Showing papers by "Alan P. Boss published in 1991"

Formation of hierarchical multiple protostellar cores

Abstract: BINARY pre-main-sequence stars1,2 seem to occur as frequently as binary main-sequence stars3,4; triple pre-main-sequence star systems have also been detected5, and hierarchical main-sequence multiple stars continue to be identified6. (Hierarchical systems contain both closely spaced stars and stars orbiting at much greater distances.) These observations suggest that essentially all binary stars were formed before the main-sequence phase of evolution. The detection of a number of binary young stellar objects7,8 seems to indicate that binary formation must occur no later than the protostellar phase (further observations are needed to establish if this is the case for multiple star systems). Here I describe numerical hydrodynamical calculations showing that stable hierarchical systems of multiple protostellar cores can form through gravitationally driven fragmentation during the collapse of an isolated gas cloud, suggesting that the hierarchical systems observed may be the result of the hydrodynamical collapse of rapidly rotating clouds.

Tidal Disruption of Inviscid Protoplanets

Abstract: Roche showed that equilibrium is impossible for a small fluid body synchronously orbiting a primary within a critical radius now termed the Roche limit Tidal disruption of orbitally unbound bodies is a potentially important process for planetary formation through collisional accumulation, because the area of the Roche limit is considerably larger then the physical cross section of a protoplanet Several previous studies were made of dynamical tidal disruption and different models of disruption were proposed Because of the limitation of these analytical models, we have used a smoothed particle hydrodynamics (SPH) code to model the tidal disruption process The code is basically the same as the one used to model giant impacts; we simply choose impact parameters large enough to avoid collisions The primary and secondary both have iron cores and silicate mantles, and are initially isothermal at a molten temperature The conclusions based on the analytical and numerical models are summarized

Formation of the protosolar nebula

Abstract: Theoretical models are discussed of the collapse of a dense molecular cloud core to form the protosolar nebula that produce the sun and the planet The theoretical models use the equations of hydrodynamics, gravitation, and radiative transfer to follow the time evolution of a cloud collapsing under its own self-gravity Both semi-analytical and fully numerical solutions (in two and three spatial dimensions) were calculated by several workers, One challenge is to find a set of initial conditions that will lead to the formation of a suitable protosolar nebula Detailed results are shown for 2-D models, both with and without turbulent viscosity for redistributing angular momentum, and for 3-D models investigating the strength of gravitational torques associated with nonaxisymmetry produced during the collapse phase

Three-dimensional evolution of early solar nebula

Abstract: The progress is reported toward the goal of a complete theory of solar nebula formation, with an emphasis on three spatial dimension models of solar nebular formation and evolution. The following subject areas are covered: (1) initial conditions for protostellar collapse; (2) single versus binary star formation; (3) angular momentum transport mechanisms; (4) three dimensional solar nebula models; and (5) implications for planetary formation.