Dynamical evolution of active detached binaries on the log Jo–log M diagram and contact binary formation

Abstract

Orbital angular momentum (OAM, Jo), systemic mass (M) and orbital period (P) distributions of chromospherically active binaries (CAB) and W Ursae Majoris (W UMa) systems were investigated. The diagrams of and log Jo–log M were formed from 119 CAB and 102 W UMa stars. The log Jo–log M diagram is found to be most meaningful in demonstrating dynamical evolution of binary star orbits. A slightly curved borderline (contact border) separating the detached and the contact systems was discovered on the log Jo–log M diagram. Since the orbital size (a) and period (P) of binaries are determined by their current Jo, M and mass ratio, q, the rates of OAM loss (d log Jo/dt) and mass loss (d log M/dt) are primary parameters to determine the direction and the speed of the dynamical evolution. A detached system becomes a contact system if its own dynamical evolution enables it to pass the contact border on the log Jo–log M diagram. The evolution of q for a mass‐losing detached system is unknown unless the mass‐loss rate for each component is known. Assuming q is constant in the first approximation and using the mean decreasing rates of Jo and M from the kinematical ages of CAB stars, it has been predicted that 11, 23 and 39 per cent of current CAB stars would transform to W UMa systems if their nuclear evolution permits them to live 2, 4 and 6 Gyr, respectively.

Universal X-ray emissivity of the stellar population in early-type galaxies: unresolved X-ray sources in NGC 3379

“…The evolution of chromospherically active stars in binaries is significantly more complicated (see e.g. Eker et al 2006), making it difficult to predict the evolution of their X-ray luminosity. Also, the orbital periods of accreting white dwarf binaries (which dominate the unresolved X-ray emission of galaxies at energies >3−5 keV) decrease with time (until they reach the so-called period minimum, see e.g.…”

Observation and Analysis of RW Doradus

“…The problem of overabundance of contact binary systems was recently revived by Paczyński et al (2006) and has been commented on by Eker et al (2006). Budding (1984) considered a variant of the Case-B mass-transfer scenario, widely believed to apply to classical Algols, in which the gainer is originally a low-mass companion less than ∼0.2 times the original primary mass and at a distance of order 10 times its radius.…”

“…Eker et al 2006). It is true that many contact binaries show photometric irregularities that could be associated with surface maculation effects.…”

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