The destructive effects of binary encounters on red giants in the GalacticCentre

We consider the destructive effects of encounters between binaries and red giant stars in the Galactic Centre. Such encounters may explain the observe d depletion of luminous red giants within the central 0.2 pc of the galaxy. We consider encounters involving 2- and 8-M-circle dot red giants, and thu s span the range of stellar masses contributing to the most luminous red gi ants observed in the Galactic Centre. To explore the phase space of encount ers thoroughly, we simulate 18 x 10(3) encounters using a modified four-bod y code in which the red giant core and components of the binary are treated as point masses, and where the envelope configuration is assumed to remain static throughout the encounter. We then rerun a small number of encounter s with a smoothed particle hydrodynamics (SPH) code to confirm the reliabil ity of conclusions drawn from the four-body runs. We see two possible pathw ays to red giant destruction. A large fraction of encounters lead to the fo rmation of common-envelope systems, where two compact objects (drawn from t he red giant core and the components of the original binary) form a binary within a common gaseous envelope, whilst the third body is ejected. The des truction of the red giant will then follow when the envelope is ejected as the binary hardens. In a smaller number of encounters, the intruding binary passes through the star and ejects the red giant core from the envelope. T he I ed giant envelope will then disperse on short timescales. We compute t he time-scales for both of these processes to occur in the Galactic Centre for a variety of binary populations.