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Beta Cephei variables are variable stars which exhibit variations in their brightness due to pulsations of the stars' surfaces. The point of maximum brightness roughly corresponds to the maximum contraction of the star. Typically, Beta Cephei variables change in brightness by 0.01 to 0.3 magnitudes with periods of 0.1 to 0.6 days. These stars are
main sequenceThe main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
stars of masses between about 7 and 20 M
.
The pulsations of Beta Cephei variables are driven by the
kappa mechanismThe κ–mechanism is the driving mechanism behind the changes in luminosity of many types of pulsating variable stars. Here, the Greek letter kappa is used to indicate the radiative opacity at any particular depth of the stellar atmosphere...
.
The prototype of these variable stars,
Beta CepheiBeta Cephei is a third magnitude star in the constellation Cepheus. It has the traditional name Alfirk , meaning "The Flock" This star, along with α Cep and η Cep , were Al Kawākib al Firḳ , meaning "the Stars of The Flock" by Ulug Beg...
, shows variation in
apparent magnitudeThe 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...
from +3.16 to +3.27 with a period of 4.57 hours.
These stars should not be confused with
Cepheid variableA Cepheid is a member of a class of very luminous variable stars. The strong direct relationship between a Cepheid variable's luminosity and pulsation period, secures for Cepheids their status as important standard candles for establishing the Galactic and extragalactic distance scales.Cepheid...
s, which are named after
Delta CepheiDelta Cephei is a binary star system approximately 891 light-years away in the constellation of Cepheus . Delta Cephei is the prototype of the Cepheid variable stars, and it is among the closest stars of this type to the Sun...
.
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