Dust dynamics during protoplanetary disc clearing

Authors

  • R. D. Alexander,

    Corresponding author
    1. JILA, University of Colorado, Boulder, CO 80309-0440, USA
      E-mail: rda@jilau1.colorado.edu
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  • P. J. Armitage

    1. JILA, University of Colorado, Boulder, CO 80309-0440, USA
    2. Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0391, USA
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E-mail: rda@jilau1.colorado.edu

ABSTRACT

We consider the dynamics of dust and gas during the clearing of protoplanetary discs. We work within the context of a photoevaporation/viscous model for the evolution of the gas disc, and use a two-fluid model to study the dynamics of dust grains as the gas disc is cleared. Small (≲10 μm) grains remain well coupled to the gas, but larger (∼1 mm) grains are subject to inward migration from large radii (∼50 au), suggesting that the time-scale for grain growth in the outer disc is ∼104–105 yr. We describe in detail the observable appearance of discs during clearing, and find that pressure gradients in the gas disc result in a strong enhancement of the local dust-to-gas ratio in a ring near to the inner disc edge. Lastly, we consider a simple model of the disc–planet interaction, and suggest that observations of disc masses and accretion rates provide a straightforward means of discriminating between different models of disc clearing.

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