9
views
0
recommends
+1 Recommend
0 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: found
      Is Open Access

      On the Ionisation Fraction in Protoplanetary Disks I: Comparing Different Reaction Networks

      Preprint
      ,

      Read this article at

      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          We calculate the ionisation fraction in protostellar disk models using a number of different chemical reaction networks, including gas-phase and gas-grain reaction schemes. The disk models we consider are conventional alpha-disks, which include viscous heating and radiative cooling. The primary source of ionisation is assumed to be X-ray irradiation from the central star. We consider a number of gas-phase chemical networks. In general we find that the simple models predict higher fractional ionisation levels and more extensive active zones than the more complex models. When heavy metal atoms are included the simple models predict that the disk is magnetically active throughout. The complex models predict that extensive regions of the disk remain magnetically uncoupled even with a fractional abundance of magnesium of 10(-8). The addition of submicron sized grains with a concentration of 10(-12) causes the size of the dead zone to increase dramatically for all kinetic models considered. We find that the simple and complex gas-grain reaction schemes agree on the size and structure of the resulting dead zone. We examine the effects of depleting the concentration of small grains as a crude means of modeling the growth of grains during planet formation. We find that a depletion factor of 10(-4) causes the gas-grain chemistry to converge to the gas-phase chemistry when heavy metals are absent. 10(-8) is required when magnesium is included. This suggests that efficient grain growth and settling will be required in protoplanetary disks, before a substantial fraction of the disk mass in the planet forming zone between 1 - 10 AU becomes magnetically active and turbulent.

          Related collections

          Author and article information

          Journal
          19 September 2005
          2005-11-09
          Article
          10.1051/0004-6361:20053678
          astro-ph/0509550
          3a08c26d-563a-404a-a979-35c4d57b447b
          History
          Custom metadata
          21 pages, 23 figures, accepted for publication in A & A Includes correction to our implementation of the Umebayashi-Nakano reaction network
          astro-ph

          Comments

          Comment on this article