Fragile Binaries: Observational Leverage on Difficult Astrophysical Problems

Abstract

Loosely bound, fragile binary stars, whose separations may reach ∼ 0.1 pc, are like open clusters with two coeval components. They provide a largely overlooked avenue for the investigation of many astrophysical questions. For example, the orbital distribution of fragile binaries with two long-lived main-sequence components provides a sensitive test of the cumulative effects of the Galactic environment. In pairs where one component is evolved, the orbits have been amplified by post-main-sequence mass loss, potentially providing useful constraints on the initial-to-final mass relation for white dwarfs. The nearly featureless spectra of cool white dwarfs usually provide little information about intrinsic radial velocity, full space motion, population membership, metallicity, etc. However, distant main sequence companions provide benchmarks against which those properties can be determined. In addition, the cooling ages of white dwarf components provide useful limits on the ages of their main sequence companions, independent of other stellar age determination methods. This paper summarizes some of the ways fragile binaries provide useful leverage on these and other problems of interest.

Commission 26: Double and Multiple Stars

“…Such wide pairs evolve as two separate but coeval stars. Oswalt and collaborators (Oswalt et al 2007;Johnston et al 2007) have studied the statistical distortion of the frequency distribution of fragile binary separations caused by the mass loss. This process provides a robust test of current theories of stellar evolution and sets constraints on the dynamics of the Galactic disk.…”