Increase of ionization fraction of dusty proto-stelLar accretion disks by damping of Alfvén waves

Abstract

The ambient of the cloud that gives rise to the process of star formationconsisted of: turbulence, magnetic field and dust. In general, in the process of star formation there is the formation of an accretion disk whose material must lose their angular momentum in order to be accreted into the central object. The magneto-rotational instability (MRI) is probably the mechanism responsible for a magnetohydrodynamic (MHD) turbulence that leads to disk accretion. However, this mechanism only exists if the gas in the disk is sufficiently ionized to be coupled to the magnetic field. Besides the viscous heating mechanism often included in the models by means of the alpha-prescription, in this work we study the damping of Alfv´en waves as an additional heating source. The waves suffer a damping near the dustcyclotron frequency, since charged grains in a magnetized disk are highly coupled to the waves due to cyclotron resonances. We study the transfer of energy from the damping of the waves to the disk and we show that this mechanism can increase the ionization fraction, making possible the presence of the MRI in a large part of the disk.