* Astronomy

Title: Asteroseismology and interferometry of the red giant star epsilon Ophiuchi
Authors: A. Mazumdar, A. Mérand, P. Demarque, P. Kervella, C. Barban, 1, F. Baudin, V. Coudé du Foresto, C. Farrington, P. J. Goldfinger, M.-J. Goupil, E. Josselin, R. Kuschnig, H. A. McAlister, J. Matthews, S. T. Ridgway, J. Sturmann, L. Sturmann, T. A. ten Brummelaar, and N. Turner

The GIII red giant star epsilon Oph has been found to exhibit several modes of oscillation by the MOST mission. We interpret the observed frequencies of oscillation in terms of theoretical radial p-mode frequencies of stellar models. Evolutionary models of this star, in both shell H-burning and core He-burning phases of evolution, are constructed using as constraints a combination of measurements from classical ground-based observations (for luminosity, temperature, and chemical composition) and seismic observations from MOST. Radial frequencies of models in either evolutionary phase can reproduce the observed frequency spectrum of epsilon Ophalmost equally well. The best-fit models indicate a mass in the range of 1.85 ±0.05 solar masses with radius of 10.55 ±0.15 Solar radii. We also obtain an independent estimate of the radius of epsilon Ophwith highly accurate interferometric observations in the infrared K' band, using the CHARA/FLUOR instrument. The measured limb-darkened disk angular diameter of epsilon Ophis 2.961 ±0.007 mas. Together with the Hipparcos parallax, this translates into a photospheric radius of R = 10.39 ±0.07 soar radii. The radius obtained from the asteroseismic analysis matches the interferometric value quite closely even though the radius was not constrained during the modelling.

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