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S. R. Majewski, P. M. Frinchaboy, R. J. Patterson (Univ. of Virginia)
Establishing the rotation curve of the Milky Way on an absolute scale is one of the fundamental contributions that SIM PlanetQuest can make to understanding the Galaxy and its mass distribution. As preparatory work for the ``Taking Measure of the Milky Way'' SIM Key Project, we have undertaken a systematic spectroscopic survey of open star clusters which can serve as tracers of Galactic disk dynamics. We report progress on our inital sample of over 100 clusters for which the Hydra multifiber spectrographs on the WIYN and Blanco telescopes have delivered ~1 km s-1 radial velocities (RVs) of many dozens of stars per cluster. The RVs are used to derive cluster membership for individual stars in these crowded fields and to derive a bulk cluster RV. The clusters selected for study have a broad spatial distribution in order to be sensitive to the disk velocity field in all Galactic quadrants and across a Galactocentric radius range as much as 2.5 kpc from the solar circle. These clusters already have published ages, distances, and metallicity estimates, but these can be improved once chemical abundances on a uniform scale are measured from the homogenous spectra, and once SIM parallaxes are obtained for member stars. The new RVs combined with Tycho proper motions (for bright members in each cluster) allow an initial investigation of the local disk dynamics, but this will be substantially improved once SIM proper motions are obtained for these and even more distant open clusters.
We acknowledge funding by NASA/JPL contract 1228235, NSF grant AST-0307851, and the F.H. Levinson Fund of the Peninsula Community Foundation. PMF is supported by a NASA-GSRP, a UVa Faculty Senate Dissertation-Year Fellowship, and the Virginia Space Grant Consortium.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.