Mira variable
A Mira variable is a cool giant star of spectral type Ke,
Me, Se, or Ce (with molecular bands) that pulsates with a period of 80 to
1,000 days and varies in brightness by 2.5 to 11 magnitudes. Mira stars,
also known as long-period variables,
are named for their prototype, Mira (Omicron Ceti).
Another well known example is R Leonis.
The brightness, large amplitude, and distinctive properties of Mira stars
make them so easy to find that more of them are known than any other type
of variable star. They occupy the high luminosity portion of the asymptotic
giant branch in the Hertzsprung-Russell diagram,
along with semi-regular variables.
Mira stars have masses similar to that of the Sun but, owing to their much
greater size, have a feeble gravitational hold on the material in their
outer layers which, as a consequence, escapes into space in the form of
a strong stellar wind at a rate of about
10-7 to 10-6 solar mass per year. Material thus shed
accumulates around the star as an extensive circumstellar shell. The rate
of mass loss is such that the Mira stage can only last about a million years
before the aging star evolves to become a white
dwarf surrounded by a planetary nebula.
The Sun itself is destined to become a Mira star within the next few billion
years.
Related entry
• variable stars
Related category
• TYPES
OF STAR
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