THE MASS-LOSS-INDUCED ECCENTRIC KOZAI MECHANISM: A NEW CHANNEL FOR THE PRODUCTION OF CLOSE COMPACT OBJECT-STELLAR BINARIES

摘要

Over a broad range of initial inclinations and eccentricities, an appreciable fraction of hierarchical triple star systems with similar masses are essentially unaffected by the Kozai-Lidov mechanism (KM) until the primary in the central binary evolves into a compact object. Once it does, it may be much less massive than the other components in the ternary, enabling the "eccentric Kozai mechanism (EKM)": the mutual inclination between the inner and outer binaries can flip signs driving the inner binary to very high eccentricity, leading to a close binary or collision. We demonstrate this "mass-loss-induced eccentric Kozai" (MIEK) mechanism by considering an example system and defining an ad hoc minimal separation between the inner two members at which tidal effects become important. For fixed initial masses and semimajor axes, but uniform distributions of eccentricity and cosine of the mutual inclination, ~10% of systems interact tidally or collide while the primary is on the main sequence (MS) due to the KM or EKM. Those affected by the EKM are not captured by earlier quadrupole-order secular calculations. We show that fully ~30% of systems interact tidally or collide for the first time as the primary swells to AU scales, mostly as a result of the KM. Finally, ~2% of systems interact tidally or collide for the first time after the primary sheds most of its mass and becomes a white dwarf (WD), mostly as a result of the MIEK mechanism. These findings motivate a more detailed study of mass loss in triple systems and the formation of close neutron star (NS)/WD-MS and NS/WD-NS/WD binaries without an initial common envelope phase.