Schedule Jan 17, 2009
On Hydrodynamics of Triple Stellar Encounters
Jamie Lombardi (Allegheny College)

Encounters between a binary and a single star are common in clusters. We model such interactions by means of Smoothed Particle Hydrodynamics (SPH), taking the initial conditions directly from N-body simulations and comparing the outcomes of our calculations against those of the sticky-sphere approximation. If mass loss is disregarded, the sticky sphere approach gives the correct qualitative outcome in approximately 75% of the cases considered. Among those cases in which the sticky-sphere algorithm finds that only two of the three stars collides, the hydrodynamic results will be in qualitative agreement about half of the time. If the sticky-sphere approach determines that all three stars merge, then the hydrodynamic simulations invariably agree. However, in such three star mergers, the hydrodynamic simulations reveal that: (1) mass lost as ejecta can be a considerable fraction of the total mass in the system (up to ~25%); (2) due to asymmetric mass loss, the collision product can sometimes recieve a kick velocity that exceeds 10 km/s, large enough to allow the collision product to escape the core of the cluster; and (3) the energy of the ejected matter can be large enough (up to 3x10^{50} erg) to remove or disturb the inter cluster gas appreciably.

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