The Dynamics of Ejecting Stellar Systems

We consider the ejection of one stellar system from the centre of another stellar system, representing both by Plummer models. Using the impulsive appoximation, we derive analytically the overall and differential energy changes and also the mass escape from the systems. We compare the results with those obtained for colliding systems.We find that the disruptive effects are considerably less in the case of ejection. If the ejected system is compact, it escapes with negligible disruptive effects.In the case of ejections, stars are also accelerated in the direction of motion of the system. Using a dimensionless parameter λ defined as the ratio of the squares of the stellar velocity perturbations in the direction of motion of the system and perpendicular to it, we find a significant difference between ejecting systems and colliding systems. In fast head-on collisions of spherical stellar systems, the systems become elongated in the direction perpendicular to the direction of motion whereas in the case of ejecting systems, they also become elongated in the direction of motion. These effects are more pronounced in the outer regions of the smaller system and the innner regions of the bigger system. These effects are enhanced if the ejected system is compact.