Context. The water snowline divides dry and icy solid material in protoplanetary disks, and has been thought to significantly affect planet formation at all stages. If dry particles break up more easily than icy ones, then the snowline causes a traffic jam, because small grains drift inward at lower speeds than larger pebbles. Aims. We aim to measure the effect of high dust concentrations around the snowline onto the gas dynamics. Methods. Using numerical simulations, we model the global radial evolution of an axisymmetric protoplanetary disk. Our model includes particle growth, evaporation and recondensation of water, and the back-reaction of dust onto the gas, taking into account the vertical distribution of dust particles.Results. We find that the dust back-reaction can stop and even reverse the flux of gas outside the snowline, decreasing the gas accretion rate onto the star to under 50% of its initial value. At the same time the dust accumulates at the snowline, reaching dust-to-gas ratios of 0.8, and delivers large amounts of water vapor towards the inner disk, as the icy particles cross the snowline. However, the accumulation of dust at the snowline and the decrease in the gas accretion rate only take place if the global dust-to-gas ratio is high (ε 0 0.03), if the viscous turbulence is low (α ν 10 −3 ), if the disk is large enough (r c 100 AU), and only during the early phases of the disk evolution (t 1 Myr). Otherwise the dust back-reaction fails to perturb the gas motion.

Context. Observations of young stars hosting transition disks show that several of them have high accretion rates, despite their disks presenting extended cavities in their dust component. This represents a challenge for theoretical models, which struggle to reproduce both features simultaneously. Aims. We aim to explore if a disk evolution model, including a dead zone and disk dispersal by X-ray photoevaporation, can explain the high accretion rates and large gaps (or cavities) measured in transition disks. Methods. We implemented a dead zone turbulence profile and a photoevaporative mass-loss profile into numerical simulations of gas and dust. We performed a population synthesis study of the gas component and obtained synthetic images and SEDs of the dust component through radiative transfer calculations. Results. This model results in long-lived inner disks and fast dispersing outer disks that can reproduce both the accretion rates and gap sizes observed in transition disks. For a dead zone of turbulence αdz = 10−4 and an extent rdz = 10 AU, our population synthesis study shows that 63% of our transition disks are still accreting with Ṁg ≥ 10−11 M⊙ yr−1 after opening a gap. Among those accreting transition disks, half display accretion rates higher than 5.0 × 10−10 M⊙ yr−1. The dust component in these disks is distributed in two regions: in a compact inner disk inside the dead zone, and in a ring at the outer edge of the photoevaporative gap, which can be located between 20 and 100 AU. Our radiative transfer calculations show that the disk displays an inner disk and an outer ring in the millimeter continuum, a feature that resembles some of the observed transition disks. Conclusions. A disk model considering X-ray photoevaporative dispersal in combination with dead zones can explain several of the observed properties in transition disks, including the high accretion rates, the large gaps, and a long-lived inner disk at millimeter emission.

Context. In the last six years, the VISTA Variable in the Vía Láctea (VVV) survey mapped 562 sq. deg. across the bulge and southern disk of the Galaxy. However, a detailed study of these regions, which includes ∼36 globular clusters (GCs) and thousands of open clusters is by no means an easy challenge. High differential reddening and severe crowding along the line of sight makes highly hamper to reliably distinguish stars belonging to different populations and/or systems. Aims. The aim of this study is to separate stars that likely belong to the Galactic GC NGC 6544 from its surrounding field by means of proper motion (PM) techniques. Methods. This work was based upon a new astrometric reduction method optimized for images of the VVV survey. Results. PSF-fitting photometry over the six years baseline of the survey allowed us to obtain a mean precision of ∼0.51 mas yr −1 , in each PM coordinate, for stars with Ks < 15 mag. In the area studied here, cluster stars separate very well from field stars, down to the main sequence turnoff and below, allowing us to derive for the first time the absolute PM of NGC 6544. Isochrone fitting on the clean and differential reddening corrected cluster color magnitude diagram yields an age of ∼11−13 Gyr, and metallicity [Fe/H] = −1.5 dex, in agreement with previous studies restricted to the cluster core. We were able to derive the cluster orbit assuming an axisymmetric model of the Galaxy and conclude that NGC 6544 is likely a halo GC. We have not detected tidal tail signatures associated to the cluster, but a remarkable elongation in the galactic center direction has been found. The precision achieved in the PM determination also allows us to separate bulge stars from foreground disk stars, enabling the kinematical selection of bona fide bulge stars across the whole survey area. Conclusions. Kinematical techniques are a fundamental step toward disentangling different stellar populations that overlap in a studied field. Our results show that VVV data is perfectly suitable for this kind of analysis.

RW Aur A has experienced various dimming events in the last years, decreasing its brightness by ∼ 2 mag for periods of months to years. Multiple observations indicate that a high concentration of dust grains, from the protoplanetary disk's inner regions, is blocking the starlight during these events. We propose a new mechanism that can send large amounts of dust close to the star on short timescales, through the reactivation of a dead zone in the protoplanetary disk. Using numerical simulations we model the accretion of gas and dust, along with the growth and fragmentation of particles in this scenario. We find that after the reactivation of the dead zone, the accumulated dust is rapidly accreted towards the star in around 15 years, at rates ofṀ d = 6 × 10 −6 M /yr and reaching dust-to-gas ratios of ≈ 5, preceding an increase in the gas accretion by a few years. This sudden rise of dust accretion can provide the material required for the dimmings, although the question of how to put the dust into the line of sight remains open to speculation.