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The nearby V4046 Sgr spectroscopic binary hosts a gas-rich disc known for its wide cavity and dusty ring. We present high resolution ($\sim$20 mas or 1.4 au) ALMA observations of the 1.3mm continuum of V4046 Sgr which, combined with SPHERE--IRDIS polarised images and a well-sampled spectral energy distribution (SED), allow us to propose a physical model using radiative transfer (RT) predictions. The ALMA data reveal a thin ring at a radius of 13.15$\pm$0.42 au (Ring13), with a radial width of 2.46$\pm$0.56 au. Ring13 is surrounded by a $\sim$10 au-wide gap, and it is flanked by a mm-bright outer ring (Ring24) with a sharp inner edge at 24 au. Between 25 and $\sim$35 au the brightness of Ring24 is relatively flat and then breaks into a steep tail that reaches out to $\sim$60 au. In addition, central emission is detected close to the star which we interpret as a tight circumbinary ring made of dust grains with a lower size limit of 0.8 mm at 1.1 au. In order to reproduce the SED, the model also requires an inner ring at $\sim$5 au (Ring5) composed mainly of small dust grains, hiding under the IRDIS coronagraph, and surrounding the inner circumbinary disc. The surprisingly thin Ring13 is nonetheless roughly 10 times wider than its expected vertical extent. The strong near-far disc asymmetry at 1.65 $\mu$m points at a very forward-scattering phase function and requires grain radii of no less than 0.4 $\mu$m., Comment: 11 pages, 7 figures

The motion is investigated of dust/gas particles in the elliptic restricted three-body problem (ER3BP) in which the less massive primary is an oblate spheroid and the more massive a luminous body surrounded by a circumbinary disk. The paper has investigated both analytically and numerically the effects of oblateness and radiation pressure of the primaries respectively together with the gravitational potential from a disk on the triangular equilibrium L4,5 of the system, all in the elliptic framework of the restricted problem of three bodies. The important result obtained therein is a move towards the line joining the primaries in the presence of any /all perturbation(s). A significant shift away from the origin as the radiation pressure factor decreases and oblateness of the smaller primary increase is also observed. It is also seen that, all aforementioned parameters in the region of stability have destabilizing tendencies resulting in a decrease in the size of the region of stability except the gravitational potential from the disc. The binary system Ruchbah in the constellation Cassiopeiae is an excellent model for the problem, using the analytic results obtained, the locations of the triangular points and the critical mass parameter are computed numerically.

B[e] supergiants have unusual circumstellar environments which may include thin, concentric rings displaying atomic line emission. GG Carinae is a B[e] supergiant binary which exhibits such a geometry in its circumbinary environment. We study atomic emission lines arising from GG Carinae's circumbinary disc in FEROS spectra collected between 1998 and 2015. We find that semi-forbidden Fe\,II] and permitted Ca\,II emission are formed in the same thin circumbinary ring previously reported to have forbidden [O\,I] and [Ca\,II] emission. We find that there are two circumbinary rings orbiting with projected velocities of $84.6\pm1.0$\,km\,s$^{-1}$ and $27.3\pm0.6$\,km\,s$^{-1}$. Deprojecting these velocities from the line-of-sight, and using updated binary masses presented by \cite{Porter2021GGPhotometry}, we find that the radii of the circumbinary rings are $2.8^{+0.9}_{-1.1}$\,AU and $27^{+9}_{-10}$\,AU for the inner ring and outer ring respectively. We find evidence of subtle dynamical change in the inner circumbinary ring over the 17 years spanned by the data, manifesting in variability in the ratio of the intensity of the blueshifted peak to the redshifted peak of its emission lines and the central velocity becoming more blueshifted. We perform smoothed-particle hydrodynamic simulations of the system which suggest that these observed changes are consistent with pumping of the eccentricity of a radially thin circumbinary ring by the inner binary. We find a systemic velocity of the GG Carinae system of $-23.2 \pm 0.4$\,km\,s$^{-1}$., Comment: 18 pages. Accepted for publication in MNRAS

Planets are observed to orbit the component star(s) of stellar binary systems on so-called circumprimary or circumsecondary orbits, as well as around the entire binary system on so-called circumbinary orbits. Depending on the orbital parameters of the binary system a planet will be dynamically stable if it orbits within some critical separation of the semimajor axis in the circumprimary case, or beyond some critical separation for the circumbinary case. We present N-body simulations of star-forming regions that contain populations of primordial binaries to determine the fraction of binary systems that can host stable planets at various semimajor axes, and how this fraction of stable systems evolves over time. Dynamical encounters in star-forming regions can alter the orbits of some binary systems, which can induce long-term dynamical instabilities in the planetary system and can even change the size of the habitable zone(s) of the component stars. However, the overall fraction of binaries that can host stable planetary systems is not greatly affected by either the assumed binary population, or the density of the star-forming region. Instead, the critical factor in determining how many stable planetary systems exist in the Galaxy is the stellar binary fraction - the more stars that are born as singles in stellar nurseries, the higher the fraction of stable planetary systems., 13 pages, 7 figures, 2 short appendices, accepted for publication in MNRAS. A video abstract created by Helena Gibbon is available here: https://youtu.be/76kANnTK9-s

Analysis of timing variation of the eclipsing binary RR Dra implies the existence of an additional object with mass of no less than 3.5(±0.2) M⊙. This third object is orbiting around the central eclipsing pair once every 98(±1) yr, making the whole a hierarchical triple system. However, reliable photometric solutions based on light curves from Transiting Exoplanet Survey Satellite and WASP show that contribution of the third-light takes only about 2 per cent of the total luminosity. It could photometrically be attributed to other unrelated star located within the aperture. The tertiary component is thus a massive object but invisible in optical wavelengths. Besides, evidence of misalignment between the barycenter and the centre of light of the system is also found. This strengthen the existence of a hidden black hole candidate in the form of the third body. The potential black hole may play an essential role in extracting angular momentum from the central binary pair, forming the current state. As a good laboratory, RR Dra is an interesting system that can help to study stellar-mass black hole under the circumbinary case.

Symbiotic stars are long-period interacting binaries where the compact objects, most commonly a white dwarf, is embedded in the dense stellar wind of an evolved companion star. UV and soft X-ray emission of the accretion disk and nuclear burning white dwarf plays a major role in shaping the ionisation balance of the surrounding wind material and giving rise to the rich line emission. In this paper, we employ 2D photoionisation calculations based on Cloudy code to study the ionisation state of the circumbinary material in symbiotic systems and to predict their emission line spectra. Our simulations are parameterized via the orbital parameters of the binary and the wind mass-loss rate of the donor star, while the mass accretion rate, temperature and luminosity of the WD are computed self-consistently. We explore the parameter space of symbiotic binaries and compute luminosities of various astrophysicaly important emission lines. The line ratios are compared to the traditional diagnostic diagrams used to distinguish symbiotic binaries from other types of sources and it is shown how the binary system parameters shape these diagrams. In the significant part of the parameter space the wind material is nearly fully ionized, except for the "shadow" behind the donor star, thus the WD emission is typically freely escaping the system, 17 pages and 23 figures (including appendix). Accepted for publication in MNRAS

As a result of various studies, it has been determined that several post-common envelope eclipsing binaries have variations in their orbital periods. These variations are thought to be caused by the existence of additional bodies in the system (hypothetical stars or planets) and/or other physical effects (such as angular momentum loss, magnetic activity) of the binary system. It is also known that the sdB+M eclipsing system NY Vir has shown such variations in the last decade, indicating additional objects and/or other physical effects. In this work, we present 51 new eclipse times for this system, which extend the time span of it is $O-C$ diagram by about three years, obtained between 2015 and 2021 using two different telescopes in Turkey. The data obtained in the last 3 years shows a new trend in the $O-C$ diagram differently from the predictions of the previous studies. Our model is consistent with the new $O-C$ diagram, which is statistically well fitted with the quadratic term and the additional two planets with masses of $M_3=2.74 \: M_\text{Jup}$ and $M_4=5.59 \: M_\text{Jup}$. However, the orbital period variation can also be related to magnetic activity. In order to better understand the mechanism causing the changes in the orbital period, new observation data is needed that will show at least one full cycle of the change in the O-C diagram., Comment: Accepted for publication in MNRAS, 10 pages, 4 figures, 3 tables

We consider a new mechanism for the removal of the angular momentum from an X-ray binary system and the change in its orbital period - the mass loss in the form of a wind from an accretion disc. Both observations and models predict powerful winds from discs in X-ray transients. We have obtained an analytical estimate for the increase in the orbital period of a binary system with a wind from the disc during an outburst, and quantitative estimates are given for the systems XTE J1118+480, A0620-00 and GRS 1124-68. Resulting rate of period grow is of order of the observed rates of secular decrease in the period. We also compare the predicted rate of change in the period of a binary system due to the flow of matter into the disc and outflow from the second Lagrange point with the observations. It is concluded that the above mechanisms cannot explain the observed secular decrease in the period of the three X-ray Novae, and it is necessary to consider a circumbinary disc that drains the binary's angular momentum., 10 pages, 7 figures, 2 tables, accepted for publication in Astronomy Letters

Made available in DSpace on 2022-05-01T05:29:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-07-01 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The Kepler-1647 is a binary system with two Sun-type stars (≈1.22 and ≈0.97 M⊙). It has the most massive circumbinary planet (≈1.52 MJup) with the longest orbital period (≈1107.6 d) detected by the Kepler probe and is located within the habitable zone (HZ) of the system. In this work, we investigated the ability to form and house an Earth-sized planet within its HZ. First, we computed the limits of its HZ and performed numerical stability tests within that region. We found that HZ has three subregions that show stability, one internal, one co-orbital, and external to the host planet Kepler-1647b. Within the limits of these three regions, we performed numerical simulations of planetary formation. In the regions inner and outer to the planet, we used two different density profiles to explore different conditions of formation. In the co-orbital region, we used eight different values of total disc mass. We showed that many resonances are located within regions causing much of the disc material to be ejected before a planet is formed. Thus, the system might have two asteroid belts with Kirkwood gaps, similar to the Solar system's main belt of asteroids. The co-orbital region proved to be extremely sensitive, not allowing the planet formation, but showing that this binary system has the capacity to have Trojan bodies. Finally, we looked for regions of stability for an Earth-sized moon. We found that there is stability for a moon with this mass up to 0.4 Hill's radius from the host planet. Laboratório de Computação Aplicada National Institute for Space Research (INPE) Grupo de Dinâmica Orbital e Planetologia São Paulo State University (UNESP) State University of Mato Grosso Do sul (UEMS) Federal Institute of Education Science and Technology of São Paulo (IFSP) Federal University of São Paulo (UNIFESP) Institute for Science and Technology Grupo de Dinâmica Orbital e Planetologia São Paulo State University (UNESP) CNPq: 305210/2018-1

We present ALMA observations of the $^{12}$CO, $^{13}$CO, C$^{18}$O J=2-1 transitions and the 1.3\,mm continuum emission for the circumbinary disc around HD 142527, at an angular resolution of $\approx$\,0\farcs3. We observe multiple spiral structures in intensity, velocity and velocity dispersion for the $^{12}$CO and $^{13}$CO gas tracers. A newly detected $^{12}$CO spiral originates from the dust horseshoe, and is rotating at super-Keplerian velocity or vertically ascending, whilst the inter-spiral gas is rotating at sub-Keplerian velocities. This new spiral possibly connects to a previously identified spiral, thus spanning > 360$^\circ$. A spatial offset of ~30 au is observed between the $^{12}$CO and $^{13}$CO spirals, to which we hypothesize that the gas layers are propagating at different speeds (``surfing'') due to a non-zero vertical temperature gradient. Leveraging the varying optical depths between the CO isotopologues, we reconstruct temperature and column density maps of the outer disc. Gas surface density peaks at r\,$\approx$\,180\,au, coincident with the peak of continuum emission. Here the dust grains have a Stokes number of $\approx$\,1, confirming radial and azimuthal trapping in the horseshoe. We measure a cavity radius at half-maximum surface density of $\approx$\,100\,au, and a cavity eccentricity between 0.3 and 0.45.

The present paper studies the locations and linear stability of the triangular equilibrium points when both primaries are radiating and considered as heterogeneous spheroid with three layers of different densities. Additionally, we include the effects of small perturbations in the Coriolis and centrifugal forces and potential from a belt (circumbinary disc). It is observed that the positions of the triangular equilibrium points are substantially affected by all parameters (except a perturbation in Coriolis force) involved in the system.The stabilty of motion is found only when $$0 < \mu < \mu_{c}$$ 0 < μ < μ c , where $$\mu_{c}$$ μ c is the critical mass value which depends on the combined effect of radiation pressures and heterogeneity of the primaries, small perturbations and the potential from a belt.It is also seen that the Coriolis force and the belt have stabilizing effect,while the centrifugal force, radiation and heterogeineity of the primaries have destabilizing behaviour.The net effect is that the size of the region of stability decreases when the value of these parameters increases where $$\mu$$ μ is the mass ratio and $$k_{1} ,k_{2}$$ k 1 , k 2 characterize heterogeneity of both primaries. A practical application of this model could be the study of motion of a dust grain near the heterogeneous and luminous binary stars surrounded by a belt.Finally, we carried out and discuss numerical experiments aiming at computing the positions of triangular points and critical masses of three binary systems: Archid, Xi Booties and Kruger 60.

How does the cavity size in circumbinary discs depend on disc and binary properties? We investigate by simulating disc cavities carved by binary companions using smoothed particle hydrodynamics (SPH). We find that a cavity is quickly opened on the dynamical time, while the cavity size is set on the viscous time. In agreement with previous findings, we find long term cavity sizes of 2-5 times the binary semi-major axis, increasing with eccentricity and decreasing with disc aspect ratio. When considering binaries inclined with respect to the disc we find three regimes: i) discs that evolve towards a coplanar orbit have a large cavity, slightly smaller than that of an initially coplanar disc; ii) discs that evolve towards a polar orbit by breaking have a small cavity, equal in size to that of an initially polar disc; iii) discs that evolve towards a polar orbit via warping have an intermediate-sized cavity. We find typical gas depletions inside the cavity of $\gtrsim 2$ orders of magnitude in surface density., Comment: 12 pages, 13 figures, accepted to MNRAS

In this paper, we consider triple systems composed of main-sequence (MS) stars, and their internal evolution due to stellar and binary evolution. Our focus is on triples that produce white dwarfs (WDs), where Roche lobe overflow of an evolving tertiary triggers accretion onto the inner binary via a circumbinary disk (CBD) driving it toward a mass ratio of unity. We present a combination of analytic- and population synthesis-based calculations performed using the \texttt{SeBa} code to constrain the expected frequency of such systems, given a realistic initial population of MS triples, and provide the predicted distributions of orbital periods. We identify the parameter space for triples that can accommodate a CBD, to inform future numerical simulations of suitable initial conditions. We find that $\lesssim$ 10\% of all MS triples should be able to accommodate a CBD around the inner binary, and compute lower limits for the production rates. This scenario broadly predicts mergers of near equal-mass binaries, producing blue stragglers (BSs), Type Ia supernovae, gamma ray bursts and gravitational wave-induced mergers, along with the presence of an outer WD tertiary companion. We compare our predicted distributions to a sample of field BS binaries, and argue that our proposed mechanism explains the observed range of orbital periods. Finally, the mechanism considered here could produce hypervelocity MS stars, WDs and even millisecond pulsars with masses close to the Chandrasekhar mass limit, and be used to constrain the maximum remnant masses at the time of any supernova explosion., Comment: 15 pages, 7 figures; accepted for publication in MNRAS

We study the morpho-kinematics of the circumbinary envelope of Mira Ceti between $\sim$100 and $\sim$350 au from the stars using ALMA observations of the SiO ($\nu$=0, $J$=5-4) and CO ($\nu$=0, $J$=3-2) emissions with the aim of presenting an accurate and reliable picture of what cannot be ignored when modelling the dynamics at stake. A critical study of the uncertainties attached to imaging is presented. The line emissions are shown to be composed of a few separated fragments. They are described in detail and plausible interpretations of their genesis are discussed. Evidence for a focusing effect of the Mira A wind by Mira B over the past century is presented; it accounts for only a small fraction of the overall observed emission but its accumulation over several orbital periods may have produced an enhancement of CO emission in the orbital plane of Mira B. We identify a South-western outflow and give arguments for the anti-correlation observed between CO and SiO emissions being the result of a recent mass ejection accompanied by a shock wave. We discuss the failure of simple scenarios that have been proposed earlier to explain some of the observed features and comment on the apparent lack of continuity between the present observations and those obtained in the close environment of the stars. Evidence is obtained for the presence of large Doppler velocity components near the line of sight aiming to the star, possibly revealing the presence of important turbulence at $\sim$5 to 10 au away from Mira A., Comment: 20 pages, 17 figures, accepted for publication in MNRAS

To date, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo gravitational wave detectors have registered several events due to merging binary black holes. It is considered that black holes are surrounded by the circumbinary accretion disc therefore such events must be followed by perturbation of the disc and an increase in the flux of electromagnetic radiation from these objects. Our recent numerical investigations have shown that the heating of matter caused by a shock wave leads to an increase in luminosity. This shock wave arises in the accretion disc due to the central object mass loss as a result of the radiation of gravitational waves. In this paper, a self-similar solution is considered. In this solution the accretion disc perturbation is described in a region, dominated by gas pressure, and the matter opacity is determined by Thomson electron scattering processes. Such an analytical model allows us to approximately estimate the magnitude of the electromagnetic response of the gravitational wave event without time-consuming numerical calculations.

We study the orbital stability of a non-zero mass, close-in circular orbit planet around an eccentric orbit binary for various initial values of the binary eccentricity, binary mass fraction, planet mass, planet semi--major axis, and planet inclination by means of numerical simulations that cover $5 \times 10^4$ binary orbits. For small binary eccentricity, the stable orbits that extend closest to the binary (most stable orbits) are nearly retrograde and circulating. For high binary eccentricity, the most stable orbits are highly inclined and librate near the so-called generalised polar orbit which is a stationary orbit that is fixed in the frame of the binary orbit. For more extreme mass ratio binaries, there is a greater variation in the size of the stability region (defined by initial orbital radius and inclination) with planet mass and initial inclination, especially for low binary eccentricity. For low binary eccentricity, inclined planet orbits may be unstable even at large orbital radii (separation $> 5 \,a_{\rm b}$). The escape time for an unstable planet is generally shorter around an equal mass binary compared with an unequal mass binary. Our results have implications for circumbinary planet formation and evolution and will be helpful for understanding future circumbinary planet observations., 11 pages, 7 figures

Most stars form in binaries, and both stars may grow by accreting material from a circumbinary disc onto their personal discs. We suspect that in many cases a wide molecular wind will envelope a collimated atomic jet emanating from close to an orbiting young star. This so-called Circumbinary Scenario is explored here in order to find common identifiable properties. The dynamical set up is studied with three dimensional simulations with chemistry and cooling included. We extract the properties on scales of order 100\,AU and compare to the Co-Orbital Scenario in which the wind and jet sources are in orbit. We find that the rapid orbital motion generates a wide ionised sheath around the jet core with a large opening angle at the base. This is independent of the presence of the surrounding molecular outflow. However, the atomic jet is recollimated beyond ~ 55 AU when the molecular outflow restricts the motion of the ambient medium which, in turn, confines the jet. These physical properties are relayed to the optical H-alpha imaging, providing a means of distinguishing between models. The high excitation sheath and recollimation region can be explored on these scales through the next generation of instruments. However, in general, the amount and location of the ionised material, whether in the knots or the sheath, will depend on several parameters including the orbital period, axis alignment and pulse amplitude., 12 pages, 13 figures, submitted to MNRAS

The distribution of the orbital inclination angles of circumbinary planets (CBPs) is an important scientific issue, and it is of great significance for estimating the occurrence rate of CBPs and studying their formation and evolution. Although the CBPs currently discovered by the transit method are nearly coplanar, the true distribution of the inclinations of CBPs is still unknown. Previous research on CBPs has mostly regarded them as isolated binary-planet systems, without considering the birth environment of their host binaries. It is generally believed that almost all stars are born in clusters. Therefore, it is necessary to consider the effects of the close encounters of stars on CBP systems. In this paper, we discuss how the close encounters of fly-by stars affect the inclinations of CBPs. Based on extensive numerical simulations, we have found that CBPs in a close binary with a spacing of ∼0.2 au are almost unaffected by fly-by stars. Their orbits remain coplanar. However, when the spacing of the binary stars is greater than 1 au, two to three fly-bys of an intruding star can excite a considerable inclination, even for a CBP near the unstable boundary of the binary. For CBPs in the outer region, the fly-by of a single star can excite an inclination to more than 5°. In particular, CBPs in near polar or retrograde orbits can naturally form through binary–star encounters. If close binaries are born in open clusters, our simulations suggest that there may be high-inclination CBPs in binaries with a spacing >1 au.

Fast radio bursts (FRBs) are transient intense radio pulses with duration of milliseconds. Although the first FRB was detected more than a decade ago, the progenitors of these energetic events are not yet known. The currently preferred formation channel involves the formation of a neutron star (NS)/magnetar. While these objects are often the end product of the core-collapse (CC) explosion of massive stars, they could also be the outcome of the merging of two massive white dwarfs. In the merger scenario the ejected material interacts with a constant-density circumbinary medium and creates supersonic shocks. We found that when a radio pulse passes through these shocks the dispersion measure (DM) increases with time during the free expansion phase. The rotation measure (RM) displays a similar trend if the power-law index, $n$, of the outer part of the ejecta is $>6$. For $n = 6$ the RM remains constant during this phase. Later, when the ejecta move into the Sedov-Taylor phase while the DM still increases, however, with a different rate, the RM reduces. This behaviour is somewhat similar to that of FRB 121102 for which a marginal increase of DM and a 10% decrease of RM have been observed over time. These features are in contrast to the CC scenario, where the DM and RM contributions to the radio signal always diminish with time., 10 pages, 3 figures, Accepted in MNRAS

Joint statistics of periods and mass ratios of close binaries and its dependence on primary mass can be explained by assuming that seed binary companions are formed by disc fragmentation at random intervals during assemblage of stellar mass and migrate inwards as they accrete from the circumbinary disk. A toy model based on simple prescriptions for the companion growth and migration reproduces such aspects of close solar-mass binaries as the distribution of binary periods P, the brown dwarf desert at short P, the nearly uniform distribution of mass ratios, and a population of equal-mass binaries (twins) that decreases linearly in frequency with logP. For massive stars, the model predicts a large fraction of early mergers, a distribution of logP with a negative slope, and a mass-ratio distribution that is also uniform but with a substantially reduced twin fraction. By treating disc fragmentation as a stochastic process, we also reproduce the observed properties of compact triples. Success of our toy model suggests that most close binaries and compact triples indeed formed by disc fragmentation followed by accretion-driven inward migration., Accepted by MNRAS; 15 pages, 11 figures

We study the evolution of accretion disk around a supermassive binary black hole with equal mass using non-relativistic hydrodynamical simulations performed with FARGO3D. Compared with previous studies with the Newtonian hydrodynamics, here, we adopt the post-Newtonian hydrodynamics using the near zone metric of the binary black hole. In contrast to the Newtonian investigation, we find that there is a dramatic difference in the post-Newtonian regime, gap formed by the circumbinary accretion disk around the binary with equal mass is wider with the post-Newtonian hydrodynamics than that with the Newtonian hydrodynamics and is independent of disk viscosity given that hydrodynamical simulations are run for about the same factor times the viscous timescale associated with different viscosities. This may present unique observable signatures of the continuum emission in such binary-disk system., 10 pages, 8 figures. Published in MNRAS

All circumbinary planets currently detected are in orbits that are almost coplanar to the binary orbit. While misaligned circumbinary planets are more difficult to detect, observations of polar aligned circumbinary gas and debris disks around eccentric binaries suggest that polar planet formation may be possible. A polar aligned planet has a stable orbit that is inclined by 90 degrees to the orbital plane of the binary with an angular momentum vector that is aligned to the binary eccentricity vector. With n- body simulations we model polar terrestrial planet formation using hydrodynamic gas disk simulations to motivate the initial particle distribution. Terrestrial planet formation around an eccentric binary is more likely in a polar alignment than in a coplanar alignment. Similar planetary systems form in a polar alignment around an eccentric binary and a coplanar alignment around a circular binary. The polar planetary systems are stable even with the effects of general relativity. Planetary orbits around an eccentric binary exhibit tilt and eccentricity oscillations at all inclinations, however, the oscillations are larger in the coplanar case than the polar case. We suggest that polar aligned terrestrial planets will be found in the future., 8 pages, 4 figures, 1 table. Accepted for publication in ApJL. arXiv admin note: text overlap with arXiv:2108.09257

With n-body simulations, we model terrestrial circumbinary planet (CBP) formation with an initial surface density profile motivated by hydrodynamic circumbinary gas disc simulations. The binary plays an important role in shaping the initial distribution of bodies. After the gas disc has dissipated, the torque from the binary speeds up the planet formation process by promoting body-body interactions but also drives the ejection of planet building material from the system at an early time. Fewer but more massive planets form around a close binary compared to a single star system. A sufficiently wide or eccentric binary can prohibit terrestrial planet formation. Eccentric binaries and exterior giant planets exacerbate these effects as they both reduce the radial range of the stable orbits. However, with a large enough stable region, the planets that do form are more massive, more eccentric and more inclined. The giant planets remain on stable orbits in all our simulations suggesting that giant planets are long-lived in planetary systems once they are formed., Accepted for publication in MNRAS, 12 pages, 5 figures

We present the evolution of rotational directions of circumstellar disks in a triple protostar system simulated from a turbulent molecular cloud core with no magnetic field. We find a new formation pathway of a counter-rotating circumstellar disk in such triple systems. The tertiary protostar forms via the circumbinary disk fragmentation and the initial rotational directions of all the three circumstellar disks are almost parallel to that of the orbital motion of the binary system. Their mutual gravito-hydrodynamical interaction for the subsequent $\sim10^4\thinspace\rm{yr}$ greatly disturbs the orbit of the tertiary, and the rotational directions of the tertiary disk and star are reversed due to the spiral-arm accretion of the circumbinary disk. The counter-rotation of the tertiary circumstellar disk continues to the end of the simulation ($\sim6.4\times10^4\thinspace\rm{yr}$ after its formation), implying that the counter-rotating disk is long-lived. This new formation pathway during the disk evolution in Class 0/I Young Stellar Objects possibly explains the counter-rotating disks recently discovered by ALMA., Accepted for publication in PASJ

Kostovet al. (2021) report the discovery of the first transitingcircumbinaryplanet, detected from a single sector of TESS data.ARCES observations played a role in helping to establish the parameters of the system.We briefly present an overview of this interesting planetary system and then discuss the challenges encountered in analyzing ARCES data to derive accurate radial velocities for this project.

A growing number of eclipsing binary systems of the "HW Vir" kind (i. e., composed by a subdwarf-B/O primary star and an M dwarf secondary) show variations in their orbital period, also called Eclipse Time Variations (ETVs). Their physical origin is not yet known with certainty: while some ETVs have been claimed to arise from dynamical perturbations due to the presence of circumbinary planetary companions, other authors suggest that the Applegate effect or other unknown stellar mechanisms could be responsible for them. In this work, we present twenty-eight unpublished high-precision light curves of one of the most controversial of these systems, the prototype HW Virginis. We homogeneously analysed the new eclipse timings together with historical data obtained between 1983 and 2012, demonstrating that the planetary models previously claimed do not fit the new photometric data, besides being dynamically unstable. In an effort to find a new model able to fit all the available data, we developed a new approach based on a global-search genetic algorithm and eventually found two new distinct families of solutions that fit the observed timings very well, yet dynamically unstable at the 10^5-year time scale. This serves as a cautionary tale on the existence of formal solutions that apparently explain ETVs but are not physically meaningful, and on the need of carefully testing their stability. On the other hand, our data confirm the presence of an ETV on HW Vir that known stellar mechanisms are unable to explain, pushing towards further observing and modelling efforts., 14 pages, 7 figures, 7 tables in the main text and 1 table in the appendix. Accepted for publication in MNRAS

The gas dissipation from a protoplanetary disk is one of the key processes affecting planet formation, and it is widely accepted that it happens on timescales of a few million years for disks around single stars. Over the last years, several protoplanetary disks have been discovered in multiple star systems, and despite the complex environment in which they find themselves, some of them seem to be quite old, a situation that may favor planet formation. A clear example of this is the disk around HD 98800 B, a binary in a hierarchical quadruple stellar system, which at a $\sim$10 Myr age seems to still be holding significant amounts of gas. Here we present a 1D+1D model to compute the vertical structure and gas evolution of circumbinary disks in hierarchical triple star systems considering different stellar and disk parameters. We show that tidal torques due to the inner binary together with the truncation of the disk due to the external companion strongly reduce the viscous accretion and expansion of the disk. Even allowing viscous accretion by tidal streams, disks in these kind of environments can survive for more than 10 Myr, depending on their properties, with photoevaporation being the main gas dissipation mechanism. We particularly apply our model to the circumbinary disk around HD 98800 B and confirm that its longevity, along with the current non-existence of a disk around the companion binary HD 98800 A, can be explained with our model and by this mechanism., 20 pages, 9 figures. Accepted for publication in ApJ

We present high resolution millimeter continuum and CO line observations for the circumbinary disk around V892 Tau to constrain the stellar and disk properties. The total mass of the two near-equal-mass A stars is estimated to be $6.0\pm0.2\,M_{\odot}$ based on our models of the Keplerian-dominated gas disk rotation. The detection of strong ionized gas emission associated with the two stars at 8 mm, when combined with previous astrometric measurements in the near-infrared, provides an updated view of the binary orbit with $a=7.1\pm0.1$ au, $e=0.27\pm0.1$, and $P=7.7\pm0.2$ yr, which is about half of a previously reported orbital period. The binary orbital plane is proposed to be near coplanar to the circumbinary disk plane (with a mutual inclination of only $\Delta=8\pm4.2$ deg; another solution with $\Delta=113$ deg is less likely given the short re-alignment timescale). An asymmetric dust disk ring peaking at a radius of 0.''2 is detected at 1.3 mm and its fainter counterparts are also detected at the longer 8 and 9.8 mm. The CO gas disk, though dominated by Keplerian rotation, presents a mild inner and outer disk misalignment, such that the inner disk to the SW and outer disk to the NE appear brighter than their counterparts at the opposite disk sides. The radial extension of the disk, its asymmetric dust ring, and the presence of a disk warp could all be explained by the interaction between the eccentric binary and the circumbinary disk, which we assume were formed with non-zero mutual inclination. Some tentatively detected gas spirals in the outer disk are likely produced by interactions with the low mass tertiary component located 4'' to the northeast. Our analyses demonstrate the promising usage of V892 Tau as an excellent benchmark system to study the details of binary--disk interactions., Comment: Accepted for publication in ApJ

In the paper a scenario of an electromagnetic response formation from the merging of two black holes is considered. In this scenario it’s assumed that the binary black hole is surrounded by an accretion disk. As a result of the black holes merging and mass loss, the accretion disk experiences a disturbance, which is accompanied by shock waves propagation of sufficiently high intensity. Heating of matter by shock waves leads to a sharp increase in the flux of electromagnetic radiation from the disk. The paper includes a calculated light curve, radiation spectrum, and the estimation of characteristic duration of the flare. This method can be used to discover of electromagnetic responses from gravitational-wave events, which registered by the LIGO (Laser Interferometer Gravitational-Wave Observatory) and the Virgo detectors. Supporting the registration of gravitational-wave events by observations in the electromagnetic channel has far-reaching prospects, since it corresponds to the multi-messenger approach to the study of astrophysical objects.

The radii of the inner and outer boundaries of the circumbinary habitable zone (CBHZ) and the radii of the circumbinary chaotic zone (CBCZ) have been calculated for close binary stars in the solar neighborhood with sufficient catalogue data. A subclass of binaries for which the CBCZ boundary is within the CBHZ boundaries (the CBCZ radius is larger than the inner CBHZ radius, but smaller than the outer CBHZ radius) has been identified for the first time: M4-V69, HATS551-027, EZ Aqr A–C, 38 Cas, HD 2070, HD 15064, HD 28394, HD 160346, and HD 181602. Since, according to present-day theories and observational data, the probability of finding planets at the CBCZ boundary is high, one might expect the presence of potentially habitable circumbinary planets in the planetary systems of the binary stars revealed in this way. For the stars CM Dra, WTS 19c-3-01405, and LP 661-13 the CBCZ radius is smaller than the radius of the inner CBHZ boundary, but planets may be present around them in outer stable orbits resonant with the orbits of planets near the CBCZ boundary. Therefore, all of the binaries of these types revealed for the first time are of considerable interest for future observations.

Recent observations have revealed that protoplanetary discs often exhibit cavities and azimuthal asymmetries such as dust traps and clumps. The presence of a stellar binary system in the inner disc regions has been proposed to explain the formation of these structures. Here, we study the dust and gas dynamics in circumbinary discs around eccentric and inclined binaries. This is done through two-fluid simulations of circumbinary discs, considering different values of the binary eccentricity and inclination. We find that two kinds of dust structures can form in the disc: a single horseshoe-shaped clump, on top of a similar gaseous over-density; or numerous clumps, distributed along the inner disc rim. The latter features form through the complex interplay between the dust particles and the gaseous spirals caused by the binary. All these clumps survive between one and several tens of orbital periods at the feature location. We show that their evolution strongly depends on the gas-dust coupling and the binary parameters. Interestingly, these asymmetric features could in principle be used to infer or constrain the orbital parameters of a stellar companion - potentially unseen - inside the inner disc cavity. Finally, we apply our findings to the disc around AB Aurigae., 12 pages, 13 figures, accepted for publication in MNRAS

We investigate the formation and evolution of misaligned accretion discs around the secondary component of a binary through mass transfer driven by Kozai-Lidov oscillations of the circumprimary disc's eccentricity and inclination. We perform SPH simulations to study the amount of mass transferred to the secondary star as a function of both the disc and binary parameters. For the range of parameters we explore, we find that increasing the disc aspect ratio, viscosity parameter and initial inclination as well as decreasing the binary mass ratio leads to larger amount of mass transfer, up to a maximum of about ten per cent of the initial mass of the primary disc. The circumsecondary disc forms with a high eccentricity and a high inclination and is also able to undergo KL oscillations. The circumsecondary disc oscillations have a shorter period than those in the disc around the primary. We find that some of the material that escapes the Roche-lobe of the two components forms a narrow misaligned circumbinary accretion disc. This study has implications for disc evolution in young binary star systems., Comment: 12 pages, 15 figures

Nearly all young stars are initially surrounded by `protoplanetary' discs of gas and dust, and in the case of single stars at least 30\% of these discs go on to form planets. The process of protoplanetary disc formation can result in initial misalignments, where the disc orbital plane is different to the stellar equator in single star systems, or to the binary orbital plane in systems with two stars. A quirk of the dynamics means that initially misaligned `circumbinary' discs -- those that surround two stars -- are predicted to evolve to one of two possible stable configurations, one where the disc and binary orbital planes are coplanar, and one where they are perpendicular (a `polar' configuration). Prior work has found coplanar circumbinary discs, but no polar examples were known until now. Here we report the first discovery of a protoplanetary circumbinary disc in the polar configuration, supporting the predictions that such discs should exist. The disc shows some characteristics that are similar to discs around single stars, and that are attributed to dust growth. Thus, the first stages of planet formation appear able to proceed in polar circumbinary discs., Comment: Submitted version - do not read. Published in Nature Astronomy, free PDF at https://rdcu.be/bgNSO

We present a 3D hydrodynamics study of gravitational instabilities (GIs) in a 0.14 M$_{\odot}$ circumbinary protoplanetary disc orbiting a 1 M$_{\odot}$ star and a 0.02 M$_{\odot}$ brown dwarf companion. We examine the thermodynamical state of the disc and determine the strengths of GI-induced density waves, nonaxisymmetric density structures, mass inflow and outflow, and gravitational torques. Results are compared with a parallel simulation of a protoplanetary disc without the brown dwarf binary companion. Simulations are performed using CHYMERA, a radiative 3D hydrodynamics code. The onset of GIs in the circumbinary disc is much more violent due to the stimulation of a strong one-armed density wave by the brown dwarf. Despite this early difference, detailed analyses show that both discs relax to a very similar quasi-steady phase by 2,500 years after the beginning of the simulations. Similarities include the thermodynamics of the quasi-steady phase, the final surface density distribution, radial mass influx, and nonaxisymmetric power and torques for spiral arm multiplicities of two or more. Effects of binarity in the disc are evident in gravitational torque profiles, temperature profiles in the inner discs, and radial mass transport. After 3,800 years, the semimajor axis of the binary decreases by about one percentage and the eccentricity roughly doubles. The mass transport in the outer circumbinary disc associated with the one-armed wave may influence planet formation.

A circumbinary disc around a pair of merging stellar-mass black holes may be shocked and heated during the recoil of the merged hole, causing a near-simultaneous electromagnetic counterpart to the gravitational wave event. The shocks occur around the recoil radius, where the disc orbital velocity is equal to the recoil velocity. The amount of mass present near this radius at the time of the merger is critical in determining how much radiation is released. We explore the evolution of a circumbinary disc in two limits. First, we consider an accretion disc that feels no torque from the binary. The disc does not survive until the merger unless there is a dead zone, a region of low turbulence. Even with the dead zone, the surface density in this case may be small. Second, we consider a disc that feels a strong binary torque that prevents accretion on to the binary. In this case there is significantly more mass in regions of interest at the time of the merger. A dead zone in this disc increases the mass close to the recoil radius. For typical binary-disc parameters we expect accretion to be significantly slowed by the resonant torque from the binary, and for a dead zone to be present. We conclude that provided significant mass orbits the binary after the formation of the black hole binary and that the radiation produced in recoil shocks can escape the flow efficiently, there is likely to be an observable electromagnetic signal from black hole binary mergers., Comment: Accepted for publication in MNRAS

Periodic quasars have been suggested to host supermassive binary black holes (BBHs) in their centers, and their optical/UV periodicities are interpreted as caused by either the Doppler-boosting (DB) effect of continuum emission from the disk around the secondary black hole (BH) or intrinsic accretion rate variation. However, no other definitive evidence has been found to confirm such a BBH interpretation(s). In this paper, we investigate the responses of broad emission lines (BELs) to the continuum variations for these quasars under two BBH scenarios, and check whether they can be distinguished from each other and from that of a single BH system. We assume a simple circumbinary broad-line region (BLR) model, compatible with BLR size estimates, with a standard $\Gamma$ distribution of BLR clouds. We find that BELs may change significantly and periodically under the BBH scenarios due to (1) the position variation of the secondary BH and (2) the DB effect, if significant, and/or intrinsic variation, which is significantly different from the case of a single BH system. For the two BBH scenarios, the responses of BELs to (apparent) continuum variations, caused by the DB effect or intrinsic rate variation, are also significantly different from each other, mainly because the DB effect has a preferred direction along the direction of motion of the secondary BH, while that due to intrinsic variation does not. Such differences in the responses of BELs from different scenarios may offer a robust way to distinguish different interpretations of periodic quasars and to identify BBHs, if any, in these systems., Comment: 16 pages, 13 figures, accepted for publication in ApJ

Misalignments within protoplanetary discs are now commonly observed, and features such as shadows in scattered light images indicate departure from a co-planar geometry. VLT/SPHERE observations of the disc around HD 143006 show a large-scale asymmetry, and two narrow dark lanes which are indicative of shadowing. ALMA observations also reveal the presence of rings and gaps in the disc, along with a bright arc at large radii. We present new hydrodynamic simulations of HD 143006, and show that a configuration with both a strongly inclined binary and an outer planetary companion is the most plausible to explain the observed morphological features. We compute synthetic observations from our simulations, and successfully reproduce both the narrow shadows and the brightness asymmetry seen in IR scattered light. Additionally, we reproduce the large dust observed in the mm continuum, due to a 10 Jupiter mass planet detected in the CO kinematics. Our simulations also show the formation of a circumplanetary disc, which is misaligned with respect to the outer disc. The narrow shadows cast by the inner disc and the planet-induced "kink" in the disc kinematics are both expected to move on a time-scale of $\sim$ 5-10 years, presenting a potentially observable test of our model. If confirmed, HD 143006 would be the first known example of a circumbinary planet on a strongly misaligned orbit., Accepted for publication in MNRAS, 10 pages, 8 figures. Movies of the simulation available at the following links: https://www.youtube.com/watch?v=F8GAw-Fzpyg&list=PLgaPAkHEP_RqxHJUvj9DIcsjEpWqbTPwQ&index=3 and https://www.youtube.com/watch?v=HCZQdS3t4l8&list=PLgaPAkHEP_RqxHJUvj9DIcsjEpWqbTPwQ&index=1

Vortices are one of the most promising mechanisms to locally concentrate millimeter dust grains and allow the formation of planetesimals through gravitational collapse. The outer disk around the binary system HD 142527 is known for its large horseshoe structure with azimuthal contrasts of 3-5 in the gas surface density and of about 50 in the dust. Using 13CO and C18O J = 3-2 transition lines, we detect kinematic deviations to the Keplerian rotation, which are consistent with the presence of a large vortex around the dust crescent, as well as a few spirals in the outer regions of the disk. Comparisons with a vortex model suggest velocity deviations up to 350 m/s after deprojection compared to the background Keplerian rotation, as well as an extension of about 40 au radially on both sides of the vortex and 200 degrees azimuthally, yielding an azimuthal-to-radial aspect ratio of 5. Another alternative for explaining the vortex-like signal implies artificial velocity deviations generated by beam smearing in association with variations of the gas velocity due to gas pressure gradients at the inner and outer edges of the circumbinary disk. The two scenarios are currently difficult to differentiate and, for this purpose, would probably require the use of multiple lines at a higher spatial resolution. The beam smearing effect, due to the finite spatial resolution of the observations and gradients in the line emission, should be common in observations of protoplanetary disks and may lead to misinterpretations of the gas velocity, in particular around ring-like structures., 15 pages, 10 figures

Recent observations have shown that circumbinary discs can be misaligned with respect to the binary orbital plane.The lack of spherical symmetry, together with the non-planar geometry of these systems, causes differential precession which might induce the propagation of warps. While gas dynamics in such environments is well understood, little is known about dusty discs. In this work, we analytically study the problem of dust traps formation in misaligned circumbinary discs. We find that pile-ups may be induced not by pressure maxima, as the usual dust traps, but by a difference in precession rates between the gas and dust. Indeed, this difference makes the radial drift inefficient in two locations, leading to the formation of two dust rings whose position depends on the system parameters. This phenomenon is likely to occur to marginally coupled dust particles $(\text{St}\gtrsim1)$ as both the effect of gravitational and drag force are considerable. We then perform a suite of three-dimensional SPH numerical simulations to compare the results with our theoretical predictions. We explore the parameter space, varying stellar mass ratio, disc thickness, radial extension, and we find a general agreement with the analytical expectations. Such dust pile-up prevents radial drift, fosters dust growth and may thus promote the planet formation in circumbinary discs., Accepted for publication in MNRAS, 12 pages, 12 figures, 2 tables, 2 appendices

Recent claimed detections of tidal disruption events (TDEs) in multi-wavelength data have opened potential new windows into the evolution and properties of otherwise dormant supermassive black holes (SMBHs) in the centres of galaxies. At present, there are several dozen TDE candidates, which share some properties and differ in others. The range in properties is broad enough to overlap other transient types, such as active galactic nuclei (AGN) and supernovae (SNe), which can make TDE classification ambiguous. A further complication is that "TDE signatures" have not been uniformly observed to similar sensitivities or even targeted across all candidates. This chapter reviews those events that are unusual relative to other TDEs, including the possibility of TDEs in pre-existing AGN, and summarises those characteristics thought to best distinguish TDEs from continuously accreting AGN, strongly flaring AGN, SNe, and Gamma-Ray Bursts (GRBs), as well as other potential impostors like stellar collisions, "micro-TDEs," and circumbinary accretion flows. We conclude that multiple observables should be used to classify any one event as a TDE. We also consider the TDE candidate population as a whole, which, for certain host galaxy or SMBH characteristics, is distinguishable statistically from non-TDEs, suggesting that at least some TDE candidates do in fact arise from SMBH-disrupted stars., 57 pages, 17 figures. Accepted for publication in Springer Space Science Reviews. Chapter in ISSI review "The Tidal Disruption of Stars by Massive Black Holes" vol. 79. Corrected several typos from previous submission

Determining habitable zones in binary star systems can be a challenging task due to the combination of perturbed planetary orbits and varying stellar irradiation conditions. The concept of "dynamically informed habitable zones" allows us, nevertheless, to make predictions on where to look for habitable worlds in such complex environments. Dynamically informed habitable zones have been used in the past to investigate the habitability of circumstellar planets in binary systems and Earth-like analogs in systems with giant planets. Here, we extend the concept to potentially habitable worlds on circumbinary orbits. We show that habitable zone borders can be found analytically even when another giant planet is present in the system. By applying this methodology to Kepler-16, Kepler-34, Kepler-35, Kepler-38, Kepler-64, Kepler-413, Kepler-453, Kepler-1647 and Kepler-1661 we demonstrate that the presence of the known giant planets in the majority of those systems does not preclude the existence of potentially habitable worlds. Among the investigated systems Kepler-35, Kepler-38 and Kepler-64 currently seem to offer the most benign environment. In contrast, Kepler-16 and Kepler-1647 are unlikely to host habitable worlds., Accepted for publication in Frontiers in Astronomy and Space Sciences

This paper examines the effects of radiation pressure and triaxiality of two stars (primaries) surrounded by a belt (circumbinary disc) on the positions and stability of a third body of an infinitesimal mass in the neighbourhood of collinear libration points in the framework of elliptic restricted three body problem (ER3BP).We have found the solutions to the location of collinear points Li (i = 1,2,3).We have investigated these collinear points numerically and graphically using radiating binary system (FL virginis and Procyon).The positions and stability of these points are found to be affected by triaxiality, radiation and the gravitational potential from the belt. The collinear libration points are found to be unstable., ER3BP; Triaxiality; Radiation; Circumbinary disc; Stability; Collinear points.

Context. HW Vir is a short-period binary that presents eclipse timing variations. Circumbinary planets have been proposed as a possible explanation, although the properties of the planets differ in each new study. Aims. Our aim is to perform robust model selection methods for eclipse timing variations (ETV) and error calculation techniques based on a frequentist approach for the case of the HW Vir system. Methods. We initially performed simultaneous light and radial velocity curve analysis to derive the masses of the binary. We then analyzed the eclipse timing variation of the system by fitting multiple models. To select the best model, we searched the confidence levels for the best model by creating an χ2 surface grid and bootstrap methods for each pair of parameters. We searched for stable orbital configurations for our adopted ETV model. Results. The masses of the binary are found as 0.413 ± 0.008 M⊙ and 0.128 ± 0.004 M⊙. Under the assumption of two light time effects superimposed on a secular change, the minimum masses of the circumbinary objects are calculated as 25.0−2.2+3.5 MJup and 13.9−0.45+0.60 MJup. The projected semi-major axes are found to be 7.8−1.0+1.4 and 4.56−0.22+0.27 au in respective order. We find that this configuration is unstable within a 3σ range on the semi-major axis and eccentricity of the outer circumbinary object.

Modern observations of protoplanetary discs are revealing a multitude of substructures in these systems, such as spiral arms, cavities, gaps, rings, and large scale asymmetries, in both the gas and dust distribution. It has long been thought that such substructures can arise due companion-disc interactions. However, confirming the existence of these companions by direct methods remains challenging. Therefore, a common method of studying the properties of these companions is through a combination of hydrodynamical simulations and radiative transfer modelling. One particular class of protoplanetary discs, known as transitional discs, are a particularly promising site for testing planet formation and planet-disc interaction theories. These discs exhibit large, cleared out cavities, which are proposed to arise due to dynamical clearing by planetary mass companions. As their name suggests, they are thought to be a transitional phase between gas rich protoplanetary discs, and gas depleted debris discs. In this thesis, I study the nature of the companions in transitional discs through the use of hydrodynamical simulations and radiative transfer modelling. I match multi-wavelength observations of these systems, ranging from near infrared scattered light to centimetre thermal emission. My work challenges some of the prominent interpretations of the structures arising in transitional discs. I show that stellar mass companions may present a more compelling explanation for the structures inside some transitional discs, such as IRS 48 and AB Aurigae. I argue that these are in fact circumbinary discs, discs which orbit around two stars, rather than transitional discs.I also show that planetary mass companions on eccentric orbits inside of the cavity of transition discs may be giving rise to the spectacular spiral arm morphology seen in the transitional disc MWC 758. This is in strong contrast to the current favoured hypothesis for the origin of these spiral arms, where the companion is external to the spiral arms.The results of my thesis imply that the population of companions in transitional discs is more eclectic than previously thought. I postulate that many of the well studied transitional discs of the last decade or so are in fact circumbinary discs. This implies that as a class, transitional discs are composed of distinct two populations; circumbinary discs, and planet hosting transitional discs. The kinematics of the disc are an important diagnostic for differentiating between these two sub-populations.

Supermassive black hole binaries are likely to accrete interstellar gas through a circumbinary disk. Shortly before merger, the inner portions of this circumbinary disk are subject to general relativistic effects. To study this regime, we approximate the spacetime metric of close orbiting black holes by superimposing two boosted Kerr-Schild terms. After demonstrating the quality of this approximation, we carry out very long-term general relativistic magnetohydrodynamic simulations of the circumbinary disk. We consider black holes with spin dimensionless parameters of magnitude 0.9, in one simulation parallel to the orbital angular momentum of the binary, but in another anti-parallel. These are contrasted with spinless simulations. We find that, for a fixed surface mass density in the inner circumbinary disk, aligned spins of this magnitude approximately reduce the mass accretion rate by 14% and counter-aligned spins increase it by 45%, leaving many other disk properties unchanged., 23 pages, 15 figures, Submitted to ApJ