Spectral Calibration and Kinematic Properties of the \\Field Horizontal Branch Stars

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Session 97 -- Milky Way
Oral presentation, Wednesday, 11, 1995, 2:00pm - 3:30pm

[97.06D] Spectral Calibration and Kinematic Properties of the \\Field Horizontal Branch Stars

R. Wilhelm, T.C. Beers (MSU), J. Sommer-Larsen, C. Flynn (Niels Bohr Inst), J.R. Pier (Naval Obs), G.W. Preston, S.A. Shectman (OCIW), R.O. Gray (Appal. State), A.C. Layden (CTIO)

Medium resolution (1-2 $\AA$), low S/N (10 $<$ S/N $<$ 20) spectroscopy and broadband UBV photometry have been obtained for over 1000 FHB/A star candidates selected from the HK objective prism survey of Beers, Preston and Shectman. Population classification, based on surface gravity measurements, and metal abundances, based on CaII K equivalent widths, have been assigned using new spectral calibrations of the H$\delta$, H$\gamma$ and CaII K line widths over a range in physical parameters, $T_{eff}$, Log g and [Fe/H], that include the FHB/A stars. Theoretical line widths and Kurucz UBV colors were used to construct an 833 point, 3-dimensional calibration grid. A technique for assigning physical parameters was developed which shows good agreement with high dispersion results for the observed standard stars. Misidentification of the stellar population is estimated to be less than 10\%.

Using radial velocity determinations, we find the rotational velocity for the FHB sample to be $V_{rot}$ = 47 $\pm$ 12 km/sec, and a velocity ellipsoid of ($\sigma_{r}$:$\sigma_{\phi}$:$\sigma_{\theta}$) = (134:142:66) km/sec. From subsamples of the FHB dataset there is kinematic evidence for halo contamination by a metal weak thick disk component down to a metallicity of [Fe/H]$ = -1.80$ . A sample of FHB stars with Z height $>$ 4.0 kpcs and [Fe/H] $< -2.0$ appear to be in counter-rotation with $V_{rot} = -98 \; \pm \; 41$ km/sec, consistent with the value found by Majewski using proper motions in the direction of the NGP, and that of Zinn's young halo globulars. The A star solutions for stars with [Fe/H] $< -1.0$ gives $V_{rot}$ = 94 $\pm$ 20 km/sec and a velocity ellipsoid of ($\sigma_{U}$:$\sigma_{V}$:$\sigma_{W}$) = (85:98:79) km/sec, similiar to the findings of Preston, Beers, and Shectman for the BMP stars. The results of this kinematic analysis are consistent with a scenerio of chaotic halo formation from accretion of distinct sub-units over an extended period of time.

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