A nearly vertical path of stellar evolution on the Hertzsprung-Russell
diagram down which an infant star progresses on its way to the main
sequence. While on the Hayashi track, a star is largely or completely
in convective equilibrium; as it progresses, its luminosity, initially very
high, decreases rapidly with contraction, but its surface temperature remains
almost the same. The sequence runs in reverse for stars leaving the main
sequence to become giants. The track is named after Chushiro Hayashi.