{
  "id": "1511.02813",
  "version": "v1",
  "published": "2015-11-09T19:34:22.000Z",
  "updated": "2015-11-09T19:34:22.000Z",
  "title": "Viscous Instability Triggered by Layered Accretion in Protoplanetary Disks",
  "authors": [
    "Yasuhiro Hasegawa",
    "Taku Takeuchi"
  ],
  "comment": "9 pages, 4 figures, accepted for publication in ApJ",
  "categories": [
    "astro-ph.EP"
  ],
  "abstract": "Layered accretion is one of the inevitable ingredients in protoplanetary disks when disk turbulence is excited by magnetorotational instabilities (MRIs). In the accretion, disk surfaces where MRIs fully operate have a high value of disk accretion rate ($\\dot{M}$), while the disk midplane where MRIs are generally quenched ends up with a low value of $\\dot{M}$. Significant progress on understanding MRIs has recently been made by a number of dedicated MHD simulations, which requires improvement of the classical treatment of $\\alpha$ in 1D disk models. To this end, we obtain a new expression of $\\alpha$ by utilizing an empirical formula that is derived from recent MHD simulations of stratified disks with Ohmic diffusion. It is interesting that this new formulation can be regarded as a general extension of the classical $\\alpha$. Armed with the new $\\alpha$, we perform a linear stability analysis of protoplanetary disks that undergo layered accretion, and find that a viscous instability can occur around the outer edge of dead zones. Disks become stable in using the classical $\\alpha$. We identify that the difference arises from $\\Sigma-$dependence of $\\dot{M}$; whereas $\\Sigma$ is uniquely determined for a given value of $\\dot{M}$ in the classical approach, the new approach leads to $\\dot{M}$ that is a multi-valued function of $\\Sigma$. We confirm our finding both by exploring a parameter space as well as by performing the 1D, viscous evolution of disks. We finally discuss other non-ideal MHD effects that are not included in our analysis, but may affect our results.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2015-11-09T19:34:22.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "protoplanetary disks",
      "layered accretion",
      "viscous instability",
      "non-ideal mhd effects",
      "1d disk models"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 9,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}