Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: III. Angular Momentum Loss and Rotational Spindown

Abstract

We examine the angular momentum loss and associated rotational spindown for magnetic hot stars with a line-driven stellar wind and a rotation-aligned dipole magnetic field. Our analysis here is based on our previous 2-D numerical MHD simulation study that examines the interplay among wind, field, and rotation as a function of two dimensionless parameters, one characterizing the wind magnetic confinement (${\eta }_{\ast }\equiv B_{eq}^2{R}_{\ast }^2/\dot{M}{v}_{\infty }$), and the other the ratio ($W\equiv V_{rot}/V_{orb}$) of stellar rotation to critical (orbital) speed. We compare and contrast the 2-D, time variable angular momentum loss of this dipole model of a hot-star wind with the classical 1-D steady-state analysis by Weber and Davis (WD), who used an idealized monopole field to model the angular momentum loss in the solar wind. Despite the differences, we find that the total angular momentum loss $\dot{J}$ averaged over both solid angle and time follows closely the general WD scaling $\dot{J}=(2/3)\dot{M}\Omega R_A^2$, where $\dot{M}$ is the mass loss rate, $\Omega$ is the stellar angular velocity, and $R_A$ is a characteristic Alfvén radius. However, a key distinction here is that for a dipole field, this Alfvén radius has a strong-field scaling $R_A/R_{\ast }\approx {\eta }_{\ast }^{1/4}$, instead of the scaling $R_A/R_{\ast }\sim \sqrt{{\eta }_{\ast }}$ for a monopole field. This leads to a slower stellar spindown time that in the dipole case scales as ${\tau }_{spin}={\tau }_{mass}1.5k/\sqrt{{\eta }_{\ast }}$, where ${\tau }_{mass}\equiv M/\dot{M}$ is the characteristic mass loss time, and $k$ is the dimensionless factor for stellar moment of inertia. The full numerical scaling relation we cite gives typical spindown times of order 1 Myr for several known magnetic massive stars.

13 pages, 7 figures, accepted for publication in MNRAS. MNRAS in press

References in corpus (5)

• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
• Accretion-Powered Stellar Winds II: Numerical Solutions for Stellar Wind Torques
• The radio lighthouse CU Virginis: the spindown of a single main sequence star
• Multicomponent radiatively driven stellar winds IV. On the helium decoupling in the wind of sigma Ori E
• Variations of the ultraviolet resonance lines of the Be IV-V star zeta Cassiopeiae

Cited by in corpus (38)

• The Mass-Dependence of Angular Momentum Evolution in Sun-Like Stars
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law
• Magnetic massive stars as progenitors of "heavy" stellar-mass black holes
• Magnetic field topology of the unique chemically peculiar star CU Virginis
• Fundamental properties of nearby single early B-type stars
• X-rays from Magnetically Confined Wind Shocks: Effect of Cooling-Regulated Shock Retreat
• An `Analytic Dynamical Magnetosphere' formalism for X-ray and optical emission from slowly rotating magnetic massive stars
• Evidence of magnetic field decay in massive main-sequence stars
• The Effect of Combined Magnetic Geometries on Thermally Driven Winds I: Interaction of Dipolar and Quadrupolar Fields
• Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey
• Magnetic braking of Sun-like and low-mass stars: Dependence on coronal temperature
• Stellar wind models of subluminous hot stars
• Magnetic field topology and chemical abundance distributions of the young, rapidly rotating chemically peculiar star HR5624
• A new type of X-ray pulsar
• HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere
• The surface magnetic field and chemical abundance distributions of the B2V helium-strong star HD184927
• The BinaMIcS project: understanding the origin of magnetic fields in massive stars through close binary systems
• Discovery of magnetic A supergiants: the descendants of magnetic main sequence B stars
• On the Effect of Magnetic Spots on Stellar Winds and Angular Momentum Loss
• Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis
• The magnetic field and spectral variability of the He-weak star HR 2949
• B field in OB stars (BOB): The outstandingly strong magnetic field in the evolved He-strong star CPD-62 2124
• Properties of six short-period massive binaries: a study of the effects of binarity on surface chemical abundances
• The pulsating magnetosphere of the extremely slowly rotating magnetic $\beta$ Cep star ${\xi }^1$ CMa
• Magnetometry of a sample of massive stars in Carina
• HD 164492C: a rapidly-rotating, H$\alpha$-bright, magnetic early B star associated with a 12.5d spectroscopic binary
• Torsional oscillations and observed rotational period variations in early-type stars
• The B Fields in OB Stars (BOB) Survey
• Effect of a magnetic field on massive star winds I: mass-loss and velocity for a dipole field
• Photometric identification of the periods of the first candidate extragalactic magnetic massive stars
• Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks
• 3D MHD simulations and synthetic radio emission from an oblique rotating magnetic massive star
• UVMag: stellar formation, evolution, structure and environment with space UV and visible spectropolarimetry
• The modulated X-ray emission of the magnetic O8.5V-star Tr16-22
• The puzzling properties of the magnetic O star Tr16-22
• ${\xi }^1$ CMa: An Extremely Slowly Rotating Magnetic B0.7 IV Star
• Mixing of CNO-cycled matter in massive stars