Magnetic Rotator Winds and Keplerian Disks of Hot Stars

Abstract

We consider rotating magnetic stars with winds and disks. We establish a theorem that relates the angular velocity of a disk region with no meridional motion to the angular velocity of the star. Also, we show that for a given value of the magnetic field strength, if the rotation rate is too high or the flow velocity into the shock boundary is too low, a Keplerian disk region will not be formed. We develop a model for the formation of disks in magnetic rotators through the processes of fill-up and diffusion into Keplerian orbits. At the end of the fill-up stage the density of the disk increases significantly and the magnetic force in the disk becomes negligible. We derive analytical expressions for the inner and outer radii of Keplerian disks in terms of the stellar rotation rate. A disk can form if the meridional component Bm of the field at the stellar surface is larger than a minimum value. The radial extent of the Keplerian region becomes larger for larger values of Bm and is largest when Bm equals an optimal value. The strengths of the minimum fields required for Keplerian disk formation in B-type stars varies from order 1G to 10G. In O-type stars they must be of order 500G. Also, we suggest that the stellar magnetic fields may be affected by rotationally driven meridional circulation leading to some of the the observed variations of disks with time.

arXiv comment44 pages, 1 figure, accepted by ApJ

References in corpus (3)

• Viscous Transonic Decretion in Disks of Be Stars
• Magnetic Fields in Massive Stars. II. The Buoyant Rise of Magnetic Flux Tubes Through the Radiative Interior
• A Magnetically Torqued Disk Model for Be Stars

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• XMM-Newton X-ray study of early type stars in the Carina OB1 association
• Discovery of X-ray flaring on the magnetic Bp-star sigma Ori E
• Identification of new classical Be stars from the LAMOST MRS survey
• The Effect of Rotational Gravity Darkening on Magnetically Torqued Be Star Disks
• Magnetic survey of emission line B-type stars with FORS1 at the VLT
• Protodiscs around Hot Magnetic Rotator Stars
• X-ray Emission from Magnetically Torqued Disks of Oe/Be Stars
• Evidence for weak magnetic fields in early-type emission stars
• Non-LTE Calculation for the Be Star Decretion Disk