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M. J. Kuchner, B. F. Lane (Caltech), M. J. Creech-Eakman (JPL/Caltech), G. T. van Belle (JPL)
Measuring Cepheid Angular Sizes Directly using the Palomar Testbed Interferometer
We are monitoring several Cepheids with the Palomar Testbed Interferometer (PTI) to measure their angular diameters at H and K bands. PTI, with its large baseline (110 meters), is sensitive to stellar diameters of 1.5-4.5 mas at K band. We have undertaken a long-term investigation of the pulsations of one cepheid, Eta Aquila, and hope to detect a 2% variation in its squared visibility that reflects a 12% variation in its angular diameter. Some of our other targets include X Cygni and Zeta Geminorum. Directly measuring Cepheid angular diameters promises to help refine the theory of Cepheid pulsation and to remove uncertainty in the zero point of the Cepheid period-luminosity relationship, a rung in the cosmological distance ladder.