Demidova, T V

Demidova T.V., Grigor'ev V.V.

Гринин В.П., Демидова Т.В.

Grigoryev V.V., Demidova T.V.

The problem of the formation of exoplanets in inclined orbits relative to the equatorial plane of the parent star or the main plane of the protoplanetary disk can be solved by introducing a smaller inclined disk. However, the question of the nature of such an internal disk remains open. In the paper, we successfully tested the hypothesis about the formation of an inclined inner disk in a protoplanetary disk near a T Tau type star as a result of a gas stream falling on it. To test the hypothesis, three-dimensional gas-dynamic calculations were performed taking into account viscosity and thermal conductivity using the PLUTO package. In the course of the analysis of calculations, it was shown that a single intersection of the matter stream with the plane of the disk cannot ensure the formation of an inclined disk near the star, while a double intersection can. In addition, in the case of a retrograde fall of matter, the angle of inclination of the resulting inner disk is significantly greater. An analysis of the observational manifestations of this event was also carried out: the potential change in the brightness of the star, the distribution of optical thickness in angles, the evolution of the accretion rate. It is shown that the decrease in brightness can reach up to 5m, taking into account scattered light, and such a decrease in brightness will last several decades. In addition, a sharp increase in the accretion rate by two orders of magnitude could potentially trigger an FU Ori-like outburst.

Grigoryev V.V., Demidova T.V.

The problem of the formation of exoplanets in inclined orbits relative to the equatorial plane of the parent star or the main plane of the protoplanetary disk can be solved by introducing a smaller inclined disk. However, the question of the nature of such an internal disk remains open. In the paper, we successfully tested the hypothesis about the formation of an inclined inner disk in a protoplanetary disk near a T Tau type star as a result of a gas stream falling on it. To test the hypothesis, three-dimensional gas-dynamic calculations were performed taking into account viscosity and thermal conductivity using the PLUTO package. In the course of the analysis of calculations, it was shown that a single intersection of the matter stream with the plane of the disk cannot ensure the formation of an inclined disk near the star, while a double intersection can. In addition, in the case of a retrograde fall of matter, the angle of inclination of the resulting inner disk is significantly greater. An analysis of the observational manifestations of this event was also carried out: the potential change in the brightness of the star, the distribution of optical thickness in angles, the evolution of the accretion rate. It is shown that the decrease in brightness can reach up to $${{5}^{m}}$$ , taking into account scattered light, and such a decrease in brightness will last several decades. In addition, a sharp increase in the accretion rate by two orders of magnitude could potentially trigger an FU Ori-like outburst.

Grinin V.P., Demidova T.V.

We propose a model of deep and prolonged eclipses in young UX Ori stars. Some of these events last for decades and existing models cannot explain them. We show that such eclipses can be caused by the infall of gas and dust clumps from the remnants of the protostellar cloud onto the protoplanetary disk. The perturbation in the disk caused by the infall of a clump leads to a burst of accretional stellar activity and, as a consequence, to a strengthening of the disk wind. If the circumstellar disk is tilted at a small angle to the line of sight, then the dust raised by the wind from the disk surface can cause a dramatic decrease in the stellar brightness that can last for decades.

Demidova T.V., Grinin V.P.

Abstract One of the early hypotheses about the origin of FU Orionis star (FUORs) outbursts explains them based on the fall of gas clumps from the remnants of protostellar clouds onto protoplanetary disks surrounding young stars. To calculate the consequences of such an event, we make 3D hydrodynamic simulations using the smoothed particle hydrodynamics method. It is shown that the fall of the clump on the disk in the vicinity of the star actually causes a burst of the star’s accretion activity, resembling in its characteristics the flares of known FUORs. In the region of incidence, an inhomogeneous gas ring is formed, which is inclined relative to the outer disk. During several revolutions around the star, this ring combines with the inner disk and forms a tilted disk. In the process of evolution, the inner disk expands, and its inclination relative to the outer disk decreases. After 100 revolutions, the angle of inclination is a few degrees. This result is of interest in connection with the discovery in recent years of protoplanetary disks, the inner region of which is inclined relative to the outer one. Such structures are usually associated with the existence in the vicinity of a star of a massive body (planet or brown dwarf), whose orbit is inclined relative to the plane of the disk. The results of our modeling indicate the possibility of an alternative explanation for this phenomenon.

Grigoryev V., Demidova T.

During the birth of a planetary system from a protoplanetary disk surrounding a young star, events such as collisions of formed dense gas and dust clumps, or the fall of such clumps of matter onto the disk from outside can occur in the disk itself. As a result of such events, a local increase in the density of matter is formed in the disk, which has a different velocity relative to the star than the surrounding matter. In this paper, we describe the numeric simulation of the evolution of a protoplanetary disk with the described heterogeneity, using for this two different approaches: the finite-volume method (PLUTO package) and the SPH method (Gadget-2 package). The computations were carried out in parallel mode. Based on the results obtained, we estimate the efficiency of parallelization at different stages of clump decay.

Демидова Т.В., Шевченко И.И.

Demidova T.V., Shevchenko I.I.

Ways of formation of azimuthal resonant patterns in circumstellar planetesimal disks with planets are considered. Our analytical estimates and massive numerical experiments show that the disk particles that initially reside in zones of low-order mean-motion resonances with the planet may eventually concentrate into potentially observable azimuthal patterns. The structuring process is rapid, usually taking $$\sim$$ 100 orbital periods of the planet. It is found that the relative number of particles that retain their resonant position increases with decreasing the mass parameter $$\mu$$ (the ratio of masses of the perturbing planet and the parent star), but a significant fraction of the particle population is always removed from the disk due to accretion of the particles onto the star and planet, as well as due to their transition to highly elongated and hyperbolic orbits. Expected radio images of azimuthally structured disks are constructed. In the considered models, azimuthal patterns associated with the $$2:1$$ and $$3:2$$ resonances are most clearly manifested; observational manifestations of the $$1:2$$ and $$2:3$$ resonances are also possible.

Demidova T., Savvateeva T., Anoshin S., Grigoryev V., Stoyanovskaya O.

Particle approaches considered to study the interaction of dust grains of the same size and a gas medium based on Smoothed Particle Hydrodynamics method. The paper compares two algorithms for solving this problem, described in [1, 2]. Both algorithms were implemented by in a modified version of the GADGET-2 program code. One-dimensional and three-dimensional tests were carried out in order to confirm the properties of the algorithms and to make performance measurements of the code.

Demidova T.

The applicability of the Bulirsh–Stoer algorithm for solving the planar restricted three-body problem is investigated. Variations in the value of the Jacobi integral are considered as the main parameter. Massive calculations were carried out with a small step in the parameter characterizing the ratio of the masses of a planet and star (the mass parameter). It is shown that violations of the Jacobi integral occur inside the planetary chaotic region. This fact can be used to determine chaotic region boundaries, as well as the boundaries of a stable structure which coorbital with the planet. The average dependences of the value of the Jacobi integral on the mass parameter, which determine the boundaries of the chaotic zone and the coorbital ring, are derived. Estimates were obtained for the maximum relative change in the Jacobi integral for different values of the accretion radius. It is shown that the value of the accretion radius corresponding to the average radius of known exoplanets does not cause significant changes in the value of the Jacobi integral. The dependences of the clearing time of the chaotic zone for different accretion radii are also given with and without taking into account the coorbital structure.

Demidova T.V., Grinin V.P.

Abstract The development of perturbations in the circumstellar disks of pre-main-sequence stars caused by clumpy accretion was investigated. Here we perform 3D smoothed particle hydrodynamics simulations of disks perturbed by a recent clump accretion event. These simulations are further explored by radiative transfer calculations to quantify the observational appearance of such disks. It was shown that the density waves in the disks were formed at the fall of the clump. After several revolutions they can transform into spirals and ring structures. Their images in millimeter wavelengths are very similar to those observed with Atacama Large Millimeter/submillimeter Array in some protoplanetary disks. We assume that clumpy accretion may be the source of such structures.

Демидова Т.В., Шевченко И.И.

Demidova T.V., Shevchenko I.I.

Extensive numerical experiments on the long-term dynamics of planetesimal disks with planets in systems of single stars have been carried out. The planetary chaotic zone clearing timescales $$T_{\mathrm{cl}}$$ as a function of mass parameter $$\mu$$ (planet–star mass ratio) have been determined numerically with a high accuracy separately for the outer and inner parts of the chaotic zone. Diffusional components $${\propto}\mu^{-6/7}$$ and $${\propto}\mu^{-2}$$ have been revealed in the dependence $$T_{\mathrm{cl}}(\mu)$$ . The results obtained are discussed and interpreted in light of existing analytical theories based on the mean motion resonance overlap criterion and in comparison with previous numerical approaches to the problem.

Демидова Т.В., Шевченко И.И.

Peißker F., Zajaček M., Labadie L., Bordier E., Eckart A., Melamed M., Karas V.

AbstractHigh-velocity stars and peculiar G objects orbit the central supermassive black hole (SMBH) Sagittarius A* (Sgr A*). Together, the G objects and high-velocity stars constitute the S cluster. In contrast with theoretical predictions, no binary system near Sgr A* has been identified. Here, we report the detection of a spectroscopic binary system in the S cluster with the masses of the components of 2.80  ±  0.50 M⊙ and 0.73  ±  0.14 M⊙, assuming an edge-on configuration. Based on periodic changes in the radial velocity, we find an orbital period of 372±3 days for the two components. The binary system is stable against the disruption by Sgr A* due to the semi-major axis of the secondary being 1.59±0.01 AU, which is well below its tidal disruption radius of approximately 42.4 AU. The system, known as D9, shows similarities to the G objects. We estimate an age for D9 of $$2.{7}_{-0.3}^{+1.9}\,\times \,1{0}^{6}$$ 2 . 7 − 0.3 + 1.9 × 1 0 6 yr that is comparable to the timescale of the SMBH-induced von Zeipel-Lidov-Kozai cycle period of about 106 yr, causing the system to merge in the near future. Consequently, the population of G objects may consist of pre-merger binaries and post-merger products. The detection of D9 implies that binary systems in the S cluster have the potential to reside in the vicinity of the supermassive black hole Sgr A* for approximately 106 years.

Demidova T.V., Grigor'ev V.V.

Quarles B., Bhaskar H.G., Li G.

Гринин В.П., Демидова Т.В.

Grinin V.P., Safonov B.S., Efimova N.V., Barsunova O.Y., Strachov I.A., Borman G.A., Shugarov S.Y.

In this article we analyze the properties of the photometric and spectral variability of the young star V718 Per, a member of the cluster IC 348, in terms of its possible binarity. The most realistic is the model where the main component of the system V718 Per A — with an effective temperature of 5200 K — is periodically shielded by two extended dust periods structures consisting of large particles and moving around the star in resonance with two planets. Their orbital periods are 4.7 years and 213 days. Their ratio with high accuracy is 1:8, and the ratio of the large semi-axes is 1:4. The masses of the planets do not exceed 6 МJup. At the moments of total eclipses of V718 Per A, the radiation of the system is dominated by a colder component with an effective temperature of 4150 ± 100 K, which explains the reddening of the star observed in the brightness minima, as well as its spectral changes during brightness weakening. Speckle interferometric observations performed on the 2.5-m telescope of the CMO of SAI MSU made it possible to estimate the upper limit of the angular distance between the components of the system: 0.1′′, which is equivalent to a projection distance of 30 a.u. The unique feature of this system is that the planes of the planetary orbits practically coincide with the line of sight. Such an orientation of the system is most favorable for measuring fluctuations in the radial velocity of a star caused by the orbital motion of planets, as well as for observing planetary transits along the disk of the main component of the system.

Grigoryev V.V., Demidova T.V.

The problem of the formation of exoplanets in inclined orbits relative to the equatorial plane of the parent star or the main plane of the protoplanetary disk can be solved by introducing a smaller inclined disk. However, the question of the nature of such an internal disk remains open. In the paper, we successfully tested the hypothesis about the formation of an inclined inner disk in a protoplanetary disk near a T Tau type star as a result of a gas stream falling on it. To test the hypothesis, three-dimensional gas-dynamic calculations were performed taking into account viscosity and thermal conductivity using the PLUTO package. In the course of the analysis of calculations, it was shown that a single intersection of the matter stream with the plane of the disk cannot ensure the formation of an inclined disk near the star, while a double intersection can. In addition, in the case of a retrograde fall of matter, the angle of inclination of the resulting inner disk is significantly greater. An analysis of the observational manifestations of this event was also carried out: the potential change in the brightness of the star, the distribution of optical thickness in angles, the evolution of the accretion rate. It is shown that the decrease in brightness can reach up to 5m, taking into account scattered light, and such a decrease in brightness will last several decades. In addition, a sharp increase in the accretion rate by two orders of magnitude could potentially trigger an FU Ori-like outburst.

Grigoryev V.V., Demidova T.V.

The problem of the formation of exoplanets in inclined orbits relative to the equatorial plane of the parent star or the main plane of the protoplanetary disk can be solved by introducing a smaller inclined disk. However, the question of the nature of such an internal disk remains open. In the paper, we successfully tested the hypothesis about the formation of an inclined inner disk in a protoplanetary disk near a T Tau type star as a result of a gas stream falling on it. To test the hypothesis, three-dimensional gas-dynamic calculations were performed taking into account viscosity and thermal conductivity using the PLUTO package. In the course of the analysis of calculations, it was shown that a single intersection of the matter stream with the plane of the disk cannot ensure the formation of an inclined disk near the star, while a double intersection can. In addition, in the case of a retrograde fall of matter, the angle of inclination of the resulting inner disk is significantly greater. An analysis of the observational manifestations of this event was also carried out: the potential change in the brightness of the star, the distribution of optical thickness in angles, the evolution of the accretion rate. It is shown that the decrease in brightness can reach up to $${{5}^{m}}$$ , taking into account scattered light, and such a decrease in brightness will last several decades. In addition, a sharp increase in the accretion rate by two orders of magnitude could potentially trigger an FU Ori-like outburst.

Grinin V.P., Safonov B.S., Efimova N.V., Barsunova O.Y., Strachov I.A., Borman G.A., Shugarov S.Y.

In this paper, we have analyzed the properties of the photometric and spectral variability of young star V718 Per, a member of the cluster IC 348, in terms of its possible binarity. The most realistic is the model where the main component of the V718 Per A system—with an effective temperature of 5200 K—is periodically shielded by two extended dust structures consisting of large particles and moving around the star in resonance with two planets. Their orbital periods are 4.7 years and 213 days. Their ratio with high accuracy is equal to 1 : 8, and the ratio of the large semi-axes is 1 : 4. The masses of the planets have not exceeded $$6 \,{{M}_{{{\text{Jup}}}}}$$ . At the moments of total eclipses V718 Per A, the radiation of the system has been dominated by a colder component with an effective temperature of $$4150 \pm 100$$ K, which has explained the reddening of the star observed in the brightness minima, as well as its spectral changes during brightness weakening. Speckle interferometric observations performed using the 2.5-m telescope of the Sternberg Astronomical Institute have made it possible to estimate the upper limit of the angular distance between the components of the system: ≤0.1 $$'' $$ , which is equivalent to a projection distance of ≤30 AU. The unique feature of this system has been that the planes of the planetary orbits practically coincide with the line of sight. Such an orientation of the system has been most favorable for measuring fluctuations in the radial velocity of a star caused by the orbital motion of planets, as well as for observing planetary transits along the disk of the main component of the system.

Burlak M.A., Dodin A.V., Zharova A.V., Zheltoukhov S.G., Ikonnikova N.P., Lamzin S.A., Potanin S.A., Safonov B.S., Strakhov I.A., Tatarnikov A.M.

The results of photometric, polarimetric, and spectroscopic observations of the young star ZZ Tau IRS in the visible and near-infrared bands are presented. Against the continuum of an M spectral type star about 50 emission lines of allowed (H I, He I, Na I, S II) and forbidden (O I, O II, O III, N I, N II, S II, Ca II, Fe II, Ni II) transitions were identified. It was found that from the autumn of 2020 to the beginning of 2023, the brightness of the star in the visible region decreased $$(\Delta I\approx 1\overset{\textrm{m}}{.}5$$ ) and then began to return to the initial level. As the visible brightness of the star declined, its color indices decreased in the visible region, but increased in the near-IR bands. At light minimum, the degree of polarization in the $$I$$ band reached approx 13 $$\%$$ , and the equivalent widths of, e.g., the H $$\alpha$$ and [S II] $$\lambda$$ 6731 lines increased to 376 and 79 $${{\text{\AA}}^{\circ}}$$ , respectively. Arguments are given in favor of ZZ Tau IRS being a UX Ori type star, and its variability being due to eclipses by dust clouds, which are inhomogeneities in the dusty disk wind. Forbidden lines are formed both in the disk wind and in the jet, the axis of what is oriented along $$PA=61^{\circ}\pm 3^{\circ}$$ . The jet mass-loss rate exceeds $$5\times 10^{-10}M_{\odot}$$ yr $${}^{-1}$$ , what is abnormally large for a star with a mass less than $$0.3M_{\odot}$$ . Apparently, the disk wind of ZZ Tau IRS is not axially symmetric, probably due to the azimuthal asymmetry of the protoplanetary disk found earlier from ALMA observations.

Encalada F.J., Looney L.W., Takakuwa S., Tobin J.J., Ohashi N., Jørgensen J.K., Li Z., Aikawa Y., Aso Y., Koch P.M., Kwon W., Lai S., Lee C.W., Lin Z.D., Santamaría-Miranda A., et. al.

Abstract 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.

Biddle L.I., Bowler B.P., Zhou Y., Franson K., Zhang Z.

Abstract Giant planets grow by accreting gas through circumplanetary disks, but little is known about the timescale and mechanisms involved in the planet-assembly process because few accreting protoplanets have been discovered. Recent visible and infrared imaging revealed a potential accreting protoplanet within the transition disk around the young intermediate-mass Herbig Ae star, AB Aurigae (AB Aur). Additional imaging in Hα probed for accretion and found agreement between the line-to-continuum flux ratio of the star and companion, raising the possibility that the emission source could be a compact disk feature seen in scattered starlight. We present new deep Keck/NIRC2 high-contrast imaging of AB Aur to characterize emission in Paβ, another accretion tracer less subject to extinction. Our narrow band observations reach a 5σ contrast of 9.6 mag at 0.″6, but we do not detect significant emission at the expected location of the companion, nor from other any other source in the system. Our upper limit on Paβ emission suggests that if AB Aur b is a protoplanet, it is not heavily accreting or accretion is stochastic and was weak during the observations.

Donati J., Finociety B., Cristofari P.I., Alencar S.H., Moutou C., Delfosse X., Fouqué P., Arnold L., Baruteau C., Kóspál Á., Ménard F., Carmona A., Grankin K., Takami M., Artigau E., et. al.

ABSTRACT We report new observations of the classical T Tauri star CI Tau with the SPIRou near-infrared spectropolarimeter and velocimeter at the Canada–France–Hawaii Telescope (CFHT) in late 2019, 2020, and 2022, complemented with observations obtained with the ESPaDOnS optical spectropolarimeter at CFHT in late 2020. From our SPIRou and ESPaDOnS spectra, to which we applied least-squares deconvolution, we infer longitudinal fields clearly modulated with the 9-d rotation period of CI Tau. Using Zeeman–Doppler imaging, we reconstruct the large-scale magnetic topology, first from SPIRou data only in all three seasons, then from our 2020 SPIRou and ESPaDOnS data simultaneously. We find that CI Tau hosts a mainly axisymmetric poloidal field, with a 1 kG dipole slightly tilted to the rotation axis and dark spots close to the pole that coincide with the footpoints of accretion funnels linking the star to the inner disc. Our results also suggest that CI Tau accretes mass from the disc in a stable fashion. We further find that radial velocities (RVs) derived from atomic and CO lines in SPIRou spectra are both rotationally modulated, but with a much lower amplitude than that expected from the putative candidate planet CI Tau b. We confirm the presence of a RV signal at a period of 23.86 d reported in a separate analysis, but detect it clearly in CO lines only and not in atomic lines, suggesting that it likely traces a non-axisymmetric structure in the inner disc of CI Tau rather than a massive close-in planet.

Grinin V.P., Demidova T.V.

We propose a model of deep and prolonged eclipses in young UX Ori stars. Some of these events last for decades and existing models cannot explain them. We show that such eclipses can be caused by the infall of gas and dust clumps from the remnants of the protostellar cloud onto the protoplanetary disk. The perturbation in the disk caused by the infall of a clump leads to a burst of accretional stellar activity and, as a consequence, to a strengthening of the disk wind. If the circumstellar disk is tilted at a small angle to the line of sight, then the dust raised by the wind from the disk surface can cause a dramatic decrease in the stellar brightness that can last for decades.

Berezina A.A.

Analytical representations of the rate of apsidal precession in the planar elliptical restricted three-body problem are considered in the case when the orbit of the disturbing body is external with respect to the orbit of the test particle. The analytical expressions are compared with the numerical data obtained for the apsidal precession rate in the form of a power series with a parameter equal to the ratio of the semi-major axis of the orbit of the test particle to that of the disturbing planet. It is shown that the analytical expressions for the rate of apsidal precession of the particle are reliable only at distances not close to the instability zone near the orbit of the disturbing planet. Near the Wisdom gap, the linear secular theory is no more valid. An empirical correction formula is proposed to calculate the apsidal procession rate at relatively high (however less than 0.5) eccentricities of the particle and disturbing planet. The proposed formulas are applied to describe the precession of orbits in real exoplanetary systems.

Hanawa T., Garufi A., Podio L., Codella C., Segura-Cox D.

ABSTRACT DG Tau is a nearby T Tauri star associated with a collimated jet, a circumstellar disc, and a streamer a few hundred au long. The streamer connects to the disc at ∼50 au from DG Tau. At this location SO emission is observed, likely due to the release of sulphur from dust grains caused by the shock of the impact of the accretion streamer onto the disc. We investigate the possibility that the DG Tau streamer was produced via cloudlet capture on the basis of hydrodynamic simulations, considering a cloudlet initiating infall at 600 au from DG Tau with low angular momentum so that the centrifugal force is smaller than the gravitational force, even at 50 au. The elongation of the cloudlet into a streamer is caused by the tidal force when its initial velocity is much less than the free-fall velocity. The elongated cloudlet reaches the disc and forms a high-density gas clump. Our hydrodynamic model reproduces the morphology and line-of-sight velocity of CS (5 − 4) emission from the northern streamer observed with Atacama Large Millimeter/submillimeter Array. We discuss the conditions for forming a streamer based on the simulations. We also show that the streamer should perturb the disc after impact for several thousands of years.

Monsch K., Lovell J.B., Berghea C.T., Edenhofer G., Keating G.K., Andrews S.M., Bayyari A., Drake J.J., Wilner D.J.

Abstract We present resolved images of IRAS 23077+6707 (“Dracula’s Chivito”) in 1.3 mm/225 GHz thermal dust and CO gas emission with the Submillimeter Array (SMA) and optical (0.5–0.8 μm) scattered light with the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). The Pan-STARRS data show a bipolar distribution of optically scattering dust that is characteristic for disks observed at high inclinations. Its scattered light emission spans ∼14″, with two highly asymmetric filaments extending along the upper bounds of each nebula by ∼9″. The SMA data measure 1.3 mm continuum dust as well as 12CO, 13CO, and C18O J = 2 − 1 line emission over 12″–14″ extents, with the gas presenting the typical morphology of a disk in Keplerian rotation, in both position–velocity space and in each CO line spectrum. IRAS 23077+6707 has no reported distance estimate, but if it is located in the Cepheus star-forming region (180–800 pc), it would have a radius spanning thousands of astronomical units. Taken together, we infer IRAS 23077+6707 to be a giant and gas-rich edge-on protoplanetary disk, which to our knowledge is the largest in extent so far discovered.

Grinin V.P., Demidova T.V.

We propose a model of deep and prolonged eclipses in young UX Ori stars. Some of these events last for decades and existing models cannot explain them. We show that such eclipses can be caused by the infall of gas and dust clumps from the remnants of the protostellar cloud onto the protoplanetary disk. The perturbation in the disk caused by the infall of a clump leads to a burst of accretional stellar activity and, as a consequence, to a strengthening of the disk wind. If the circumstellar disk is tilted at a small angle to the line of sight, then the dust raised by the wind from the disk surface can cause a dramatic decrease in the stellar brightness that can last for decades.

Mikryukov D.V., Shevchenko I.I.

ABSTRACT We study how close passages of interstellar objects of planetary and substellar masses may affect the immediate and long-term dynamics of the Solar system. We consider two nominal approach orbits, namely the orbits of actual interstellar objects 1I/’Oumuamua and 2I/Borisov, assuming them to be typical or representative for interstellar swarms of matter. Thus, the nominal orbits of the interloper in our models cross the inner part of the Solar system. Series of massive numerical experiments are performed, in which the interloper’s mass is varied with a small step over a broad range. We find that, even if a Jovian-mass interloper does not experience close encounters with the Solar system planets (and this holds for our nominal orbits), our planetary system can be destabilized on time-scales as short as several million years. In what concerns substellar-mass interlopers (free-floating brown dwarfs), an immediate (on a time-scale of ∼10–100 yr) consequence of such a massive interstellar object (MISO) flyby is a sharp increase in the orbital eccentricities and inclinations of the outer planets. On an intermediate time-scale (∼103 to 105 yr after the MISO flyby), Uranus or Neptune can be ejected from the system, as a result of their mutual close encounters and encounters with Saturn. On a secular time-scale (∼106 to 107 yr after the MISO flyby), the perturbation wave formed by secular planetary interactions propagates from the outer Solar system to its inner zone.

Hanawa T., Garufi A., Podio L., Codella C., Segura-Cox D.

ABSTRACT DG Tau is a nearby T Tauri star associated with a collimated jet, a circumstellar disc, and a streamer a few hundred au long. The streamer connects to the disc at ∼50 au from DG Tau. At this location SO emission is observed, likely due to the release of sulphur from dust grains caused by the shock of the impact of the accretion streamer onto the disc. We investigate the possibility that the DG Tau streamer was produced via cloudlet capture on the basis of hydrodynamic simulations, considering a cloudlet initiating infall at 600 au from DG Tau with low angular momentum so that the centrifugal force is smaller than the gravitational force, even at 50 au. The elongation of the cloudlet into a streamer is caused by the tidal force when its initial velocity is much less than the free-fall velocity. The elongated cloudlet reaches the disc and forms a high-density gas clump. Our hydrodynamic model reproduces the morphology and line-of-sight velocity of CS (5 − 4) emission from the northern streamer observed with Atacama Large Millimeter/submillimeter Array. We discuss the conditions for forming a streamer based on the simulations. We also show that the streamer should perturb the disc after impact for several thousands of years.

Skliarevskii A.M., Vorobyov E.I.

FU Orionis type objects (fuors) are characterized by rapid (tens to hundreds years) episodic outbursts, during which the luminosity increases by orders of magnitude. One of the possible causes of such events is a close encounter between stars and protoplanetary disks. Numerical simulations show that the fuor-like outburst ignition requires a very close encounter ranging from a few to a few tens of astronomical units. In contrast, the observed stellar objects in fuor binaries are usually hundreds of astronomical units apart. Simple mathematical estimates show that if such a close approach took place, the binary stellar components would have an unrealistic relative velocity, at least an order of magnitude greater than the observed velocity dispersion in young stellar clusters. Thus, the bursts are either triggered with a certain delay after passage of the periastron or their ignition does not necessary require a close encounter and hence the outburst is not caused by the primordial gravitational perturbation of the protoplanetary disk. In this work, an encounter of a star surrounded by a protoplanetary disk with a diskless external stellar object was modeled using numerical hydrodynamics simulations. We showed that even fly-bys with a relatively large periastron (at least 500 AU) can result in fuor-like outbursts. Moreover, the delay between the periastron passage and the burst ignition can reach several kyr. It was shown for the first time by means of numerical modeling that the perturbation of the disk caused by the external object can trigger a cascade process, which includes the development of the thermal instability in the innermost disk followed by the magneto-rotational instability ignition. Because of the sequential development of these instabilities, the rapid increase in the accretion rate occurs, resulting in the luminosity increase by more than two orders of magnitude.

Demidova T.V., Grinin V.P.

Abstract One of the early hypotheses about the origin of FU Orionis star (FUORs) outbursts explains them based on the fall of gas clumps from the remnants of protostellar clouds onto protoplanetary disks surrounding young stars. To calculate the consequences of such an event, we make 3D hydrodynamic simulations using the smoothed particle hydrodynamics method. It is shown that the fall of the clump on the disk in the vicinity of the star actually causes a burst of the star’s accretion activity, resembling in its characteristics the flares of known FUORs. In the region of incidence, an inhomogeneous gas ring is formed, which is inclined relative to the outer disk. During several revolutions around the star, this ring combines with the inner disk and forms a tilted disk. In the process of evolution, the inner disk expands, and its inclination relative to the outer disk decreases. After 100 revolutions, the angle of inclination is a few degrees. This result is of interest in connection with the discovery in recent years of protoplanetary disks, the inner region of which is inclined relative to the outer one. Such structures are usually associated with the existence in the vicinity of a star of a massive body (planet or brown dwarf), whose orbit is inclined relative to the plane of the disk. The results of our modeling indicate the possibility of an alternative explanation for this phenomenon.

Grinin V.P., Tambovtseva L.V., Barsunova O.Y., Shakhovskoy D.N.

Kulikov I.M., Chernykh I.G., Sapetina A.F., Vorobyov E.I., Elbakyan V.G.

Cuello N., Ménard F., Price D.J.

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 $$\le ~2$$  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.

Unno M., Hanawa T., Takasao S.

Abstract Recent observations suggest late accretion, which is generally nonaxisymmetric, onto protoplanetary disks. We investigated nonaxisymmetric late accretion considering the effects of magnetic fields. Our model assumes a cloudlet encounter event at a few hundred astronomical units scale, where a magnetized gas clump (cloudlet) encounters a protoplanetary disk. We studied how the cloudlet size and the magnetic field strength affect the rotational velocity profile in the disk after the cloudlet encounter. The results show that a magnetic field can either decelerate or accelerate the rotational motion of the cloudlet material, primarily depending on the relative size of the cloudlet to the disk thickness. When the cloudlet size is comparable to or smaller than the disk thickness, magnetic fields only decelerate the rotation of the colliding cloudlet material. However, if the cloudlet size is larger than the disk thickness, the colliding cloudlet material can be super-Keplerian as a result of magnetic acceleration. We found that the vertical velocity shear of the cloudlet produces a magnetic tension force that increases the rotational velocity. The acceleration mechanism operates when the initial plasma β is β ≲ 2 × 101. Our study shows that magnetic fields modify the properties of spirals formed by tidal effects. These findings may be important for interpreting observations of late accretion.

Borchert E.M., Price D.J., Pinte C., Cuello N.

Abstract 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 (∼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.

Demidova T.

The applicability of the Bulirsh–Stoer algorithm for solving the planar restricted three-body problem is investigated. Variations in the value of the Jacobi integral are considered as the main parameter. Massive calculations were carried out with a small step in the parameter characterizing the ratio of the masses of a planet and star (the mass parameter). It is shown that violations of the Jacobi integral occur inside the planetary chaotic region. This fact can be used to determine chaotic region boundaries, as well as the boundaries of a stable structure which coorbital with the planet. The average dependences of the value of the Jacobi integral on the mass parameter, which determine the boundaries of the chaotic zone and the coorbital ring, are derived. Estimates were obtained for the maximum relative change in the Jacobi integral for different values of the accretion radius. It is shown that the value of the accretion radius corresponding to the average radius of known exoplanets does not cause significant changes in the value of the Jacobi integral. The dependences of the clearing time of the chaotic zone for different accretion radii are also given with and without taking into account the coorbital structure.

Albrecht S.H., Dawson R.I., Winn J.N.

Abstract The rotation of a star and the revolutions of its planets are not necessarily aligned. This article reviews the measurement techniques, key findings, and theoretical interpretations related to the obliquities (spin–orbit angles) of planet-hosting stars. The best measurements are for stars with short-period giant planets, which have been found on prograde, polar, and retrograde orbits. It seems likely that dynamical processes such as planet–planet scattering and secular perturbations are responsible for tilting the orbits of close-in giant planets, just as those processes are implicated in exciting orbital eccentricities. The observed dependence of the obliquity on orbital separation, planet mass, and stellar structure suggests that in some cases, tidal dissipation damps a star’s obliquity within its main-sequence lifetime. The situation is not as clear for stars with smaller or wider-orbiting planets. Although the earliest measurements of such systems tended to find low obliquities, some glaring exceptions are now known in which the star’s rotation is misaligned with respect to the coplanar orbits of multiple planets. In addition, statistical analyses based on projected rotation velocities and photometric variability have found a broad range of obliquities for F-type stars hosting compact multiple-planet systems. The results suggest it is unsafe to assume that stars and their protoplanetary disks are aligned. Primordial misalignments might be produced by neighboring stars or more complex events that occur during the epoch of planet formation.

Hammond I., Christiaens V., Price D.J., Ubeira-Gabellini M.G., Baird J., Calcino J., Benisty M., Lodato G., Testi L., Pinte C., Toci C., Fedele D.

ABSTRACT We present new high-contrast images in near-infrared wavelengths (λc = 1.04, 1.24, 1.62, 2.18, and 3.78 μm) of the young variable star CQ Tau, aiming to constrain the presence of companions in the protoplanetary disc. We reached a Ks-band contrast of 14 mag with SPHERE/IRDIS at separations greater than 0${_{.}^{\prime\prime}}$4 from the star. Our mass sensitivity curve rules out giant planets above 4 MJup immediately outside the spiral arms at ∼60 au and above 2–3 MJup beyond 100 au to 5σ confidence assuming hot-start models. We do, however, detect four spiral arms, a double-arc and evidence for shadows in scattered light cast by a misaligned inner disc. Our observations may be explained by an unseen close-in companion on an inclined and eccentric orbit. Such a hypothesis would also account for the disc CO cavity and disturbed kinematics.

Crotts K.A., Draper Z.H., Matthews B.C., Duchêne G., Esposito T.M., Wilner D., Mazoyer J., Padgett D., Kalas P., Stapelfeldt K.

Abstract We observed the nearly edge-on debris disk system HD 111520 at the HJ and K1 near-infrared (NIR) bands using both the spectral and polarization modes of the Gemini Planet Imager. With these new observations, we have performed an empirical analysis in order to better understand the disk morphology and its highly asymmetrical nature. We find that the disk features a large brightness and radial asymmetry, most prominent at shorter wavelengths. We also find that the radial location of the peak polarized intensity differs on either side of the star by 11 au, suggesting that the disk may be eccentric, although, such an eccentricity does not fully explain the large brightness and radial asymmetry observed. Observations of the disk halo with the Hubble Space Telescope also show the disk to be warped at larger separations, with a bifurcation feature in the northwest, further suggesting that there may be a planet in this system creating an asymmetrical disk structure. Measuring the disk color shows that the brighter extension is bluer compared to the dimmer extension, suggesting that the two sides have different dust grain properties. This finding, along with the large brightness asymmetry, are consistent with the hypothesis that a giant impact occurred between two large bodies in the northern extension of the disk, although confirming this based on NIR observations alone is not feasible. Follow-up imaging with the Atacama Large Millimeter/submillimeter Array to resolve the asymmetry in the dust mass distribution is essential in order to confirm this scenario.