Cepheid Stars

Cepheid stars are stars that have evolved off the main sequence into the Cepheid instability strip. They are regular radial-pulsating stars, with a well-defined period-luminosity relationship, which makes them ideal stars to be used as primary distance indicating standard candles. These stars also show radial velocity variations which correspond to the photometric curves. Brighter cepheids have longer periods than fainter (less luminous!) cepheids.

Classical Cepheid stars are supergiants of greater than 2-3 solar masses, that at the end of main-sequence H burning move across the HR diagram to become red giants, crossing the Cepheid instability strip.

The type-II Cepheids are low-mass, high-luminosity pulsators, with periods from 1-40 days. These evolved stars have a He core surrounded by an outer H shell. The type-II's are sub-divided into the BLHer, WVir, and RVTau sub-types.

Dwarf Cepheids are short period pulsators that are found where the Cepheid instability strip crosses the main sequence. The delSct sub-type of dwarf cepheids have periods of 30-min - 8-hours, spectral types A-F, and have photometric amplitude variations of > 0.3 magnitude.

RRLyr stars are short period (< 1 day) pulsators, horizontal branch stars that are in the Cepheid instability strip. The RRLyr stars are older, less-luminous stars than the classical Cepheids.

Cepheid stars are common, click here for a short catalog of representative Cepheid stars.