Heating mechanisms of protostellar accretion disks

Abstract

Accretion disks are commonly found around young stars, such as T Tauri stars. In order to occur the transport of matter to the star, the particles of the disk need to loose some of their rotational energy and fall towards the central object. The most promising mechanism of angular momentum transport is the magneto-rotational instability (IMR). However, this instability requires that the particles be coupled to the magnetic field lines. For this to happen, at least a fraction of the particles needs to be charged. As the temperatures through the disk are low, the ionization rates are also very small. Thus for the IMR to occur throughthe whole disk, the temperatures must be higher. There are in the literature models that include the damping of Alfvén waves as an additional heating source, in particular, the nonlinear, turbulent and the ressonant damping of surface Alfvén waves. The objective of the present project is to analyze which of these damping mechanisms is the most efficient for the disk heating as a function of radial distance and height. Although in the literature these damping mechanisms were used independently they can act together. In this way, we will investigate the way in which this coupling can be obtained in a way to maximize theheating of the disk. In addition, the fraction of ionization that each damping mechanism contributes to the heating of the disk will be calculated. In parallel, a numerical code will be constructed in order to solve the disk equations, including the combination the three cited mechanisms as an additional source of energy. (AU)