Frank P. Maloney

Fundamental Properties and Distances of the Large Magellanic Cloud from Eclipsing Binaries. II. HV 982

We have determined the distance to a second eclipsing binary (EB) system in the Large Magellanic Cloud, HV 982 (DB1 IVV ) DB1 IVV). The measurement of the distanceamong other properties of the systemis based on optical photometry and spectroscopy and space-based UV/optical spectropho- tometry. The analysis combines the ii classical ˇˇ EB study of light and radial velocity curves, which yields the stellar masses and radii, with a new analysis of the observed energy distribution, which yields the eUective temperature, metallicity, and reddening of the system plus the distance ii attenuation factor,ˇˇ essentially (radius/distance)2. Combining the results gives the distance to HV 982, which is 50.2 ^ 1.2 kpc. This distance determination consists of a detailed study of well-understood objects (B stars) in a well-understood evolutionary phase (core H burning). The results are entirely consistent withbut do not depend onstellar evolution calculations. There are no ii zero-point ˇˇ uncertainties as, for example, with the use of Cepheid variables. Neither is the result subject to sampling biases, as may aUect tech- niques that utilize whole stellar populations, such as red giant branch stars. Moreover, the analysis is insensitive to stellar metallicity (although the metallicity of the stars is explicitly determined), and the eUects of interstellar extinction are determined for each object studied. After correcting for the location of HV 982, we —nd an implied distance to the optical center of the LMCs bar of kpc. d LMC \ 50.7 ^ 1.2 This result diUers by nearly 5 kpc from our earlier result for the EB HV 2274, which implies a bar distance of 45.9 kpc. These results may either re—ect marginally compatible measures of a unique LMC distance or, alternatively, suggest a signi—cant depth to the stellar distribution in the LMC. Some evi- dence for this latter hypothesis is discussed. Subject headings: binaries: eclipsingdistance scaleMagellanic Cloudsstars: distances ¨ stars: fundamental parametersstars: individual (HV 982)

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 14th to 15th magnitude eclipsing binaries in the Large and Small Magellanic Clouds (LMC and SMC). Eclipsing binaries with well-defined double-line radial 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 measured with an accuracy and directness unachievable by any other means. The study of stars in the LMC and SMC, where the metal abundances are significantly lower than solar (by one-third to one-tenth) provides an important opportunity to test opacities and stellar atmosphere, interior, and evolution models. For the first time, we can also measure direct mass-luminosity relations for stars outside our Galaxy. In a previous paper we demonstrated how a precise distance to the LMC—corresponding to (V0 - Mv)LMC = 18.30 ± 0.07 mag—could be determined using the 14th magnitude LMC eclipsing binary HV 2274. In this paper we concentrate on the determination of the orbital and physical properties of HV 2274 and its component stars from analyses of light curves and new radial velocity curves formed from Hubble Space Telescope (HST)/Goddard High-Resolution Spectrograph observations. HV 2274 (B1-2 IV-III + B1-2 IV-III; Vmax ≈ +14.2; P = 5.73 days) is a particularly appealing star because it is a detached binary that has an eccentric orbit (e = 0.136) and shows rapid apsidal motion. The results of these analyses yield reliable masses and absolute radii, as well as other physical and orbital properties of the stars and the system. From UV/optical spectrophotometry (1150-4820 A) of HV 2274 obtained with the HST Faint Object Spectrograph, the temperatures and the metallicity ([Fe/H] = -0.45 ± 0.06) of the stars were found, as well as the interstellar extinction of the system. The values of the mass, absolute radius, and effective temperature 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, respectively. The age of the system (τ = 17 ± 2 Myr), helium abundance (Y = 0.26 ± 0.03), and a lower limit of the convective core overshooting parameter of αov ≈ 0.2 were obtained by fitting the stellar data with evolution models of Claret & Gimenez. HV 2274 has a relatively well 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 corroborates that some amount of convective core overshooting (αov between 0.2 and 0.5) is needed.

Eclipsing binary stars as tests of gravity theories : new solutions for AS Camelopardalis

AS Cam (BD + 69 325, HD 35311) is one of several eclipsing binary systems thought to be in violation of the classical relativistic theory governing apsidal motion. To evaluate the systems parameters accurately, the photometric data obtained by Padalia and Srivastava (1975), the V-band photometry reported by Khaliullin and Kozyreva (1983), and the spectroscopic data of Hilditch (1972) were subjected to the procedure described by Wilson (1979) to provide improved orbital elements and physical parameters of the AS Cam system in a unified manner. It is shown that the value for the orbital eccentricity e = 0.10 reported by Krzesinski et al. (1990) from an analysis of the times of minimum light is inconsistent with the photometry and spectroscopy and that the upper limit for the eccentricity might be closer to 0.16. The nature of the failure of the method employed by Krzesinski et al. is discussed. 16 refs.