AAS 201st Meeting, January, 2003
Session 50. The Milky Way: From Center to Halo
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[50.08] The Asymmetric Thick Disk: A Star Count and Kinematic Analysis

J.E. Parker, R.M. Humphreys (U of Minnesota), J.A. Larsen (LPL)

We present both a star count and kinematic analysis of halo, thick disk, and disk stars on either side of the Sun-Center line from l = ±20° to ±75° and b = ±20° to ±50°. Star counts using data from the Automated Plate Scanner for 80 POSS I fields yields a 30-40% excess in the number of thick disk stars both above and below the galactic plane in quadrant I when compared to quadrant IV. We produce a map of the asymmetry’s morphology and extent. Possible explanations include a bar-induced ``wake" or a triaxial thick disk. Optical spectra for a sub-sample of 7 matching POSS I plate pairs was taken at the CTIO 4m and the KPNO / WIYN 3.5m. Over 1000 ( \sigma ±10 km/s) were obtained using the multi-object spectrometer HYDRA. Radial velocity measurements confirm 85% of the stars sampled are consistent with thick disk velocities (vr = 40-60 km/s), and initial spectral classifications show F-G dwarfs dominate; however, there is a significant contribution of A dwarfs.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.