Stellar encounters involving red giants in globular cluster cores

A 3D smoothed particle hydrodynamics code is used to simulate collisions between a 0.8 solar mass red giant and impactors of mass 0.4 and 0.6 solar mass. The red giant is modeled as a massive core surrounded by a gaseous envelope, while the impactor, assumed to be a white dwarf or a main-sequence star, is treated as a single particle. Encounters at various impact parameters and with relative velocities pertinent to global clusters are studied. It is found that, if the impactor passes within twice the radius of the red giant, mass loss occurs from the red giant envelope and both objects are left bound in elliptical orbits. Calculations suggest that if the impactor has an initial distance at the closest approach of approximately 1.6 R(RG) or less, the impactor will spiral into the red giant envelope on subsequent periastron passages. For bound systems with a greater separation, the orbit may circularize with a radius approximately double that of the initial counter.