Hayashi track

Summary

The Hayashi track is the path in the Hertzsprung–Russell diagram followed by a fully convective star of given mass. An example is a young star that contracts towards the main sequence. Along it, the surface temperature stays nearly constant while the luminosity drops. So the track is almost vertical, and it lies at low surface temperatures, around $3000$ to $5000 \, \mathrm{K}$. It also marks a boundary: no star in hydrostatic equilibrium can be cooler at its surface than the Hayashi track of its mass. The region beyond the track is the Hayashi forbidden zone. It was described by Chūshirō Hayashi in 1961.