Dynamics of magnetic flux tubes and IR-variability of young stellar objects

Abstract

We simulate the dynamics of slender magnetic flux tubes (MFTs) in the accretion disks of T Tauri stars. The dynamical equations of our model take into account aerodynamic and turbulent drag forces, and the radiative heat exchange between the MFT and ambient gas. The structure of the disk is calculated with the help of our MHD model of the accretion disks. We consider the MFTs formed at distances of 0.027 − 0.8 au from the star with various initial radii and plasma betas β 0 . The simulations show that MFTs with a weak magnetic field (β 0 = 10) rise slowly with speeds less than the speed of sound. MFTs with β 0 = 1 form an outflowing magnetized corona above the disk. Strongly magnetized MFTs (β 0 = 0.1) can cause outflows with velocities 20 − 50 km s −1 . The tubes rise periodically over times from several days to several months according to our simulations. We propose that periodically rising MFTs can absorb stellar radiation and contribute to the IR-variability of young stellar objects.

Dynamics of magnetic flux tubes in accretion discs of T Tauri stars

“…The MFT with weak magnetic field (β 0 = 10) have velocities of 0.05 − 0.5 km s −1 . The MFT with plasma β = 1 accelerate to velocity ≈ 0.2 − 4 km s −1 comparable with sound speed, in agreement with analytical estimates of Khaibrakhmanov et al (2018). The MFT with strong initial magnetic field (plasma beta < 1) can reach supersonic velocity up to ∼ 10 − 15 km s −1 .…”

“…We formulate the equations of slender MFT dynamics taking into account the aerodynamic and turbulent drags. Khaibrakhmanov et al (2018) have investigated the MFT dynamics taking into account the heat exchange with the external medium of constant temperature. The radiative flux has been estimated in the diffusion approximation.…”

“…In this section we consider MFT dynamics for plasma beta in range [0.01, 10] to study the dependence of MFT characteristics on the initial magnetic field strength. Khaibrakhmanov et al (2018) have shown that the characteristics of MFT near disc surface practically do not depend on the initial position z 0 . In this section, we present calculations for z 0 = 0.5H.…”

“…We investigate MFT dynamics in the accretion discs of young stars taking into account the radiative heat exchange between MFT and ambient gas, effects of the aerodynamic and turbulent drag, and external magnetic field. Some particular aspects of MFT dynamics in the accretion discs of young stars were considered by Dudorov & Khaibrakhmanov (2016) and Khaibrakhmanov et al (2018). Structure of the accretion disc is calculated with the help our MHD model of the accretion discs (Dudorov & Khaibrakhmanov 2014;.…”

Rising magnetic flux tubes as a source of IR-variability of the accretion disks of young stars

“…This instability leads to formation of slender magnetic flux tubes (MFT, see Parker 1979), that rise from the disk and carry away the excess of magnetic flux (see . In this work, we present our model of MFT dynamics in the accretion disks of young stars (see details in Khaibrakhmanov et al 2018;Dudorov et al 2019).…”