Henyey track

A Henyey track is a track along a H-R diagram (HRD) showing the evolution of a particular late phase of some pre-main-sequence stars (PMSs), each point on the track indicating the position of that body at some point in time within that phase. A PMS follows this track after it follows the Hayashi track if it is massive enough to form a radiation zone, i.e., more massive than a red dwarf (which remains fully convective). This track shows the changing characteristics of such a more-massive star during the latter part of its pre-main-sequence gravitational collapse, ending when collapse ceases and hydrogen burning begins (though these may not be simultaneous), the star entering the main-sequence during which its further shifting on the HRD is much slower. On the Henyey track, the star's luminosity changes less than on the Hayashi track, so there is less up/down movement on the HRD. I find little information about the amount of time spent on the Henyey track: the original paper included timescales in millions and tens of millions of years but considered this to be rough at best. Another source suggests less than a million years.