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Navi, Gamma Cassiopeiae, 27 Cassiopeiae

Proper NamesCih, Navi
Bayer DesignationGamma Cassiopeiae
Flamsteed Number27 Cassiopeiae
HR (BSC)264
Right Ascension0h 56m 43s
Declination+60° 43' 0"
Distance613 light years
188 parsecs
MagnitudeApparent: +2.2
Absolute: -4.0
Spectral ClassB0IVnpe(shell) blue subgiant
Optimum VisibilityOctober (Usually visible from northern latitudes)
NotesThe blue shell star Cih is the prototype of the Gamma Cassiopeiae class of variables, and also the first Be or shell star to be identified. Stars like this show an accretion disc extending out from their equator, but in the case of variables like Cih, this disc is not a permanent feature, and its recurrent formation and collapse account for the variability of the star.

Cih is the central star of Cassiopeia's famous 'W' shape. Despite its 'gamma' designation, it outshines both Schedar and Caph, the Alpha and Beta stars of its home constellation. This fact is due to its variable magnitude: the star has brightened considerably over time (it has reached first magnitude within the last century, though its apparent brightness at present has lessened slightly to +2.2).

At the heart of this multiple system is a luminous blue star, highly volatile in nature. Its habit of casting rings of matter out into space causes the variation in its brightness, and also makes it the prototype for a class of stars showing similar properties, the Gamma Cassiopeiae variables. The intense radiation emitted by the star lights up nearby interstellar material, creating a rippling shroud of light known as the Gamma Cassiopeiae Nebula.

In a very close orbit around the main blue star is a tiny companion at a distance of a little under two Astronomical Units (and therefore barely more distant from the primary star than Mars is from the Sun). At least one other companion star also orbits the primary, but at a much greater distance than the close companion. This outlying member of the system is a bright yellow dwarf about 370 AU from the main star.


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