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S Cassiopeiae (S Cas, HD 7769) is a Mira variable star in the constellation Cassiopeia.
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Distance
In the absence of a measure of its parallax by the Hipparcos satellite, its distance from the solar system is estimated between 1,860 and 27,700 light-years.
Spectral type
Spectral type S3,4e-S5,8e, S Cassiopeiae is an S-type star, similar to Chi Cygni; these are asymptotic giant branch stars similar to those of class M, except that the dominant spectral bands of metal oxides are formed by metals of the fifth period of the periodic table as zirconium or yttrium. Another feature of this class of stars is the high mass loss; in the case of S Cassiopeiae it is estimated at 3.5 x 10-6 solar masses per year.
Characteristics
It has a radius of 930 solar radii; if placed at the center of the Solar System, it would extend past the orbit of Mars. Its effective temperature is 1,800 K and its luminosity is 15,275 times the solar luminosity.
The second variable discovered in this constellation after R Cassiopeiae, S Cassiopeiae is, like this, a variable Mira. Its brightness between +7.9 and +16.1 magnitude over a period of 612.43 days. Look variables are stars in the last stages of its evolution whose instability comes from pulsations in its surface, causing changes in color and brightness. Some of them, among which is S Cassiopeiae show SiO maser emission.