Context. X-ray-and EUV-(XEUV-) driven photoevaporative winds acting on protoplanetary disks around young T-Tauri stars may crucially impact disk evolution, affecting both gas and dust distributions. Aims. We investigate the dust entrainment in XEUV-driven photoevaporative winds and compare our results to existing MHD and EUV-only models. Methods. We used a 2D hydrodynamical gas model of a protoplanetary disk irradiated by both X-ray and EUV spectra from a central T-Tauri star to trace the motion of passive Lagrangian dust grains of various sizes. The trajectories were modelled starting at the disk surface in order to investigate dust entrainment in the wind. Results. For an X-ray luminosity of LX = 2·10 30 erg/s emitted by a M * = 0.7 M star, corresponding to a wind mass-loss rate ofṀw 2.6 · 10 −8 M /yr, we find dust entrainment for sizes a0 11 µm (9 µm) from the inner 25 AU (120 AU). This is an enhancement over dust entrainment in less vigorous EUV-driven winds withṀw 10 −10 M /yr. Our numerical model also shows deviations of dust grain trajectories from the gas streamlines even for µm-sized particles. In addition, we find a correlation between the size of the entrained grains and the maximum height they reach in the outflow.Conclusions. X-ray-driven photoevaporative winds are expected to be dust-rich if small grains are present in the disk atmosphere.Key words. protoplanetary disks -stars: T-Tauri -dust entrainment -photoevaporative winds: XEUV -methods: numerical -silicate grains -young stellar objects -interstellar dust processes 1 The ionization parameter is defined as ξ = L * /(n r 2 ), with L * the stellar luminosity, n the gas density, and r the (spherical) radial distance from the star. 2 '2.5D' meaning a 2D coordinate system (r, ϑ) with 3D velocity information (vr, v ϑ , vϕ).Article number, page 2 of 18 R. Franz et al.: Dust entrainment in photoevaporative winds: The impact of X-rays

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. X-ray- and extreme-ultraviolet- (together: XEUV-) driven photoevaporative winds acting on protoplanetary disks around young T-Tauri stars may crucially impact disk evolution, affecting both gas and dust distributions. Aims. We constrain the dust densities in a typical XEUV-driven outflow, and determine whether these winds can be observed at μm-wavelengths. Methods. We used dust trajectories modelled atop a 2D hydrodynamical gas model of a protoplanetary disk irradiated by a central T-Tauri star. With these and two different prescriptions for the dust distribution in the underlying disk, we constructed wind density maps for individual grain sizes. We used the dust density distributions obtained to synthesise observations in scattered and polarised light. Results. For an XEUV-driven outflow around a M* = 0.7 M⊙ T-Tauri star with LX = 2 × 1030 erg s−1, we find a dust mass-loss rate Ṁdust ≲ 4.1 × 10−11 M⊙ yr−1 for an optimistic estimate of dust densities in the wind (compared to Ṁgas ≈ 3.7 × 10−8 M⊙ yr−1). The synthesised scattered-light images suggest a distinct chimney structure emerging at intensities I∕Imax < 10−4.5 (10−3.5) at λobs = 1.6 (0.4) μm, while the features in the polarised-light images are even fainter. Observations synthesised from our model do not exhibit clear features for SPHERE IRDIS, but show a faint wind signature for JWST NIRCam under optimal conditions. Conclusions. Unambiguous detections of photoevaporative XEUV winds launched from primordial disks are at least challenging with current instrumentation; this provides a possible explanation as to why disk winds are not routinely detected in scattered or polarised light. Our calculations show that disk scale heights retrieved from scattered-light observations should be only marginally affected by the presence of an XEUV wind.

Context. X-ray- and extreme-ultraviolet- (XEUV-) driven photoevaporative winds acting on protoplanetary disks around young T Tauri stars may strongly impact disk evolution, affecting both gas and dust distributions. Small dust grains in the disk are entrained in the outflow and may produce a detectable signal. In this work, we investigate the possibility of detecting dusty outflows from transition disks with an inner cavity. Aims. We compute dust densities for the wind regions of XEUV-irradiated transition disks and determine whether they can be observed at wavelengths 0.7 ≲ λobs [μm] ≲ 1.8 with current instrumentation. Methods. We simulated dust trajectories on top of 2D hydrodynamical gas models of two transition disks with inner holes of 20 and 30 AU, irradiated by both X-ray and EUV spectra from a central T Tauri star. The trajectories and two different settling prescriptions for the dust distribution in the underlying disk were used to calculate wind density maps for individual grain sizes. Finally, the resulting dust densities were converted to synthetic observations in scattered and polarised light. Results. For an XEUV-driven outflow around a M* = 0.7 M⊙ T Tauri star with LX = 2 × 1030 erg s-1, we find dust mass-loss rates Ṁdust ≲ 2.0 × 10−3 Ṁgas, and if we invoke vertical settling, the outflow is quite collimated. The synthesised images exhibit a distinct chimney-like structure. The relative intensity of the chimneys is low, but their detection may still be feasible with current instrumentation under optimal conditions. Conclusions. Our results motivate observational campaigns aimed at the detection of dusty photoevaporative winds in transition disks using JWST NIRCam and SPHERE IRDIS.

Photoevaporative disc winds play a key role in our understanding of circumstellar disc evolution, especially in the final stages, and they might affect the planet formation process and the final location of planets. The study of transition discs (i.e. discs with a central dust cavity) is central for our understanding of the photoevaporation process and disc dispersal. However, we need to distinguish cavities created by photoevaporation from those created by giant planets. Theoretical models are necessary to identify possible observational signatures of the two different processes, and models to find the differences between the two processes are still lacking. In this paper we study a sample of transition discs obtained from radiation-hydrodynamic simulations of internally photoevaporated discs, and focus on the dust dynamics relevant for current ALMA observations. We then compared our results with gaps opened by super Earths/giant planets, finding that the photoevaporated cavity steepness depends mildly on gap size, and it is similar to that of a 1 MJ mass planet. However, the dust density drops less rapidly inside the photoevaporated cavity compared to the planetary case due to the less efficient dust filtering. This effect is visible in the resulting spectral index, which shows a larger spectral index at the cavity edge and a shallower increase inside it with respect to the planetary case. The combination of cavity steepness and spectral index might reveal the true nature of transition discs.