2009A&A...503..521M

The GIII red giant star ε 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 ε Oph almost equally well. The best-fit models indicate a mass in the range of 1.85±0.05M_☉ with radius of 10.55±0.15R_☉. We also obtain an independent estimate of the radius of ε Oph with highly accurate interferometric observations in the infrared K' band, using the CHARA/FLUOR instrument. The measured limb-darkened disk angular diameter of ε Oph is 2.961±0.007mas. Together with the Hipparcos parallax, this translates into a photospheric radius of R=10.39±0.07R_☉. The radius obtained from the asteroseismic analysis matches the interferometric value quite closely even though the radius was not constrained during the modelling.