magnetohydrodynamics (mhd) of protoplanetary disks. however, the ionization state can depend on the gas dynamics, because electric fields induced by mhd turbulence can heat up plasmas and thereby affect the ionization balance. to study this nonlinear feedback, we ... | the nonlinear ohm's law: plasma heating by strong electric fields and its effects on the ionization balance in protoplanetary disks |
swift j1753.5-0127 (j1753) is a candidate black hole low-mass x-ray binary (bh-lmxb) that was discovered in outburst in 2005 may. it remained in outburst for ∼12 yr, exhibiting a wide range of variability on various time-scales, before entering quiescence after two short-lived, low-luminosity `mini-outbursts' in 2017 a... | the curious case of swift j1753.5-0127: a black hole low-mass x-ray binary analogue to z cam type dwarf novae |
previous comparisons of experimental data with nonlinear numerical simulations of density stratified taylor-couette (tc) flows revealed nonlinear interactions of strato-rotational instability (sri) modes that lead to periodic changes in the sri spirals and their axial propagation. these pattern changes are associated w... | a parameter study of strato-rotational low-frequency modulations: impacts on momentum transfer and energy distribution |
gro j1744-28, commonly known as the `bursting pulsar', is a low-mass x-ray binary containing a neutron star and an evolved giant star. this system, together with the rapid burster (mxb 1730-33), are the only two systems that display the so-called type ii x-ray bursts. these types of bursts, which last for tens of secon... | the evolution of x-ray bursts in the `bursting pulsar' gro j1744-28 |
increasing observational and theoretical evidence points to binary white dwarf (wd) mergers as the origin of some, if not most, normal type ia supernovae (sne ia). in this paper, we discuss the post-merger evolution of binary wd mergers and their relevance to the double-degenerate channel of sne ia. we present 3d simul... | one-armed spiral instability in double-degenerate post-merger accretion disks |
we investigated the quasi-periodic oscillation (qpo) features in the accretion-powered x-ray pulsar cen x-3 observed by insight-hxmt. for two observations in 2020 when cen x-3 was in an extremely soft state, the power density spectrum revealed the presence of obvious qpo features at ~40 mhz with an averaged fractional ... | detection of a quasi-periodic oscillation at40 mhz in cen x-3 with insight-hxmt |
based on previous studies of quasi-periodic oscillations (qpos) in neutron star (ns) low-mass x-ray binaries, mhz qpos are believed to be related to “marginally stable” burning on the ns surface. our study of phase-resolved energy spectra of these oscillations in 4u 1636-53 shows that the oscillations are not caused by... | millihertz quasi-periodic oscillations in 4u 1636-536: putting possible constraints on the neutron star size |
it is quite likely that self-gravity will play an important role in the evolution of accretion discs, in particular, those around young stars, and those around supermassive black holes. we summarise, here, our current understanding of the evolution of such discs, focussing more on discs in young stellar system, than on... | the evolution of self-gravitating accretion discs |
the physical mechanism of angular momentum transport in poorly ionized regions of protoplanetary discs, the dead zones (dzs), is not understood. the presence of a dz naturally leads to conditions susceptible to the rossby wave instability (rwi), which produces vortices and spiral density waves that may revive the dz an... | rossby wave instability and long-term evolution of dead zones in protoplanetary discs |
damping of the previously discovered resonant drag instability (rdi) of dust streaming in the protoplanetary disc is studied using the local approach to dynamics of gas-dust perturbations in the limit of the small dust fraction. turbulence in a disc is represented by the effective viscosity and diffusivity in equations... | the resonant drag instability of dust streaming in turbulent protoplanetary disc |
the magnetorotational instability (mri) is thought to be a powerful source of turbulence in keplerian accretion disks. motivated by recent laboratory experiments, we study the mri driven by an azimuthal magnetic field in an electrically conducting fluid sheared between two concentric rotating cylinders. by adjusting th... | transport properties of the azimuthal magnetorotational instability |
recently, two empirical correlations related to the minimum variability timescale (mts) of the light curves are discovered in gamma-ray bursts (grbs). one is the anti-correlation between mts and lorentz factor γ, and the other is the anti-correlation between the mts and gamma-ray luminosity lγ . both of the two correla... | what can we learn about grb from the variability timescale related correlations? |
we present optical photometry of superoutbursts that occurred in 2016 of two wz sge-type dwarf novae (dne), asassn-16dt and asassn-16hg. their light curves showed a dip in brightness between the first plateau stage with no ordinary superhumps (or early superhumps) and the second plateau stage with ordinary superhumps. ... | asassn-16dt and asassn-16hg: promising candidate period bouncers |
the low mass star asassn-13db experienced an exor outburst in 2013, which identified it as a young stellar object (yso). then, from 2014 to 2017 it had another outburst, longer and more luminous than the earlier. we analyze the observations of the second outburst, and compare it to eruptions of intermediate luminosity ... | asassn-13db 2014–2017 eruption as an intermediate luminosity optical transient |
depending on the values of the energy and angular momentum per unit mass in the gas supplied at large radii, inviscid advection-dominated accretion flows can display velocity profiles with either preshock deceleration or preshock acceleration. nakayama has shown that these two types of flow configurations are expected ... | standing shock instability in advection-dominated accretion flows |
we investigate the 2d instability recently discussed by gallet et al. (2010) and ilin \& morgulis (2013) which arises when a radial crossflow is imposed on a centrifugally-stable swirling flow. by finding a simpler rectilinear example of the instability - a sheared half plane, the minimal ingredients for the instab... | instability driven by boundary inflow across shear: a way to circumvent rayleigh's stability criterion in accretion disks? |
according to rayleigh's criterion, rotating flows are linearly stable when their specific angular momentum increases radially outward. the celebrated magnetorotational instability opens a way to destabilize those flows, as long as the angular velocity is decreasing outward. using a local approximation we demonstrate th... | destabilization of rotating flows with positive shear by azimuthal magnetic fields |
the milky way galaxy hosts a four million solar mass black hole, sgr a*, that underwent a major accretion episode approximately 3-6 myr ago. during the episode, hundreds of young massive stars formed in a disc orbiting sgr a* in the central half parsec. the recent discovery of a hypervelocity star (hvs) s5-hvs1, ejecte... | forming young and hypervelocity stars in the galactic centre via tidal disruption of a molecular cloud |
we study the hydrogen ionization instability mechanism in the context of low-mass x-ray binaries with a black hole as a central object. we make numerical calculations of the predicted outbursts' light curves and compare them to the data observed by x-ray satellites. the comparison to the data is done for five sources o... | ionization instability driven outbursts in sxts |
magnetic dynamo action caused by the magnetorotational instability is studied in the shearing-box approximation with no imposed net magnetic flux. consistent with recent studies, the dynamo action is found to be sensitive to the aspect ratio of the box: it is much easier to obtain in tall boxes (stretched in the direct... | magnetorotational dynamo action in the shearing box |
we investigate magnetohydrodynamic turbulence driven by the magnetorotational instability (mri) in keplerian disks with a nonzero net azimuthal magnetic field using shearing box simulations. as distinct from previous studies, we analyze turbulence dynamics in fourier ({\boldsymbol{k}}-) space to understand its sustenan... | nonlinear transverse cascade and sustenance of mri turbulence in keplerian disks with an azimuthal magnetic field |
we investigate the conditions required for planet formation via gravitational instability (gi) and protoplanetary disc (ppd) fragmentation around m-dwarfs. using a suite of 64 sph simulations with 106 particles, the parameter space of disc mass, temperature, and radius is explored, bracketing reasonable values based on... | fragmentation of protoplanetary discs around m-dwarfs |
we present results of the first global magnetohydrodynamic simulations of accretion disks fed by roche-lobe overflow, including vertical stratification, in order to investigate the roles of spiral shocks, magnetorotational instability (mri), and the accretion stream in disk structure and evolution. our models include a... | stratified global mhd models of accretion disks in semidetached binaries |
dw cnc is an intermediate polar which has previously been observed in both high and low states. observations of the high state of dw cnc have previously revealed a spin period at ~38.6 min, however, observations from the 2018 to 2019 low state showed no evidence of the spin period. we present results from our analysis ... | the return of the spin period in dw cnc and evidence of new high state outbursts |
we have investigated the outburst properties of low-mass x-ray binary transients (lmxbts) based on a comprehensive study of the outbursts observed in the past few decades. the outburst rates were estimated based on the x-ray monitoring data from swift/bat, rxte/asm, and maxi and previous reports in the literature. we f... | the relation between outburst rate and orbital period in low-mass x-ray binary transients |
we present high-resolution numerical simulations of the colliding wind system η carinae, showing accretion on to the secondary star close to periastron passage. our hydrodynamical simulations include self-gravity and radiative cooling. the smooth stellar winds collide and develop instabilities, mainly the non-linear th... | accretion at the periastron passage of eta carinae |
we studied dynamical balances in magnetorotational instability (mri) turbulence with a net vertical field in the shearing box model of disks. analyzing the turbulence dynamics in fourier ({\boldsymbol{k}}-)space, we identified three types of active modes that define the turbulence characteristics. these modes have leng... | active modes and dynamical balances in mri turbulence of keplerian disks with a net vertical magnetic field |
several hundred young stars lie in the innermost parsec of our galaxy. the supermassive black hole (smbh) might capture planets orbiting these stars and bring them onto nearly radial orbits. the same fate might occur to planetary embryos (pes), i.e., protoplanets born from gravitational instabilities in protoplanetary ... | signatures of planets and protoplanets in the galactic center: a clue to understanding the g2 cloud? |
we present results from three-dimensional, numerical relativity simulations of a tilted black hole-thick accretion disc system. the simulations are analysed using tracer particles in the disc which are advected with the flow. such tracers, which we employ in these new simulations for the first time, provide a powerful ... | on the dynamics of tilted black hole-torus systems |
> accretion disc theory is less developed than stellar evolution theory although a similarly mature phenomenological picture is ultimately desired. while the interplay of theory and numerical simulations has amplified community awareness of the role of magnetic fields in angular momentum transport, there remains a l... | motivation and challenge to capture both large-scale and local transport in next generation accretion theory |
iw and stars are a recently recognized group of dwarf novae which are characterized by a repeated sequence of brightening from a standstill-like phase with damping oscillations followed by a deep dip. kimura et al. (2019, pasj, submitted) recently proposed a model based on thermal-viscous disk instability in a tilted d... | iw and-type state in im eridani |
in an early work, the rossby wave instability was proposed to explain the variability thought to originate in the close vicinity of black holes but this was done in the pseudo-newtonian approach. here we present the first general relativistic (gr) hydrodynamics simulations of this instability not only proving its theor... | impact of the gravity of a schwarzschild black hole upon the rossby wave instability |
high-resolution sub-mm observations of some protoplanetary discs reveal non-axisymmetric features, which can often be interpreted as dust concentrations in vortices that form at the edges of gaps carved out by the embedded planets. we use recent results on the time-scale for the planet-driven vortex development in low-... | vortex weighing and dating of planets in protoplanetary discs |
when the accretion disc around a weakly magnetised neutron star (ns) meets the stellar surface, it should brake down to match the rotation of the ns, forming a boundary layer. as the mechanisms potentially responsible for this braking are apparently inefficient, it is reasonable to consider this layer as a spreading la... | kilohertz quasi-periodic oscillations from neutron star spreading layers |
context. the disc instability model (dim) successfully explains why many accreting compact binary systems exhibit outbursts during which their luminosity increases by orders of magnitude. the dim correctly predicts which systems should be transient and works regardless of whether the accretor is a black hole, a neutron... | hystereses in dwarf nova outbursts and low-mass x-ray binaries |
massive quiescent compact galaxies have been discovered at high redshifts, associated with rapid compaction and cessation of star formation (sf). in this work, we set out to quantify the time-scales in which sf is quenched in compact galaxies at intermediate redshifts. for this, we select a sample of green valley galax... | compact galaxies at intermediate redshifts quench faster than normal-sized galaxies |
based on early kepler data, østensen et al. found that kic 9202990 showed a 4-h and a two-week photometric period. they suggested the 4-h period was a signature of an orbital period; the longer period was possibly due to precession of an accretion disc and kic 9202990 was a cataclysmic variable with an accretion disc w... | continuous `stunted' outbursts detected from the cataclysmic variable kic 9202990 using kepler data |
context. fo aquarii, an asynchronous magnetic cataclysmic variable (intermediate polar) went into a low state in 2016, from which it slowly and steadily recovered without showing dwarf nova outbursts. this requires explanation since in a low state, the mass-transfer rate is in principle too low for the disc to be fully... | the disappearance and reformation of the accretion disc during a low state of fo aquarii |
recent submillimeter observations show nonaxisymmetric brightness distributions with a horseshoe-like morphology for more than a dozen transition disks. the most-accepted explanation for the observed asymmetries is the accumulation of dust in large-scale vortices. protoplanetary disks’ vortices can form by the excitati... | interpreting brightness asymmetries in transition disks: vortex at dead zone or planet-carved gap edges? |
context. some intermediate polars (ips) show outbursts that are much shorter than those observed in normal dwarf novae, and their origin remains unclear.aims: we examine the case of v1223 sgr, an intermediate polar that showed a short outburst in 1984, and compare the outburst characteristics with the predictions of th... | magnetically gated accretion model: application to short bursts in the intermediate polar v1223 sgr |
the redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disc (ppd) evolution. the magnetorotational instability (mri) is considered a likely mechanism. we present the results of a study involving multifluid global simulations including ohmic dissipation, ambipolar diffus... | global multifluid simulations of the magnetorotational instability in radially stratified protoplanetary discs |
the dynamical response of edge waves under the influence of self-gravity is examined in an idealised two-dimensional model of a proto-stellar disc, characterised in steady state as a rotating vertically infinite cylinder of fluid with constant density except for a single density interface at some radius ?. the fluid in... | on the mechanism of self gravitating rossby interfacial waves in proto-stellar accretion discs |
negative superhumps are believed to arise in cataclysmic variable systems when the accretion disk is tilted with respect to the orbital plane. slow retrograde precession of the line-of-nodes results in a signal—the negative superhump—with a period slightly less than the orbital period. previous studies have shown that ... | the emergence of negative superhumps in cataclysmic variables: smoothed particle hydrodynamics simulations |
we study the stability of density stratified flow between corotating vertical cylinders with rotation rates ωo<ωi and radius ratio ri/ro=0.877 , where subscripts o and i refer to the outer and inner cylinders. just as in stellar and planetary accretion disks, the flow has rotation, anticyclonic shear, and a stabiliz... | observations of the stratorotational instability in rotating concentric cylinders |
how a black hole accretes matter and how this process is regulated are fundamental but unsolved questions in astrophysics. in transient black-hole binaries, a lot of mass stored in an accretion disk is suddenly drained to the central black hole because of thermal-viscous instability. this phenomenon is called an outbur... | optical variability correlated with x-ray spectral transition in the black-hole transient asassn-18ey = maxi j1820+070 |
neutron star high-mass x-ray binaries with superorbital modulations in luminosity host warped inner accretion disks that occult the neutron star during precession. in smc x-1, the instability in the warped disk geometry causes superorbital period "excursions": times of instability when the superorbital period decreases... | constraining the evolution of the unstable accretion disk in smc x-1 with nicer |
circumplanetary discs can be linearly unstable to the growth of disc tilt in the tidal potential of the star-planet system. we use 3d hydrodynamical simulations to characterize the disc conditions needed for instability, together with its long-term evolution. tilt growth occurs for disc aspect ratios, evaluated near th... | kozai-lidov oscillations triggered by a tilt instability of detached circumplanetary discs |
we study the central mass accretion rate and its variation with time during the outburst of x-ray transients using disk irradiation effect once the outer boundary of the disk is defined by the binary parameters. we show that the decay of the light curve and its characteristics time are well linked to the disk aspect ra... | estimating disk parameters of black hole x-ray binary maxi j1543-564: effect of disk irradiation |
a new accretion picture based on a small disk surrounding a black hole is developed for the wind-fed source cyg x-1. the hard and soft spectral states of cyg x-1 are interpreted in terms of co-spatial two-component flows for the innermost region of an accretion disk. the state transitions result from the outward expans... | a model for spectral states and their transition in cyg x-1 |
context. gravitational collapse of molecular cloud or cloud core/clump may lead to the formation of geometrically flattened, rotating accretion flow surrounding the new born star or star cluster. gravitational instability may occur in such accretion flow when the gas to stellar mass ratio is high (e.g., over 10%).aims:... | interpreting observations of edge-on gravitationally unstable accretion flows. the case of g10.6-0.4 |
we observed the 2018 november outburst of cs ind and confirmed that it was a genuine superoutburst with a very long [0.12471(1) d on average] superhump period. the superoutburst was preceded by a long precursor, which was recorded for the first time in su uma-type dwarf novae. our interpretation is that the combination... | cs indi: su uma-type dwarf nova with long precursor outburst |
an attractive scenario for producing type ia supernovae (sne ia) is a double detonation, where detonation of an accreted helium layer triggers ignition of a c/o core. whether or not such a mechanism can explain some or most sne ia depends on the properties of the helium burning, which in turn is set by the composition ... | turbulent mixing on helium-accreting white dwarfs |
using an advanced semi-analytical model (sam) for galaxy formation, we investigated the statistical effects of assuming two different mechanisms for triggering agn activity on the properties of agn host galaxies. we considered a first accretion mode where agn activity is triggered by disk instabilities (di) in isolated... | physical properties of agn host galaxies as a probe of supermassive black hole feeding mechanisms |
context. disk accretion onto weakly magnetized stars leads to the formation of a boundary layer (bl) where the gas loses its excess kinetic energy and settles onto the star. there are still many open questions concerning the bl, for instance the transport of angular momentum (am) or the vertical structure.aims: it is t... | wave mediated angular momentum transport in astrophysical boundary layers |
the electromagnetic signature of a point explosion near a kerr black hole (bh) is evaluated. the first repetitions produced by gravitational lensing are not periodic in time; periodicity emerges only as the result of multiple circuits of the prograde and retrograde light rings and is accompanied by exponential dimming.... | impulsive electromagnetic emission near a black hole |
we present optical photometry of a wz sge-type dwarf nova (dn), asassn-15jd. its light curve showed a small dip in the middle of the superoutburst in 2015 for the first time among wz sge-type dne. the unusual light curve implies a delay in the growth of the 3 : 1 resonance tidal instability. also, the light curve is si... | asassn-15jd: wz sge-type star with intermediate superoutburst between single and double ones |
the current superactive state of the recurrent nova t coronae borealis (t crb) has been observed with unprecedented detail. previously published observations provide strong evidence that this state is due to an enhancement of the flow of material through the accretion disk, which increased the optical depth of its most... | dissecting a disk-instability outburst in a symbiotic star: nustar and swift observations of t coronae borealis during the rise to the “superactive” state |
the magnetorotational instability (mri) is a shear instability and thus its sensitivity to the shear parameter q = -d ln ω/d ln r is of interest to investigate. motivated by astrophysical discs, most (but not all) previous mri studies have focused on the keplerian value of q = 1.5. using simulation with eight vertical ... | sensitivity of the magnetorotational instability to the shear parameter in stratified simulations |
recent observations indicate that the mass of supermassive black holes (smbhs) correlate differently with different galaxy stellar components. comparing such observations with the results of "ab initio" galaxy formation models can provide insight on the mechanisms leading to the growth of smbhs. here we use a state-of-... | relative growth of black holes and the stellar components of galaxies |
magnetic fields of strongly magnetized stars can trap conducting matter due to frozen-in condition. in the force-free regime, the motion of the matter along the field lines may be considered in the 'bead on a wire' approximation. such a motion, if gravity and centrifugal forces are taken into account, has equilibrium p... | inertial oscillation modes of an inclined dipolar magnetosphere as a source of band-limited noise in x-ray pulsars |
the polluted white dwarf (wd) system sdss j122859.93+104032.9 (sdss j1228) shows variable emission features interpreted as originating from a solid core fragment held together against tidal forces by its own internal strength, orbiting within its surrounding debris disk. estimating the size of this orbiting solid body ... | reinterpreting the polluted white dwarf sdss j122859.93+104032.9 in light of thermohaline mixing models: more polluting material from a larger orbiting solid body |
we present unstratified 3d magnetohydrodynamical (mhd) simulations of an accretion disc with a boundary layer (bl) that have a duration of ∼1000 orbital periods at the inner radius of the accretion disc. we find the surprising result that angular momentum piles up in the boundary layer, which results in a rapidly rotat... | inefficient angular momentum transport in accretion disc boundary layers: angular momentum belt in the boundary layer |
the availability of multi-wavelength observations and parallaxes from the space missions and very comprehensive models of agb evolution that include the accretion of matter from the circumbinary disc have strongly impacted our understanding of these enigmatic objects. the important developments made in the recent times... | recent advances in rv tauri stars |
swift j1357.2-0933 underwent an episodic accretion in 2011 and provided very regular temporal and spectral evolution, making it an ideal source for exploring the nature of very faint x-ray transients. in this work, we present a detailed analysis on both x-ray and near-ultraviolet (nuv) light curves. the fluxes at all w... | multiwavelength light-curve evolution of swift j1357.2-0933 during its 2011 outburst |
bondi accretion assumes that there is a sink of mass at the centre - which in the case of a black hole (bh) corresponds to the advection of matter across the event horizon. other stars, such as a neutron star (ns), have surfaces and hence the infalling matter has to slow down at the surface. we study the initial value ... | spherical accretion: the influence of inner boundary and quasi-periodic oscillations |
we explore the formation process of a black hole (bh) through the pair-instability collapse of a rotating population iii very massive star in axisymmetric numerical relativity. as the initial condition, we employ a progenitor star that is obtained by evolving a rapidly rotating zero-age main-sequence star with mass 320... | black hole formation and explosion from rapidly rotating very massive stars |
we report the analysis of 22 b-band light curves of the dwarf nova v4140 sgr obtained with soar optical imager (soi)/soar during two nights along the decline of a superoutburst in 2006 september 12-24 and in quiescence over 50 d following the superoutburst. 3d eclipse mapping of the outburst light curves indicates that... | soar observations of the high-viscosity accretion disc of the dwarf nova v4140 sagitarii in quiescence and in outburst |
we report on two superoutbursts of the am cvn-type object cr boo in 2014 april-march and 2015 may-june. a precursor outburst accompanied both of these superoutbursts. during the rising branch of the main superoutburst in 2014, we detected growing superhumps (stage a superhumps) whose period was 0.017669(24) d. assuming... | superoutburst of cr bootis: estimation of mass ratio of a typical am cvn star by stage a superhumps |
in this article, we proceed to study convection as a possible factor of episodic accretion in protoplanetary disks. within the model presented in article i, the accretion history is analyzed at different rates and areas of matter inflow from the envelope onto the disk. it is shown that the burst-like regime occurs in a... | evolution of a viscous protoplanetary disk with convectively unstable regions. ii. accretion regimes and long-term dynamics |
it has been shown that the behaviour of primordial gas collapsing in a dark matter minihalo can depend on the adopted choice of three-body h2 formation rate. the uncertainties in this rate span two orders of magnitude in the current literature, and so it remains a source of uncertainty in our knowledge of population ii... | the role of three-body h2 formation in the fragmentation of primordial gas |
we analysed the four-decades-long x-ray light curve of the low-luminosity active galactic nucleus (llagn) ngc 7213 and discovered a fast-rise-exponential-decay (fred) pattern, i.e. the x-ray luminosity increased by a factor of ≈4 within 200 d, and then decreased exponentially with an e-folding time ≈8116 d (≈22.2 yr). ... | a decades-long fast-rise-exponential-decay flare in low-luminosity agn ngc 7213 |
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