Be stars are non-supergiant B-type stars whose spectra have, or had at some time, one or more Balmer lines in emission. The mystery of the "Be phenomenon" is that the emission, which is well understood to originate from a flattened circumstellar envelope or disk, can come and go episodically on time scales of days to decades.

This has yet to be explained as a predictable consequence of stellar evolution theory, although many contributing factors have been discussed, including:

• rapid rotation
• radiation-driven winds
• nonradial pulsation
• flarelike magnetic activity
• binary interaction

Limber Observatory - P.O. Box 63599 - Pipe Creek TX 78063 Maintained by David McDavid - last update: 18 December 2020.