Circumbinary Structure Research Articles

Early Planet Formation in Embedded Disks (eDisk). XIII. Aligned Disks with Nonsettled Dust around the Newly Resolved Class 0 Protobinary R CrA IRAS 32

Young protostellar binary systems, with expected ages less than ∼105 yr, are little modified since birth, providing key clues to binary formation and evolution. We present a first look at the young, Class 0 binary protostellar system R CrA IRAS 32 from the Early Planet Formation in Embedded Disks ALMA large program, which observed the system in the 1.3 mm continuum emission, 12CO (2−1), 13CO (2−1), C18O (2−1), SO (65−54), and nine other molecular lines that trace disks, envelopes, shocks, and outflows. With a continuum resolution of ∼0.″03 (∼5 au, at a distance of 150 pc), we characterize the newly discovered binary system with a separation of 207 au, their circumstellar disks, and a circumbinary disklike structure. The circumstellar disk radii are 26.9 ± 0.3 and 22.8 ± 0.3 au for sources A and B, respectively, and their circumstellar disk dust masses are estimated as 22.5 ± 1.1 M ⊕ and 12.4 ± 0.6 M ⊕, respectively. The circumstellar disks and the circumbinary structure have well-aligned position angles and inclinations, indicating formation in a smooth, ordered process such as disk fragmentation. In addition, the circumstellar disks have a near/far-side asymmetry in the continuum emission, suggesting that the dust has yet to settle into a thin layer near the midplane. Spectral analysis of CO isotopologues reveals outflows that originate from both of the sources and possibly from the circumbinary disklike structure. Furthermore, we detect Keplerian rotation in the 13CO isotopologues toward both circumstellar disks and likely Keplerian rotation in the circumbinary structure; the latter suggests that it is probably a circumbinary disk.

Collapse of turbulent massive cores with ambipolar diffusion and hybrid radiative transfer

Context.Massive stars form in magnetized and turbulent environments and are often located in stellar clusters. The accretion and outflows mechanisms associated with forming massive stars and the origin of the stellar multiplicity of their system are poorly understood.Aims.We study the effect of magnetic fields and turbulence on the accretion mechanism of massive protostars and their multiplicity. We also focus on disk formation as a prerequisite for outflow launching.Methods.We present a series of four radiation-magnetohydrodynamical simulations of the collapse of a massive magnetized, turbulent core of 100M⊙with the adaptive-mesh-refinement code RAMSES, including a hybrid radiative transfer method for stellar irradiation and ambipolar diffusion. We varied the Mach and Alfvénic Mach numbers to probe sub- and super-Alfvénic turbulence and sub- and supersonic turbulence regimes.Results.Sub-Alfvénic turbulence leads to single stellar systems, and super-Alfvénic turbulence leads to binary formation from disk fragmentation following the collision of spiral arms, with mass ratios of 1.1–1.6 and a separation of several hundred AU that increases with initial turbulent support and with time. In these runs, infalling gas reaches the individual disks through a transient circumbinary structure. Magnetically regulated, thermally dominated (plasma betaβ> 1) Keplerian disks form in all runs, with sizes 100–200 AU and masses 1–8M⊙. The disks around primary and secondary sink particles have similar properties. We obtain mass accretion rates of ~10−4M⊙yr−1onto the protostars and observe higher accretion rates onto the secondary stars than onto their primary star companion. The primary disk orientation is found to be set by the initial angular momentum carried by turbulence rather than by magnetic fields. Even without turbulence, axisymmetry and north–south symmetry with respect to the disk plane are broken by the interchange instability and thermally dominated streamers, respectively.Conclusions.Small (≲300 AU) massive protostellar disks such as those that are frequently observed today can so far only be reproduced in the presence of (moderate) magnetic fields with ambipolar diffusion, even in a turbulent medium. The interplay between magnetic fields and turbulence sets the multiplicity of stellar clusters. A plasma betaβ> 1 is a good indicator for distinguishing streamers and individual disks from their surroundings.

Formation of magnetized spatial structures in the Beta Lyrae system. III. Reflection of magnetically controlled matter in circumbinary structures in helium lines, in particular arising from metastable levels

Spatial gaseous structures in the Beta Lyrae system have been studied with the fact of change in the longitudinal component of the donor's magnetic field during the orbital period in mind. The investigation was based primarily on the study of the dynamics of the circumstellar structures surrounding the binary system as a whole. The special emphasis was placed on the study of complex helium lines, in particular those arising from metastable levels. A number of different observable facts from the ultraviolet to the red spectral region were analyzed. The configuration of the donor magnetic field is a factor that not only enhances mass transfer and influences the formation of spatial gas structures between stellar components but, to some extent, also affects the outflow of matter and the formation of external gas structures around this interacting binary system. Together with previous articles \citep{Skulskyy2020a, Skulskyy2020b}, the pieces of evidence of this work, confirming the reflection of magnetically controlled matter in circumbinary structures, define the basis for a coherent picture of the mass exchange between components and outflows of matter outwards

Selected aspects of the analysis of molecular line observations of edge-on circumbinary disks

Context. Inner cavities, accretion arms, and density waves are characteristic structures in the density distribution of circumbinary disks. They are the result of the tidal interaction of the non-axisymmetric gravitational forces of the central binary with the surrounding disk and are most prominent in the inner region, where the asymmetry is most pronounced. Aims. The goal of this study is to test the feasibility of reconstructing the gas density distribution and quantifying properties of structures in the inner regions of edge-on circumbinary disks using multiple molecular line observations. Methods. The density distribution in circumbinary disks is calculated with 2D hydrodynamic simulations. Subsequently, molecular line emission maps are generated with 3D radiative transfer simulations. Based on these, we investigate the observability of characteristic circumbinary structures located in the innermost region for spatially resolved and unresolved disks. Results. We find that it is possible to reconstruct the inner cavity, accretion arms, and density waves from spatially resolved multi-wavelength molecular line observations of circumbinary disks seen edge-on. For the spatially unresolved observations only, an estimate can be derived for the density gradient in the transition area between the cavity and the disk’s inner rim.

Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks

Abstract We report results of -resolution observations toward the O-type proto-binary system IRAS 16547–4247 with the Atacama Large Millimeter/submillimeter Array. We present dynamical and chemical structures of the circumbinary disk, circumstellar disks, outflows, and jets, illustrated by multi-wavelength continuum and various molecular lines. In particular, we detect sodium chloride, silicon compounds, and vibrationally excited water lines as probes of the individual protostellar disks at a scale of 100 au. These are complementary to typical hot-core molecules tracing the circumbinary structures on a 1000 au scale. The H2O line tracing inner disks has an upper-state energy of , indicating a high temperature of the disks. On the other hand, despite the detected transitions of NaCl, SiO, and SiS not necessarily having high upper-state energies, they are enhanced only in the vicinity of the protostars. We posit that these molecules are the products of dust destruction, which only happens in the inner disks. This is the second detection of alkali metal halide in protostellar systems after the case of the disk of Orion Source I, and also one of few massive protostellar disks associated with high-energy transition water and silicon compounds. These new results suggest that these “hot-disk” lines may be common in innermost disks around massive protostars, and have great potential for future research of massive star formation. We also tentatively find that the twin disks are counter-rotating, which might give a hint of the origin of the massive proto-binary system IRAS 16547–4247.

Super-Keplerian equatorial outflows in SS 433

Context. The microquasar SS 433 is the only known steady supercritical accretor in the Galaxy. It is well-known for its relativistic baryonic jets, but the system also drives equatorial outflows. These have been routinely detected in radio images, and components associated with a circumbinary disk have also been suggested in optical emission lines.Aims. We aim to spatially resolve the regions producing the stationary emission lines of SS 433 to shed light on its circumbinary structure and outflows. With an estimated binary orbit size of ≲0.1 mas, this requires optical interferometry.Methods. We use the optical interferometer VLTI+GRAVITY to spatially resolve SS 433 in the near-infraredKband at high spectral resolution (R ≈ 4000) on three nights in July 2017. This is the second such observation, after the first one in July 2016.Results. The stationary Brγline in the 2017 observation is clearly dominated by an extended ∼1 mas ∼ 5 AU circumbinary structure perpendicular to the jets with a strong rotation component. The rotation direction is retrograde relative to the jet precession, in accordance with the slaved disk precession model. The structure has a very high specific angular momentum and is too extended to be a stable circumbinary disk in Keplerian rotation; interpreting it as such leads to a very high enclosed massM ≳ 400 M⊙. We instead interpret it as the centrifugal ejection of the circumbinary disk, with the implication that there must be an efficient transfer of specific angular momentum from the binary to the disk. We suggest that the equatorial outflows sometimes seen in radio images result from similar episodes of circumbinary disk centrifugal ejection. In addition to the equatorial structure, we find a very extended ∼6 mas ∼ 30 AU spherical wind component to the Brγline: the entire binary is engulfed in an optically thin spherical line emission envelope.

Accretion of clumpy cold gas on to massive black hole binaries: the challenging formation of extended circumbinary structures

Massive black hole binaries (MBHBs) represent an unavoidable outcome of hierarchical galaxy formation, but their dynamical evolution at sub-parsec scales is poorly understood, due to a combination of uncertainties in theoretical models and lack of firm observational evidence. In gas rich environments, it has been shown that a putative extended, steady circumbinary gaseous disc plays an important role in the MBHB evolution, facilitating its coalescence. How gas on galactic scales is transported to the nuclear region to form and maintain such a stable structure is, however, unclear. If, following a galaxy merger, turbulent gas is condenses in cold clumps and filaments that are randomly scattered, gas is naturally transported on parsec scales and interacts with the MBHB in discrete incoherent pockets. The aim of this work is to investigate the gaseous structures arising from this interaction. We employ a suite of smoothed-particle-hydrodynamic simulations to study the formation and evolution of gaseous structures around a MBHB constantly perturbed by the incoherent infall of molecular clouds. We investigate the influence of the infall rate and angular momentum distribution of the clouds on the geometry and stability of the arising structures. We find that the continuous supply of incoherent clouds is a double-edge sword, resulting in the intermittent formation and disruption of circumbinary structures. Anisotropic cloud distributions featuring an excess of co-rotating events generate more prominent co-rotating circumbinary discs. Similar structures are seen when mostly counter-rotating clouds are fed to the binary, even though they are more compact and less stable. In general, our simulations do not show the formation of extended smooth and stable circumbinary discs, typically assumed in analytical and numerical investigations of the the long term evolution of MBHBs. (Abridged)

The geometry of the close environment of SV Piscium as probed by VLTI/MIDI

Context. SV Psc is an asymptotic giant branch (AGB) star surrounded by an oxygen-rich dust envelope. The mm-CO line profile of the object's outflow shows a clear double-component structure. Because of the high angular resolution, mid-IR interferometry may give strong constraints on the origin of this composite profile. Aims. The aim of this work is to investigate the morphology of the environment around SV Psc using high-angular resolution interferometry observations in the mid-IR with the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI). Methods. Interferometric data in the N-band taken at different baseline lengths (ranging from 32-64 m) and position angles (73- 142{\deg}) allow a study of the morphology of the circumstellar environment close to the star. The data are interpreted on the basis of 2-dimensional, chromatic geometrical models using the fitting software tool GEM-FIND developed for this purpose. Results. The results favor two scenarios: (i) the presence of a highly inclined, optically thin, dusty disk surrounding the central star; (ii) the presence of an unresolved binary companion at a separation of 13.7 AU and a position angle of 121.8{\deg} NE. The derived orbital period of the binary is 38.1 yr. This detection is in good agreement with hydrodynamic simulations showing that a close companion could be responsible for the entrainment of the gas and dust into a circumbinary structure.

The Circumstellar Environment of T Tauri S at High Spatial and Spectral Resolution

We have obtained the first high spatial (0.05) and spectral (R~35,000) resolution 2 μm spectrum of the T Tau S tight binary system using adaptive optics on the Keck II telescope. We have also obtained the first 3.8 and 4.7 μm images that resolve the three components of the T Tau multiple system, as well as new 1.6 and 2.2 μm images. Together with its very red near-infrared colors, the spectrum of T Tau Sb shows that this T Tauri star is extincted by a roughly constant extinction of AV~15 mag, which is probably the 0.7×0.5 circumbinary structure recently observed in absorption in the ultraviolet. T Tau Sa, which is also observed through this screen and is actively accreting, further possesses a small edge-on disk that is evidenced by warm (390 K), narrow overtone CO rovibrational absorption features in our spectrum. We find that T Tau Sa is most likely an intermediate-mass star surrounded by a semitransparent 2-3 AU radius disk whose asymmetries and short Keplerian rotation explain the large photometric variability of the source on relatively short timescales. We also show that molecular hydrogen emission exclusively arises from the gas that surrounds T Tau S and that its spatial and kinematic structure, while providing suggestive evidence of a jetlike structure, is highly complex.

High-Resolution λ = 2.7 Millimeter Observations of L1551 IRS 5: A Protobinary System?

We present subarcsecond resolution imaging of the λ = 2.7 mm continuum emission from the young, embedded system L1551 IRS 5 using the nine-element, high-resolution configuration of the BIMA array. The observed emission arises from two compact sources separated by 035, coinciding with the two sources seen at λ = 2 cm and λ = 1.3 cm. When the high-resolution data are combined with data from two compact configurations, L1551 IRS 5 is argued to consist of a protobinary system separated by ~50 AU with individual circumstellar disks, a circumbinary structure, and a large-scale envelope. The characteristic masses of the components are 0.024 M☉ for the northern circumstellar disk, 0.009 M☉ for the southern circumstellar disk, 0.04 M☉ for the circumbinary material, and 0.28 M☉ for the envelope.