Magnetically controlled spasmodic accretion during star formation. I. Formulation of the problem and method of solution

Konstantinos Tassis, Telemachos Ch Mouschovias

Research output: Contribution to journalArticle

Abstract

We formulate the problem of the late accretion phase of the evolution of an isothermal magnetic disk surrounding a forming star. The evolution is described by the six-fluid MHD equations, accounting for the presence of neutrals, atomic and molecular ions, electrons, and neutral, positively, and negatively charged grains. Only the electron fluid is assumed to be attached to the magnetic field, in order to investigate the effect of the detachment of the ions from the magnetic field lines that begins at densities as low as 10 8 cm-3. The "central sink approximation" is used to circumvent the problem of describing the evolution inside the opaque central region for densities greater than 1011 cm-3. In this way, the structure and evolution of the isothermal disk surrounding the forming star can be studied at late times without having to implement the numerically costly radiative transfer required by the physics of the opaque core. The mass and magnetic flux accumulating in the forming star are calculated, as are their effects on the structure & evolution of the surrounding disk. The numerical method of solution first uses an adaptive grid and later, after a central region a few AU in radius becomes opaque, switches to a stationary but nonuniform grid with a central sink cell. It also involves an implicit time integrator, an advective difference scheme that possesses the transportive property, a second-order difference approximation of forces inside a cell, an integral approximation of the gravitational and magnetic fields, and tensor artificial viscosity that permits an accurate investigation of the formation and evolution of shocks in the neutral fluid.

Original languageEnglish (US)
Pages (from-to)769-782
Number of pages14
JournalAstrophysical Journal
Volume618
Issue number2 I
DOIs
StatePublished - Jan 10 2005

Keywords

  • Accretion, accretion disks
  • Dust, extinction
  • MHD -shock waves
  • Magnetic fields
  • Stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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