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Session 81 - Variable Cool and Late Type Stars.
Display session, Wednesday, January 15
Metropolitan Ballroom,

[81.14] Radial Velocity Dispersion of Field Horizontal Branch Stars

J. L. Sievers (MIT), G. W. Preston (OCIW), P. L. Schechter (MIT), S. A. Shectman (OCIW), C. C. Wiegert (U. Chicago)

We present the results of a photometric and spectroscopic search for blue horizontal branch stars in an effort to determine the radial velocity dispersion of the galactic halo. From drift scans of a field of 12 square degrees centered at l=359.5 and b=-13.5, 672 candidate field horizontal branch stars were selected, on the basis of V (16.5 < V < 17.5) and B - V (-0.1 < B - V < 0.3), for follow-up spectroscopic study. Medium resolution spectra of the candidates were obtained using the muluti-fiber system on the 2.5m DuPont Telescope at Las Campanas Observatory. Of the 672 candidates, 188 were classified as horizontal branch stars on the basis of their colors and the widths of H gamma and H delta at 20continuum. Radial velocities were measured using the spectra, and a radial velocity dispersion of 105 +/- 8 km/s was found. The location of the field and magnitude of the candidates place the horizontal branch stars at the solar circle on the opposite side of the galaxy, so the measured velocity dispersion should be the radial component of the local Population II velocity ellipsoid.

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