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E.L. Fitzpatrick, I. Ribas, E.F. Guinan, L.E. DeWarf, F.P. Maloney (Villanova University), D.L. Massa (Raytheon ITSS)
We have determined the distance to a second eclipsing binary system (EB) in the Large Magellanic Cloud, HV982 (B1 IV-V + B1 IV-V). The measurement of the distance - among other properties of the system - is based on optical photometry and spectroscopy and space-based UV/optical spectrophotometry. The analysis combines the "classical" EB study of light and radial velocity curves, which yield the stellar masses and radii, with a new analysis of the observed energy distribution, which yields the effective temperature, metallicity, and reddening of the system, plus the distance ``attenuation factor,'' essentially (radius/distance)2. This distance determination is extremely robust. It consists of a detailed study of well-understood objects (B stars) in a well-understood evolutionary phase (core H burning), whose results are entirely consistent with stellar evolution calculations. There are no ``tuneable'' parameters. There are no ``zeropoint'' uncertainties. The analysis is insensitive to stellar metallicity, although the metallicity is explicitly determined and incorporated. The reddening of the system is also determined explicitly and incorporated in the analysis. Moreover, the results depend on no statistical averages and are susceptible to no sampling biases.
In this poster we describe the analysis technique and present the new results for HV982. The results are consistent - to within the measurement errors - with those published earlier by us for the EB system HV2274 and offer a very strong argument in favor of the "short" LMC distance scale, corresponding to V0 - MV = 18.3.