The Helmholtz-Kelvin time scale for stars of very low massin presence of internal non-rigid rotationand magnetic field

摘要

Under the assumption that the contracting stars in convective equilibrium evolve vertically downward in the H-R diagram, an expression for the Helmholtz-Kelvin time scale is derived in presence of internal non-rigid rotation and magnetic field. This model is applied to the pre-main sequence stars and the Helmholtz-Kelvin time scale is obtained to be less than 10() years while the earlier estimations, based on horizontal evolution, in absence of both internal rotation and magnetic field gave a time scale greater lhat 100 billion years.