Speaker
Description
Alpha Cygni variables are O-, B-, and A-type supergiants that show low-amplitude irregular or quasi-period photometric variability on timescales of days to weeks. There is not a consensus on their causes of variability or evolutionary state, and they may not be a homogeneous class. 185 alpha Cygni variables are listed in the AAVSO Variable Star Index (VSX), including the well-known bright stars Deneb and Rigel.
Because alpha Cygni variables are not strictly periodic, long time-series observations are necessary to characterize their behavior. We will show example light curves from the Transiting Exoplanet Survey Satellite (TESS) and 8.6-year light curves recently processed from the Solar Mass Ejection Imager (SMEI) satellite in Earth orbit between 2003 and 2011.
We also discuss the locations of alpha Cygni variables across the upper Hertzsprung-Russell Diagram in relation to other classes of pulsating stars and discuss whether some may have masses and evolutionary states relevant to future evolution into super-AGB stars. Continued study of their photometric variability and stellar parameters may help clarify the causes of their variation and their place in later stellar evolution.