Cepheid variable
A Cepheid variable ( or ) is a star that pulsates radially, varying in both temperature and diameter to produce brightness changes with a well-defined stable period and amplitude.
A strong direct relationship between a Cepheid variable's luminosity and pulsation period secures for Cepheids their status as important distance indicators for establishing the galactic and extragalactic distance scales.
The term Cepheid originates from Delta Cephei in the constellation Cepheus, the first star of this type identified, by John Goodricke in 1784.
Classes
Cepheid variables are divided into several subclasses which exhibit markedly different masses, ages, and evolutionary histories: classical Cepheids, type II Cepheids, and anomalous Cepheids. Delta Scuti variables are A class stars on or near the main sequence at the lower end of the instability strip and were originally referred to as dwarf Cepheids. RR Lyrae variables have short periods and lie on the instability strip where it crosses the horizontal branch. Delta Scuti variables and RR Lyrae variables are not generally treated with Cepheid variables although their pulsations originate with the same helium ionisation kappa mechanism.
