clusters such as M67 are sufficiently old that they show a pronounced subgiant branch in their color–magnitude diagrams. ω Centauri actually shows several separate subgiant branches for reasons that are still not fully understood, but appear to represent stellar populations of different ages within the cluster. Variability Several types of variable star include subgiants: Beta Cephei variables, early B main sequence and subgiant stars Slowly pulsating B-type stars, mid to late B main sequence and subgiant stars Delta Scuti variables, late A and early F main sequence and subgiant stars Subgiants more massive than the sun cross the Cepheid instability strip, called the first crossing since they may cross the strip again later on a blue loop. In the range, this includes Delta Scuti variables such as β Cas. At higher masses the stars would pulsate as Classical Cepheid variables while crossing the instability strip, but massive subgiant evolution is very rapid and it is difficult to detect examples. SV Vulpeculae has been proposed as a subgiant on its first crossing but was subsequently determined to be on its second crossing Planets Planets in orbit around subgiant stars include Kappa Andromedae b, Kepler-36 b and c, and HD 224693 b. References Bibliography External links Post-main sequence evolution through helium burning Long period variables – period luminosity relations and classification in the Gaia Mission Star types