IC 59 and IC 63 are two comet shaped nebulae which form a triangle with the bright star Gamma Cassiopeiae , the prime energy source of their illumination. The cometary shape likely forms from the radiation pressure of the nearby star. The difference in shape and color of the two nebulas are probably explained best by differences in their distance from gamma cas. IC 63 being closer to the star shows more brightening of its leading edge and stronger overall HII emission. IC 59 being somewhat further away shows a weaker level of HII emission leaving its reflection component to appear more pronounced.
Gamma Cassiopeiae (gamma cas) belongs to
a special group of variable stars called Be stars. In fact gamma
cas was the very first Be star discovered. Be stars are massive
type "O" stars which show peculiar emission spectra.
They make up about 20% of all B type stars and are distinguished
by rapid rotation up to 450km/sec at their equator (150 times
faster than our own sun) which causes substantial variability
in brightness. Gamma cas has enormous luminosity at 70,000 times
the brightness of our sun. The rapid rotation which concentrates
the stars winds at its disk plus the great luminosity conspire
to drive mass from the star. The mass loss in turn produces specific
emission lines and causes marked variability in brightness over
time. Mass outflow is often followed by visual dimming of the
star. Between 1935 and 1940 Gamma Cas varied in brightness from
1.6 to 3.0 and significantly changed the appearance of the constellation
of casseiopeia during that time.