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S. Meibom, R. D. Mathieu, K. T. Hole (U. Wisconsin, Madison)
Tidal circularization in a population of solar-type binary stars causes a transition from eccentric to circular orbits for the closest binaries (shortest orbital period). This characteristic fingerprint is found on all populations of late-type binaries. Determining the stellar separation (orbital period) at which this transition occurs as a function of age is a powerful observational constraint on the theory of tidal circularization.
Proper determination of this transition between eccentric and circular orbits requires large samples of binary orbits from homogeneous stellar populations. A comprehensive radial-velocity survey using the WIYN 3.5m telescope and the HYDRA Multi-Object Spectrograph has produced such large samples of 30-50 binary orbits in the open clusters M35 (150 Myr), NGC6819 (2.5 Gyr), and NGC188 (7 Gyr).
We propose a new robust method for determination of the transition between eccentric and circular orbits, and use it to determine the transition period for the established binary populations of the Pleiades, Hyades/Praesepe and M67 as well as new binary populations in M35, NGC6819, and NGC188. An estimate of the uncertainty on transition period is obtained through Monte Carlo experiments. Finally, we compare the new distribution of derived transition periods vs. population ages to the theories of evolution of tidal circularization.
This work is supported by NSF AST 9731302 and the Danish Research Agency.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.