Testing Models of Stellar Evolution for Metal-poor Stars: An Interferometric-spectroscopic Orbit for the Binary HD 195987

We report spectroscopic and interferometric observations of the moderately metal-poor double-lined binary system HD 195987, with an orbital period of 57.3 days. By combining our radial-velocity and visibility measurements, we determine the orbital elements and derive absolute masses for the components of MA = 0.844 ± 0.018 M⊙ and MB = 0.6650 ± 0.0079 M⊙, with relative errors of 2% and 1%, respectively. We also determine the orbital parallax, πorb = 46.08 ± 0.27 mas, corresponding to a distance of 21.70 ± 0.13 pc. The parallax and the measured brightness difference between the stars in V, H, and K yield the component absolute magnitudes in those bands. We also estimate the effective temperatures of the stars as T = 5200 ± 100 K and T = 4200 ± 200 K. Together with detailed chemical abundance analyses from the literature giving [Fe/H] ≈ -0.5 (corrected for binarity) and [α/Fe] = +0.36, we use these physical properties to test current models of stellar evolution for metal-poor stars. Among the four that we considered, we find that no single model fits all observed properties at the measured composition, although we identify the assumptions in each one that account for the discrepancy, and we conclude that a model with the proper combination of assumptions should be able to reproduce all the radiative properties. The indications from the isochrone fits and the pattern of enhancement of the metals in HD 195987 are consistent with this being a thick disk object, with an age of 10–12 Gyr.

[1]  J. B. Laird,et al.  A Survey of Proper-Motion Stars. XV. Orbital Solutions for 34 Double-lined Spectroscopic Binaries , 2002 .

[2]  Brian D. Mason,et al.  The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog , 2001 .

[3]  G. Torres,et al.  Absolute Dimensions of the M-Type Eclipsing Binary YY Geminorum (Castor C): A Challenge to Evolutionary Models in the Lower Main Sequence , 2001, astro-ph/0111167.

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

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

[6]  D. VandenBerg,et al.  Models for Old, Metal-poor Stars with Enhanced α-Element Abundances. III. Isochrones and Isochrone Population Functions , 2001, astro-ph/0102480.

[7]  J. Carpenter.  Color Transformations for the 2MASS Second Incremental Data Release , 2001, astro-ph/0101463.

[8]  B. Paczynski,et al.  Cluster AgeS Experiment: The Age and Distance of the Globular Cluster ω Centauri Determined from Observations of the Eclipsing Binary OGLEGC 17 , 2000, astro-ph/0012493.

[9]  J. Prochaska,et al.  The Galactic Thick Disk Stellar Abundances , 2000, astro-ph/0008075.

[10]  J. Fulbright.  Abundances and Kinematics of Field Halo and Disk Stars. I. Observational Data and Abundance Analysis , 2000, astro-ph/0006260.

[11]  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.

[12]  D. Alexander,et al.  Models for Old, Metal-poor Stars with Enhanced α-Element Abundances. I. Evolutionary Tracks and ZAHB Loci; Observational Constraints , 2000 .

[13]  B. Lane,et al.  A Preliminary Visual Orbit of BY Draconis , 2000, astro-ph/0001138.

[14]  E. Pluzhnik,et al.  Binary star speckle measurements during 1992-1997 from the SAO 6-m and 1-m telescopes in Zelenchuk , 1999 .

[15]  M. J. Creech-Eakman,et al.  The Visual Orbit and Evolutionary State of 12 Bootis , 1999, astro-ph/9910245.

[16]  L. Girardi,et al.  Evolutionary tracks and isochrones for low- and intermediate-mass stars: From 0.15 to 7 , and from to 0.03 , 1999, astro-ph/9910164.

[17]  B. Oppenheimer,et al.  The Visual Orbit of 64 Piscium , 1999, astro-ph/9905207.

[18]  J. Hershey,et al.  Hubble Space Telescope Astrometric Observations of the Metal‐poor Spectroscopic Binary HD 20039 , 1999 .

[19]  G. L. Wycoff,et al.  Speckle Interferometry of New and Problem Hipparcos Binaries , 1999 .

[20]  John E. Norris,et al.  Estimation of Stellar Metal Abundance. II. A Recalibration of the Ca II K Technique, and the Autocorrelation Function Method , 1999 .

[21]  J. Wallace,et al.  The Visual Orbit of ι Pegasi , 1998, astro-ph/9811029.

[22]  D. Mozurkewich,et al.  Navy Prototype Optical Interferometer Observations of the Double Stars Mizar A and Matar , 1998 .

[23]  M. Colavita.  Fringe Visibility Estimators for the Palomar Testbed Interferometer , 1998, astro-ph/9810462.

[24]  Michael Shao,et al.  Visibility calibrations with the Palomar Testbed Interferometer , 1998, Astronomical Telescopes and Instrumentation.

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

[26]  D. Popper.  Orbits of detached main-sequence eclipsing binaries of types late F to K. II. UV leonis, UV piscium, and BH virginis. , 1997 .

[27]  Bruce W. Carney,et al.  THE CONSTANCY OF [ALPHA/FE] IN GLOBULAR CLUSTERS OF DIFFERING [FE/H] AND AGE , 1996 .

[28]  J. Tomkin,et al.  The r-process element europium in galactic disk F and G dwarf stars , 1995 .

[29]  R. Wyse,et al.  Chemistry and Kinematics in the Solar Neighborhood: Implications for Stellar Populations and for Galaxy Evolution , 1995, astro-ph/9509007.

[30]  J. Mermilliod,et al.  Catalogue of Mean UBV Data on Stars , 1994 .

[31]  J. B. Laird,et al.  A survey of proper motion stars. 12: an expanded sample , 1994 .

[32]  Andreas Quirrenbach,et al.  Very high precision orbit of capella by long baseline interferometry , 1994 .

[33]  Oscar Straniero,et al.  The alpha -enhanced Isochrones and Their Impact on the FITS to the Galactic Globular Cluster System , 1993 .

[34]  Michael Shao,et al.  The orbit of Phi Cygni measured with long-baseline optical interferometry - Component masses and absolute magnitudes , 1992 .

[35]  P. Demarque,et al.  Ages of globular clusters and helium diffusion , 1992 .

[36]  A. Chieffi,et al.  Isochrones for H-burning Globular Cluster Stars. II. The Metallicity Range -2.3 < [Fe/H] < -0.5 , 1991 .

[37]  David Mozurkewich,et al.  Angular diameter measurements of stars , 1991 .

[38]  Johannes Andersen,et al.  Accurate masses and radii of normal stars , 1991 .

[39]  J. B. Laird,et al.  A Survey of Proper-Motion Stars. VIII. On the Galaxy's Third Population , 1989 .

[40]  M. Bessell,et al.  JHKLM PHOTOMETRY: STANDARD SYSTEMS, PASSBANDS, AND INTRINSIC COLORS , 1988 .

[41]  T. Mazeh,et al.  A survey of proper-motion stars. VI: Orbits for 40 spectroscopic binaries , 1988 .

[42]  J. B. Laird,et al.  A Survey of Proper-Motion Stars. III. Reddenings, Distances, and Metallicities , 1988 .

[43]  J. B. Laird,et al.  A Survey of Proper-Motion Stars. II. Extracting Metallicities from High-Resolution, Low S/N Spectra , 1987 .

[44]  J. Elias,et al.  Comparison of the MT. Stromlo/AAO and Caltech/Tololo infrared photometric systems. , 1983 .

[45]  B. Carney.  A Photometric Search for Halo Binaries - Part Two - Results , 1983 .

[46]  G. Neugebauer,et al.  Infrared standard stars , 1982 .

[47]  B. Carney.  Subdwarf ultraviolet excesses and metal abundances , 1979 .

[48]  H. Giclas.  Status of the Lowell Proper Motion Survey , 1965 .

[49]  E. Guinan,et al.  Theory and Tests of Convection In Stellar Structure , 1999 .

[50]  Accepted for publication in the Astrophysical Journal. Scheduled for Vol. 510 #1 (Jan. 1, 1999). The Palomar Testbed Interferometer , 1998 .

[51]  Paolo Persi,et al.  The Impact of Large Scale Near-IR Sky Surveys , 1997 .

[52]  E. D. Hoffleit,et al.  The general catalogue of trigonometric [stellar] parallaxes , 1995 .

[53]  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 .

[54]  K. Janes.  The formation and evolution of star clusters , 1991 .

[55]  J. Wheeler,et al.  Abundance Ratios as a Function of Metallicity , 1989 .

[56]  T. Gehren.  Chemical Abundances in Stars. , 1988 .

[57]  B. Carney,et al.  A survey of proper-motion stars. I - UBV photometry and radial velocities , 1987 .

[58]  A. Sandage.  NEW SUBDWARFS. II. RADIAL VELOCITIES, PHOTOMETRY, AND PRELIMINARY SPACE MOTIONS FOR 112 STARS WITH LARGE PROPER MOTION. , 1969 .

[59]  J. Greenstein,et al.  NEUTRAL OXYGEN IN LATE-TYPE STARS. , 1967 .