Henyey track

The astronomer Louis G. Henyey and his colleagues in the 1950s showed that the pre-main-sequence star can remain in radiative equilibrium throughout some period of its contraction to the main sequence.

The Henyey track is characterized by a slow collapse in near hydrostatic equilibrium, approaching the main sequence almost horizontally in the Hertzsprung–Russell diagram (i.e. the luminosity remains almost constant).

These stars will continue to contract, until the central core reaches a certain temperature threshold, where the H- ions will break apart, causing a decrease in opacity.

Stars that are massive enough (0.6 solar mass) will deviate onto the Henyey Track, depicted as a near-horizontal line on an HR diagram.

[4] At the end of the track, the star will undergo nuclear burning, however, will experience a dip in luminosity, until it reaches the main sequence.

An HR Diagram of PMS stars with different masses. The Hayashi Track is depicted as vertical lines, while the Henyey are horizontal. Higher mass stars spend very little time on the Hayashi Track, while the lowest mass stars never reach the Heyney Track, with a gradient seen of time spent on each track as the mass increases. [ 1 ]