Physical and chemical vertical structure of magnetostatic accretion disks of young stars

TL;DR

This study models the vertical physical and chemical structure of magnetized accretion disks around young stars, revealing temperature, magnetic, and molecular distributions, and suggests observational methods to measure magnetic fields.

Contribution

It provides a comprehensive magnetostatic equilibrium model of young star disks, integrating magnetic, thermal, and chemical structures, and highlights the role of magnetic fields in disk thickness and molecular distribution.

Findings

Temperature decreases with height within 50 au of the star.

Magnetic field strength peaks within the disk, affecting its structure.

CN molecule concentration peaks near the photosphere and disk atmosphere.

Abstract

The vertical structure of the accretion disks of young stars with fossil large-scale magnetic field is studied. The equations of magnetostatic equilibrium of the disk are solved taking into account the stellar gravity, gas and magnetic pressure, turbulent heating, and heating by stellar radiation. The modelled physical structure of the disk is used to simulate its chemical structure, in particular, to study the spatial distribution of CN molecules. The disk of the typical T Tauri star is considered. Simulations show that the temperature within the disk in the region $r<50$ au decreases with height and density profiles are steeper than in the isothermal case. Outside the `dead' zone, vertical profiles of the azimuthal component of the magnetic field are nonmonotonic, and the magnetic field strength maximum is reached within the disk. The magnetic pressure gradient can cause an increase in the disk thickness in comparison with the hydrostatic one. The CN molecule concentration is maximum near the photosphere and in the disk atmosphere where the magnetic field strength at chosen parameters is $\sim 0.01$ G. Measurements of the Zeeman splitting of CN lines in the submm range can be used to determine the magnetic field strength in these regions of accretion disks.