Protodiscs around Hot Magnetic Rotator Stars

Abstract

We develop equations and obtain solutions for the structure and evolution of a protodisc region that is initially formed with no radial motion and super-Keplerian rotation speed when wind material from a hot rotating star is channelled towards its equatorial plane by a dipole-type magnetic field. Its temperature is around $10^7$K because of shock heating and the inflow of wind material causes its equatorial density to increase with time. The centrifugal force and thermal pressure increase relative to the magnetic force and material escapes at its outer edge. The protodisc region of a uniformly rotating star has almost uniform rotation and will shrink radially unless some instability intervenes. In a star with angular velocity increasing along its surface towards the equator, the angular velocity of the protodisc region decreases radially outwards and magnetorotational instability (MRI) can occur within a few hours or days. Viscosity resulting from MRI will readjust the angular velocity distribution of the protodisc material and may assist in the formation of a quasi-steady disc. Thus, the centrifugal breakout found in numerical simulations for uniformly rotating stars does not imply that quasi-steady discs with slow outflow cannot form around magnetic rotator stars with solar-type differential rotation.

Accepted for publication in MNRAS. 16 pages, 1 figure, 7 tables

References in corpus (6)

• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
• Centrifugal Breakout of Magnetically Confined Line-Driven Stellar Winds
• Convective envelopes in rotating OB stars
• The Effect of Rotational Gravity Darkening on Magnetically Torqued Be Star Disks
• Radio observations of candidate magnetic O stars

Cited by in corpus (10)

• A coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, $\delta$ Orionis Aa: IV. A multiwavelength, non-LTE spectroscopic analysis
• Early magnetic B-type stars: X-ray emission and wind properties
• A scaling relationship for non-thermal radio emission from ordered magnetospheres: from the top of the Main Sequence to planets
• Low-frequency monitoring of flare star binary CR Draconis: Long-term electron-cyclotron maser emission
• The detection of variable radio emission from the fast rotating magnetic hot B-star HR7355 and evidence for its X-ray aurorae
• A new type of X-ray pulsar
• Evidence for radio and X-ray auroral emissions from the magnetic B-type star rho Oph A
• A combined multiwavelength VLA/ALMA/Chandra study unveils the complex magnetosphere of the B-type star HR5907
• Magnetic survey of emission line B-type stars with FORS1 at the VLT
• The Hanle Effect as a Diagnostic of Magnetic Fields in Stellar Envelopes. V. Thin Lines from Keplerian Disks