Pre-main-sequence Evolution

Abstract

IT is several years since the first discovery of stellar clusters which appeared to be so young that a number of stars in them were still in the process of contracting onto the main sequence^1–4. The first theoretical model covering the evolution of stars, on the assumption that their self gravitational energy is the only energy source available, was produced by Henyey, LeLevier and Levée⁵. The results of these computations have been used to produce a theoretical Hertzsprung–Russell diagram for young stellar clusters^6,7. In this theory, the evolution of the stars is governed by the equations and where L, R, T and M denote the luminosity, radius, effective temperature and mass, respectively, all in solar units, and in which τ denotes the age in units of the Helmholtz–Kelvin contraction time, α and β are constants with approximate values given by Huang⁶ as α = 5.4 and β=0.79.