Alpha Cygni variable
Encyclopedia
Alpha Cygni variables are variable star
s which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time others parts expand. They are supergiant
stars of spectral types
B or A. Variations in brightness on the order of 0.1 magnitudes
are associated with the radial pulsations, which often seem irregular
, due to beat
ing of multiple pulsation periods. The pulsations typically have periods of several days to several weeks.
The prototype of these stars, Deneb
(α Cygni), exhibits fluctuations in brightness between magnitudes +1.21 and +1.29.
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time others parts expand. They are supergiant
Supergiant
Supergiants are among the most massive stars. They occupy the top region of the Hertzsprung-Russell diagram. In the Yerkes spectral classification, supergiants are class Ia or Ib . They typically have bolometric absolute magnitudes between -5 and -12...
stars of spectral types
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
B or A. Variations in brightness on the order of 0.1 magnitudes
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
are associated with the radial pulsations, which often seem irregular
Irregular variable
An irregular variable is a type of variable star in which variations in brightness show no regular periodicity. There are two main sub-types of irregular variable: eruptive and pulsating.Eruptive irregular variables are divided into three categories:...
, due to beat
Beat (acoustics)
In acoustics, a beat is an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies....
ing of multiple pulsation periods. The pulsations typically have periods of several days to several weeks.
The prototype of these stars, Deneb
Deneb
Deneb is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle. It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25. A blue-white supergiant, Deneb is also one of the most luminous nearby stars...
(α Cygni), exhibits fluctuations in brightness between magnitudes +1.21 and +1.29.