Related papers: Be star discs: powered by a non-zero central torqu…

Be stars are rapidly rotating, with angular frequency around $0.7-0.8$ of their Keplerian break up frequency, as a result of significant accretion during the earlier stellar evolution of a companion star. Material from the equator of the Be…

In the past decade, a consensus has emerged regarding the nature of classical Be stars: They are very rapidly rotating main sequence B stars, which, through a still unknown, but increasingly constrained process, form an outwardly diffusing…

Circumstellar discs of Be stars are thought to be formed from material ejected from a fast-spinning central star. This material possesses large amounts of angular momentum and settles in a quasi-Keplerian orbit around the star. This simple…

We explore the pulsationally driven orbital mass ejection mechanism for Be star disc formation using isothermal, 3D magnetohydrodynamic (MHD) and hydrodynamic simulations. Non-radial pulsations are added to a star rotating at 95\% of…

As the largest population of high mass X-ray binaries, Be/X-ray binaries provide an excellent laboratory to investigate the extreme physics of neutron stars. It is generally accepted that Be stars possess a circumstellar disc, providing an…

Classical Be stars are an enigmatic subclass of rapidly rotating hot stars characterized by dense equatorial disks of gas that have been inferred to orbit with Keplerian velocities. Although these disks seem to be ejected from the star and…

Despite extensive study, the mechanisms by which Be star disks acquire high densities and angular momentum while displaying variability on many time scales are still far from clear. In this paper, we discuss how magnetic torquing may help…

This paper presents a detailed statistical determination of the equatorial rotation rates of classical Be stars. The rapid rotation of Be stars is likely to be linked to the ejection of gas that forms dense circumstellar disks. The physical…

Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post main sequence binaries, as a…

Hot, massive stars (spectral types O and B) have extreme luminosities ($10^4 -10^6 L_\odot$) that drive strong stellar winds through UV line-scattering. Some massive stars also have disks, formed by either decretion from the star (as in the…

The theory of radiatively-induced warps in accretion discs is applied to the discs of Be stars. It is found that these discs may develop warps in their inner regions, although once the warp amplitude is large enough then the interaction…

The spin-down of Be stars due to angular momentum transport from star to disc has been considered. This has been prompted by empirical studies of observed optical and IR line profile studies indicating that the disc is rotating in a…

A Magnetic Rotator Wind-Disk(MRWD) model is considered for the formation of Keplerian disks around Be stars. Material from low latitudes of the stellar surface flows along magnetic flux tubes and passes through a shock surface to form a…

Spectropolarimetric surveys reveal that 8-10\% of OBA stars harbor large-scale magnetic fields, but thus far no such fields have been detected in any classical Be stars. Motivated by this, we present here MHD simulations for how a…

While the presence of discs around classical Be stars is well established, their origin is still uncertain. To understand what processes result in the creation of these discs and how angular momentum is transported within them, their…

Be stars are main-sequence massive stars with emission features in their spectrum, which originates in circumstellar gaseous discs. Even though the viscous decretion disc (VDD) model can satisfactorily explain most observations, two…

Circumstellar discs around Be stars are formed by the material ejected by the central star. This process removes excess angular momentum from the star as viscosity facilitates the mass and angular momentum transfer within the disc and its…

It is assumed that Be star discs are driven by viscosity. Emission from disc models is calculated and is confronted with continuum observations. It is found that the outflowing viscous disc models can reproduce the observed IR continuum…

A radiation-driven disk wind model is proposed that offers great promise of explaining the extreme mass loss signatures of massive young stellar objects (the BN-type objects and more luminous Herbig Be stars). It is argued that the dense…

We formulate a general, steady-state model for the torque on a magnetized star from a surrounding accretion disc. For the first time, we include the opening of dipolar magnetic field lines due to the differential rotation between the star…