Red clump

Red clump stellar properties vary depending on their origin, most notably on the metallicity of the stars, but typically they have early K spectral types and effective temperatures around 5,000 K. The absolute visual magnitude of red clump giants near the sun has been measured at an average of +0.81 with metallicities between −0.6 and +0.4 dex.

Lower envelope masses result in weaker hydrogen shell fusion and give hotter and slightly less luminous stars strung along the horizontal branch.

This occurs in ω Centauri where metal-poor red-giant-branch stars have the same or hotter temperatures as more metal-rich red clump giants.

For stars only a little more massive than the sun, around 2 M☉, the blue loop is very short and at a luminosity similar to the red clump giants.

This is again a very rapid phase of evolution, but stars such as OU Andromedae are found in the red clump region (5,500 K and 100 L☉) even though it is thought to be a subgiant crossing the Hertzsprung gap.

Variations due to metallicity, mass, age, and extinctions affect visual observations too much for them to be useful, but the effects are much smaller in the infrared.

[11] Other well-known examples include: Arcturus has sometimes been thought to be a clump giant,[16] but is now more commonly considered to be on the red-giant branch, somewhat cooler and more luminous than a red-clump star.