Constraints on the Distribution of Dark Matter within the Milky Way

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It is widely believed that most of the mass in our Galaxy lies in one or more unseen "dark" components. In the absence of direct detection, the distribution of dark matter can be mapped by observing its gravitational effects on suitably chosen tracers of the Milky Way's potential energy. Observations of two different tracers, Cepheid variable stars and K dwarfs, will be used to determine (a) the distance from the Sun to the center of the Galaxy, (b) the deviation from axisymmetry of the closed orbits passing near the Sun, and (c) the mass surface density of the disk of the Galaxy at the Sun's position. The deviation from axisymmetry will be obtained by way of a search for new Cepheids toward galactic longitude l = 60 degrees, complementing a recent successful search carried out toward l = 300 degrees. Followup photometry will be obtained in the near infrared at 1.2, 1.6, and 2.2 microns, where the effects of interstellar extinction are substantially reduced.