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Convergence of Simulations of Self-Gravitating Accretion Discs - II: Sensitivity to the Implementation of Radiative Cooling and Artificial Viscosity

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http://arxiv.org/abs/1311.7355
http://adsabs.harvard.edu/abs/2014MNRAS.438.1593R
Original languageEnglish
Pages (from-to)1593-1602
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume438
Issue number2
DOIs
StatePublished - 1 Feb 2014

Abstract

Recently, it has been suggested that the fragmentation boundary in smoothed particle hydrodynamic (SPH) and FARGO simulations of self-gravitating accretion discs with beta-cooling do not converge as resolution is increased. Furthermore, this recent work suggests that by carefully optimizing the artificial viscosity parameters in these codes, it can be shown that fragmentation may occur for much longer cooling times than earlier work suggests. If correct, this result is intriguing as it suggests that gas giant planets could form, via direct gravitational collapse, reasonably close to their parent stars. This result is, however, slightly surprising and there have been a number of recent studies suggesting that the result is likely an indication of a numerical problem with the simulations. One suggestion, in particular, is that the SPH results are influenced by the manner in which the cooling is implemented. We extend this work here and show that if the cooling is implemented in a manner that removes a known numerical artefact in the shock regions, the fragmentation boundary converges to a value consistent with earlier work and that fragmentation is unlikely for the long cooling times suggested by this recent work. We also investigate the optimization of the artificial viscosity parameters and show that the values that appear optimal are likely introducing numerical problems in both the SPH and FARGO simulations. We therefore conclude that earlier predictions for the cooling times required for fragmentation are likely correct and that, as suggested by this earlier work, fragmentation cannot occur in the inner parts (r <50 au) of typical protostellar discs.

    Research areas

  • accretion, accretion discs, gravitation, instabilities, planets and satellites: formation, stars: formation

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