AAS 205th Meeting, 9-13 January 2005
Session 54 Pulsating Stars: RR Lyraes, Miras, Cepheids, etc.
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[54.08] Cepheid Brightness Distribution Detection by the Stellar Imager

L. Watson (U. of Florida), M. Karovska, D. Sasselov, M. Marengo (CfA), Stellar Imager Vision Mission Team

A space based interferometer with a sub-milliarcsecond resolution could be used to make accurate measurements of the disk brightness distributions for several nearby Cepheids. The direct imaging of Cepheids disk brightness distributions will allow a significant improvement of our understanding of Cepheid atmospheres and pulsation processes and will yield a more accurate determination of the cosmological distance scale based on the Cepheids period-luminosity zero point. We present the results from our feasibility study of the disk brightness distribution imaging of the nearby Cepheid zeta Gem using the Stellar Imager (SI) (see http://hires.gsfc.nasa.gov./~si/). The SI, a NASA Vision Mission study project, is conceived as a large, multispacecraft sparse aperture (20-30 mirrors) imaging interferometer with ~ 500m maximum baseline operating at UV-optical wavelengths. We carried out simulations of the disk brightness distributions for the nearby Cepheid zeta Gem using time-dependent hydrodynamic atmospheric models and radiative transfer modeling in the MgII h&k lines and in the nearby continuum. Images obtained at several pulsation phases were used to produce simulated SI images. Our simulations, made with two different configurations of the interferometer, show that SI will be able to measure changes in the zeta Gem brightness distribution at different pulsational phases. We also discuss the potential and challenges of a sparse aperture interferometry for imaging Cepheid surfaces.

Acknowledgement: This work was supported by the NSF, grant number 9731923, the SAO Summer Intern Program, and by the SI Vision Mission study grant NNG04GM92G from NASA/GSFC to SAO. MK is a member of the Chandra X-ray Center (NASA contract NAS8-39073).

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© 2004. The American Astronomical Society.