A Lifetime of Influence: Abstracts, Talks, and Posters
 

Tidal effects and periastron events in binary stars

Gloria Koenigsberger
Instituto de Ciencias Fisicas, Universidad Nacional Autonoma de Mexico, Cuernavaca, Mor., Mexico

Edmundo Moreno
Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Mexico D.F. 04510

Binary stars in eccentric orbits are frequently reported to present increasing levels of activity around periastron passage. We have computed the energy dissipation rate dE/dt generated by the dissipation of kinetic energy of the viscous flows thatare driven by the tidal interactions in order to explore the possibility that this mechanism may be responsible for the periastron effects and events. We will illustrate the manner in which stellar radius, equatorial rotational velocity and orbital eccentricity affect the orbital phase-dependence of the tidal energy dissipation rates. We note that in stars that are near the Eddington limit, tidal flows may propitiate enhanced mass ejection events, explaining in part the peculiar behavior of systems such as $\eta$ Carinae, WR 140 and HD 5980, as well as the more moderate effects observed in many binary systems of all spectral types. We speculate that delays between periastron passage and the observable manifestation of the effects may be associated with the depth of the layer in which the maximum energy deposition occurs and with the timescale for the outer layers to respond to the added energy. We also speculate on the possibility that as a star evolves, the tidal forcing may resonate with the star's normal pulsation modes leading to major mass-shedding events such as the 1994 eruption of HD 5980 and even perhaps the major eruptions in Eta Carinae.