PI Total time #CoIs, team John Pritchard 107h (ELT 42m) 5-10 people who will reduce and analyse spectra and do NLTE atmospheric and radial velocity curve modelsing Not Further but Fainter: Eclipsing Binaries in the Magellanic Clouds Eclipsing binaries provide accurate Stellar masses, radii, luminosities and distances. EBs in the Magellanic Clouds allow the study of low metalicity EB systems as well as the distance and structure of these cosmologically important galaxies themselves. The ELT will open the way to make detailed spectroscopic studies of systems up to 3 magnitudes fainter than is currently possible. In this proposal we will take high resolution spectra of 30 MCEBs in the range V~16 -- V~18mag to give Radial Velocity curves and allow detailed atmospheric modeling thus increasing by factor of 3 the number of well studied such systems.

Scientific Rationale Accurate stellar parameters at Low Metallicity: Masses, Radii, Effective Temperatures, Luminosities Critical tests of stellar evolution, structure, formation models Distance LMC is the first rung of the cosmic distance scale ladder, everything more distant than LMC is measured relative to the LMC Internal structure of the MCs

Immediate Objectives High resolution spectroscopy for Radial velocity curves and NLTE atmospheric modeling Increase sample of well studied systems from less than 10 to ~40. Study later spectral types than has so far been possible Detailed studies of long period systems with a Cepheid component

RunTargetR.A.Dec.ToTMagNotes ABCD40 MCEBs1h,5h-60-75˚517h16-19S/N ~ 50 ABC30 MCEBs1h,5h-60-75˚107h16-18S/N ~ 50 ELT Justification: Exposure times are prohibitively long on (for example) Data Reduction: No problems expected, “standard” techniques. RunMPModeAOT.FOVPixel Notes A1R=50kGLAO5h5’100440nmB band/V~16 B1R=50kGLAO21h5’100440nmB band/V~17 C1R=50kGLAO81h5’100440nmB band/V~18 D1R=50kGLAO410h5’100440nmB band/V~19

ESO-3.6m and the Milkyway