Be star
Non-supergiant B stars with Balmer emission lines, often surrounded by a gaseous disk.
Wikipedia / Wikimedia Commons
Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as classical Be stars, is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer emission lines.
- type
- Stellar classification
- spectral_type
- B (also O and A shell stars)
- defining_feature
- Balmer emission lines
- first_recognized
- Gamma Cassiopeiae (1866)
- brightest_example
- Achernar (recognized 1976)
- variability_classification
- Gamma Cassiopeiae variables or BE
Lore & Background
The first star recognized as a Be star was Gamma Cassiopeiae, observed in 1866 by Angelo Secchi. Many other bright stars were found to show similar spectra, although many of these are no longer considered to be classical Be stars. The brightest is Achernar, although it was not recognised as a Be star until 1976.
Reader's Guide
Be stars are primarily considered to be main sequence stars, but a number of subgiants and giant stars are also included. Although the Be type spectrum is most strongly produced in class B stars, it is also detected in O and A shell stars, and these are sometimes included under the 'Be star' banner. Be stars are often visually and spectroscopically variable. They can be classified as Gamma Cassiopeiae variables when a transient or variable disk is observed. Be stars that show variability without clear indication of the mechanism are listed simply as BE in the General Catalogue of Variable Stars. Some of these are thought to be pulsating stars and are sometimes called Lambda Eridani variables.
Did You Know?
- All the observational characteristics of Be stars can now be explained with a gaseous disk that is formed of material ejected from the star.
- The infrared excess and the polarization result from the scattering of stellar light in the disk, while the line emission is formed by re-processing stellar ultraviolet light in the gaseous disc.
- Some Be stars exhibit spectral features interpreted as a detached 'shell' of gas, thought to be caused when the disc of gas is aligned edge on to us, creating very narrow absorption lines.
More in Stars And Stellar Phenomena 1-24
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