Physical Orbit for λ Virginis and a Test of Stellar Evolution Models

Creators: Zhao, M.; Monnier, J. D.; Torres, G.; Boden, A. F.; Claret, A.; Millan-Gabet, R.; Pedretti, E.; Berger, J.-P.; Traub, W. A.; Schloerb, F. P.; Carleton, N. P.; Kern, P.; Lacasse, M. G.; Malbet, F.; Perraut, K.

Abstract

The star λ Virginis is a well-known double-lined spectroscopic Am binary with the interesting property that both stars are very similar in abundance but one is sharp-lined and the other is broad-lined. We present combined interferometric and spectroscopic studies of λ Vir. The small scale of the λ Vir orbit (~20 mas) is well resolved by the Infrared Optical Telescope Array (IOTA), allowing us to determine its elements, as well as the physical properties of the components, to high accuracy. The masses of the two stars are determined to be 1.897 and 1.721 M_☉, with 0.7% and 1.5% errors, respectively, and the two stars are found to have the same temperature of 8280 ± 200 K. The accurately determined properties of λ Vir allow comparisons between observations and current stellar evolution models, and reasonable matches are found. The best-fit stellar model gives λ Vir a subsolar metallicity of Z = 0.0097 and an age of 935 Myr. The orbital and physical parameters of λ Vir also allow us to study its tidal evolution timescales and status. Although atomic diffusion is currently considered to be the most plausible cause of the Am phenomenon, the issue is still being actively debated in the literature. With the present study of the properties and evolutionary status of λ Vir, this system is an ideal candidate for further detailed abundance analyses that might shed more light on the source of the chemical anomalies in these A stars.

Additional Information

© 2009 American Astronomical Society. Received 2006 September 11; accepted 2006 December 1. We thank C. R. Cowley for helpful discussion and advice, and J. R. Caruso, R. J. Davis, D. W. Latham, T. Mazeh, A. A. E. Milone, R. P. Stefanik, and J. M. Zajac for obtaining most of the spectroscopic observations used in this work. We also thank the referee for a number of helpful comments. We gratefully acknowledge support for IOTA from the Smithsonian Astrophysical Observatory, the National Aeronautics and Space Administration (NASA) (for third telescope development, NNG05G1180G; for data analysis support, NNG04GI33G), and the National Science Foundation (NSF) (AST 01-38303, AST 03-52723).G. T. wishes to acknowledge partial support for this work from NSF grant AST 04-06183 and NASA's MASSIF SIM Key Project (BLF57-04). A. B. also gratefully acknowledges the support of NASA. The IONIC3 instrument has been developed by LAOG and LETI in the context of the IONIC collaboration (LAOG, IMEP, LETI). The IONIC project is funded by the CNRS and CNES (France). This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and NASA's Astrophysics Data System Abstract Service. This publication makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/ California Institute of Technology, funded by NASA and NSF. This work also makes use of services produced at the Michelson Science Center (http://msc.caltech.edu) at the California Institute of Technology.

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