Circumbinary disks are considered to exist in a wide variety of astrophysical objects, e.g., young binary stars, protoplanetary systems, and massive binary black hole systems in active galactic nuclei (AGNs). However, there is no definite evidence for the circumbinary disk except for some in a few young binary star systems. In this Letter, we study possible oscillation modes in circumbinary disks around eccentric and circular binaries. We find that progarde, nonaxisymmetric waves are induced in the inner part of the circumbinary disk by the tidal potential of the binary. Such waves would cause variabilities in emission line profiles from circumbinary disks. Because of prograde precession of the waves, the distance between each component of the binary and the inner edge of the circumbinary disk varies with the beat period between the precession period of the wave and the binary orbital period. As a result, light curves from the circumbinary disks are also expected to vary with the same period. The current study thus provides a new method to detect circumbinary disks in various astrophysical systems.
We investigate the accretion flows onto the supermassive binary black holes (SMBBHs) from the circumbinary disk with the equal mass, eccentric binary on the subparsec scale, using Smoothed Particle Hydrodynamics (SPH) code. We find that the material can be supplied from circumbinary disk, which leads to the formation of two accretion disks around the SMBBHs. The mass accretion rates significantly modulate with the binary orbital motion. These could provide the observable diagnosis of the existence of the supermassive binary black holes (e.g. OJ287) on the subparsec scale in merged galactic nuc…
We present the results of hydrodynamical simulations of low mass protoplanets embedded in circumbinary accretion disks. The aim is to examine the migration and long term orbital evolution of the protoplanets, in order to establish the stability properties of planets that form in circumbinary disks. Simulations were performed using a grid--based hydrodynamics code. First we present a set of calculations that study how a binary interacts with a circumbinary disk. We evolve the system for 10^5 binary orbits, which is the time needed for the system to reach a quasi-equilibrium state. From this tim…
CoKu Tau/4 has been labeled as one of the very few known transition disk objects: disks around young stars that have their inner disks cleared of dust, arguably due to planetary formation. We report aperture-masking interferometry and adaptive optics imaging observations showing that CoKu Tau/4 is in fact a near-equal binary star of projected separation $\sim$53 mas ($\sim$8 AU). The spectral energy distribution of the disk is then naturally explained by inner truncation of the disk through gravitational interactions with the binary star system. We discuss the possibility that such ``unseen'' …
Circumbinary (CB) disks have been proposed as a mechanism to extract orbital angular momentum from cataclysmic variables (CVs) during their evolution. As proposed by Taam & Spruit, these disks extend outwards to several a.u. and should be detected observationally via their infrared flux or by absorption lines in the ultraviolet spectra of the CV. We have made use of archival HST/STIS spectra as well as our own near-IR imaging to search for observational evidence of such CB disks in seven CVs. Based on the null result, we place an upper limit on the column density of the disk of N_H~10^17 cm^-2…
We investigate the structure and evolution of a geometrically thin viscous Keplerian circumbinary (CB) disk, using detailed models of their radiative/convective vertical structure. We use a simplified description for the evolution of the cataclysmic binary and focus on cases where the circumbinary disk causes accelerated mass transfer (> 1e-8 Msun/yr). The inner edge of the disk is assumed to be determined by the tidal truncation radius and the mass input rate into the disk is assumed to be a small fraction (1e-5-0.01) of the mass transfer rate. Under the action of the viscous stresses in the …
We have found a photoevaporated disk in the Orion Nebula that includes a wide binary. HST/ACS observations of the proplyd 124-132 show two point-like sources separated by 0".15, or about 60 AU at the distance of Orion. The two sources have nearly identical I and z magnitudes. We analyze the brightest component, Source N, comparing the observed magnitudes with those predicted using a 1 Myr Baraffe/NEXTGEN isochrone with different accretion luminosities and extinctions. We find that a low mass (\simeq 0.04 M_\odot) brown dwarf ~1 Myr old with mass accretion rate \log\dot{M}\simeq -10.3, typical …
The quadruple young stellar system HD 98800 consists of two spectroscopic binary pairs with a circumbinary disk around the B component. Recent work by Boden and collaborators using infrared interferometry and radial velocity data resulted in a determination of the physical orbit for HD 98800 B. We use the resulting inclination of the binary and the measured extinction toward the B component stars to constrain the distribution of circumbinary material. Although a standard optically and geometrically thick disk model can reproduce the spectral energy distribution, it can not account for the obse…
We study the evolution of circumbinary disks surrounding classical T Tau stars. High resolution numerical simulations are employed to model a system consisting of a central eccentric binary star within an accretion disk. The disk is assumed to be infinitesimally thin, however a detailed energy balance including viscous heating and radiative cooling is applied. A novel numerical approach using a parallelized Dual-Grid technique on two different coordinate systems has been implemented. Physical parameters of the setup are chosen to model the close systems of DQ Tau and AK Sco, as well as the wid…
The influence of a circumbinary (CB) disk on the evolution of cataclysmic variable (CV) binary systems is investigated. We show that CB mass surface densities sufficient to influence the evolution rate are plausibly provided by the outflows observed in CVs, if the net effect of these winds is to deliver $10^{-4}$--$10^{-3}$ of the mass transfer rate to the CB disk. The torque exerted by the CB disk provides a positive feedback between mass transfer rate and CB disk mass which can lead to mass transfer rates of $\sim 10^{-8} -10^{-7} \mpy$. This mechanism may be responsible for causing the rang…
It is generally thought that conservative mass transfer in Algol binaries causes their orbits to be wider, in which the less massive star overflows its Roche-lobe. The observed decrease in the orbital periods of some Algol binaries suggests orbital angular momentum loss during the binary evolution, and the magnetic braking mechanism is often invoked to explain the observed orbital shrinkage. Here we suggest an alternative explanation, assuming that a small fraction of the transferred mass forms a circumbinary disk, which extracts orbital angular momentum from the binary through tidal torques. …
We study the evolution and emission of circumbinary disks around close classical T Tauri binary systems. High resolution numerical hydrodynamical simulations are employed to model a system consisting of a central eccentric binary star within an irradiated accretion disk. A detailed energy balance including viscous heating, radiative cooling and irradiation from the central star is applied to calculate accurately the emitted spectral energy distribution. Numerical simulations using two different methods, the previously developed Dual-Grid technique with a finite difference discretization, and t…
We present deep, near-infrared images of the circumbinary disk surrounding the pre-main-sequence binary star, GG Tau A, obtained with NICMOS aboard the Hubble Space Telescope. The spatially resolved proto-planetary disk scatters roughly 1.5% of the stellar flux, with a near-to-far side flux ratio of ~1.4, independent of wavelength, and colors that are comparable to the central source; all of these properties are significantly different from the earlier ground-based observations. New Monte Carlo scattering simulations of the disk emphasize that the general properties of the disk, such as disk f…
We explore test particle orbits in the orbital plane of eccentric stellar binary systems, searching for ``invariant loops'': closed curves that change shape periodically as a function of binary orbital phase as the test particles in them move under the stars' gravity. Stable invariant loops play the same role in this periodically-varying potential as stable periodic orbits do in stationary potentials; in particular, when dissipation is weak, gas will most likely follow the non-intersecting loops, while nearby particle orbits librate around them. We use this method to set bounds on the sizes of…
Hierarchical structure formation inevitably leads to the formation of supermassive binary black holes (BBHs) with a sub-parsec separation in galactic nuclei. However, to date there has been no unambiguous detection of such systems. In an effort to search for potential observational signatures of supermassive BBHs, we performed high-resolution smoothed particle hydrodynamics (SPH) simulations of two black holes in a binary of moderate eccentricity surrounded by a circumbinary disk. Building on our previous work, which has shown that gas can periodically transfer from the circumbinary disk to th…
Hubble Space Telescope Advanced Camera for Surveys images of the young binary GG Tauri and its circumbinary disk in V and I bandpasses were obtained in 2002 and are the most detailed of this system to date. The confirm features previously seen in the disk including: a "gap" apparently caused by shadowing from circumstellar material; an asymmetrical distribution of light about the line of sight on the near edge of the disk; enhanced brightness along the near edge of the disk due to forward scattering; and a compact reflection nebula near the secondary star. New features are seen in the ACS imag…
We have obtained new near-infrared images of both GG Tau and UY Aur circumbinary disks with the polarimetric modes of NICMOS aboard the Hubble Space Telescope. The 1 micron intensity map of GG Tau reveals a more complete elliptical shape than in previous ground-based images. Its eastern and western sides are definitely asymmetric. Our image strongly supports the ring geometry proposed by Guilloteau, Dutrey & Simon (1999) on the basis of their millimetre interferometry images: a geometrically thick and sharply edged ring surrounding an empty gap around the binary. Around UY Aur, we identify str…
We report the discovery of a circumbinary disk around the Herbig Ae/Be system v892 Tau. Our detailed mid-infrared images were made using segment-tilting interferometry on the Keck-1 Telescope and reveal an asymmetric disk inclined at ~60 degs with an inner hole diameter of 250 mas (35 AU), approximately 5X larger than the apparent separation of the binary components. In addition, we report a new measurement along the binary orbit using near-infrared Keck aperture masking, allowing a crude estimate of orbital parameters and the system mass for the first time. The size of the inner hole appears …
We propose that the large, radius of ~1000 AU, circumbinary rotating disks observed around some post-asymptotic giant branch (post-AGB) binary stars are formed from slow AGB wind material that is pushed back to the center of the nebula by wide jets. We perform 2D-axisymmetrical numerical simulations of fast and wide jets that interact with the previously ejected slow AGB wind. In each system there are two oppositely launched jets, but we use the symmetry of the problem and simulate only one jet. A large circularization-flow (vortex) is formed to the side of the jet which together with the ther…
Close pre-main-sequence binary stars are expected to clear central holes in their protoplanetary disks, but the extent to which material can flow from the circumbinary disk across the gap onto the individual circumstellar disks has been unclear. In binaries with eccentric orbits, periodic perturbation of the outer disk is predicted to induce mass flow across the gap, resulting in accretion that varies with the binary period. This accretion may manifest itself observationally as periodic changes in luminosity. Here we present a search for such periodic accretion in the pre-main-sequence spectro…
The population of non magnetic cataclysmic variables evolving under the influence of a circumbinary disk is investigated for systems above the upper edge of the period gap at orbital periods greater than 2.75hr. For a fractional mass input rate into the disk, corresponding to 3e-4 of the mass transfer rate, the model systems exhibit a bounce at orbital periods greater than 2.75hr. The simulations reveal that (1) some systems can exist as dwarf nova type systems throughout their lifetime, (2) dwarf nova type systems can evolve into nova-like systems as their mass transfer rate increases with in…
We have analysed the EUVE spectrum of the DAO white dwarf RE J0720-318. In contrast to the optical spectrum, which can only be fitted with a homogeneously mixed atmosphere, we find the EUVE spectrum can only be matched with a stratified structure. The H layer mass of 3x10**-14 solar masses is a factor ~10 below upper limits from previous EUVE observations of white dwarfs. In addition we detect an unprecedented HeI/HI ratio of ~1 for the absorbing column along the line of sight, implying an H ionisation fraction >90% if all this material resides in the local ISM. We suggest that, since this is …
We study the accretion flows from the circumbinary disks onto the supermassive binary black holes in a subparsec scale of the galactic center, using a smoothed particles hydrodynamics (SPH) code. Simulation models are presented in four cases of a circular binary with equal and unequal masses, and of an eccentric binary with equal and unequal masses. We find that the circumblack-hole disks are formed around each black holes regardless of simulation parameters. There are two-step mechanisms to cause an accretion flow from the circumbinary disk onto supermassive binary black holes: First, the tid…
We present the first visible wavelength images of the GG Tauri circumbinary ring, obtained with the Hubble Space Telescope's Wide Field and Planetary Camera 2. Scattered light from the ring is detected in both V and I band images. The images show that the ring is smooth, except for a small gap that could be a shadow caused by material between the stars and the ring. The spokes seen extending from the stars to the ring in ground-based adaptive optics images are not seen in our data, which suggests that they may be image artifacts. The nearside/farside surface brightness ratio is 6.9 in I band, …
We present a two-dimensional grid-based hydrodynamic simulation of a thin, viscous, locally-isothermal corotating disk orbiting an equal-mass Newtonian binary point mass on a fixed circular orbit. We study the structure of the disk after multiple viscous times. The binary maintains a central hole in the viscously-relaxed disk with radius equal to about twice the binary semimajor axis. Disk surface density within the hole is reduced by orders of magnitude relative to the density in the disk bulk. The inner truncation of the disk resembles the clearing of a gap in a protoplanetary disk. An initi…
The population synthesis of cataclysmic variables below the period is investigated. A grid of detailed binary evolutionary sequences has been calculated and included in the simulations to take account of additional angular momentum losses beyond that associated with gravitational radiation and mass loss, due to nova outbursts, from the system. As a specific example, we consider the effect of a circumbinary disk to gain insight into the ingredients necessary to reproduce the observed orbital period distribution. The resulting distributions show that the period minimum lies at about 80 minutes w…
We present sub-arcsecond thermal infrared imaging of HD 98800, a young quadruple system composed of a pair of low-mass spectroscopic binaries separated by 0.8'' (38 AU), each with a K-dwarf primary. Images at wavelengths ranging from 5 to 24.5 microns show unequivocally that the optically fainter binary, HD 98800B, is the sole source of a comparatively large infrared excess upon which a silicate emission feature is superposed. The excess is detected only at wavelengths of 7.9 microns and longer, peaks at 25 microns, and has a best-fit black-body temperature of 150 K, indicating that most of th…
