They have decretion disks around the equatorial region, which sometimes reform or disappear. Typically, they are fast spinning class B subgiants, giants or sometimes main sequence stars, that show brightness variations with larger amplitudes than other Be stars. Gamma Cassiopeiae and other variables of this type are eruptive stars. If they are believed to be pulsating stars, they are classified as Lambda Eridani variables. If there is a transient disk, they are classified as Gamma Cassiopeiae variables. Many Be stars are variable in brightness. The emission lines in these stars are believed to come from circumstellar disks of material ejected from the stellar surfaces as a result of rapid rotation. Achernar was only recognized as a Be star in 1976. The brightest star belonging to this group is Achernar in the constellation Eridanus, the ninth brightest star in the sky. It was the first star to be identified as a Be star, by the Italian astronomer Angelo Secchi in 1866. Gamma Cassiopeiae is classified as a Be star, a non-supergiant blue class B star showing Balmer (hydrogen) emission lines in its spectrum. The variations in brightness are caused by shell episodes, where shell features appear in the star’s spectrum, significantly increasing or decreasing brightness. Gamma Cassiopeiae itself usually shines at magnitude 2.25, but it has been observed to fade to magnitude 3.0 and brighten to magnitude 1.6. Their brightness varies with an amplitude of about a magnitude. These stars exhibit irregular brightness variations over periods of decades. Gamma Cassiopeiae is a prototype for its own class of variable stars known as the Gamma Cassiopeiae variables. The decretion disk causes both brightness variations and hydrogen emission lines in the star’s spectrum. Other bright stars that are examples of this include Achernar, Alderamin, Altair, Rasalhague, Regulus, and Vega.Īs another effect of the star’s fast rotation, a lot of material from the surface is ejected and forms a hot disk of gas. Its poles are closer to the centre of mass and therefore hotter and more luminous than the equatorial region. Like its neighbour Caph, Gamma Cassiopeiae is an example of gravity darkening. As a result, its equatorial radius is larger than its polar radius, giving the star a flattened shape. Gamma Cassiopeiae is an exceptionally fast spinner, with a projected rotational velocity of 432 km/s. Its high mass seals its fate as a supernova in the not-too-distant astronomical future. Like other exceptionally massive stars, it has evolved very quickly and will not live a very long life. The star’s estimated age is only 8 million years.Įven though it is a very young star, Gamma Cassiopeiae has already left the main sequence and is in the late stages of its existence. With a surface temperature of 25,000 K, it is 34,000 times more luminous than the Sun, but most of its output is in the invisible ultraviolet. Gamma Cassiopeiae has a mass 17 times that of the Sun and, as it ended its main sequence lifetime, it has expanded to a size of 10 solar radii. These lines are caused by a circumstellar disk of material lost from the star. The “e” suffix indicates hydrogen emission lines in the star’s spectrum. The star is running out of the supply of hydrogen in its core and is on its way to evolving into a giant. Gamma Cassiopeiae has the stellar classification B0.5 IVe, indicating a subgiant star appearing blue or blue-white in colour. It is one of the five stars that form Cassiopeia’s recognizable W asterism. Gamma Cassiopeiae lies at a distance of 550 light years from Earth. With an apparent magnitude that varies from 1.6 to 3.0, it sometimes outshines its neighbours Schedar, Caph and Segin to become the constellation’s brightest star. Informally known as Navi, it is one of the four brightest stars in Cassiopeia. Still not sure? Click on the star name to listen to an audio clip.Gamma Cassiopeiae (γ Cas) is a spectroscopic binary star located in the constellation Cassiopeia. This comprehensive, free online guide to the pronunciation of stars and constellations will help amateur astronomers, and laymen with the basic hard to pronounce astronomical objects and stellar formations. The most comprehensive free online guide on how to pronounce stars and constellations. With Audio !!!Use the right column to hear the pronunciation of stars and constellations.Ĭlick on the star or constellation name for Wikipedia information.
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