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Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages (a so-called 'fly-by'), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems: AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the individuals' contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205. We discuss the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution, namely with ALMA continuum and gas emission. Collective observational data can constrain the systems' geometry and stellar trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction., 23 pages, 17 figures, accepted for publication in MNRAS

We perform 3D hydrodynamics simulations of disc-disc stellar flybys with on-the-fly Monte Carlo radiative transfer. We show that pre-existing circumstellar discs around both stars result in fast rising ($\sim$yrs) outbursts lasting 2-5 times longer than for a star-disc flyby. The perturber always goes into outburst ($\dot{M}>10^{-5}~{\rm M_{\odot}~ yr^{-1}}$). Whereas we find that the primary goes into a decades long outburst only when the flyby is retrograde to the circumprimary disc rotation. High accretion rates during the outburst are triggered by angular momentum cancellation in misaligned material generated by the encounter. A large fraction of accreted material is alien., 11 pages, 9 figures, accepted for publication in MNRAS

We investigate the mechanism of polar alignment for accretion discs in hierarchical systems (HSs) with more than two stars. In eccentric binary systems, low mass discs that are sufficiently tilted to the binary orbit align in a polar configuration with respect to the binary plane by aligning their angular momentum to the binary eccentricity vector. In HSs, secular evolution of the orbital parameters makes the eccentricity vector of the system precess with time. This precession undermines the stability of the polar orbit for accretion discs hosted in HSs. We analytically show that the binary criteria for polar alignment derived in the literature are necessary but not sufficient conditions for polar alignment in HSs. Then, we derive an analytical criterion for polar alignment in HSs. In general, we find that discs orbiting the innermost level of a HS can go polar. Conversely, radially extended discs orbiting the outer levels of a HS cannot polarly align and evolve as orbiting around a circular binary. We confirm our findings through detailed numerical simulations. Also, our results are compatible with the observed distribution of disc-orbit mutual inclination. Finally, we compare the observed distribution of disc inclinations in the binary and in the HS populations. Binaries host mainly coplanar discs, while HSs show a wide range of disc inclinations. We suggest that the wider range of inclinations in HSs results from the secular oscillation of their orbital parameters (such as Kozai-Lidov oscillations), rather than from a different initial condition or evolution between HSs and binaries., 11 pages, 9 figures, accepted for publication on MNRAS

Episodic accretion is a low-mass pre-main sequence phenomenon characterized by sudden outbursts of enhanced accretion. These objects are classified into two: protostars with elevated levels of accretion that lasts for decades or more, called FUors, and protostars with shorter and repetitive bursts, called EXors. HBC 494 is a FUor object embedded in the Orion Molecular Cloud. Earlier Atacama Large (sub-)Millimeter Array (ALMA) continuum observations showed an asymmetry in the disk at 0.''2 resolution. Here, we present follow-up observations at ~0.''03, resolving the system into two components: HBC 494 N (primary) and HBC 494 S (secondary). No circumbinary disk was detected. Both disks are resolved with a projected separation of ~0.''18 (75 au). Their projected dimensions are 84+/-1.8 x 66.9+/-1.5 mas for HBC 494 N and 64.6+/-2.5 x 46.0+/-1.9 mas for HBC 494 S. The disks are almost aligned and with similar inclinations. The observations show that the primary is ~5 times brighter/more massive and ~2 times bigger than the secondary. We notice that the northern component has a similar mass to the FUors, while the southern has to EXors. The HBC 494 disks show individual sizes that are smaller than single eruptive YSOs. In this work, we also report 12CO, 13CO, and C18O molecular line observations. At large scale, the 12CO emission shows bipolar outflows, while the 13CO and C18O maps show a rotating and infalling envelope around the system. At a smaller scale, the 12CO and 13CO moment zero maps show cavities within the continuum disks' area, which may indicate continuum over-subtraction or slow-moving jets and chemical destruction along the line-of-sight., Comment: Published in MNRAS. Main text (11 pages, 8 figures). Appendix (11 pages, 9 figures). Total (22 pages, 17 figures)

We review the role of stellar flybys and encounters in shaping planet-forming discs around young stars, based on the published literature on this topic in the last 30 years. Since most stars $\leq~2$ Myr old harbour protoplanetary discs, tidal perturbations affect planet formation. First, we examine the probability of experiencing flybys or encounters: More than 50\% of stars with planet-forming discs in a typical star forming environment should experience a close stellar encounter or flyby within 1000 au. Second, we detail the dynamical effects of flybys on planet-forming discs. Prograde, parabolic, disc-penetrating flybys are the most destructive. Grazing and penetrating flybys in particular lead to the capture of disc material by the secondary to form a highly misaligned circumsecondary disc with respect to the disc around the primary. One or both discs may undergo extreme accretion and outburst events, similar to the ones observed in FU Orionis-type stars. Warps and broken discs are distinct signatures of retrograde flybys. Third, we review some recently observed stellar systems with discs where a stellar flyby or an encounter is suspected -- including UX Tau, RW Aur, AS 205, Z CMa, and FU Ori. Finally, we discuss the implications of stellar flybys for planet formation and exoplanet demographics, including possible imprints of a flyby in the Solar System in the orbits of trans-Neptunian objects and the Sun's obliquity., 16 pages, 7 figures, 1 table, 255 references. Invited review article accepted in EPJ+

This essay reviews a set of contemporary experiences of sex-political organization in the history of the Argentinian antagonistic imagination. It sketches an experimental, theoretical diagram of the power of queer negativity as it has been mobilized by several strategies of public space occupation. Addressing the interference and discontinuity of political time in the wake of new experiences of strike allows one to identify other forms of critical approaches to the streets’ heteronormative control systems. It also allows one to trace how new agencies of common organization can be activated for destabilizing the projective direction of emancipatory Left utopias, creating space for new vital protests.

Young multiple systems accrete most of their final mass in the first few Myr of their lifetime, during the protostellar and protoplanetary phases. Previous studies showed that in binary systems the majority of the accreted mass falls onto the lighter star, thus evolving to mass equalisation. However, young stellar systems often comprise more than two stars, which are expected to be in hierarchical configurations. Despite its astrophysical relevance, differential accretion in hierarchical systems remains to be understood. In this work, we investigate whether the accretion trends expected in binaries are valid for higher order multiples. We performed a set of 3D Smoothed Particle Hydrodynamics simulations of binaries and of hierarchical triples (HTs) embedded in an accretion disc, with the code Phantom. We identify for the first time accretion trends in HTs and their deviations compared to binaries. These deviations, due to the interaction of the small binary with the infalling material from the circum-triple disc, can be described with a semi-analytical prescription. Generally, the smaller binary of a HT accretes more mass than a single star of the same mass as the smaller binary. We found that in a HT, if the small binary is heavier than the third body, the standard differential accretion scenario (whereby the secondary accretes more of the mass) is hampered. Reciprocally, if the small binary is lighter than the third body, the standard differential accretion scenario is enhanced. The peculiar differential accretion mechanism we find in HTs is expected to affect their mass ratio distribution., Comment: Accepted for publication in MNRAS, 15 pages, 13 figures, 1 tables, 2 appendices

Close encounters between young stellar objects in star forming clusters are expected to dramatically perturb circumstellar disks. Such events are witnessed in numerical simulations of star formation, but few direct observations of ongoing encounters have been made. Here we report sub-0".1 resolution Atacama Large Millimeter Array (ALMA) and Jansky Very Large Array (JVLA) observations towards the million year old binary protostar Z CMa in dust continuum and molecular line emission. A point source ~4700 au from the binary has been discovered at both millimeter and centimeter wavelengths. It is located along the extension of a ~2000 au streamer structure previously found in scattered light imaging, whose counterpart in dust and gas emission is also newly identified. Comparison with simulations shows signposts of a rare flyby event in action. Z CMa is a "double burster", as both binary components undergo accretion outbursts, which may be facilitated by perturbations to the host disk by flybys., Comment: Published in Nature Astronomy. Here is the authors' version with the Supplementary Information integrated into the Methods section

In recent years, technical and theoretical work to detect moons and rings around exoplanets has been attempted. The small mass/size ratios between moons and planets means this is very challenging, having only one exoplanetary system where spotting an exomoon might be feasible (i.e. Kepler-1625b i). In this work, we study the dynamical evolution of ringed exomoons, dubbed "cronomoons" after their similarity with Cronus (Greek for Saturn), and after Chronos (the epitome of time), following the Transit Timing Variations (TTV) and Transit Duration Variation (TDV) that they produce on their host planet. Cronomoons have extended systems of rings that make them appear bigger than they actually are when transiting in front of their host star. We explore different possible scenarios that could lead to the formation of such circumsatellital rings, and through the study of the dynamical/thermodynamic stability and lifespan of their dust and ice ring particles, we found that an isolated cronomoon can survive for time-scales long enough to be detected and followed up. If these objects exist, cronomoons' rings will exhibit gaps similar to Saturn's Cassini Division and analogous to the asteroid belt's Kirkwood gaps, but instead raised due to resonances induced by the host planet. Finally, we analyse the case of Kepler-1625b i under the scope of this work, finding that the controversial giant moon could instead be an Earth-mass cronomoon. From a theoretical perspective, this scenario can contribute to a better interpretation of the underlying phenomenology in current and future observations., Accepted to MNRAS. See a Twitter thread at @MarioSucerquia. Press release: http://www.npf.cl/ 14 pages, 11 figures

Most of the planetary systems discovered around binary stars are located at approximately three semi-major axes from the barycentre of their system, curiously close to low-order mean-motion resonances (MMRs). The formation mechanism of these circumbinary planets is not yet fully understood. In situ formation is extremely challenging because of the strong interaction with the binary. One possible explanation is that, after their formation, the interactions between these planets and the surrounding protoplanetary disc cause them to migrate at velocities dependent on the nature of the disc and the mass of the exoplanet. Although extensive data can be obtained with direct hydrodynamical simulations, their computational cost remains too high. On the other hand, the direct n-body simulations approach allows us to model a large variety of parameters at much lower cost. We analyse the planetary migration around a wide variety of binary stars using Stokes-like forces that mimic planetary migration at a constant rate. Our goal is to identify the main parameters responsible for the ejection of planets at different resonances with the inner binary. We performed 4200 n-body simulations with Stokes-like forces and analysed their evolution and outcome as a function of the properties of each system. For each simulated exoplanet, we applied an ensemble learning method for classification in order to clarify the relationship between the inspected parameters and the process of MMR capture. We identify the capture probability for different N/1 MMRs, 4/1 being the most prone to capture exoplanets, with 37% probability, followed by MMR 5/1 with $\sim$ 23% of probability. The eccentricity of the binary is found to be the most important parameter in determining the MMR capture of each circumbinary exoplanet, followed by the mass ratio of the binary and the initial eccentricity of the planet., Comment: 13 pages, 10 figures, A\&A accepted

Tidal encounters in star clusters perturb discs around young protostars. In Cuello et al. (2019a, Paper I) we detailed the dynamical signatures of a stellar flyby in both gas and dust. Flybys produce warped discs, spirals with evolving pitch angles, increasing accretion rates, and disc truncation. Here we present the corresponding observational signatures of these features in optical/near-infrared scattered light and (sub-) millimeter continuum and CO line emission. Using representative prograde and retrograde encounters for direct comparison, we post-process hydrodynamical simulations with radiative transfer methods to generate a catalogue of multi-wavelength observations. This provides a reference to identify flybys in recent near-infrared and sub-millimetre observations (e.g., RW Aur, AS 205, HV Tau & DO Tau, FU Ori, V2775 Ori, and Z CMa)., 11 pages, 5 figures, accepted for publication in MNRAS

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

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

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

Planets form in young circumstellar disks called protoplanetary disks. However, it is still difficult to catch planet formation in-situ. Nevertheless, from recent ALMA/SPHERE data, encouraging evidence of the direct and indirect presence of embedded planets has been identified in disks around young stars: co-moving point sources, gravitational perturbations, rings, cavities, and emission dips or shadows cast on disks. The interpretation of these observations needs a robust physical framework to deduce the complex disk geometry. In particular, protoplanetary disk models usually assume the gas pressure scale-height given by the ratio of the sound speed over the azimuthal velocity $H/r = c_{s\rm }/v_{\rm k}$. By doing so, \textit{radiative} pressure fields are often ignored, which could lead to a misinterpretation of the real vertical structure of such disks. We follow the evolution of a gaseous disk with an embedded Jupiter mass planet through hydrodynamical simulations, computing the disk scale-height including radiative pressure, which was derived from a generalization of the stellar atmosphere theory. We focus on the vertical impact of the radiative pressure in the vicinity of circumplanetary disks, where temperatures can reach $\gtrsim 1000$ K for an accreting planet, and radiative forces can overcome gravitational forces from the planet. The radiation-pressure effects create a vertical optically thick column of gas and dust at the proto-planet location, casting a shadow in scattered light. This mechanism could explain the peculiar illumination patterns observed in some disks around young stars such as HD 169142 where a moving shadow has been detected, or the extremely high aspect-ratio $H/r \sim 0.2$ observed in systems like AB Aur and CT Cha., 12 pages, 7 figures. Accepted for publication by ApJ

We examine whether stellar flyby simulations can initiate FU Orionis outbursts using 3D hydrodynamics simulations coupled to live Monte Carlo radiative transfer. We find that a flyby where the secondary penetrates the circumprimary disc triggers a 1-2 year rise in the mass accretion rate to $10^{-4}~{\rm M_{\odot}~ yr^{-1}}$ that remains high ($\gtrsim 10^{-5}~{\rm M_{\odot}~yr^{-1}}$) for more than a hundred years, similar to the outburst observed in FU Ori. Importantly, we find that the less massive star becomes the dominant accretor, as observed., Comment: 5 pages, 4 figures, accepted for publication in MNRAS, movies available at https://emborchert.github.io/videos, press release available at https://www.monash.edu/science/news/current/astronomers-find-clue-to-solar-system-formation-through-well-known-star

During the Argentine process called “Democratic Spring” (1983), a series of countercultural movements emerged in which we can recognize a common desire to dismantle the censorship fences installed by the authoritarianism of the previous military coup. In this context, a set of minority strategies carried out by young punks, prostitutes, sexual dissidents, and lumpen artists aimed to disrupt the imaginable order through the complicity of insurgent action against the demand for integrationist visibility and democratic consensus, guided by the energy of negative affects. This work asks about the ways in which these events can be historized, recognizing the disappointment, dizziness, hesitation, and precariousness of their political positions as structures of a brown queer common, recovering the epistemological potential of oral history as an impure decolonization methodology.

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$\alpha$ 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 $\theta\lesssim 30^\circ$ 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., Comment: 19 pages, 14 figures, 1 table, accepted for publication in MNRAS

We present observations of the young multiple system UX Tauri to look for circumstellar disks and for signs of dynamical interactions. We obtained SPHERE/IRDIS deep differential polarization images in the J and H bands. We also used ALMA archival CO data. Large extended spirals are well detected in scattered light coming out of the disk of UX Tau A. The southern spiral forms a bridge between UX Tau A and C. These spirals, including the bridge connecting the two stars, all have a CO (3-2) counterpart seen by ALMA. The disk of UX Tau C is detected in scattered light. It is much smaller than the disk of UX Tau A and has a major axis along a different position angle, suggesting a misalignment. We performed PHANTOM SPH hydrodynamical models to interpret the data. The scattered light spirals, CO emission spirals and velocity patterns of the rotating disks, and the compactness of the disk of UX Tau C all point to a scenario in which UX Tau A has been perturbed very recently (about 1000 years) by the close passage of UX Tau C., Comment: Accepted for publication in Astronomy & Astrophysics Letters. (8pages, 8 figures). 2 movies will be available on-line

In recent years, several protoplanetary discs have been observed to exhibit spirals, both in scattered light and (sub)millimetre continuum data. The HD 100453 binary star system hosts such a disc around its primary. Previous work has argued that the spirals were caused by the gravitational interaction of the secondary, which was assumed to be on a circular orbit, coplanar with the disc (meaning here the large outer disc, as opposed to the very small inner disc). However, recent observations of the CO gas emission were found incompatible with this assumption. In this paper, we run SPH simulations of the gas and dust disc for seven orbital configurations taken from astrometric fits and compute synthetic observations from their results. Comparing to high-resolution ALMA $^{12}$CO data, we find that the best agreement is obtained for an orbit with eccentricity $e=0.32$ and semi-major axis $a=207$ au, inclined by $61^\circ$ relative to the disc plane. The large misalignment between the disc and orbit planes is compatible with the tidal evolution of a circumprimary disc in an eccentric, unequal-mass binary star., Accepted for publication in MNRAS. 21 pages, 28 figures

Spiral arms in protoplanetary discs are thought to be linked to the presence of companions. We test the hypothesis that the double spiral arm morphology observed in the transition disc MWC 758 can be generated by an $\approx 10$ M$_{\rm Jup}$ companion on an eccentric orbit internal to the spiral arms. Previous studies on MWC 758 have assumed an external companion. We compare simulated observations from three dimensional hydrodynamics simulations of disc-companion interaction to scattered light, infrared and CO molecular line observations, taking into account observational biases. The inner companion hypothesis is found to explain the double spiral arms, as well as several additional features seen in MWC 758 -- the arc in the northwest, substructures inside the spiral arms, the cavity in CO isotopologues, and the twist in the kinematics. Testable predictions include detection of fainter spiral structure, detection of a point source south-southeast of the primary, and proper motion of the spiral arms., Comment: 13 pages, 6 figures, resubmitted to MNRAS

Trojans are defined as objects that share the orbit of a planet at the stable Lagrangian points $L_4$ and $L_5$. In the Solar System, these bodies show a broad size distribution ranging from micrometer($\mu$m) to centimeter(cm) particles (Trojan dust) and up to kilometer (km) rocks (Trojan asteroids). It has also been theorized that earth-like Trojans may be formed in extra-solar systems. The Trojan formation mechanism is still under debate, especially theories involving the effects of dissipative forces from a viscous gaseous environment. We perform hydro-simulations to follow the evolution of a protoplanetary disk with an embedded 1--10 Jupiter-mass planet. On top of the gaseous disk, we set a distribution of $\mu$m--cm dust particles interacting with the gas. This allows us to follow dust dynamics as solids get trapped around the Lagrangian points of the planet. We show that large vortices generated at the Lagrangian points are responsible for dust accumulation, where the leading Lagrangian point $L_4$ traps a larger amount of submillimeter (submm) particles than the trailing $L_5$, which traps mostly mm--cm particles. However, the total bulk mass, with typical values of $\sim M_{\rm moon}$, is more significant in $L_5$ than in $L_4$, in contrast to what is observed in the current Solar System a few gigayears later. Furthermore, the migration of the planet does not seem to affect the reported asymmetry between $L_4$ and $L_5$. The main initial mass reservoir for Trojan dust lies in the same co-orbital path of the planet, while dust migrating from the outer region (due to drag) contributes very little to its final mass, imposing strong mass constraints for the in situ formation scenario of Trojan planets., Comment: 18 pages, 18 figures. Accepted for publication in Astronomy & Astrophysics

We now have several observational examples of misaligned broken protoplanetary discs, where the disc inner regions are strongly misaligned with respect to the outer disc. Current models suggest that this disc structure can be generated with an internal misaligned companion (stellar or planetary), but the occurrence rate of these currently unobserved companions remains unknown. Here we explore whether a strong misalignment between the inner and outer disc can be formed without such a companion. We consider a disc that has an existing gap --- essentially separating the disc into two regions --- and use a flyby to disturb the discs, leading to a misalignment. Despite considering the most optimistic parameters for this scenario, we find maximum misalignments between the inner and outer disc of $\sim$45$^{\circ}$ and that these misalignments are short-lived. We thus conclude that the currently observed misaligned discs must harbour internal, misaligned companions., Accepted for publication in MNRAS. 9 pages with 6 figures

As planets grow the exchange of angular momentum with the gaseous component of the protoplanetary disc produces a net torque resulting in a variation of the semi-major axis of the planet. For low-mass planets not able to open a gap in the gaseous disc this regime is known as type I migration. Pioneer works studied this mechanism in isothermal discs finding fast inward type I migration rates that were unable to reproduce the observed properties of extrasolar planets. In the last years, several improvements have been made in order to extend the study of type I migration rates to non-isothermal discs. Moreover, it was recently shown that if the planet's luminosity due to solid accretion is taken into account, inward migration could be slowed down and even reversed. In this work, we study the planet formation process incorporating, and comparing, updated type I migration rates for non-isothermal discs and the role of planet's luminosity over such rates. We find that the latter can have important effects on planetary evolution, producing a significant outward migration for the growing planets., Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society

Close-in giant planets represent the most significant evidence of planetary migration. If large exomoons form around migrating giant planets which are more stable (e.g. those in the Solar System), what happens to these moons after migration is still under intense research. This paper explores the scenario where large regular exomoons escape after tidal-interchange of angular momentum with its parent planet, becoming small planets by themselves. We name this hypothetical type of object a \textit{ploonet}. By performing semi-analytical simulations of tidal interactions between a large moon with a close-in giant, and integrating numerically their orbits for several Myr, we found that in $\sim$50 per cent of the cases a young ploonet may survive ejection from the planetary system, or collision with its parent planet and host star, being in principle detectable. Volatile-rich ploonets are dramatically affected by stellar radiation during both planetocentric and siderocentric orbital evolution, and their radius and mass change significantly due to the sublimation of most of their material during time-scales of hundred of Myr. We estimate the photometric signatures that ploonets may produce if they transit the star during the phase of evaporation, and compare them with noisy lightcurves of known objects ("Kronian" stars and non-periodical dips in dusty lightcurves). Additionally, the typical transit timing variations (TTV) induced by the interaction of a ploonet with its planet are computed. We find that present and future photometric surveys' capabilities can detect these effects and distinguish them from those produced by other nearby planetary encounters., Published in Monthly Notices of the Royal Astronomical Society. 11 pages, 7 figures

We test the hypothesis that the disc cavity in the `transition disc' Oph IRS 48 is carved by an unseen binary companion. We use 3D dust-gas smoothed-particle hydrodynamics simulations to demonstrate that marginally coupled dust grains concentrate in the gas over-density that forms in in the cavity around a low binary mass ratio binary. This produces high contrast ratio dust asymmetries at the cavity edge similar to those observed in the disc around IRS 48 and other transition discs. This structure was previously assumed to be a vortex. However, we show that the observed velocity map of IRS 48 displays a peculiar asymmetry that is not predicted by the vortex hypothesis. We show the unusual kinematics are naturally explained by the non-Keplerian flow of gas in an eccentric circumbinary cavity. We further show that perturbations observed in the isovelocity curves of IRS 48 may be explained as the product of the dynamical interaction between the companion and the disc. The presence of a $\sim$0.4 M$_{\odot}$ companion at a $\sim$10 au separation can qualitatively explain these observations. High spatial resolution line and continuum imaging should be able to confirm this hypothesis., Comment: 9 pages, 7 figures, accepted for publication in MNRAS

Context. Dynamical studies suggest that most circumbinary discs (CBDs) should be coplanar. However, some theoretical works show that under certain conditions a CBD can become polar, which means that its rotation vector is orthogonal with respect to the binary orbital plane. Interestingly, very recent observations show that polar CBDs exist in nature (e.g. HD 98800). Aims. We test the predictions of CBD alignment around eccentric binaries based on linear theory. In particular, we compare prograde and retrograde CBD configurations. Then, assuming planets form in these systems, we thoroughly characterise the orbital behaviour and stability of misaligned (P-type) particles. This is done for massless and massive particles. Methods. The evolution of the CBD alignment for various configurations was modelled through three-dimensional hydrodynamical simulations. For the orbital characterisation and the analysis stability, we relied on long-term N-body integrations and structure and chaos indicators, such as $\Delta e$ and MEGNO. Results. We confirm previous analytical predictions on CBD alignment, but find an unexpected symmetry breaking between prograde and retrograde configurations. Therefore, the likelihood of becoming polar for a highly misaligned CBD is higher than previously thought. Regarding the stability of circumbinary P-type planets (also know as Tatooines), polar orbits are stable over a wide range of binary parameters. In particular, for binary eccentricities below 0.4 the orbits are stable for any value of the binary mass ratio. In the absence of gas, planets with masses below $10^{-5}\,M_{\odot}$ have negligible effects on the binary orbit. Finally, we suggest that mildly eccentric equal-mass binaries should be searched for polar Tatooines., Comment: 9 pages, 9 figures; Astronomy & Astrophysics (in press)

Context. Despite the recent discovery of spiral-shaped features in protoplanetary discs in the near-infrared and millimetric wavelengths, there is still an active discussion to understand how they formed. In fact, the spiral waves observed in discs around young stars can be due to different physical mechanisms: planet/companion torques, gravitational perturbations or illumination effects. Aims. We study the spirals formed in the gaseous phase due to two diametrically opposed shadows cast at fixed disc locations. The shadows are created by an inclined non-precessing disc inside the cavity, which is assumed to be optically thick. In particular, we analyse the effect of these spirals on the dynamics of the dust particles and discuss their detectability in transition discs. Methods. We perform gaseous hydrodynamical simulations with shadows, then we compute the dust evolution on top of the gaseous distribution, and finally we produce synthetic ALMA observations of the dust emission based on radiative transfer calculations. Results. Our main finding is that mm- to cm-sized dust particles are efficiently trapped inside the shadow-triggered spirals. We also observe that particles of various sizes starting at different stellocentric distances are well mixed inside these pressure maxima. This dynamical effect would favour grain growth and affect the resulting composition of planetesimals in the disc. In addition, our radiative transfer calculations show spiral patterns in the disc at 1.6 {\mu}m and 1.3 mm. Due to their faint thermal emission (compared to the bright inner regions of the disc) the spirals cannot be detected with ALMA. Our synthetic observations prove however that shadows are observable as dips in the thermal emission., Comment: 15 pages, 11 figures, accepted for publication in A&A

We present 3D hydrodynamical models of the HD142527 protoplanetary disc, a bright and well studied disc that shows spirals and shadows in scattered light around a 100 au gas cavity, a large horseshoe dust structure in mm continuum emission, together with mysterious fast radial flows and streamers seen in gas kinematics. By considering several possible orbits consistent with the observed arc, we show that all of the main observational features can be explained by one mechanism - the interaction between the disc and the observed binary companion. We find that the spirals, shadows and horseshoe are only produced in the correct position angles by a companion on an inclined and eccentric orbit approaching periastron - the 'red' family from Lacour et al. (2016). Dust-gas simulations show radial and azimuthal concentration of dust around the cavity, consistent with the observed horseshoe. The success of this model in the HD142527 disc suggests other mm-bright transition discs showing cavities, spirals and dust asymmetries may also be explained by the interaction with central companions., 16 pages, 12 figures, accepted to MNRAS. Movies at http://users.monash.edu.au/~dprice/pubs/HD142527/

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We present 3D smoothed particle hydrodynamics simulations of protoplanetary discs undergoing a flyby by a stellar perturber on a parabolic orbit lying in a plane inclined relative to the disc mid-plane. We model the disc as a mixture of gas and dust, with grains ranging from 1 {\mu}m to 10 cm in size. Exploring different orbital inclinations, periastron distances and mass ratios, we investigate the disc dynamical response during and after the flyby. We find that flybys induce evolving spiral structure in both gas and dust which can persist for thousands of years after periastron. Gas and dust structures induced by the flyby differ because of drag-induced effects on the dust grains. Variations in the accretion rate by up to an order of magnitude occur over a time-scale of order 10 years or less, inducing FU Orionis-like outbursts. The remnant discs are truncated and warped. The dust disc is left more compact than the gas disc, both because of disc truncation and accelerated radial drift of grains induced by the flyby., Comment: 27 pages, 24 figures, accepted for publication in MNRAS

FU Orionis objects are low-mass pre-main sequence stars characterized by dramatic outbursts of several magnitudes in brightness. These outbursts are linked to episodic accretion events in which stars gain a significant portion of their mass. The physical processes behind these accretion events are not yet well understood. The archetypical FU Ori system, FU Orionis, is composed of two young stars with detected gas and dust emission. The continuum emitting regions have not been resolved until now. Here, we present 1.3 mm observations of the FU Ori binary system with ALMA. The disks are resolved at 40 mas resolution. Radiative transfer modeling shows that the emission from FU Ori north (primary) is consistent with a dust disk with a characteristic radius of $\sim$11 au. The ratio between major and minor axes shows that the inclination of the disk is $\sim$37 deg. FU Ori south is consistent with a dust disk of similar inclination and size. Assuming the binary orbit shares the same inclination angle as the disks, the deprojected distance between north and south components is 0.6'', i.e. $\sim$250 au. Maps of $^{12}$CO emission show a complex kinematic environment with signatures disk rotation at the location of the northern component, and also (to a lesser extent) for FU Ori south. The revised disk geometry allows us to update FU Ori accretion models (Zhu et al.), yielding a stellar mass and mass accretion rate of FU Ori north of 0.6 M$_{\odot}$ and 3.8$\times10^{-5}$ M$_{\odot}$ yr$^{-1}$, respectively., 9 pages, 4 figures, accepted for publication in ApJ

Dynamical studies suggest that most of the circumbinary discs (CBDs) should be coplanar. However, under certain initial conditions, the CBD can evolve toward polar orientation. Here we extend the parametric study of polar configurations around detached close-in binaries through $N$-body simulations. For polar configurations around binaries with mass ratios $q$ below $0.7$, the nominal location of the mean motion resonance (MMR) $1~:~4$ predicts the limit of stability for $e_{B} > 0.1$. Alternatively, for $e_{B} < 0.1$ or $q \sim 1$, the nominal location of the MMR $1~:~3$ is the closest stable region. The presence of a} giant planet increases the region of forbidden polar configurations around low mass ratio binaries with eccentricities $e_B\sim0.4$ with respect to rocky earth-like planets. For equal mass stars, the eccentricity excitation $\Delta e$ of polar orbits smoothly increases with decreasing distance to the binary. For $q, Comment: 9 pages. 7 figures. Accepted for publication in the special issue of the Journal of Physics: Conference Series aimed to the works presented at the Brazilian Colloquium on Orbital Dynamics - CBDO 2018

Shadows and spirals seem to be common features of transition discs. Among the spiral-triggering mechanisms proposed, only one establishes a causal link between shadows and spirals so far. In fact, provided the presence of shadows in the disc, the combined effect of temperature gradient and differential disc rotation, creates strong azimuthal pressure gradients. After several thousand years, grand-design spirals develop in the gas phase. Previous works have only considered static shadows caused by an inclined inner disc. However, in some cases, the inner regions of circumbinary discs can break and precess. Thus, it is more realistic to consider moving shadow patterns in the disc. In this configuration, the intersection between the inner and the outer discs defines the line of nodes at which the shadows are cast. Here, we consider moving shadows and study the resulting circumbinary disc structure. We find that only static and prograde shadows trigger spirals, in contrast to retrograde ones. Interestingly, if a region of the disc corotates with the shadow, a planet-like signature develops at the co-rotation position. The resulting spirals resemble those caused by a planet embedded in the disc, with similar pitch angles., Comment: 6 pages, 4 figures. Accepted for publication in MNRAS letters

The size and density of dust grains determine their response to gas drag in protoplanetary discs. Aerodynamical (size x density) sorting is one of the proposed mechanisms to explain the grain properties and chemical fractionation of chondrites. However, the efficiency of aerodynamical sorting and the location in the disc in which it could occur are still unknown. Although the effects of grain sizes and growth in discs have been widely studied, a simultaneous analysis including dust composition is missing. In this work we present the dynamical evolution and growth of multicomponent dust in a protoplanetary disc using a 3D, two-fluid (gas+dust) Smoothed Particle Hydrodynamics (SPH) code. We find that the dust vertical settling is characterised by two phases: a density-driven phase which leads to a vertical chemical sorting of dust and a size-driven phase which enhances the amount of lighter material in the midplane. We also see an efficient radial chemical sorting of the dust at large scales. We find that dust particles are aerodynamically sorted in the inner disc. The disc becomes sub-solar in its Fe/Si ratio on the surface since the early stage of evolution but sub-solar Fe/Si can be also found in the outer disc-midplane at late stages. Aggregates in the disc mimic the physical and chemical properties of chondrites, suggesting that aerodynamical sorting played an important role in determining their final structure., Comment: Astroph version. MNRAS: Accepted 2017 March 30. Received 2017 March 30; in original form 2016 May 10

Photophoresis is a physical process based on momentum exchange between an illuminated dust particle and its gaseous environment. Its net effect in protoplanetary discs (PPD) is the outward transport of solid bodies from hot to cold regions. This process naturally leads to the formation of ring-shaped features where dust piles up. In this work, we study the dynamical effects of photophoresis in PPD by including the photophoretic force in the two-fluid (gas+dust) smoothed particle hydrodynamics (SPH) code developed by Barri\`ere-Fouchet et al. (2005). We find that the conditions of pressure and temperature encountered in the inner regions of PPD result in important photophoretic forces, which dramatically affect the radial motion of solid bodies. Moreover, dust particles have different equilibrium locations in the disc depending on their size and their intrinsic density. The radial transport towards the outer parts of the disc is more efficient for silicates than for iron particles, which has important implications for meteoritic composition. Our results indicate that photophoresis must be taken into account in the inner regions of PPD to fully understand the dynamics and the evolution of the dust composition., Comment: 11 pages, 10 figures, 2 tables

Calcium Aluminium Inclusions (CAIs) formed in the Solar System, some 4,567 million years ago. CAIs are almost always surrounded by Wark-Lovering Rims (WLRs), which are a sequence of thin, mono/bi-mineralic layers of refractory minerals, with a total thickness in the range of 1 to 100 microns. Recently, some CAIs have been found that have tektite-like bowl-shapes. To form such shapes, the CAI must have travelled through a rarefied gas at hypersonic speeds. We show how CAIs may have been ejected from the inner solar accretion disc via the centrifugal interaction between the solar magnetosphere and the inner disc rim. They subsequently punched through the hot, inner disc rim wall at hypersonic speeds. This re-entry heating partially or completely evaporated the CAIs. Such evaporation could have significantly increased the metal abundances of the inner disc rim. High speed movement through the inner disc produced WLRs. To match the observed thickness of WLRs required metal abundances at the inner disc wall that are of order ten times that of standard solar abundances. The CAIs cooled as they moved away from the protosun, the deduced CAI cooling rates are consistent with the CAI cooling rates obtained from experiment and observation. The speeds and gas densities required to form bowl-shaped CAIs are also consistent with the expected speeds and gas densities for larger, ~ 1 cm, CAIs punching through an inner accretion disc wall., Comment: 70 pages, 41 figures

In this work we demonstrate that the inner spiral structure observed in AB Aurigae can be created by a binary star orbiting inside the dust cavity. We find that a companion with a mass-ratio of 0.25, semi-major axis of 40 au, eccentricity of 0.5, and inclination of 90{\deg} produces gaseous spirals closely matching the ones observed in $^{12}$CO (2-1) line emission. Based on dust dynamics in circumbinary discs (Poblete, Cuello, and Cuadra 2019), we constrain the inclination of the binary with respect to the circumbinary disc to range between 60{\deg} and 90{\deg}. We predict that the stellar companion is located roughly 0.18 arcsec from the central star towards the east-southeast, above the plane of the disc. Should this companion be detected in the near future, our model indicates that it should be moving away from the primary star at a rate of 6 mas/yr on the plane of the sky. Since our companion is inclined, we also predict that the spiral structure will appear to change with time, and not simply co-rotate with the companion., Comment: Accepted for publication in MNRAS. 11 Pages, 7 Figures

The protoplanetary disc HD 100453 exhibits a curious combination of spirals, shadows and a relative misalignment between the observed outer disc and inferred inner disc. This disc is accompanied by a secondary star on a bound orbit exterior to the disc. Recent observations have suggested there may be an additional low-mass companion residing within the disc inner cavity. In our companion paper the orbit of the secondary was shown to be misaligned by 61 degrees to the plane of the outer disc. Here we investigate the properties of the inner companion and the origin of the misalignment between the inner and outer disc. Using numerical simulations and synthetic observations, we show that the disc structure and kinematics are consistent with a $\lesssim$ 5 Jupiter mass planet located at 15-20au. We find that the disc evolution over around 50 binary orbits (about 10$^5$ yrs) is governed by differential precession and to a lesser extent, the Kozai-Lidov effect. In our proposed model the misalignment observed between the outer and inner disc arises naturally as a result of the misaligned outer companion driving the outer disc to precess more rapidly than the inner disc., Comment: Accepted for publication in MNRAS, 12 pages, 6 figures. Movie of simulations available at https://youtu.be/MvH8TO21W_4