The GIII red giant star \epsilon~ { } \mathrm { 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~ { } \mathrm { Oph } almost equally well .
The best-fit models indicate a mass in the range of 1.85 \pm 0.05 M _ { \odot } with radius of 10.55 \pm 0.15 R _ { \odot } .
We also obtain an independent estimate of the radius of \epsilon~ { } \mathrm { Oph } using high accuracy interferometric observations in the infrared K ^ { \prime } band , using the CHARA/FLUOR instrument .
The measured limb darkened disk angular diameter of \epsilon~ { } \mathrm { Oph } is 2.961 \pm 0.007 mas .
Together with the Hipparcos parallax , this translates into a photospheric radius of R = 10.39 \pm 0.07 R _ { \odot } .
The radius obtained from the asteroseismic analysis matches the interferometric value quite closely even though the radius was not constrained during the modelling .