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      The FRIED grid of mass loss rates for externally irradiated protoplanetary discs

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          Abstract

          We present an open access grid of 3930 calculations of externally evaporating protoplanetary discs. This spans a range of disc sizes (1-400AU), disc masses, UV field strengths (10-10\(^4\)G\(_0\)) and stellar masses (0.05-1.9M\(_\odot\)). The grid is publicly available for download, and offers a means of cheaply including external photoevaporation in disc evolutionary calculations. It can also be queried using an online tool for quick estimates of instantaneous mass loss rates (e.g for convenient evaluation of real observed systems). The `FRIED' grid itself illustrates that for discs around stars \(\leq0.3\)M\(_\odot\) external photoevaporation is effective down to small radii (\(<50\)AU) down to UV fields at least as weak as 10G\(_0\). At the other end of the scale, in a \(10^4\)G\(_0\) environment photoevaporation is effective down to 1AU even for stellar masses at least as high as 1.9M\(_\odot\). We also illustrate in which regimes CO survives in the photoevaporative outflow for significant mass loss rates; marking a system a good candidate to detect external photoevaporation in weak-intermediate UV environments through sub-Keplerian rotation. Finally we make illustrative mass loss rate estimates for discs in Taurus based on the Guilloteau et al. (2011) star-disc parameters, finding that around half are expected to have both significant mass loss and retain CO in the photoevaporative outflow.

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          A self-similar solution for thermal disc winds

          We derive a self-similar description for the 2D streamline topology and flow structure of an axi-symmetric, thermally driven wind originating from a disc in which the density is a power law function of radius. Our scale-free solution is strictly only valid in the absence of gravity or centrifugal support; comparison with 2D hydrodynamic simulations of winds from Keplerian discs however demonstrates that the scale-free solution is a good approximation also in the outer regions of such discs, and can provide a reasonable description even for launch radii well within the gravitational radius of the flow. Although other authors have considered the flow properties along streamlines whose geometry has been specified in advance, this is the first isothermal calculation in which the flow geometry and variation of flow variables along streamlines is determined self-consistently. It is found that the flow trajectory is very sensitive to the power-law index of radial density variation in the disc: the steeper the density gradient, the stronger is the curvature of streamlines close to the flow base that is required in order to maintain momentum balance perpendicular to the flow. Steeper disc density profiles are also associated with more rapid acceleration, and a faster fall-off of density, with height above the disc plane. The derivation of a set of simple governing equations for the flow structure of thermal winds from the outer regions of power law discs offers the possibility of deriving flow observables without having to resort to hydrodynamical simulation.
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            Author and article information

            Journal
            22 August 2018
            Article
            1808.07484
            eb4c63a9-ed06-4467-ad97-a25f60f3e9fb

            http://arxiv.org/licenses/nonexclusive-distrib/1.0/

            History
            Custom metadata
            16 pages, 9 figures. Accepted for publication in MNRAS
            astro-ph.SR astro-ph.EP

            Planetary astrophysics,Solar & Stellar astrophysics
            Planetary astrophysics, Solar & Stellar astrophysics

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