Asymmetric MHD outflows/jets from accreting T Tauri stars

作者：Dyda S; Lovelace R V E^*; Ustyugova G V; Lii P S; Romanova M M; Koldoba A V

来源：Monthly Notices of the Royal Astronomical Society, 2015, 450(1): 481-493.

DOI：10.1093/mnras/stv623

• accretion, accretion discs
• MHD
• stars: jets
• stars: protostars
• stars: variables: T Tauri, Herbig Ae/Be
• stars: winds, outflows

Observations of jets from young stellar objects reveal the asymmetric outflows from some sources. A large set of 2.5D magnetohydrodynamic simulations was carried out for axisymmetric viscous/diffusive disc accretion to rotatingmagnetized stars for the purpose of assessing the conditions where the outflows are asymmetric relative to the equatorial plane. We consider initial magnetic fields that are symmetric about the equatorial plane and consist of a radially distributed field threading the disc (disc field) and a stellar dipole field. (1) For pure disc-fields the symmetry or asymmetry of the outflows is affected by the mid-plane plasma beta of the disc. For discs with small plasma beta, outflows are symmetric to within 10 per cent over time-scales of hundreds of inner disc orbits. For higher beta discs, the coupling of the upper and lower coronal plasmas is broken, and quasi-periodic field motion leads to asymmetric episodic outflows. (2) Accreting stars with a stellar dipole field and no disc-field exhibit episodic, two component outflows - a magnetospheric wind and an inner disc wind. Both are characterized by similar velocity profiles but the magnetospheric wind has densities greater than or similar to 10 times that of the disc wind. (3) Adding a disc field parallel to the stellar dipole field enhances the magnetospheric winds but suppresses the disc wind. (4) Adding a disc field which is antiparallel to the stellar dipole field in the disc suppresses the magnetospheric and disc winds. Our simulations reproduce some key features of observations of asymmetric outflows of T Tauri stars.

• 出版日期2015-6-11