Be Star Phenomena and Circumstellar Disk Dynamics
Summary
Be stars are non-supergiant B-type stars that exhibit Balmer emission lines arising from a gaseous, equatorial circumstellar disc. These stars rotate at velocities approaching their critical break-up speed, enabling the formation of viscous decretion discs through the combined effects of rapid rotation, nonradial pulsations and episodic mass ejection. The resulting disc is supported by Keplerian rotation and maintained by angular-momentum transport, giving rise to characteristic double-peaked emission profiles and infrared excess. Disc density and geometry evolve on timescales from days to decades, driven by processes including viscous spreading, tidal truncation in binary systems, disc warping and precession. Interactions with a companion star can strip material to form hot subdwarf or white-dwarf companions, influence disc feeding through mass transfer and induce phase-locked variations in emission lines. Observational techniques such as spectroscopy, polarimetry, photometric monitoring and long-baseline interferometry have together mapped disc structure, traced variability cycles and probed binarity. Understanding Be star discs informs broader astrophysical issues of angular-momentum evolution, binary interactions and the physics of astrophysical discs in regimes of low accretion rate and high rotation.
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Be Star Phenomena and Circumstellar Disk Dynamics publication trend
The graph below shows the total number of articles in be star phenomena and circumstellar disk dynamics across all publications each year (not limited to Nature Index journals).
Technical terms
Be star: A rapidly rotating, non-supergiant B-type star exhibiting Balmer-line emission due to a circumstellar gas disc.
Decretion disk: A viscous, gaseous disc formed by material expelled from the stellar equator, maintained by angular-momentum transport.
Keplerian rotation: Motion wherein disc material orbits the central star under gravity with velocity proportional to radius^−1/2.
Mass transfer: The exchange of mass from one star to another in a binary, often spinning up the mass gainer and affecting disc formation.
Interferometry: A technique combining light from multiple telescopes to achieve high angular resolution, enabling direct measurement of disc and orbital parameters.
Precession: The slow, conical motion of a misaligned disc’s rotation axis caused by gravitational torques from a companion.
References
- Gaia uncovers difference in B and Be star binarity at small scales: evidence for mass transfer causing the Be phenomenon. Monthly Notices of the Royal Astronomical Society (2023).
- Disc precession in Be/X-ray binaries drives superorbital variations of outbursts and colour. Monthly Notices of the Royal Astronomical Society: Letters (2023).
- The Role of Disk Tearing and Precession in the Observed Variability of Pleione. The Astrophysical Journal (2022).
- Searching for Phase-Locked Variations of the Emission-Line Profiles in Binary Be Stars. Galaxies (2023).
- The Orbital and Physical Properties of Five Southern Be+sdO Binary Systems. The Astronomical Journal (2023).
- The CHARA Array Interferometric Program on the Multiplicity of Classical Be Stars: New Detections and Orbits of Stripped Subdwarf Companions. The Astrophysical Journal (2024).
- Interferometric Detections of sdO Companions Orbiting Three Classical Be Stars. The Astrophysical Journal (2022).
- Gamma Cas Stars as Be+White Dwarf Binary Systems. The Astrophysical Journal Letters (2022).
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