Dust entrainment in photoevaporative winds: The impact of X-rays

¹ Faculty of Physics, University Observatory, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
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² Excellence Cluster Origin and Structure of the Universe, Boltzmannstr. 2, 85748 Garching, Germany

Received: 2 September 2019
Accepted: 8 January 2020

Abstract

Context. X-ray- and extreme ultraviolet (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 magnetohydrodynamic 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 L_X = 2 × 10³⁰ erg s⁻¹ emitted by a M_* = 0.7 M_⊙ star, corresponding to a wind mass-loss rate of Ṁ_w ≃ 2.6 × 10⁻⁸ M_⊙ yr⁻¹, 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 with Ṁ_w ≃ 10⁻¹⁰ M_⊙ yr⁻¹. 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.