Alpha Cygni variable

Alpha Cygni stars are variable stars with periods between 10 and 100 days. You are supergiants of late B or Spektralklassentyps A. The amplitude of the brightness variations in the range of 0.01 to 0.1 mag and is multi periodically at each intensively observed Alpha Cygni star. The period values ​​are too long to occur by radial pulsations. The brightness changes are associated with a complex structure in the variability of the absorption lines. The Alpha Cygni stars are as massive that it will explode in the course of its further development as a core-collapse supernova.

The prototype of this star is Deneb ( α Cygni ). It shows variations in brightness between the apparent magnitude of 1.21 and 1.29 mag.

For the reasons of the variability of two causes are discussed:

• Non- radial pulsations can occur in stars with masses greater than 40 solar masses and lead to strange -modes. These occur in zones with increased opacity as the second ionization of helium and are not excited far from the Eddington limit for stars. However, the calculated amplitude of the strange -modes is much larger than is observed in Alpha Cygni stars.
• The long periods of the order of months at Alpha Cygni stars could be stimulated by the epsilon- mechanism, while the short periods with a duration of days to weeks are controlled by the conventional kappa mechanism. The epsilon- mechanism is based on a variation of the energy through nuclear reactions. The Alpha Cygni stars a bowl with active hydrogen burning is located in a zone with radiative energy transport, which could be sensitive to instability.

During the development of massive stars, there are two phases when they cross the instability strip in the Hertzsprung -Russell diagram. Once shortly after the main sequence phase of the star migrate rapidly through the instability strip, and then evolve into a red supergiant, losing at this stage a lot of bulk. Due to the strong mass loss, the helium- burning stars move in the HR diagram to the left again and come back into the area of ​​the instability strip for supergiants. However, the Alpha Cygni variability seems to occur only during the second phase, since, according to simulations by the loss of the outer shells of the conditions are created in which pulsations can be excited. These theoretical calculations are, however, highly dependent on only difficult to model assumptions about the internal mixing and the strength of the stellar wind.

Swell

• Star class