Asteroseismic Investigations of the Binary System HD176465

Abstract

HD 176465 is a binary system whose both components are solar-like pulsators and whose oscillation frequencies were observed by the \kepler\ mission. In this paper we have modeled the asteroseismic and spectroscopic data of the stars, and have determined their convection-zone helium abundances using the signatures left by the He{\sc ii} ionization zone on the mode frequencies. As expected we find that the components of the binary have the same age within uncertainties ($3.087\pm 0.580$ Gyr and $3.569\pm 0.912$ Gyr); they also have the same initial helium abundance (Y${}_{\mathrm{init}}$=0.253 $\pm$ 0.006 and 0.254 $\pm$ 0.008). Their current metallicity ([Fe/H]=$-0.275\pm 0.04$ and $-0.285\pm 0.04$) is also the same within errors. Fits to the signature of the He{\sc ii} acoustic glitch yields current helium abundances of $Y_{\mathrm{A}}=0.224\pm 0.006$ and $Y_{\mathrm{B}}=0.233\pm 0.008$ for the two components. Analyzing the complete ensemble of models generated for this investigation we find that both the amplitude and acoustic depth of the glitch signature arising from the second helium ionization zone and the base of the convection zone (CZ) are functions of mass. We show that the acoustic depths of these glitches are positively correlated with each other. The analysis can help us to detect the internal structure and constrain the chemical compositions.

32 pages, 10 figures and 3 tables. This paper has been accepted by ApJ on 20 February 2018

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