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 when 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.