arXiv subjects

Enrico Ragusa

Publications and source records attributed to Enrico Ragusa.

At least 19 recordsLinked to original sources

arXiv2026

Exploring the radial velocity variations of RY Lup with VLT/ESPRESSO: Binary versus spot hypotheses

Stellar multiplicity is a possible cause for creating protoplanetary disc substructures, as tidal forces from a close-in spectroscopic companion can carve out gaps and shape disc architecture. However, in young, active systems, the radial velocity (RV) signatures are often complicated by stellar activity. We investigate RY Lup, a classical T Tauri star hosting a disc with a ~60 au cavity, where studies with Gaia astrometry and VLT/SPHERE imaging hinted at an unseen companion. Using high-resolution VLT/ESPRESSO spectra and the least-squares deconvolution (LSD) technique, we analyse RV variations over 327 days. We detect significant line profile variations with a periodic signal of ~3.75 days, aligning with prior photometric estimates. The variations are compatible with a close-in binary system at ~0.04 au and a mass ratio of q ~ 0.6. Combined analysis of RV data and ALMA dynamical mass estimates, using 13CO and 18CO, reveals a highly misaligned system. The nearly face-on binary i ~ 13 deg is misaligned to both the inner and outer discs i ~ 50 deg and ~70 deg, respectively. The derived orbital separation is compatible with the inner disc size, with the inner rim at a = 0.12 au, measured from VLTI/GRAVITY, which suggests a highly warped disc structure. Nonetheless, the short orbital period conflicts with the derived eccentricity (e ~ 0.23). To explore alternative explanations, we assess the impact of stellar spots on RV signals. While the LSD deformations can be modelled by different cool spot configurations, a 15% dispersion in retrieved v sin i values -- coupled with the lack of a significant periodic signal -- suggests that spots alone cannot explain the observed variability. As neither hypothesis is ruled out, we recommend future combined RV and interferometric monitoring to clarify the nature of the spectroscopic variability.

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arXiv2026

Revisiting the picture of circumbinary disc truncation

Circumbinary discs are observed to develop central cavities carved by the gravitational influence of the binary. Analytical estimates of cavity sizes predict truncation at $\sim 2 \textrm{--} 3$ binary separations, depending on the binary properties. However, numerical studies show only qualitative agreement with these predictions: cavity sizes often evolve on long timescales and can exceed substantially the analytically predicted values. In this work, we revise this paradigm, suggesting that tidal truncation in circumbinary discs responds to additional dynamical parameters that have so far been neglected. We analyse a suite of 80 numerical simulations of circumbinary discs to re-examine the physical mechanism responsible for cavity truncation and to provide a prescription for the cavity size independent of the state of evolution of the system. We find that truncation depends not only on the binary parameters $a_{\rm bin}$, $e_{\rm bin}$, and mass ratio $q$, but also on the instantaneous cavity eccentricity $e_{\rm cav}$ and the relative apsidal orientation $\varpi_{\rm bin}-\varpi_{\rm cav}$. These quantities jointly determine the pericentre of the innermost stable disc orbit $R_{\rm p}$, in a way that shares some similarities with orbital stability in the restricted three body problem. Hydrodynamical effects introduce secondary corrections, with the disc scale height $H$ and viscosity $α$ mildly shifting the cavity edge relative to the purely gravitational prediction. We introduce a semi-analytical prescription that captures these dependences for $R_{\rm p}$ and cavity semi-major axis $a_{\rm cav}$. We conclude that cavity truncation for binaries with mass ratios $q>0.05$ is a process where the instantaneous orbital properties of the disc ($e_{\rm cav}$, $\varpi_{\rm cav}$) play a fundamental role and should be taken into account to accurately evaluate the truncation efficiency.

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arXiv2026

The Circumbinary Disc of HD 34700A II. Analysis of a strong dust asymmetry

ALMA observations have shown that substructures are ubiquitous in protoplanetary discs. A sub-group, the transition discs, shows large cavities and rings in dust continuum. Among these, some present very high contrast asymmetries possibly due to the presence of vortices. HD 34700A is a binary system featuring a cavity, a ring, and multiple spiral arms detected in scattered light, a prominent crescent in the ALMA continuum and a complex gas morphology possibly connected with ongoing infall. We present new ALMA band 6 (1.3 mm) continuum images of the circumbinary disc around HD 34700A and compare them with two other systems showcasing high ($\gtrsim30$, measured as the peak-to-azimuthal-average ratio) contrast continuum asymmetries, IRS 48 and HD 142527. We aim to characterise the crescent morphology and discuss their possible origin. We perform visibility modelling of the new high resolution (0.''11x0.''09) ALMA band 6 continuum data of HD 34700A, together with improved visibility modelling of the other two targets. Our visibility model is in remarkable agreement with the HD 34700A data, featuring only localised residuals in the region of the disc corresponding to the tail of the asymmetry. We reproduce the double-peaked emission in HD 142527, and recover the crescent shape in IRS 48. We then run a hydrodynamic model of a vortex with different dust fluids, reproducing the general asymmetric crescent morphology observed in the HD 34700A and IRS 48 systems. With a combination of visibility, dust evolution and hydrodynamical models, we have constrained the morphology of the dust continuum emission of HD 34700A for the first time, and improved existing models for IRS 48 and HD 142527. The high azimuthal contrast of the asymmetries rules out the orbit clustering of eccentric cavities scenario, while the dust evolution models we consider suggest that the vortex scenario is a plausible option.

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arXiv2026

Astrometric view of companions in the inner dust cavities of protoplanetary disks

Protoplanetary disks with inner dust cavities (often referred to as "transition disks") are potential signposts of planet formation. We use Gaia astrometry to search for planetary and stellar companions in a sample of 98 transition disks, assessing the occurrence rate of such companions and their potential influence on cavity formation. For the 98 Young Stellar Objects (YSOs), we compute Gaia proper motion anomalies which, together with the RUWE, identify companions with mass ratios $q \gtrsim 0.01$ at $\sim$0.1-30 au. We assess the impact of disk gravity, accretion, disk-scattered light, dippers, starspots, jets, and outflows on the measured proper motion anomalies, concluding that astrometric techniques such as the one of this work can be robustly applied to YSOs. Significant proper motion anomalies are found in 31 transition disks (32% of the sample), indicative of companions. We recover 85% of known companions within our sensitivity range. We model the semi-major axis and mass required for a companion to reproduce the observed astrometric signals. Most inferred companions have $M > 30$ M$\rm{_{J}}$, placing many within or near the stellar mass regime. Seven sources host companions compatible with a planetary mass ($M < 13$ M$\rm{_{J}}$, HD 100453, J04343128+1722201, J16102955-3922144, MHO6, MP Mus, PDS 70, and Sz 76). For the non-detections, we provide the companion masses and semi-major axes that can be excluded in future searches. About half (53%) of detected companions cannot be reconciled with having carved the observed dust cavities. We find that transition disks host as many companions within our sensitivity range as do randomly sampled groups of YSOs and main-sequence stars. If dust cavities are shaped by companions, such companions must reside at larger orbital separations than those of the companions detected here, and we predict them to be of planetary mass. [abridged]

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arXiv2025

Coordinated Space- and Ground-based Monitoring of Accretion Bursts in a Protoplanetary Disk: The Orbital and Accretion Properties of DQ Tau

Multiplicity in pre-main-sequence (PMS) systems shapes circumstellar and circumbinary disks, often producing features such as inner cavities, spiral arms, and gas streamers that facilitate mass transfer between the disk and stars. Consequently, accretion in eccentric close binaries is highly variable and synchronized with their orbits, producing bursts near periastron passages. In this study, we examine the orbital and accretion properties of the eccentric Classical T-Tauri binary DQ Tau using medium- to high-resolution spectroscopy from the Very Large Telescope (VLT) X-Shooter and UVES instruments. The data were taken during a monitoring of inner disk chemistry with JWST, and our analysis is needed for correct interpretation of JWST data. We refine the orbital parameters and report an increment in the argument of periastron of 30 degrees. This apsidal motion may be caused by the massive disk acting as a third body. We also explore the possibility that it is due to a still undetected additional (sub-)stellar companion, estimating a lower limit of 15 MJ for its mass at the cavity edge (a=3 abin). We investigate accretion of the primary and secondary using the Ca II 849.8 nm emission line. The primary accretes more at periastron than in previous quiescent phases, while the secondary dominates post-periastron. Additionally, we report elevated Lacc at apastron, possibly due to interaction with irregularly shaped structures near the closest approach to the circumbinary disk. Finally, we derive each star's accretion luminosity across disentangled epochs and compare it to UV-excess-based results, finding good agreement. The individual Lacc values can be used as input for chemical models.

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arXiv2025

Eccentric discs as a gateway to giant planets outward migration

Recent studies on planet-dominated Type II migration demonstrated the presence of a correlation between the direction of planet migration and the parameter K describing the depth of the planetary gap. It was found that high (low) value for K correspond to outward (inward) migration. In this paper we aim at understanding the mechanism driving inward/outward migration and why it correlates with the gap depth. We performed a suite of 2D, live-planet, long-term simulations of massive planets migrating in discs with the hydro-code Fargo3D. We focus on a range of planet masses (1-13 m_J) and disc aspect ratios (0.03-0.1) and analyze the evolution of orbital elements and gap structure. We also study the torque contributions from outer Lindblad resonances to investigate their role in the migration outcome. We find that, while all planets initially migrate inwards, those with high enough K eventually enter a phase in which the torque reverses sign and migration becomes outwards, until eventually stalling. This behavior is associated with eccentricity growth in the outer disc and changes in the gap structure. We identify the surface density ratio at the 1:2 and 1:3 outer Lindblad resonances as a key output diagnostic that correlates with the migration direction. This ratio regulates the migration for all the cases where the massive planet remains in an almost circular orbit and the outer gap region exhibits moderate eccentricity. This characteristic sequence of inward-reversal-outwards-stalling occurs for a variety of K values and thus further work is required to identify the simulation input parameters that determine the onset of this sequence. Our results suggest that outward migration in the planet-dominated regime is primarily governed by the relative importance of the 1:2 and 1:3 resonances and, therefore, the gap profile plays a crucial role in determining the direction of migration.

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arXiv2025

The likelihood of not detecting cavity-carving companions in transition discs -- A statistical approach

Protoplanetary discs with cavities, also known as ``transition discs'', constitute ~10% of protoplanetary discs at sub-mm wavelengths. Among several explanations, one hypothesis suggests these cavities are carved by undetected stellar or planetary companions. We present a novel approach to quantify the likelihood that a cavity-carving companion goes undetected because it is either too close to the star (i.e., has a small projected separation) or too faint to be resolved. We generate two independent samples of stellar and planetary companions with random sky orientations, assuming distributions in eccentricity, mass ratio, and time-weighted orbital phases, to study the statistical properties of the cavities they produce. We calculate the likelihood that a companion appears with a projected separation $d$ relative to its semi-major axis $a_{bin}$ ($d/a_{bin}$). Then, using a disc truncation model, we calculate the likelihood that companions carve a cavity with size $a_{cav}$ relative to its semi-major axis $a_{bin}$ and projected separation $d$, deriving distributions of $a_{bin}/a_{cav}$ and $d/a_{cav}$. We find that stellar companions carve cavities with median sizes ~3 times larger than their projected separation $d$ ($a_{cav}\sim3d$, $a_{cav}\sim1.7 d$ for planets), but with a statistically significant tail towards larger values ($a_{cav}\gg 3d$). We estimate the likelihood that cavity-carving companions go undetected due to projection effects when the system is observed with spatial resolution $R$, $P(d< R)$. Considering observational constraints on companion masses, we apply this framework to 13 well-known transition discs. We find that undetected stellar companions are unlikely in 8 out of 13 systems we considered, with 5 notable exceptions: ABAur, MWC758, HD135344B, CQTau and HD169142. The presence of undetected planets cannot be excluded in any of the transition discs considered.

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arXiv2025

Eccentricity evolution during planet-disc interaction

During the process of planet formation, the planet-discs interactions might excite (or damp) the orbital eccentricity of the planet. In this paper, we present two long ($t\sim 3\times 10^5$ orbits) numerical simulations: (a) one (with a relatively light disc, $M_{\rm d}/M_{\rm p}=0.2$) where the eccentricity initially stalls before growing at later times and (b) one (with a more massive disc, $M_{\rm d}/M_{\rm p}=0.65$) with fast growth and a late decrease of the eccentricity. We recover the well-known result that a more massive disc promotes a faster initial growth of the planet eccentricity. However, at late times the planet eccentricity decreases in the massive disc case, but increases in the light disc case. Both simulations show periodic eccentricity oscillations superimposed on a growing/decreasing trend and a rapid transition between fast and slow pericentre precession. The peculiar and contrasting evolution of the eccentricity of both planet and disc in the two simulations can be understood by invoking a simple toy model where the disc is treated as a second point-like gravitating body, subject to secular planet-planet interaction and eccentricity pumping/damping provided by the disc. We show how the counterintuitive result that the more massive simulation produces a lower planet eccentricity at late times can be understood in terms of the different ratios of the disc-to-planet angular momentum in the two simulations. In our interpretation, at late times the planet eccentricity can increase more in low-mass discs rather than in high-mass discs, contrary to previous claims in the literature.

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arXiv2024

Discs are born eccentric

Recent observations have begun probing the early phases of disc formation, but little data yet exists on disc structure and morphology of Class 0 objects. Using simulations, we are able to lay out predictions of disc morphologies expected in future surveys of young discs. Based on detailed simulations of ab initio star formation by core collapse, we predict that early discs must be eccentric. In this letter, we study the morphology and, in particular, the eccentricity of discs formed in non-ideal magnetohydrodynamic (MHD) collapse simulations. We attempt to show that discs formed by cloud collapse are likely to be eccentric. We ran non-ideal MHD collapse simulations in the adaptive mesh refinement code RAMSES with radiative transfer. We used state-of-the-art analysis methods to measure the disc eccentricity. We find that despite no asymmetry in the initial conditions, the discs formed are eccentric, with eccentricities on the order of 0.1. These results may have important implications for protoplanetary disc dynamics and planet formation. The presence of eccentricity in young discs that is not seen at later stages of disc evolution is in tension with current viscous eccentricity damping models. This implies that there may be an as-yet undiscovered circularisation mechanism in circumstellar discs.

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arXiv2024

The Santa Barbara Binary-Disk Code Comparison

We have performed numerical calculations of a binary interacting with a gas disk, using eleven different numerical methods and a standard binary-disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution, and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed state of the binary-disk system. We find that all codes can agree on a converged solution (depending on the diagnostic being measured). The zone spacing required for most codes to reach a converged measurement of the torques applied to the binary by the disk is roughly 1% of the binary separation in the vicinity of the binary components. For our disk model to reach a relaxed state, codes must be run for at least 200 binary orbits, corresponding to about a viscous time for our parameters, $0.2 (a^2 Ω_B /ν)$ binary orbits, where $ν$ is the kinematic viscosity. We did not investigate dependence on binary mass ratio, eccentricity, disk temperature, or disk viscosity; therefore, these benchmarks may act as guides towards expanding converged solutions to the wider parameter space but might need to be updated in a future study that investigates dependence on system parameters. We find the most major discrepancies between codes resulted from the dimensionality of the setup (3D vs 2D disks). Beyond this, we find good agreement in the total torque on the binary between codes, although the partition of this torque between the gravitational torque, orbital accretion torque, and spin accretion torque depends sensitively on the sink prescriptions employed. In agreement with previous studies, we find a modest difference in torques and accretion variability between 2D and 3D disk models. We find cavity precession rates to be appreciably faster in 3D than in 2D.

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arXiv2024

Orbital dynamics in the GG Tau A system: investigating its enigmatic disc

GG Tau is one of the most studied multiple young stellar systems: GG Tau A is a hierarchical triple surrounded by a massive disc and its companion, GG Tau B, is also a binary. Despite numerous observational attempts, an understanding of the geometry of the GG Tau A system is still elusive. We provide new astrometric measures of the system and we run a set of hydrodynamical simulations with two representative orbits to test how they impact a disc composed of dust and gas. We test the dynamical evolution of the two scenarios on short and long timescales. We obtain synthetic flux emission from our simulations and we compare them with 1300 $μ$m ALMA dust continuum emission and 1.67 $μ$m SPHERE dust scattering images to infer the most likely orbital arrangement. We extend the analysis of the binary orbital parameters using six new epochs from archival data, showing that the current measurements alone are not capable of breaking the degeneracy between families of coplanar and misaligned orbits. We found that the time-scale for the onset of the disc eccentricity growth, $τ_{ecc}$, is a fundamental time-scale for the morphology of the system. Results from numerical simulations show that the best match between is obtained with the misaligned configuration ($Δθ= 30^\circ$) on timescales shorter than $τ_{ecc}$. The results exhibit an almost circular cavity and dust ring. However, for both scenarios, the cavity size and its eccentricity quickly grow for timescales longer than $τ_{ecc}$ and the models do not reproduce the observed morphology anymore. This implies that either the age of the system is shorter than $τ_{ecc}$ or that the disc eccentricity growth is not triggered or dissipated. This finding raises questions on the future evolution of the GG Tau A system and, more in general, on the time evolution of eccentric binaries and their circumbinary discs.

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arXiv2024

Probing the eccentricity in protostellar discs -- Modeling kinematics and morphologies

Protostellar discs are mostly modelled as circular structures of gas and dust orbiting a protostar. However, a number of physical mechanisms, e.g. the presence of a (sub)stellar companion or initial axial asymmetry, can cause the gas and dust orbital motion to become eccentric. Theoretical studies have revealed that, when present, disc eccentricity is expected to occur with predictable profiles that can be long-lasting and potentially observable in protostellar systems. We construct an analytical model predicting the typical features of the kinematics and morphology of eccentric protostellar discs, with the final goal of characterising the observational appearance of eccentricity in discs. We validate the model using a numerical simulation of a circumbinary disc (where the binary makes the disc eccentric). We finally post-process the simulation with Monte Carlo Radiative Transfer to study how eccentric features would appear through the "eyes" of ALMA. Besides the motion of the material on eccentric Keplerian orbits in the disc orbital plane, the most characteristic eccentric feature emerging from the analytical model is strong vertical motion with a typical anti-symmetric pattern (with respect to the disc line of pericentres). A circumbinary disc with a $\approx 40$ au eccentric cavity ($e_{\rm cav}=0.2$), carved by an $a_{\rm bin}=15$ au binary, placed at a distance $d=130$ pc, is expected to host in its upper emission surface vertical oscillations up to $v_{z}\sim 400\, {\rm ms}^{-1}$ close to the cavity edge, i.e. well within ALMA spectral and spatial resolution capabilities. A residual spiral pattern in the vertical velocity $Δv_{z}\sim 150\, {\rm ms}^{-1}$ of the simulation cannot be captured by the theoretical model, we speculate it to be possibly linked to the presence of a companion in the system.

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arXiv2024

Small and Large Dust Cavities in Disks around mid-M Stars in Taurus

High-angular resolution imaging by ALMA has revealed the near-universality and diversity of substructures in protoplanetary disks. However, disks around M-type pre-main-sequence stars are still poorly sampled, despite the prevalence of M-dwarfs in the galaxy. Here we present high-resolution (~50 mas, 8 au) ALMA Band 6 observations of six disks around mid-M stars in Taurus. We detect dust continuum emission in all six disks, 12CO in five disks, and 13CO line in two disks. The size ratios between gas and dust disks range from 1.6 to 5.1. The ratio of about 5 for 2M0436 and 2M0450 indicates efficient dust radial drift. Four disks show rings and cavities and two disks are smooth. The cavity sizes occupy a wide range: 60 au for 2M0412, and ~10 au for 2M0434, 2M0436 and 2M0508. Detailed visibility modeling indicates that small cavities of 1.7 and 5.7 au may hide in the two smooth disks 2M0450 and CIDA 12. We perform radiative transfer fitting of the infrared SEDs to constrain the cavity sizes, finding that micron-sized dust grains may have smaller cavities than millimeter grains. Planet-disk interactions are the preferred explanation to produce the large 60 au cavity, while other physics could be responsible for the three ~10 au cavities under current observations and theories. Currently, disks around mid-to-late M stars in Taurus show a higher detection frequency of cavities than earlier type stars, although a more complete sample is needed to evaluate any dependence of substructure on stellar mass.

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arXiv2023

A Large Double-ring Disk around the Taurus M Dwarf J04124068+2438157

Planet formation imprints signatures on the physical structures of disks. In this paper, we present high-resolution ($\sim$50 mas, 8 au) Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and CO line emission toward the disk around the M3.5 star 2MASS J04124068+2438157. The dust disk consists only of two narrow rings at radial distances of 0.47 and 0.78 arcsec ($\sim$70 and 116 au), with Gaussian $σ$ widths of 5.6 and 8.5 au, respectively. The width of the outer ring is smaller than the estimated pressure scale height by $\sim25\%$, suggesting dust trapping in a radial pressure bump. The dust disk size, set by the location of the outermost ring, is significantly larger (by $3σ$) than other disks with similar millimeter luminosity, which can be explained by an early formation of local pressure bump to stop radial drift of millimeter dust grains. After considering the disk's physical structure and accretion properties, we prefer planet--disk interaction over dead zone or photoevaporation models to explain the observed dust disk morphology. We carry out high-contrast imaging at $L'$ band using Keck/NIRC2 to search for potential young planets, but do not identify any source above $5σ$. Within the dust gap between the two rings, we reach a contrast level of $\sim$7 mag, constraining the possible planet below $\sim$2--4 $M_{\rm Jup}$. Analyses of the gap/ring properties suggest a $\sim$Saturn mass planet at $\sim$90 au is likely responsible for the formation of the outer ring, which can be potentially revealed with JWST.

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arXiv2021

The Bardeen-Petterson effect in accreting supermassive black-hole binaries: disc breaking and critical obliquity

The inspiral of supermassive black-hole binaries in gas-rich environment is driven by the presence of an accretion disc and viscous interactions tend to align the spin of the black holes with the orbital angular momentum of the disc. Recent work introduced a new iterative approach to describe the alignment process and the resulting non-linear evolution of the surrounding warped accretion disc. Their model predicted that black-hole spins reach either full alignment or a critical obliquity where solutions to the warp equations cease to exist. In this paper, we show that this critical region corresponds to the disc breaking phenomenon, where the disc is disrupted into two or more discrete sections. We use 3D hydrodynamical simulations to (i) recover the predictions of the semi-analytic model and (ii) unveil a richer phenomenology where the disc exhibits either unsuccessful, single and multiple breaks. We additionally identify hydrodynamic effects such as spiral arms that are able to stabilise the disc against breaking beyond criticality. Our results show that when disc breaking occurs, the ability of black holes and disc to align is compromised and in some cases even prevented as the binary inspirals.

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arXiv2021

The evolution of large cavities and disc eccentricity in circumbinary discs

We study the mutual evolution of the orbital properties of high mass ratio, circular, co-planar binaries and their surrounding discs, using 3D Smoothed Particle Hydrodynamics simulations. We investigate the evolution of binary and disc eccentricity, cavity structure and the formation of orbiting azimuthal over-dense features in the disc. Even with circular initial conditions, all discs with mass ratios $q>0.05$ develop eccentricity. We find that disc eccentricity grows abruptly after a relatively long time-scale ($\sim 400\textrm{--}700$ binary orbits), and is associated with a very small increase in the binary eccentricity. When disc eccentricity grows, the cavity semi-major axis reaches values $a_{\rm cav}\approx 3.5\, a_{\rm bin}$. We also find that the disc eccentricity correlates linearly with the cavity size. Viscosity and orbit crossing, appear to be responsible for halting the disc eccentricity growth -- eccentricity at the cavity edge in the range $e_{\rm cav}\sim 0.05\textrm{--} 0.35$. Our analysis shows that the current theoretical framework cannot fully explain the origin of these evolutionary features when the binary is almost circular ($e_{\rm bin}\lesssim 0.01$); we speculate about alternative explanations. As previously observed, we find that the disc develops an azimuthal over-dense feature in Keplerian motion at the edge of the cavity. A low contrast over-density still co-moves with the flow after 2000 binary orbits; such an over-density can in principle cause significant dust trapping, with important consequences for protoplanetary disc observations.

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arXiv2021

Circumbinary and circumstellar discs around the eccentric binary IRAS 04158+2805 -- a testbed for binary-disc interaction

IRAS~04158+2805 has long been thought to be a very low mass T-Tauri star (VLMS) surrounded by a nearly edge-on, extremely large disc. Recent observations revealed that this source hosts a binary surrounded by an extended circumbinary disc with a central dust cavity. In this paper, we combine ALMA multi-wavelength observations of continuum and $^{12}$CO line emission, with H$α$ imaging and Keck astrometric measures of the binary to develop a coherent dynamical model of this system. The system features an azimuthal asymmetry detected at the western edge of the cavity in Band~7 observations and a wiggling outflow. Dust emission in ALMA Band 4 from the proximity of the individual stars suggests the presence of marginally resolved circumstellar discs. We estimate the binary orbital parameters from the measured arc of the orbit from Keck and ALMA astrometry. We further constrain these estimates using considerations from binary-disc interaction theory. We finally perform three SPH gas + dust simulations based on the theoretical constraints; we post-process the hydrodynamic output using radiative transfer Monte Carlo methods and directly compare the models with observations. Our results suggest that a highly eccentric $e\sim 0.5\textrm{--}0.7$ equal mass binary, with a semi-major axis of $\sim 55$ au, and small/moderate orbital plane vs. circumbinary disc inclination $θ\lesssim 30^\circ$ provides a good match with observations. A dust mass of $\sim 1.5\times 10^{-4} {\rm M_\odot}$ best reproduces the flux in Band 7 continuum observations. Synthetic CO line emission maps qualitatively capture both the emission from the central region and the non-Keplerian nature of the gas motion in the binary proximity.

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arXiv2021

The Architecture of the V892 Tau System: the Binary and its Circumbinary Disk

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 $Δ=8\pm4.2$ deg; another solution with $Δ=113$ 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.

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