林轨迹（Hayashi track）是原恒星在赫罗图上经历原恒星云之后达到趋近静力学平衡的路径。

1961年林忠四郎显示有一个最小的有效温度（相当于在赫罗图的右侧边界）存在，这个临界温度大约是4000K，低于这个温度静力学平衡便不能维持。因此原恒星云低于此温度时必需经由收缩以提高温度，直到达到临界温度。一但达到临界温度，原恒星将继续收缩至克赫时标，但是有效温度不会继续上升，而始终维持在林界限，因此林轨迹在赫罗图上几乎是垂直的。

恒星在林界限上是完全的对流体：这是因为他们是低温和高度的不透明，因此辐射性的能量传输是毫无效率的，并且内部因而有大的温度阶梯。质量低于0.5太阳质量的恒星在由前主序星状态进入主序星时会维持在林轨迹（意思是完全的对流体）的状态，并在林轨迹的底部进入主序带。质量高于0.5太阳质量的恒星，当林轨迹结束时，亨耶迹的状态就会开始，当恒星内部的温度上升到足够高时，中央的不透明度便会降低，辐射传输能量的效率相对的被提升，会比对流更有效率：对一定质量的恒星而言，在林轨迹中光度最低的恒星是因为他依然完全以对流来传输能量。

The Hayashi track is a luminosity–temperature relationship obeyed by infant stars of less than 3 M_☉ in the pre-main-sequence phase (PMS phase) of stellar evolution. It is named after Japanese astrophysicist Chushiro Hayashi. On the Hertzsprung–Russell diagram, which plots luminosity against temperature, the track is a nearly vertical curve. After a protostar ends its phase of rapid contraction and becomes a T Tauri star, it is extremely luminous. The star continues to contract, but much more slowly. While slowly contracting, the star follows the Hayashi track downwards, becoming several times less luminous but staying at roughly the same surface temperature, until either a radiative zone develops, at which point the star starts following the Henyey track, or nuclear fusion begins, marking the beginning of the main sequence.