AAS 207th Meeting, 8-12 January 2006
Session 186 Eclipsing Binaries
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[186.04] Eclipsing Binary Systems with Cepheid Components in the Large Magellanic Cloud: A Key to the Extragalactic Distance Scale

E. Guinan, E. Fitzpatrick, I. Ribas, S. Engle (Villanova University), D. Welch, D. Lepischak (McMaster University)

Several long period eclipsing binary systems with Cepheid components have been discovered in the Magellanic Clouds from the OGLE and MACHO microlensing photometry programs (Udalski et al. 1999; Alcock et al. 2002). The astrophysical and cosmological importance of finding a Cepheid as a member of an eclipsing binary is considerable. If an eclipsing binary is a double-line system, the mass, radius, and luminosity can be directly determined from the analysis of the light and radial velocity curves. From spectrophotometry, the stellar temperatures and chemical abundances, as well as ISM reddenings and precise distances, can also be secured. Moreover, the study of Cepheids in eclipsing binaries offers an important opportunity to investigate the structure and evolution of Cepheids as well as tests of pulsational theories. These systems provide opportunity to minimize the dependence of the Cosmic Distance Scale and Hubble's constant (Ho) on uncertainties in assumed "zero-points".

In this poster we discuss the progress being made in our ongoing study of two important LMC eclipsing binaries containing Cepheid components. These stars are: the 14.5 mag, 397d LMC EB (SC21 40876 = MACHO 6.6454.5), which contains a classical Cepheid with a pulsation period of 4.97d and the 17th mag, 801d LMC EB (SC16 119952) which contains a Cepheid with a 2.03d period. We discuss the initial results of the analysis of HST-STIS FUV to near-IR spectrophotometry as well as the analysis of their light curves and (partial) radial velocity observations. The study of these systems represents an unprecedented opportunity to probe the distance to the LMC, to "self-calibrate" the P-L and P-L-C relations, to test the Baade-Wesselink pulsational parallax method, and to directly determine fundamental physical properties and ages of the Cepheids themselves.

This research is supported by NASA HST Grant GO-09176 and NSF/RUI Grant AST05-07542 which we very gratefully acknowledge.

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