The Large Magellanic Cloud eclipsing binary HV 2274: Fundamental properties and comparison with evolutionary models

We are carrying out an international, multiwavelength program to determine the fundamental properties and independent distance estimates of selected 1 4th to 15th magnitude eclipsing binaries in the Large and Small Magellanic Clouds (LMC and SMC). Eclipsing binaries with well-defined double-line radi al velocity curves and light curves provide valuable information on orbital and physical properties of their component stars. These properties include , among other characteristics, stellar mass and radius. These can be measur ed with an accuracy and directness unachievable by any other means. The stu dy of stars in the LMC and SMC, where the metal abundances are significantl y lower than solar (by one-third to one-tenth) provides an important opport unity to test opacities and stellar atmosphere, interior, and evolution mod els. For the first time, we can also measure direct mass-luminosity relatio ns for stars outside our Galaxy. In a previous paper we demonstrated how a precise distance to the LMC-corresponding to (V-0 - M-v)(LMC) = 18.30 +/- 0 .07 mag-could be determined using the 14th magnitude LMC eclipsing binary H V 2274. In this paper we concentrate on the determination of the orbital an d physical properties of HV 2274 and its component stars from analyses of l ight curves and new radial velocity curves formed from Hubble Space Telesco pe (HST)/Goddard High-Resolution Spectrograph observations. HV 2274 (B1-2 I V-III + B1-2. IV-III; V-max approximate to + 14.2; P = 5.73 days) is a part icularly appealing star because it is a detached binary that has an eccentr ic orbit (e = 0.136) and shows rapid apsidal motion. The results of these a nalyses yield reliable masses and absolute radii, as well as other physical and orbital properties of the stars and the system. From UV/optical spectr ophotometry (1150-4820 Angstrom) of HV 2274 obtained with the HST Faint Obj ect Spectrograph, the temperatures and the metallicity ([Fe/H] = - 0.45 +/- 0.06) of the stars were found, as well as the interstellar extinction of t he system. The values of the mass, absolute radius, and effective temperatu re for the primary and secondary stars are 12.2 +/- 0.7 M., 9.9 +/- 0.2 R., 23000 +/- 180 K and 11.4 +/- 0.7 M., 9.0 +/- 0.2 R., 23110 +/- 180 K, resp ectively. The age of the system (tau = 17 +/- 2 Myr), helium abundance (Y = 0.26 +/- 0.03), and a lower limit of the convective core overshooting para meter of alpha(ov) approximate to 0.2 were obtained by fitting the stellar data with evolution models of Claret & Gimenez. HV 2274 has a relatively we ll determined (and fast) apsidal motion period of U = 123 +/- 3 yr. From an analysis of apsidal motion, additional information and constraints on the structure of the stars can be obtained. The apsidal motion analysis corrobo rates that some amount of convective core overshooting (alpha(ov) between 0 .2 and 0.5) is needed.