The nearly vertical path on the Hertzsprung–Russell diagram that is followed by a fully convective star as it evolves (see diagram). Forming stars (protostars) descend such tracks on to the main sequence, becoming less luminous with time but maintaining a roughly constant surface temperature. The process occurs in reverse in old stars leaving the main sequence for the giant branch. It is named after the Japanese astrophysicist Chushiro Hayashi (1920–2010).

Hayashi track:

The Hayashi track (the near-vertical part of the evolutionary pathways) and Henyey track (the near-horizontal parts) for stars of different mass evolving on to the main sequence.