Volume 545, September 2012
|Number of page(s)||9|
|Section||Stellar structure and evolution|
|Published online||29 August 2012|
Fundamental properties of the Population II fiducial stars HD 122563 and Gmb 1830 from CHARA interferometric observations
1 Laboratoire Lagrange, UMR 7293, CNRS, Observatoire de la Côte d’Azur, Université de Nice Sophia-Antipolis, Nice, France
2 Center for High Angular Resolution Astronomy, Georgia State University, PO Box 3965, Atlanta, Georgia 30302-3965, USA
3 Hubble Fellow
4 LESIA-Observatoire de Paris, CNRS UMR 8109, UPMC, Univerité Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
5 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP. 226, Boulevard du Triomphe, 1050 Bruxelles, Belgium
6 European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
7 Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
8 Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
9 Astronomical Observatory/Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
10 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, Arizona, 86001, USA
Received: 22 May 2012
Accepted: 19 July 2012
We have determined the angular diameters of two metal-poor stars, HD 122563 and Gmb 1830, using CHARA and Palomar Testbed Interferometer observations. For the giant star HD 122563, we derive an angular diameter θ3D = 0.940 ± 0.011 milliarcseconds (mas) using limb-darkening from 3D convection simulations and for the dwarf star Gmb 1830 (HD 103095) we obtain a 1D limb-darkened angular diameter θ1D = 0.679 ± 0.007 mas. Coupling the angular diameters with photometry yields effective temperatures with precisions better than 55 K (Teff = 4598 ± 41 K and 4818 ± 54 K – for the giant and the dwarf star, respectively). Including their distances results in very well-determined luminosities and radii (L = 230 ± 7 L⊙, R = 24.1 ± 1.1 R⊙ and L = 0.213 ± 0.002 L⊙, R = 0.665 ± 0.014 R⊙, respectively). We used the CESAM2k stellar structure and evolution code in order to produce models that fit the observational data. We found values of the mixing-length parameter α (which describes 1D convection) that depend on the mass of the star. The masses were determined from the models with precisions of <3% and with the well-measured radii excellent constraints on the surface gravity are obtained (log g = 1.60 ± 0.04, 4.59 ± 0.02 dex, respectively). The very small errors on both log g and Teff provide stringent constraints for spectroscopic analyses given the sensitivity of abundances to both of these values. The precise determination of Teff for the two stars brings into question the photometric scales for metal-poor stars.
Key words: stars: fundamental parameters / stars: individual: HD 122563 / stars: low-mass / stars: Population II / Galaxy: halo / stars: individual: HD 103095
© ESO, 2012
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