Asteroseismology and interferometry of the red giant star epsilon Oph

TL;DR

This study combines asteroseismic data from MOST and interferometric measurements to accurately determine the physical parameters of the red giant star epsilon Oph, demonstrating the effectiveness of integrated observational approaches.

Contribution

It provides a detailed analysis of epsilon Oph using both seismic and interferometric data, achieving consistent stellar radius estimates without radius constraints in modeling.

Findings

Asteroseismic models reproduce observed frequencies well.

Interferometric radius closely matches seismic estimates.

Star's mass is approximately 1.85 solar masses.

Abstract

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 Oph almost equally well. The best-fit models indicate a mass in the range of 1.85 +/- 0.05 Msun with radius of 10.55 +/- 0.15 Rsun. We also obtain an independent estimate of the radius of epsilon Oph using high accuracy interferometric observations in the infrared K' band, using the CHARA/FLUOR instrument. The measured limb darkened disk angular diameter of epsilon Oph is 2.961 +/- 0.007 mas. Together with the Hipparcos parallax, this translates into a photospheric radius of 10.39 +/- 0.07 Rsun. The radius obtained from the asteroseismic analysis matches the interferometric value quite closely even though the radius was not constrained during the modelling.