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the magnetorotational instability (mri) is considered to be a promising mechanism to amplify the magnetic field in fast-rotating protoneutron stars. in contrast to accretion discs, radial buoyancy driven by entropy and lepton fraction gradients is expected to have a dynamical role as important as rotation and shear. we... | numerical simulations of the magnetorotational instability in protoneutron stars - i. influence of buoyancy |
we propose the formation of massive pristine dark-matter (dm) haloes with masses of ∼108 m⊙, due to the dynamical effects of frequent mergers in rare regions of the universe with high baryonic streaming velocity relative to dm. since the streaming motion prevents gas collapse into dm haloes and delays prior star format... | massive black hole and population iii galaxy formation in overmassive dark-matter haloes with violent merger histories |
we present results from multi-wavelength simultaneous x-ray and radio observations of the black hole x-ray binary v404 cyg in quiescence. our coverage with nustar provides the very first opportunity to study the x-ray spectrum of v404 cyg at energies above 10 kev. the unabsorbed broadband (0.3-30 kev) quiescent luminos... | characterizing x-ray and radio emission in the black hole x-ray binary v404 cygni during quiescence |
this review, based on lectures given at the 45th saas-fee advanced course "from protoplanetary disks to planet formation", introduces physical processes in protoplanetary disks relevant to accretion and the initial stages of planet formation. after a brief overview of the observational context, i introduce the elementa... | physical processes in protoplanetary disks |
the magnetorotational instability (mri) can be a powerful mechanism amplifying the magnetic field in core-collapse supernovae. whether initially weak magnetic fields can be amplified by this instability to dynamically relevant strengths is still a matter of debate. one of the main uncertainties concerns the process tha... | termination of the magnetorotational instability via parasitic instabilities in core-collapse supernovae |
we investigate how the detectability of signatures of self-gravity in a protoplanetary disk depends on its temporal evolution. we run a one-dimensional model for secular timescales to follow the disk mass as a function of time. we then combine this with three-dimensional global hydrodynamics simulations that employ a h... | the temporal requirements of directly observing self-gravitating spiral waves in protoplanetary disks with alma |
recent discoveries of gas giant exoplanets around m-dwarfs from transiting and radial velocity surveys are difficult to explain with core-accretion models. we present here a homogeneous suite of 162 models of gravitationally unstable gaseous disks. these models represent an existence proof for gas giants more massive t... | forming gas giants around a range of protostellar m-dwarfs by gas disk gravitational instability |
we present the discovery of two galaxy overdensities in the hubble space telescope udf: a proto-cluster, hudfj0332.4-2746.6 at z=1.84+/- 0.01, and a group, hudfj0332.5-2747.3 at z=1.90 ± 0.01. assuming viralization, the velocity dispersion of hudfj0332.4-2746.6 implies a mass of {{m}200}=(2.2+/- 1.8)× {{10}14} {{m}⊙ },... | star-forming blue etgs in two newly discovered galaxy overdensities in the hudf at z=1.84 and 1.9: unveiling the progenitors of passive etgs in cluster cores |
we observed the high-mass protostellar core g335.579-0.272 alma1 at ~200 au (0.″05) resolution with the atacama large millimeter/submillimeter array (alma) at 226 ghz (with a mass sensitivity of 5σ = 0.2 m ⊙ at 10 k). we discovered that at least a binary system is forming inside this region, with an additional nearby b... | digging into the interior of hot cores with alma (dihca). ii. exploring the inner binary (multiple) system embedded in g335 mm1 alma1 |
we carry out two-fluid, two-dimensional global hydrodynamic simulations to test whether protostellar infall can trigger the rossby wave instability (rwi) in protoplanetry disks. our results show that infall can trigger the rwi and generate vortices near the outer edge of the mass landing on the disk (i.e., centrifugal ... | are protoplanetary disks born with vortices? rossby wave instability driven by protostellar infall |
the phenomenological disc instability model has been successful in reproducing the observed light curves of dwarf nova outbursts by invoking an enhanced shakura-sunyaev α parameter ∼0.1-0.2 in outburst compared to a low value ∼0.01 in quiescence. recent thermodynamically consistent simulations of magnetorotational inst... | dwarf nova outbursts with magnetorotational turbulence |
observations of the near-infrared excess object g2/dso increased attention toward the galactic center and its vicinity. the predicted flaring event in 2014 and the outcome of the intense monitoring of the supermassive black hole in the center of our galaxy did not fulfill all predictions about a significantly enhanced ... | the apparent tail of the galactic center object g2/dso |
context. protoplanetary discs are cold, dense, and weakly ionised environments that witness planetary formation. among these discs, transition discs (tds) are characterised by a wide cavity (up to tens of au) in the dust and gas distribution. despite this lack of material, a considerable fraction of tds are still stron... | magnetised winds in transition discs. i. 2.5d global simulations |
recent results by martin et al. showed in 3d smoothed particle hydrodynamics simulations that tilted discs in binary systems can be unstable to the development of global, damped kozai-lidov (kl) oscillations in which the discs exchange tilt for eccentricity. we investigate the linear stability of kl modes for tilted in... | kozai-lidov disc instability |
context. in the disc-mediated accretion scenario for the formation of the most massive stars, high densities and high accretion rates could induce gravitational instabilities in the disc, forcing it to fragment and produce companion objects.aims: we investigate the effects of inclination and spatial resolution on the o... | disc kinematics and stability in high-mass star formation. linking simulations and observations |
ultraluminous x-ray sources (ulxs) are our best laboratories for studying extreme super-eddington accretion. most studies of these objects are of relatively persistent sources; however, there is growing evidence to suggest a large fraction of these sources are transient. here we present a sample of five newly reported ... | a new sample of transient ultraluminous x-ray sources serendipitously discovered by swift/xrt |
disc accretion rate onto low mass protostar fu ori suddenly increased hundreds of times 85 yr ago and remains elevated to this day. we show that the sum of historic and recent observations challenges existing fu ori models. we build a theory of a new process, extreme evaporation (ee) of young gas giant planets in discs... | extreme evaporation of planets in hot thermally unstable protoplanetary discs: the case of fu ori |
we present results of our analysis of up to 15 yr of photometric data from eight am cvn systems with orbital periods between 22.5 and 26.8 min. our data have been collected from the goto, ztf, pan-starrs, asas-sn, and catalina all-sky surveys and amateur observations collated by the aavso. we find evidence that these i... | evidence that short-period am cvn systems are diverse in outburst behaviour |
context. the observed signatures of winds from x-ray binaries are broadly consistent with thermal winds, which are driven by x-ray irradiation of the outer accretion disc. thermal winds produce mass outflow rates that can exceed the accretion rate in the disc.aims: we aim to study the impact of thermal wind mass loss o... | the impact of thermal winds on the outburst lightcurves of black hole x-ray binaries |
we present a new zoom-in hydrodynamical simulation, `erisbh', which features the same initial conditions, resolution, and sub-grid physics as the close milky way-analogue `eris' (guedes et al. 2011), but it also includes prescriptions for the formation, growth and feedback of supermassive black holes. this enables a de... | black hole starvation and bulge evolution in a milky way-like galaxy |
the origin of the spins of giant planets is an open question in astrophysics. as planets and stars accrete from discs, if the specific angular momentum accreted corresponds to that of a keplerian orbit at the surface of the object, it is possible for planets and stars to be spun-up to near-break-up speeds. however, acc... | on the terminal spins of accreting stars and planets: boundary layers |
gravitationally unstable accretion disks emerge in a variety of astrophysical contexts—giant planet formation, fu orioni outbursts, feeding of active galactic nuclei, and the origin of pop iii stars. when a gravitationally unstable disk is unable to cool rapidly, it settles into a quasi-stationary, fluctuating gravitot... | viscosity prescription for gravitationally unstable accretion disks |
the existence of giant planets on wide orbits ($\stackrel{\gt }{_\sim }100\rm ~au$) challenge planet formation theories; the core accretion scenario has difficulty in forming them, whereas the disc instability model forms an overabundance of them that is not seen observations. we perform n-body simulations investigatin... | on the survivability of a population of gas giant planets on wide orbits |
context. angular momentum transport in accretion discs is often believed to be due to magnetohydrodynamic turbulence mediated by the magnetorotational instability (mri). despite an abundant literature on the mri, the parameters governing the saturation amplitude of the turbulence are poorly understood and the existence... | angular momentum transport and large eddy simulations in magnetorotational turbulence: the small pm limit |
low-frequency quasi-periodic oscillations, or lfqpos, are ubiquitous in black hole x-ray binaries and provide strong constraints on the accretion-ejection processes. although several models have been proposed, none has been proven to reproduce all observational constraints, and no consensus has emerged so far. we make ... | are low-frequency quasi-periodic oscillations in accretion flows the disk response to jet instability? |
turbulent radiation flow is ubiquitous in many physical systems where light–matter interaction becomes relevant. photon bubble instabilities, in particular, have been identified as a possible source of turbulent radiation transport in astrophysical objects such as massive stars and black hole accretion disks. here, we ... | quasi-static and dynamic photon bubbles in cold atom clouds |
we use the galform semi-analytical model of galaxy formation and the planck-millennium simulation to investigate the origins of stellar mass in galaxies and their spheroids. we compare the importance of mergers and disc instabilities, as well as the starbursts that they trigger. we find that the fraction of galaxy stel... | the buildup of galaxies and their spheroids: the contributions of mergers, disc instabilities, and star formation |
it is likely that young protostellar disks undergo a self-gravitating phase. such systems are characterized by the presence of a spiral pattern that can be either in a quasi-steady state or in a nonlinear unstable condition. this spiral wave affects both the gas dynamics and kinematics, resulting in deviations from the... | investigating protoplanetary disk cooling through kinematics: analytical gi wiggle |
local models of gaseous accretion discs have been successfully employed for decades to describe an assortment of small-scale phenomena, from instabilities and turbulence, to dust dynamics and planet formation. for the most part, they have been derived in a physically motivated but essentially ad hoc fashion, with some ... | local models of astrophysical discs |
x-ray transients, such as accreting neutron stars, periodically undergo outbursts, thought to be caused by a thermal-viscous instability in the accretion disc. usually outbursts of accreting neutron stars are identified when the accretion disc has undergone an instability, and the persistent x-ray flux has risen to a t... | enhanced optical activity 12 d before x-ray activity, and a 4 d x-ray delay during outburst rise, in a low-mass x-ray binary |
negative superhumps (nshs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. based on tess photometry, we find nine new cataclysmic variable stars (cvs) with nshs. three (asas j1420, tz per, and v392 hya) of these s... | nine new cataclysmic variable stars with negative superhumps |
ah her is a z cam-type dwarf nova with an orbital period of ~0.258 days. dwarf nova oscillations and long-period dwarf nova oscillations have been detected, but no quasiperiodic oscillations (qpos) and negative superhumps (nshs) have been found. we investigated the association between nshs, qpos, and outbursts of ah he... | evolution of negative superhumps, quasiperiodic oscillations, and outbursts in the z cam-type dwarf nova ah her |
context. the physics of early stellar evolution (e.g. accretion processes) is often not properly included in the calculations of pre-main-sequence models, leading to insufficient model grids and hence systematic errors in the results.aims: we aim to investigate current and improved approaches for the asteroseismic mode... | pulsational instability of pre-main-sequence models from accreting protostars. ii. modelling echelle diagrams of δ scuti stars without rotational splitting |
theories of planet formation predict that low-mass stars should rarely host exoplanets with masses exceeding that of neptune. we used radial velocity observations to detect a neptune-mass exoplanet orbiting lhs 3154, a star that is nine times less massive than the sun. the exoplanet’s orbital period is 3.7 days, and it... | a neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models |
we revisit the conditions present in supermassive discs (smds) formed by the merger of gas-rich, metal-enriched galaxies at redshift z ~ 10. we find that smds naturally form hydrostatic cores which go through a rapidly accreting supermassive star phase, before directly collapsing into massive black holes via the genera... | direct collapse of exceptionally heavy black holes in the merger-driven scenario |
the main problems of nonvacuum numerical relativity, compact binary mergers and stellar collapse, involve hydromagnetic instabilities and turbulent flows, so that kinetic energy at small scales leads to mean effects at large scale that drive the secular evolution. notable among these effects is momentum transport. we i... | comparison of momentum transport models for numerical relativity |
context. it is now widely accepted that most ultraluminous x-ray sources (ulxs) are binary systems whose large (above 1039 erg s-1) apparent luminosities are explained by super-eddington accretion onto a stellar-mass compact object. many of the ulxs, especially those containing magnetized neutron stars, are highly vari... | models of ultraluminous x-ray transient sources |
we propose a framework for understanding the fragmentation criterion for self-gravitating discs which, in contrast to studies that emphasize the `gravoturbulent' nature of such discs, instead focuses on the properties of their quasi-regular spiral structures. within this framework there are two evolutionary paths to fr... | dependence of fragmentation in self-gravitating accretion discs on small-scale structure |
context. the hierarchical process of star formation has so far mostly been studied on scales from thousands of au to parsecs, but the smaller sub-1000 au scales of high-mass star formation are still largely unexplored in the submillimeter regime.aims: we aim to resolve the dust and gas emission at the highest spatial r... | high-mass star formation at sub-50 au scales |
the local properties of turbulence driven by the magnetorotational instability (mri) in rotating, shearing flows are studied in the framework of a shearing-box model. based on numerical simulations, we propose that the mri-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field a... | on the nature of magnetic turbulence in rotating, shearing flows |
we carry out three dimensional radiation hydrodynamical simulations of gravitationally unstable discs to explore the movement of mass in a disc following its initial fragmentation. we find that the radial velocity of the gas in some parts of the disc increases by up to a factor of ≈10 after the disc fragments, compared... | triggered fragmentation in self-gravitating discs: forming fragments at small radii |
aims: it is well known that low-mass young stellar objects (lmysos) gain a significant portion of their final mass through episodes of very rapid accretion, with mass accretion rates up to ṁ∗ ∼ 10−4 m⊙ yr−1. recent observations of high-mass young stellar objects (hmysos) with masses m∗ ≳ 10 m⊙ uncovered outbursts with ... | accretion bursts in high-mass protostars: a new test bed for models of episodic accretion |
we propose that the accretion discs fueling active galactic nuclei (agn) are supported vertically against gravity by a strong toroidal (φ-direction) magnetic field that develops naturally as the result of an accretion disc dynamo. the magnetic pressure elevates most of the gas carrying the accretion flow at r to large ... | magnetically elevated accretion discs in active galactic nuclei: broad emission-line regions and associated star formation |
binary black holes in which both spins are aligned with the binary's orbital angular momentum do not precess. however, the up-down configuration, in which the spin of the heavier (lighter) black hole is aligned (anti-aligned) with the orbital angular momentum, is unstable to spin precession at small orbital separations... | endpoint of the up-down instability in precessing binary black holes |
young protoplanetary discs and the outer radii of active galactic nuclei may be subject to gravitational instability and, as a consequence, fall into a 'gravitoturbulent' state. while in this state, appreciable angular momentum can be transported; alternatively, the gas may collapse into bound clumps, the progenitors o... | gravitoturbulence and the excitation of small-scale parametric instability in astrophysical discs |
context. the hard-to-soft state transition of the outbursts in x-ray binaries (xrbs) is triggered by the rising of the mass accretion rate as a result of the disk instability. the hard x-ray transition luminosity is found to be tightly correlated to the soft x-ray peak luminosity in the soft state, the physical origin ... | magnetic accretion disk-outflow model for the state transition in x-ray binaries |
context. vela x-1 is the prototype of the classical super-giant high mass x-ray binary systems. recent continuous and long monitoring campaigns revealed a large hard x-rays variability amplitude with strong flares and off-states. this activity has been interpreted by invoking clumpy stellar winds and/or magnetic gating... | origin of the x-ray off-states in vela x-1 |
the assembly of the milky way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. that is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. the dominant scenario f... | was the milky way bulge formed from the buckling disk instability, hierarchical collapse, accretion of clumps, or all of the above? |
the ubiquity of earth- to super-earth-sized planets found very close to their host stars has motivated in situ formation models. in particular, inside-out planet formation is a scenario in which planets coalesce sequentially in the disk, at the local gas pressure maximum near the inner boundary of the dead zone. the pr... | inside-out planet formation. v. structure of the inner disk as implied by the mri |
based on the framework of kaniadakis' statistics and its related kinetic theory, the jeans instability for self-gravitational systems in the background of eddington-inspired born-infield (eibi) gravity is revisited. a dispersion relation generalizing the jeans modes is derived by modifying the maxwellian distribution t... | jeans gravitational instability with κ-deformed kaniadakis distribution in eddington-inspired born-infield gravity |
in outburst sources, quasi-periodic oscillation (qpo) frequency is known to evolve in a certain way: in the rising phase, it monotonically goes up until a soft intermediate state is achieved. in the propagating oscillatory shock model, oscillation of the compton cloud is thought to cause qpos. thus, in order to increas... | is compton cooling sufficient to explain evolution of observed quasi-periodic oscillations in outburst sources? |
we present new narrow-band hα imaging for 24 nearby edge-on galaxies in the continuum halos in nearby galaxies—an evla survey (chang-es). we use the images in conjunction with the wide-field infrared survey explorer 22 μm imaging of the sample to estimate improved star formation rates (sfrs) using the updated recipe fr... | chang-es. xvii. hα imaging of nearby edge-on galaxies, new sfrs, and an extreme star formation region—data release 2 |
ax j1745.6-2901 is a low-mass x-ray binary with an accreting neutron star, showing clear evidence for highly ionized absorption. strong ionized fe kα and kβ absorption lines are always observed during the soft state, whereas they disappear during the hard state. we computed photoionization stability curves for the hard... | photoionization instability of the fe k absorbing plasma in the neutron star transient ax j1745.6-2901 |
self-gravitating discs are believed to play an important role in astrophysics in particular regarding the star and planet formation process. in this context, discs subject to an idealized cooling process, characterized by a cooling time-scale β expressed in unit of orbital time-scale, have been extensively studied. we ... | a two-step gravitational cascade for the fragmentation of self-gravitating discs |
we investigate the disk formation process in the tng50 simulation, examining the profiles of sfr surface density (σsfr), gas inflow and outflow, and the evolution of the angular momentum of inflowing gas particles. the tng50 galaxies tend to have larger star-forming disks, and they also show larger deviations from expo... | the formation of star-forming disks in the tng50 simulation |
context. to better understand the formation of high-mass stars, it is fundamental to investigate how matter accretes onto young massive stars, how it is ejected, and how all this differs from the low-mass case. the massive protocluster g31.41+0.31 is the ideal target to study all these processes because observations at... | the sharp alma view of infall and outflow in the massive protocluster g31.41+0.31 |
rapidly growing black holes are surrounded by accretion disks that make them the brightest objects in the universe. their brightness is known to be variable, but the causes of this are not implied by simple disk models and still debated. due to the small size of accretion disks and their great distance, there are no re... | universality in the random walk structure function of luminous quasi-stellar objects |
aims: exor-type objects are protostars that display powerful uv-optical outbursts caused by intermittent and powerful events of magnetospheric accretion. these objects are not yet well investigated and are quite difficult to characterize. several parameters, such as plasma stream velocities, characteristic densities, a... | inferring possible magnetic field strength of accreting inflows in exor-type objects from scaled laboratory experiments |
we have obtained alma band 7 observations of the fu ori outburst system at a 0.″6 × 0.″5 resolution to measure the link between the inner disk instability and the outer disk through submillimeter continuum and molecular line observations. our observations detect continuum emission that can be well-modeled by two unreso... | the early alma view of the fu ori outburst system |
we present a detailed study of v899 mon (a new member in the fuors/exors family of young low-mass stars undergoing outburst), based on our long-term monitoring of the source starting from 2009 november to 2015 april. our optical and near-infrared photometric and spectroscopic monitoring recorded the source transitionin... | v899 mon: an outbursting protostar with a peculiar light curve, and its transition phases |
ss cyg has long been recognized as the prototype of a group of dwarf novae that show only outbursts. however, this object has entered a quite anomalous event in 2021, which at first appeared to be standstill, i.e., an almost constant luminosity state observed in z cam-type dwarf novae. this unexpected event gives us a ... | on the nature of the anomalous event in 2021 in the dwarf nova ss cygni and its multi-wavelength transition |
by using a large, highly obscured ( ${n}_{{\rm{h}}}\gt {10}^{23}\ {\mathrm{cm}}^{-2}$ ) active galactic nucleus (agn) sample (294 sources at z ∼ 0-5) selected from detailed x-ray spectral analyses in the deepest chandra surveys, we explore distributions of these x-ray sources in various optical/infrared/x-ray color-col... | piercing through highly obscured and compton-thick agns in the chandra deep fields. ii. are highly obscured agns the missing link in the merger-triggered agn-galaxy coevolution models? |
disks of gas accreting onto supermassive black holes, powering active galactic nuclei (agn), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. the density and thermal conditions of these disks can result in rapid accretion onto embedded stars, dramatically altering their ... | the influence of disk composition on the evolution of stars in the disks of active galactic nuclei |
turbulent radiation flow is commonplace in systems with strong, incoherent, light-matter interactions. in astrophysical contexts, photon bubble turbulence is considered a key mechanism behind enhanced radiation transport, and its importance has been widely asserted for a variety of high energy objects such as accretion... | photon bubble turbulence in cold atom gases |
this white paper submitted for 2020 decadal assessment of plasma science concerns the importance of multi-spacecraft missions to address fundamental questions concerning plasma turbulence. plasma turbulence is ubiquitous in the universe, and it is responsible for the transport of mass, momentum, and energy in such dive... | [plasma 2020 decadal] disentangling the spatiotemporal structure of turbulence using multi-spacecraft data |
we model the intermediate-mass black hole hlx-1, using the hubble space telescope, xmm-newton and swift. we quantify the relative contributions of a bluer component, function of x-ray irradiation, and a redder component, constant and likely coming from an old stellar population. we estimate a black hole mass {≈ } (2^{+... | outbursts of the intermediate-mass black hole hlx-1: a wind-instability scenario |
estimates of the accretion rate in symbiotic recurrent novae (rne) often fall short of theoretical expectations by orders of magnitude. this apparent discrepancy can be resolved if the accumulation of mass by the white dwarf (wd) is highly sporadic, and most observations are performed during low states. here we use a r... | increasing activity in t crb suggests nova eruption is impending |
gravitational waves can be emitted by accretion discs if they undergo instabilities that generate a time varying mass quadrupole. in this work we investigate the gravitational signal generated by a thick accretion disc of 1 m⊙ around a static supermassive black hole of 106 m⊙, assumed to be formed after the tidal disru... | gravitational wave emission from unstable accretion discs in tidal disruption events |
we consider the parallaxes of sixteen cataclysmic variables and related objects that are included in the tgas catalogue, which is part of the gaia first data release, and compared these with previous parallax measurements. the parallax of the dwarf nova ss cyg is consistent with the parallax determination made using th... | distances of cataclysmic variables and related objects derived from gaia data release 1 |
we present high-time-resolution photometry and phase-resolved spectroscopy of the short-period ({p_orb}= 80.52 min) cataclysmic variable sdss j123813.73-033933.0, observed with the hubble space telescope (hst), the kepler/k2 mission, and the very large telescope (vlt). we also report observations of the first detected ... | evidence for mass accretion driven by spiral shocks onto the white dwarf in sdss j123813.73-033933.0 |
we present fully general-relativistic numerical evolutions of self-gravitating tori around spinning black holes with dimensionless spin a /m =0.7 parallel or antiparallel to the disk angular momentum. the initial disks are unstable to the hydrodynamic papaloizou-pringle instability which causes them to grow persistent ... | gravitational waves from disks around spinning black holes: simulations in full general relativity |
context. the vertical shear instability is one of several known mechanisms that are potentially active in the so-called dead zones of protoplanetary accretion disks. a recent analysis of the instability mechanism indicates that a subset of unstable modes shows unbounded growth - both as resolution is increased and when... | linear analysis of the vertical shear instability: outstanding issues and improved solutions |
we present fully three-dimensional magnetohydrodynamic jet-launching simulations of a jet source orbiting in a binary system. we consider a time-dependent binary gravitational potential, and thus all tidal forces are experienced in the non-inertial frame of the jet-launching primary. we investigate systems with differe... | long-term simulation of mhd jet launching in an orbiting star-disk system |
horseshoe-shaped brightness asymmetries of several transitional discs are thought to be caused by large-scale vortices. anticyclonic vortices efficiently collect dust particles, therefore they can play a major role in planet formation. former studies suggest that the disc self-gravity weakens vortices formed at the edg... | vortex stretching in self-gravitating protoplanetary discs |
using the eris zoom-in cosmological simulation of assembly of a milky way analogue, we study the chemical enrichment of stars due to accretion of metal-enriched gas from the interstellar medium (ism) during the galaxy's development. we consider metal-poor and old stars in the galactic halo and bulge through the use of ... | chemical enrichment of stars due to accretion from the ism during the galaxy's assembly |
in zombie vortex instability (zvi), perturbations excite critical layers in stratified, rotating shear flow (as in protoplanetary disks (ppds)), causing them to generate vortex layers, which roll up into anticyclonic zombie vortices and cyclonic vortex sheets. the process is self-sustaining as zombie vortices perturb n... | zombie vortex instability. ii. thresholds to trigger instability and the properties of zombie turbulence in the dead zones of protoplanetary disks |
we expand the relativistic precession model to include nonequatorial and eccentric trajectories and apply it to quasi-periodic oscillations (qpos) in black hole x-ray binaries (bhxrbs) and associate their frequencies with the fundamental frequencies of the general case of nonequatorial (with carter's constant, $q\ne 0$... | a geometric origin for quasi-periodic oscillations in black hole x-ray binaries |
we observed the 2015 july-august long outburst of v1006 cyg and established this object to be an su uma-type dwarf nova in the period gap. our observations have confirmed that v1006 cyg is the second established object showing three types of outbursts (normal, long normal, and superoutbursts) after tu men. we have succ... | v1006 cygni: dwarf nova showing three types of outbursts and simulating some features of the wz sge-type behavior |
the neutron star (ns) low-mass x-ray binary (lmxb) the rapid burster (rb; mxb 1730-335) uniquely shows both type i and type ii x-ray bursts. the origin of the latter is ill-understood but has been linked to magnetospheric gating of the accretion flow. we present a spectral analysis of simultaneous swift, nustar and xmm... | a strongly truncated inner accretion disc in the rapid burster |
v476 cyg (nova cyg 1920) is a bright, fast nova reaching a photographic magnitude of 2.0. using the zwicky transient facility (ztf) public database, i found that this nova is currently a dwarf nova with a cycle length of ~24 d. compared to other classical novae currently in dwarf nova-type states, outbursts of v476 cyg... | v476 cyg (nova cyg 1920) is currently a dwarf nova -- first such an object in the period gap? |
taylor-couette flow (tcf) is often used as a simplified model for complex rotating flows in the interior of stars and accretion discs. the flow dynamics in these objects is influenced by magnetic fields. for example, quasi-keplerian flows in taylor-couette geometry become unstable to a travelling or standing wave in an... | transition to chaos and modal structure of magnetized taylor-couette flow |
the theory of instability of accretion disks about black holes, neutron stars, or protoplanets is revisited by means of the recent method of the spectral web. the cylindrical accretion disk differential equation is shown to be governed by the forward and backward doppler-shifted continuous alfvén spectra ${{\rm{\omega ... | the super-alfvénic rotational instability in accretion disks about black holes |
we present the results of local, vertically stratified, radiation magnetohydrodynamic shearing-box simulations of magnetorotational instability (mri) turbulence for a (hydrogen poor) composition applicable to accretion disks in am cvn type systems. many of these accreting white dwarf systems are helium analogs of dwarf... | convection enhances magnetic turbulence in am cvn accretion disks |
we study the evolution of close binary systems formed by a normal (solar composition), intermediate-mass-donor star together with a neutron star. we consider models including irradiation feedback and evaporation. these nonstandard ingredients deeply modify the mass-transfer stages of these binaries. while models that n... | the quasi-roche lobe overflow state in the evolution of close binary systems containing a radio pulsar |
astrophysical objects possessing a material surface (white dwarfs, young stars, etc.) may accrete gas from the disc through the so-called surface boundary layer (bl), in which the angular velocity of the accreting gas experiences a sharp drop. acoustic waves excited by the supersonic shear in the bl play an important r... | boundary layers of accretion discs: wave-driven transport and disc evolution |
context. the equatorial accretion scenario, caused by the development of the rayleigh-taylor (rt) instability at the disk edge, was suggested by accurate three-dimensional magnetohydrodynamic (mhd) modelling, but no observational or experimental confirmation of such phenomena has been evidenced yet.aims: we studied the... | laboratory modelling of equatorial `tongue' accretion channels in young stellar objects caused by the rayleigh-taylor instability |
a sudden increase in the rate at which material reaches the most internal part of an accretion disk, i.e., the boundary layer, can change its structure dramatically. we have witnessed such a change for the first time in the symbiotic recurrent nova t crb. our analysis of xmm-newton, swift burst alert telescope (bat)/x-... | dramatic change in the boundary layer in the symbiotic recurrent nova t coronae borealis |
the disk instability picture gives a plausible explanation for the behavior of soft x-ray transient systems if self-irradiation of the disk is included. we show that there is a simple relation between the peak luminosity (at the start of an outburst) and the decay timescale. we use this relation to place constraints on... | x-ray transients: hyper- or hypo-luminous? |
recent work by levitan et al. has expanded the long-term photometric database for am cvn stars. in particular, their outburst properties are well correlated with orbital period and allow constraints to be placed on the secular mass transfer rate between secondary and primary if one adopts the disk instability model for... | constraining the physics of am canum venaticorum systems with the accretion disk instability model |
the radial transport, or drift, of dust has taken a critical role in giant planet formation theory. however, it has been challenging to identify dust drift pileups in the hard-to-observe inner disk. we find that the im lup disk shows evidence that it has been shaped by an episode of dust drift. using radiative transfer... | a potential site for wide-orbit giant planet formation in the im lup disk |
context. most massive stars are located in multiple stellar systems. the modeling of disk fragmentation, a mechanism that may plausibly lead to stellar multiplicity, relies on parallel 3d simulation codes whose agreement remains to be evaluated.aims: cartesian adaptive-mesh refinement (amr) and spherical codes have fre... | disk fragmentation around a massive protostar: comparison of two 3d codes |
during their formation phase, stars gain most of their mass in violent episodic accretion events, such as observed in fu orionis (fuor) and exor stars. v346 normae is a well-studied fuor that underwent a strong outburst beginning around 1980. here, we report on photometric and spectroscopic observations, which show tha... | v346 normae: first post-outburst observations of an fu orionis star |
non-linear evolution of the parametric instability of inertial waves inherent to eccentric discs is studied by way of a new local numerical model. mode coupling of tidal deformation with the disc eccentricity is known to produce exponentially growing eccentricities at certain mean-motion resonances. however, the detail... | non-linear hydrodynamic instability and turbulence in eccentric astrophysical discs with vertical structure |
short gamma-ray bursts (grbs) are thought to result from the merger of two neutron stars (nss) or an ns and a stellar mass black hole (bh). the final stages of the merger are generally accompanied by the production of one or more tidal "tails" of ejecta, which fall back onto the remnant-disk system at late times. using... | variability in short gamma-ray bursts: gravitationally unstable tidal tails |
we study in detail the evolution of the 2015 outburst of gs 1354-64 (bw cir) at optical, uv and x-ray wavelengths using faulkes telescope south/las cumbres observatory global telescope network, small & moderate aperture research telescope system and swift. the outburst was found to stay in the hard x-ray state, alb... | a `high-hard' outburst of the black hole x-ray binary gs 1354-64 |
the extent of the accretion disk in the low/hard state of stellar mass black hole x-ray binaries remains an open question. there is some evidence suggesting that the inner accretion disk is truncated and replaced by a hot flow, while the detection of relativistic broadened iron emission lines seems to require an accret... | nustar and xmm-newton observations of the 2015 outburst decay of gx 339-4 |
v341 ara was recently recognized as one of the closest (d ≃ 150 pc) and brightest (v ≃ 10) nova-like cataclysmic variables. this unique system is surrounded by a bright emission nebula, likely to be the remnant of a recent nova eruption. embedded within this nebula is a prominent bow shock, where the system's accretion... | bow shocks, nova shells, disc winds and tilted discs: the nova-like v341 ara has it all |
accreting binary black holes (bbhs) are multimessenger sources, emitting copious electromagnetic (em) and gravitational waves. one of their most promising em signatures is the light-curve modulation caused by a strong unique and extended azimuthal overdensity structure orbiting at the inner edge of the circumbinary dis... | on the origin of the lump in circumbinary discs |
the inner few parsecs of the milky way's galactic center contain the central accreting supermassive black hole, over a million stars, and multiple large gaseous structures. in the past, the structures at these length scales have generally been modeled independently of each other. it is consequently not well understood ... | the inner 2 pc of sagittarius a*: simulations of the circumnuclear disk and multiphase gas accretion in the galactic center |
recent observations of the protoplanetary disc surrounding ab aurigae have revealed the possible presence of two giant planets in the process of forming. the young measured age of 1-4 myr for this system allows us to place strict time constraints on the formation histories of the observed planets. hence, we may be able... | ab aurigae: possible evidence of planet formation through the gravitational instability |
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