[Previous] | [Session 109] | [Next]
M. H. Siegel (UVa, STScI)
I present the results of two related programs aimed at obtaining insight into the formation of the Milky Way. The first is a CCD starcounts survey of several Kapteyn Selected Areas designed to evaluate the spatial distribution of the stellar populations of the Milky Way. I find that the distribution of stars is best described by low scale height (280 pc) thin disk, a moderate scale height (750 pc) thick disk, a flattened inner halo and a spherical outer halo. While these provide a reasonable fit to the data, the description is still imperfect. This may be the result of substructure in the outer halo. This density distribution is consistent with expectations from models that posit a merger origin to the thick disk, a global collapse origin to the inner halo and an accretive origin to the outer halo.
The second portion is a detailed examination of several outer halo objects, with a particular emphasis on testing the proposal that outer halo dSph galaxies and globular clusters formed in several discrete accretion events. I examine the color-magnitude diagrams and proper motions of the Pal 13 globular cluster, the Leo II dSph and the Sculptor dSph as well as the variable stars of Leo II. While their properities are consistent with an accretion origin for the outer halo, no specific accretion event(s) is implicated as the origin of these clusters. Pal 13 also show signs of undergoing present disruption by the Galaxy.