Gamma Cassiopeiae

Encyclopedia : G : GA : GAM : Gamma Cassiopeiae

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Tsih, 27 Cassiopeiae, HR 264, BD+59°144, HD 5394, SAO 11482, FK5 32, ADS 782, MX0053+60, WDS 00567+6043, HIP 4427, CCDM J00567+6043

|} Gamma Cassiopeiae (γ Cas / γ Cassiopeiae) is an eruptive variable star, whose brightness changes irregularly between +2.20 mag and +3.40 mag. It is the prototype of the Gamma Cassiopeiae variable stars. Although it is a fairly bright star, it has no traditional Arabic or Latin name. In Chinese, however, it has the name Tsih, meaning "the whip". It is located at the center of the distinctive "W" shape that forms the Cassiopeia constellation. The United States' second astronaut, Virgil Ivan "Gus" Grissom, nicknamed the star Navi after his own middle name spelled backwards. The star was used as an easily identifiable navigational reference point during space missions.

The apparent magnitude of this star was +2.2 in 1937, +3.4 in 1940, +2.9 in 1949, +2.7 in 1965 and now it is +2.15. At maximum intensity, γ Cassiopeiae outshines both α Cassiopeiae (magnitude +2.25) and β Cassiopeiae (magnitude +2.3).

This is a rapidly spinning star that bulges outward along the equator. When combined with the high luminosity, the result is mass loss that forms a disk around the star. The emissions and brightness variations are apparently caused by this disk.

Gamma Cassiopeiae is also a bright source of X-rays, and is a spectroscopic binary. The companion has an orbital period of 203.59 days with an eccentricity (e) of 0.26. The mass of the companion is believed to be similar to our own Sun (Harmanec et al. 2000). The X-ray emission could be explained if the companion were a dense object with a high surface gravity, such as a white dwarf or a neutron star. The escaping gas from Gamma Cassiopeiae could accrete on the surface of the companion, transforming gravitational potential into thermal energy.

This is also a visual double star system, with the designation of ADS782AB.

References

P. Harmanec, P. et al, "Binary Nature and Orbital Elements of Gamma Cas", 2000, Astronomy and Astrophysics, 364, L85.

External links

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