Emission from Magnetized Accretion Disks around Young Stars

TL;DR

This study models the emission from magnetized protoplanetary disks around young stars, revealing how magnetic strength influences their thermal and emission properties, with implications for interpreting millimeter observations.

Contribution

It provides a detailed calculation of spectral energy distributions and antenna temperature profiles for magnetized disks, highlighting the impact of magnetic field strength on disk emission characteristics.

Findings

Disks with weaker magnetization emit more due to higher density and temperature.

Magnetization level affects optical depth at millimeter wavelengths.

Disks around FU Ori stars are generally optically thick at 7 mm.

Abstract

We calculate the emission of protoplanetary disks threaded by a poloidal magnetic field and irradiated by the central star. The radial structure of these disks was studied by Shu and collaborators and the vertical structure was studied by Lizano and collaborators. We consider disks around low mass protostars, T Tauri stars, and FU Ori stars with different mass-to-flux ratios $\lambda_{\rm sys}$. We calculate the spectral energy distribution and the antenna temperature profiles at 1 mm and 7 mm convolved with the ALMA and VLA beams. We find that disks with weaker magnetization (high values of $\lambda_{\rm sys}$) emit more than disks with stronger magnetization (low values of $\lambda_{\rm sys}$). This happens because the former are denser, hotter and have larger aspect ratios, receiving more irradiation from the central star. The level of magnetization also affects the optical depth at millimeter wavelengths, being larger for disks with high $\lambda_{\rm sys}$. In general, disks around low mass protostars and T Tauri stars are optically thin at 7 mm while disks around FU Ori are optically thick. A qualitative comparison of the emission of these magnetized disks, including heating by an external envelope, with the observed millimeter antenna temperature profiles of HL Tau indicates that large cm grains are required to increase the optical depth and reproduce the observed 7 mm emission at large radii.