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

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.

[1]  B. Skiff,et al.  VizieR Online Data Catalog , 2009 .

[2]  W. Traub,et al.  Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be Stars , 2006, astro-ph/0606052.

[3]  E. Böhm-Vitense.  The Puzzle of the Metallic Line Stars , 2006 .

[4]  G. Torres.  The Astrometric-Spectroscopic Binary System HIP 50796: An Overmassive Companion , 2005, astro-ph/0510455.

[5]  J. Richer,et al.  Atomic Diffusion and ο Leonis , 2005 .

[6]  W. Traub,et al.  Robust determination of optical path difference: fringe tracking at the infrared optical telescope array interferometer. , 2005, Applied optics.

[7]  Jong-Hak Woo,et al.  Y2 Isochrones with an Improved Core Overshoot Treatment , 2004 .

[8]  A. Claret,et al.  New grids of stellar models including tidal-evolution constants up to carbon burning. III. From 0.8 , 2004 .

[9]  Rafael Millan-Gabet,et al.  The PICNIC Interferometry Camera at IOTA , 2004 .

[10]  F. P. Schloerb,et al.  First Results with the IOTA3 Imaging Interferometer: The Spectroscopic Binaries λ Virginis and WR 140 , 2004, astro-ph/0401268.

[11]  Rafael Millan-Gabet,et al.  An integrated-optics 3-way beam combiner for IOTA , 2003, SPIE Astronomical Telescopes + Instrumentation.

[12]  Rafael Millan-Gabet,et al.  New beam-combination Techniques at IOTA , 2003, SPIE Astronomical Telescopes + Instrumentation.

[13]  T. Sigut,et al.  A highly sensitive search for magnetic fields in B, A and F stars , 2002 .

[14]  Bruce W. Carney,et al.  A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries , 2002 .

[15]  R. Griffin.  Composite Spectra. XII. o Leonis: An Evolving Am Binary , 2002 .

[16]  G. Torres,et al.  Spectroscopic Binaries in a Sample of ROSAT X-Ray Sources South of the Taurus Molecular Clouds , 2001, astro-ph/0112294.

[17]  C. Ree,et al.  Toward Better Age Estimates for Stellar Populations: The Y2 Isochrones for Solar Mixture , 2001, astro-ph/0104292.

[18]  David Mozurkewich,et al.  Orbital and Stellar Parameters of Omicron Leonis from Spectroscopy and Interferometry , 2001 .

[19]  H. Abt.  Does Rotation Alone Determine Whether an A-Type Star’s Spectrum Is Abnormal or Normal? , 2000 .

[20]  A. Cox,et al.  Allen's astrophysical quantities , 2000 .

[21]  A. Jorissen,et al.  Re-processing the Hipparcos Transit Data and intermediate astrometric data of spectroscopic binaries: I. Ba, CH and Tc-poor S stars , 2000, astro-ph/0006175.

[22]  D. Latham,et al.  Absolute Dimensions of Eclipsing Binaries. XXIII. The F-Type System EI Cephei , 2000 .

[23]  J. Richer,et al.  The Evolution of AmFm Stars, Abundance Anomalies, and Turbulent Transport , 2000 .

[24]  D. Latham,et al.  Radial-Velocity Standard Stars , 1999 .

[25]  D. Evans,et al.  On the use of the Hipparcos intermediate astrometric data , 1998 .

[26]  F. LeBlanc,et al.  Radiative Accelerations for Evolutionary Model Calculations , 1998 .

[27]  France.,et al.  A standard stellar library for evolutionary synthesis - II. The M dwarf extension , 1997, astro-ph/9710350.

[28]  Jens Viggo Clausen,et al.  The Absolute Dimensions of Eclipsing Binaries. XXII. The Unevolved F-Type System HS Hydrae , 1997 .

[29]  J.-C. Mermilliod,et al.  The General Catalogue of Photometric Data (GCPD). II. , 1997 .

[30]  Robert L. Kurucz,et al.  A calibration of Geneva photometry for B to G stars in terms of Teff, log g and $[M/H]$ , 1997 .

[31]  J.-M. Mariotti,et al.  Deriving object visibilities from interferograms obtained with a fiber stellar interferometer , 1997 .

[32]  N. Morrell,et al.  The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars , 1995 .

[33]  L. Balona.  Effective temperature bolometric correction and mass calibration for O–F stars , 1994 .

[34]  Tsevi Mazeh,et al.  STUDY OF SPECTROSCOPIC BINARIES WITH TODCOR. I: A NEW TWO-DIMENSIONAL CORRELATION ALGORITHM TO DERIVE THE RADIAL VELOCITIES OF THE TWO COMPONENTS , 1994 .

[35]  Y. Kondo,et al.  Evolutionary Processes in Interacting Binary Stars , 1992 .

[36]  A. Tutukov,et al.  Evolution of Stars: The Photospheric Abundance Connection , 1991 .

[37]  F. A. Seiler,et al.  Numerical Recipes in C: The Art of Scientific Computing , 1989 .

[38]  D. Lambert,et al.  Carbon, nitrogen, and oxygen abundances in the chemically peculiar stars of the upper main sequence , 1987 .

[39]  M. Dworetsky,et al.  Grids for the determination of effective temperature and surface gravity of B, A and F stars using uvby-beta photometry , 1985 .

[40]  G. Michaud.  The astrophysical context of diffusion in stars , 1980 .

[41]  D. Crawford.  Empirical Calibrations of the UVBY, Beta Systems - Part Three - the A-Type Stars , 1979 .

[42]  M. Breger.  Catalog of Spectrophotometric Scans of Stars , 1976 .

[43]  Eugene H. Avrett,et al.  Blanketed model atmospheres for early-type stars , 1974 .

[44]  C. Jaschek,et al.  A study of the bright A stars. I. A catalogue of spectral classifications. , 1969 .

[45]  Helmut A. Abt,et al.  The Frequency of Binaries among Metalmc-Line Stars. , 1961 .

[46]  W. W. Morgan,et al.  On the Classification of the a Stars. I. The Spectral Types of the Brighter Members of the Hyades Cluster. , 1940 .

[47]  K. Schwarzschild,et al.  The Observatory , 1886 .

[48]  W. W. Campbell,et al.  Sixty-eight stars whose radial velocities vary , 1911 .