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P.K. Lu (Yale and WCSU), R. Mendez (CTIO,NOAO), W. van Altena, I. Platais, T.M. Girard, V. Kozhurina-Platais (Yale Univ.), C.E. Lopez (Univ. of San Juan, Argentina)
Spectrophotometric data have been obtained with the 2DF spectrograph at CTIO and with Hydra at the WYIN telescope for nearly 2000 A,F and G stars towards the SGP. Using 1311 radial velocities, 2300 uvbyHb photometric measurements and 1650 Yale SPM (Southern Proper Motion) absolute proper motions, peculiar velociteis were derived to determine the galactice gravitationa force perpendicular to the Galactic plane, K(z), first described by Oort (1932). Our preliminary results, as derived from the early-type stars (A0-F5), support Bahcall's (1984) local volumen density, implying that dark matter exists in the galactic disk. Our results are also in apparent agreement with the total surface density derived by Kuijken and Gilmore (1989), implying that there is no dark matter in the disk when using late type stars (F6-G8). The derived hehavior of K(z) versus distance from the Galactic plane shows the well-known peak at about 400pc. A second peak at about 1100pc exhibited by dwarf main-sequence stars, but not for the giants, suggests that this second peak is due to a thick-disk population of metal-poor objects.