Photoevaporation of planet-forming discs by high energy radiation from the central star is potentially a crucial mechanism for disc evolution and it may play an important role in the formation and evolution of planetary systems. We present here a new generation of X-ray photoevaporation models for solar-type stars, based on hydrodynamical simulations, which account for stellar irradiation via a significantly improved parameterisation of gas temperatures, based on detailed photoionisation and radiation transfer calculations. This is the first of a series of papers aiming at providing a library of models which cover the observed parameter space in stellar and disc mass, metallicity and stellar X-ray properties. We focus here on solar-type stars (0.7 M ) with relatively low-mass discs (1% of the stellar mass) and explore the dependence of the wind mass-loss rates on stellar X-ray luminosity. We model primordial discs and transition discs at various stages of evolution. Our 2D hydrodynamical models are then used to derive simple recipes for the mass-loss rates that are suitable for one-dimensional disc evolution and/or planet formation models typically employed for population synthesis studies. Line profiles from typical wind diagnostics ([OI] 6300Å and [NeII] 12.8 µm) are also calculated for our models and found to be roughly in agreement with previous studies. Finally, we perform a population study of transition discs by means of one-dimensional viscous evolution models including our new photoevaporation prescription and find that roughly a half of observed transition discs cavities and accretion rates could be reproduced by our models.

Aims. Disks around a central binary system play an important role in star and planet formation as well as for the evolution of galactic disks. These circumbinary disks are strongly disturbed by the time varying potential of the binary system and display a complex dynamical evolution that is not well understood. Our goal is to investigate the impact of disk and binary parameters to the dynamical aspects of the disk. Methods. We study the evolution of circumbinary disks under the gravitational influence of the binary using two-dimensional hydrodynamical simulations. To distinguish between physical and numerical effects we apply three hydrodynamical codes. First we analyse in detail numerical issues concerning the conditions at the boundaries and grid resolution. We then perform a series of simulations with different binary (eccentricity, mass ratio) and disk parameters (viscosity, aspect ratio) starting from a reference model with Kepler-16 parameter.Results. Concerning the numerical aspects we find that the inner grid radius must be of the order of the binary semi-major axis, with free outflow conditions applied such that mass can flow onto the central binary. A closed inner boundary leads to unstable evolutions. We find that the inner disk turns eccentric and precesses for all investigated physical parameters. The precession rate is slow with periods (T prec ) starting at around 500 binary orbits (T bin ) for high viscosity and large H/R where the inner hole is smaller and more circular. Reducing α and H/R increases the gap size and T prec reaches 2500 T bin . For varying binary mass ratios q bin the gap size remains constant whereas T prec decreases for increasing q bin . For varying binary eccentricities e bin we find two separate branches in the gap size and eccentricity diagram. The bifurcation occurs at around e crit ≈ 0.18 where the gap is smallest with the shortest T prec . For e bin smaller and larger than e crit the gap size and T prec increase. Circular binaries create the most eccentric disks.

High-resolution spectra of typical wind diagnostics ([O i] 6300 Å and other forbidden emission lines) can often be decomposed into multiple components: high-velocity components with blueshifts up to several 100 km s−1 are usually attributed to fast jets, while narrow (NLVC) and broad (BLVC) low-velocity components are believed to trace slower disc winds. Under the assumption that the line broadening is dominated by Keplerian rotation, several studies have found that the BLVCs should trace gas launched between 0.05 and 0.5 au and correlations between the properties of BLVCs and NLVCs have been interpreted as evidence for the emission tracing an extended magnetohydrodynamics (MHD) wind and not a photoevaporative wind. We calculated synthetic line profiles obtained from detailed photoionization calculations of an X-ray photoevaporation model and a simple MHD wind model and analysed the emission regions of different diagnostic lines and the resulting spectral profiles. The photoevaporation model reproduces most of the observed NLVCs but not the BLVCs or HVCs. The MHD model is able to reproduce all components but produces Keplerian double peaks at average inclinations that are rarely observed. The combination of MHD and photoevaporative winds could solve this problem. Our results suggest that the Gaussian decomposition does not allow for a clear distinction of flux from different wind regions and that the line broadening is often dominated by the velocity gradient in the outflow rather than by Keplerian rotation. We show that observed correlations between BLVC and NLVC do not necessarily imply a common origin in an extended MHD wind.

Context. Recent observations from NASA's Kepler mission detected the first planets in circumbinary orbits. The question we try to answer is where these planets formed in the circumbinary disk and how far inside they migrated to reach their present location. Aims. We investigate the first and most delicate phase of planet formation when planetesimals accumulate to form planetary embryos. Methods. We use the hydrodynamical code FARGO to study the evolution of the disk and of a test population of planetesimals embedded in it. With this hybrid hydrodynamical-N-body code we can properly account for the gas drag force on the planetesimals and for the gravitational force of the disk on them.Results. The numerical simulations show that the gravity of the eccentric disk on the planetesimal swarm excites their eccentricities to much higher values than those induced by the binary perturbations only within 10 AU from the stars. Moreover, the disk gravity prevents a full alignment of the planetesimal pericenters. Both these effects lead to high impact velocities, beyond the critical value for erosion. Conclusions. Planetesimal accumulation in circumbinary disks appears to be prevented close to the stellar pair by the gravitational perturbations of the circumbinary disk. The observed planets possibly formed in the outer regions of the disk and then migrated inside by tidal interaction with the disk.

Recently, the vertical shear instability (VSI) has become an attractive purely hydrodynamic candidate for the anomalous angular momentum transport required for weakly ionized accretion disks. In direct three-dimensional numerical simulations of VSI turbulence in disks, a meridional circulation pattern was observed that is opposite to the usual viscous flow behavior. Here, we investigate whether this feature can possibly be explained by an anisotropy of the VSI turbulence. Using three-dimensional hydrodynamical simulations, we calculate the turbulent Reynolds stresses relevant for angular momentum transport for a representative section of a disk. We find that the vertical stress is significantly stronger than the radial stress. Using our results in viscous disk simulations with different viscosity coefficients for the radial and vertical direction, we find good agreement with the VSI turbulence for the stresses and meridional flow; this provides additional evidence for the anisotropy. The results are important with respect to the transport of small embedded particles in disks.

We predict magnitudes for young planets embedded in transition discs, still affected by extinction due to material in the disc. We focus on Jupiter-size planets at a late stage of their formation, when the planet has carved a deep gap in the gas and dust distributions and the disc starts being transparent to the planet flux in the infrared (IR). Column densities are estimated by means of three-dimensional hydrodynamical models, performed for several planet masses. Expected magnitudes are obtained by using typical extinction properties of the disc material and evolutionary models of giant planets. For the simulated cases located at 5.2 AU in a disc with local unperturbed surface density of 127 g · cm −2 , a 1 M J planet is highly extincted in J-, H-and Kbands, with predicted absolute magnitudes ≥ 50 mag. In L-and M-bands extinction decreases, with planet magnitudes between 25 and 35 mag. In the N-band, due to the silicate feature on the dust opacities, the expected magnitude increases to ∼ 40 mag. For a 2 M J planet, the magnitudes in J-, H-and K-bands are above 22 mag, while for L-, M-and N-bands the planet magnitudes are between 15 and 20 mag. For the 5 M J planet, extinction does not play a role in any IR band, due to its ability to open deep gaps. Contrast curves are derived for the transition discs in CQ Tau, PDS 70, HL Tau, TW Hya and HD 163296. Planet mass upper-limits are estimated for the known gaps in the last two systems.

Context. We have been observing, thanks to ALMA, the dust distribution in the region of active planet formation around young stars. This is a powerful tool that can be used to connect observations with theoretical models and improve our understanding of the processes at play. Aims. We want to test how a multiplanetary system shapes its birth disk and to study the influence of the planetary masses and particle sizes on the final dust distribution. Moreover, we apply our model to the HL Tau system in order to obtain some insights on the physical parameters of the planets that are able to create the observed features. Methods. We follow the evolution of a population of dust particles, treated as Lagrangian particles, in two-dimensional locally isothermal disks where two equal-mass planets are present. The planets are kept in fixed orbits and they do not accrete mass.Results. The outer planet plays a major role in removing the dust particles in the co-orbital region of the inner planet and in forming a particle ring which have a steeper density gradient close to the gap edge respect to the single-planet scenario, promoting the development of vortices. The ring and gap width depend strongly on the planetary mass and particle stopping times, and for the more massive cases on the ring clumps in few stable points that are able to collect a high mass fraction. The features observed in the HL Tau system can be explained through the presence of several massive cores that shape the dust disk where the inner planet(s) have a mass of the order of 0.07 M Jup and the outer one(s) of the order of 0.35 M Jup . These values can be significantly lower if the disk mass turns out to be less than previously estimated. By decreasing the disk mass by a factor of 10, we obtain similar gap widths for planets with a mass of 10 M ⊕ and 20 M ⊕ for the inner and outer planets, respectively. Although the particle gaps are prominent, the expected gaseous gaps are barely visible.

The growth process of protoplanets can be sped up by accreting a large number of solid, pebble-sized objects that are still present in the protoplanetary disc. It is still an open question on how efficient this process works in realistic turbulent discs. We investigate the accretion of pebbles in turbulent discs that are driven by the purely hydrodynamical vertical shear instability (VSI). For this purpose, we performed global 3D simulations of locally isothermal, VSI turbulent discs that have embedded protoplanetary cores from 5 to 100 M ⊕ , which are placed at 5.2 au distance from the star. In addition, we followed the evolution of a swarm of embedded pebbles of different sizes under the action of drag forces between gas and particles in this turbulent flow. Simultaneously, we performed a set of comparison simulations for laminar viscous discs where the particles experience stochastic kicks. For both cases, we measured the accretion rate onto the cores as a function of core mass and Stokes number (τ s ) of the particles and compared these values to recent magneto-rotational instability (MRI) turbulence simulations. Overall the dynamic is very similar for the particles in the VSI turbulent disc and the laminar case with stochastic kicks. For small mass planets (i.e. 5 − 10 M ⊕ ), well-coupled particles with τ s = 1, which have a size of about one metre at this location, we find an accretion efficiency (rate of particles accreted over drifting inwards) of about 1.6 − 3%. For smaller and larger particles this efficiency is higher. However, the fast inwards drift for τ s = 1 particles makes them the most effective for rapid growth, leading to mass doubling times of about 20, 000 yr. For masses between 10 and 30 M ⊕ the core reaches the pebble isolation mass and the particles are trapped at the pressure maximum just outside of the planet, shutting off further particle accretion.