The red clump is a feature in the Hertzsprung–Russell diagram of stars. The red clump is considered the metal-rich counterpart to the horizontal branch. Stars in this part of the Hertzsprung–Russell diagram are sometimes called clump giants. These stars are more luminous than main sequence stars of the same surface temperature (or colder than main sequence stars of comparable luminosity), or above and to the right of the main sequence on the Hertzsprung–Russell diagram. This period in a star's evolution corresponds to the core helium-burning phase, whereas the main sequence is the core hydrogen-burning phase.
In theory, the absolute luminosities of stars in the red clump are fairly independent of stellar composition or age so that consequently they make good standard candles for estimating astronomical distances both within our galaxy and to nearby galaxies and clusters.
- Sato, Bun'ei; et al. (2007). "A Planetary Companion to the Hyades Giant ε Tauri". The Astrophysical Journal 661 (1): 527–531. Bibcode:2007ApJ...661..527S. doi:10.1086/513503.