Dynamical Interactions in Star-Forming Regions and the Origin of Stellar Masses

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Session 99 -- Molecular Clouds and Star Formation
Oral presentation, Friday, January 14, 2:15-3:45, Salon VI Room (Crystal Gateway)

[99.04] Dynamical Interactions in Star-Forming Regions and the Origin of Stellar Masses

Nigel M. Price, Ph. Podsiadlowski (IoA, Cambridge)

Recent observations of giant molecular cloud cores suggest that star formation in the Galaxy occurs predominantly in a dense protocluster environment rather than in isolated low-mass cores.

We propose that collisions between protostellar cores (each a low mass core with a central accreting protostar) or the passage of previously exposed protostars through the gaseous envelopes of protostellar cores can eject protostars from their cores. We construct a stellar initial mass function using a simple model for the star-forming process in which the masses of stars are determined by a relevant collision timescale rather than the mass contained in a core. This mass function has a Salpeter-like power law, a high-mass exponential cut-off which depends on the environment and is flat at small masses. We construct a self-consistent, self-regulated star formation model, in which energy injected into the star forming environment by accreting protostars determines their rate of formation, and we calculate collision rates for the two types of dynamical interaction considered. Using this model we examine the dependence of the mass function on the star forming environment including giant molecular cloud cores, protoglobular clusters and high-mass star formation.

Using smooth particle hydrodynamics simulations, we have performed a systematic study of dynamical interactions between young stellar objects, the results of which are presented. In particular, we have investigated the conditions under which a star passing through a protostellar core does not eject the central protostar but displaces it sufficiently from the centre of the gas distribution that a second protostar can form. The binaries formed thus will begin to spiral together with several possible outcomes (merger, close binary, wide binary, hierarchical multiple system). This process has a larger cross-section than simple protostar ejection and is capable of forming binaries with a wide range of eccentricities and separations, with a frequency of order 100\%.

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