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B. Lane (Caltech GPS)
Cepehid variables are a fundamental link in the chain of methods used in determining cosmological distances. As such it is important that the well-known Cepheid period-luminosity relation be calibrated, preferably via multiple independent distance determinations to galactic Cepheids. The very high angular resolution achievable with modern stellar interferometers allows one to directly resolve several of the closest Cepheids, and in some cases directly measure the change in angular size during the pulsational cycle. When combined with radial-velocity measurements this allows one to determine the distance to the Cepheid (the Baade-Wesselink method). I will presnt the results of ongoing work in this area being done at the Palomar Testbed Interferometer, as well as our plans for the future.