The Axial Ratio of the Galactic Stellar Spheroid

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Session 58 -- The Galaxy
Display presentation, Thursday, 2, 1994, 9:20-6:30

[58.03] The Axial Ratio of the Galactic Stellar Spheroid

J.A. Larsen, R.M. Humphreys (University of Minnesota)

We present our results for the axial ratio of the spheroid derived from the APS Catalog of the POSS I. Star counts were made in two colors in 16 square degree fields covering the $l=90^{\circ}$-$270^{\circ}$ plane at 10 different galactic latitudes. The fields have an average completeness limit of 20.5 magnitudes in O and 19.5 magnitudes in E. The entire set has more than 400000 stars, allowing a statistically significant study of the spheroid's spatial distribution. We derive an average value of $c/a\sim 0.6$ for those fields at $b=40^{\circ}$ and an average value of $c/a\sim 0.7$ for those fields at $b=50^{\circ}$. Our derived values are interpreted in the context of a standard deVaucouleurs $r^{0.25}$ model for the stellar spheroid. For many of these fields we present color-magnitude diagrams and luminosity functions.

New multicolor star counts are also derived along the $l=0^{\circ}$-$180^{\circ}$ plane. Using least-squares methods, we calculate several other parameters of interest to galactic structure, including the distance of the Sun above the thin-disk mid plane.

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