AAS 204th Meeting, June 2004
Session 8 UV/Optical Universe at Ultra-High Angular Resolution
Topical Realted Poster, Monday, May 31, 2004, 9:20am-6:30pm, Ballroom

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[8.07] Cepheids Geometrical Distances Using Space Interferometry

M. Marengo, M. Karovska, D.D. Sasselov (Harvard-Smithsonian CfA), M. Sanchez (Dept. of Physics, Harvard University)

A space based interferometer with a sub-milliarcsecond resolution in the UV-optical will provide a new avenue for the calibration of primary distance indicators with unprecedented accuracy, by allowing very accurate and stable measurements of Cepheids pulsation amplitudes at wavelengths not accessible from the ground. Sasselov & Karovska (1994) have shown that interferometers allow very accurate measurements of Cepheids distances by using a ``geometric'' variant of the Baade-Wesselink method. This method has been succesfully applied to derive distances and radii of nearby Cepheids using ground-based near-IR and optical interferometers, within a 15% accuracy level. Our study shows that the main source of error in these measurements is due to the perturbing effects of the Earth atmosphere, which is the limiting factor in the interferometer stability. A space interferometer will not suffer from this intrinsic limitations, and can potentially lead to improve astronomical distance measurements by an order of magnitude in precision.

We discuss here the technical requirements that a space based facility will need to carry out this project, allowing distance measurements within a few percent accuracy level.

We will finally discuss how a sub-milliarcsecond resolution will allow the direct distance determination for hundreds of galactic sources, and provide a substantial improvement in the zero-point of the Cepheid distance scale.

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