The First Million Years of the Sun: A Calculation of the Formation and Early Evolution of a Solar Mass Star

We present the first coherent dynamical study of the cloudfragmentation-phase, collapse and early stellar evolution of a solar mass star.We determine young star properties as the consequence of the parent cloudevolution. Mass, luminosity and effective temperature in the first millionyears of the proto-Sun result from gravitational fragmentation of a molecularcloud region that produces a cluster of prestellar clumps. We calculate theglobal dynamical behavior of the cloud using isothermal 3D hydrodynamics andfollow the evolution of individual protostars in detail using a 1Dradiation-fluid-dynamic system of equations that comprises a correct standardsolar model solution, as a limiting case. We calculate the pre-main sequence(PMS) evolutionary tracks of a solar mass star in a dense stellar clusterenvironment and compare it to one that forms in isolation. Up to an age of950.000 years differences in the accretion history lead to significantlydifferent temperature and luminosity evolution. As accretion fades and thestars approach their final masses the two dynamic PMS tracks converge. Afterthat the contraction of the quasi-hydrostatic stellar interiors dominate theoverall stellar properties and proceed in very similar ways. Hence the positionof a star in the Hertzsprung-Russell diagram becomes a function of age and massonly. However, our quantitative description of cloud fragmentation, starformation and early stellar evolution predicts substantial corrections to theclassical, i.e. hydrostatic and initially fully convective models: At an age of1 million years the proto-Sun is twice as bright and 500 Kelvin hotter thanaccording to calculations that neglect the star formation process.Comment: Four pages, accepted for publication in ApJ Letter