Stellar dynamicists have long recognized that encounters involving binary stars supply the inevitable energy flow out of the cores of star clusters. Specifically, “hard binaries” – binaries with orbital velocities greater than the internal motions of cluster stars – act as energy sources for star clusters.
Such binaries are also the ones discoverable with precise radial-velocity measurements, which reveal both the variations of their orbital motions and – with enough measurements – their orbital parameters. The WIYN Hydra Multi-Object-Spectrograph was perfectly designed for surveys for short-period binary stars among thousands of stars spread over one-degree fields – a perfect match for open clusters.
UW students have obtained more than 60,000 radial velocity measurements of more than 12,000 solar-type stars in 10 open clusters. This database is a remarkable treasure trove for studying binary populations and thereafter the dynamical evolution of star clusters through detailed N-body simulations.
Current student work:
- A. Geller (Lindheimer Fellow, Northwestern University) – N-body simulations of the very old cluster NGC 188
- K. Milliman, WIYN Observatory – Comprehensive survey of the intermediate-age cluster NGC 7789