Premain-sequence Evolution

Premain-sequence evolutionary path is understood as follows: Consider a situation that a star with $M_*$ is left when accretion stops. Figure 4.19 indicates that a less-massive star with $M_* < M_1$ is fully convective. Thus, this evolves along the convective Hayashi track (Hayashi 1961) down to the main-sequence. In contrast, a massive star with $M_* > M_3$ (Fig.4.19) is fully radiative and evolves along the radiative Henyey track (Henyey, LeLevier, & Levee 1955) to the main-sequence. These differences are clearly indicated in Figure 4.21. We can see veritical Hayashi track is seen essentially for stars with $M \mbox{\raisebox{0.3ex}{$<$}\hspace{-1.1em} \raisebox{-0.7ex}{$\sim$}} 1.5M_\odot$. Massive stars with $M \mbox{\raisebox{0.3ex}{$>$}\hspace{-1.1em} \raisebox{-0.7ex}{$\sim$}} 2.5M_\odot$ evolve to the upper-left direction along the Henyey track.