The Distance to the Galactic Center From Cepheid Kinematics

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Session 22 -- Galaxy Structure and Kinematics
Oral presentation, Monday, 30, 1994, 2:00-3:30

[22.07] The Distance to the Galactic Center From Cepheid Kinematics

M.R. Metzger, P.L. Schechter (MIT)

We report a measurement of the distance to the Galactic center using radial velocities and optical/infrared photometry of Cepheid variables. A significant amount of new data on faint Galactic Cepheids that can improve such a measurement has recently become available, and we also report here radial velocity measurements of newly discovered distant Cepheids in the southern hemisphere. The new data is combined with existing data on Milky Way Cepheids to constrain parameters of rotation curve models, and determine the Galactic center distance $R_0$. The new Cepheids significantly reduce the internal error over previous models, yielding a precision of $< 5$\%. At this level systematic errors begin to dominate, however, and limit the overall accuracy to $\sim 8$\%. Deviations the true rotation law from our kinematic model assumptions, such as a non-axisymmetric rotation curve, can lead to additional systematic error. We examine models that incorporate an elliptical rotation curve, and show the effects on $R_0$ derived from the Cepheid data.

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