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Paper: Contact Binaries
Volume: 293, 3D Stellar Evolution
Page: 76
Authors: Webbink, R. F.
Abstract: Despite being the most abundant (by space density) of interacting binary stars, W~Ursae Majoris (W~UMa) stars are not understood structurally. Their stellar components are in physical contact, and share a common convective envelope. Observations demand large-scale energy exchange between components, as do considerations of hydrostatic and thermal equilibrium. Yet solutions in complete equilibrium can account for only a few of the bluest W~UMa binaries. Models which permit departures from thermal equilibrium can reproduce the observable properties of later-type W~UMa binaries, but they develop relaxation oscillations, during a substantial portion of which the binary components break thermal contact and develop very different effective temperatures, contrary to observational statistics. Massive, early-type contact binaries are also known to exist, but the nature of energy and mass exchange in common radiative envelopes remains virtually unexplored.
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