The fundamental parameters of the roAp star $\gamma$ Equulei

Abstract

Physical processes working in the stellar interiors as well as the evolution of stars depend on some fundamental stellar properties, such as mass, radius, luminosity, and chemical abundances. A classical way to test stellar interior models is to compare the predicted and observed location of a star on theoretical evolutionary tracks in a H-R diagram. This requires the best possible determinations of stellar mass, radius, luminosity and abundances. To derive its fundamental parameters, we observed the well-known rapidly oscillating Ap star, $\gamma$ Equ, using the visible spectro-interferometer VEGA installed on the optical CHARA array. We computed the calibrated squared visibility and derived the limb-darkened diameter. We used the whole energy flux distribution, the parallax and this angular diameter to determine the luminosity and the effective temperature of the star. We obtained a limb-darkened angular diameter of 0.564~$\pm$~0.017~mas and deduced a radius of $R$~=~2.20~$\pm$~0.12~${\mathrm{R}}_{\odot }$. Without considering the multiple nature of the system, we derived a bolometric flux of $(3.12\pm 0.21)\times 10^{-7}$ erg~cm${}^{-2}$~s${}^{-1}$ and an effective temperature of 7364~$\pm$~235~K, which is below the effective temperature that has been previously determined. Under the same conditions we found a luminosity of $L$~=~12.8~$\pm$~1.4~${\mathrm{L}}_{\odot }$. When the contribution of the closest companion to the bolometric flux is considered, we found that the effective temperature and luminosity of the primary star can be, respectively, up to $\sim$~100~K and up to $\sim$~0.8~L${}_{\odot }$ smaller than the values mentioned above.These new values of the radius and effective temperature should bring further constraints on the asteroseismic modelling of the star.

arXiv commentAccepted by A&A

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• The fundamental parameters of the roAp star 10 Aql
• Fundamental properties of a selected sample of Ap stars: Inferences from interferometric and asteroseismic constraints
• Interferometry of chemically peculiar stars: theoretical predictions vs. modern observing facilities
• The operation of VEGA/CHARA : from the scientific idea to the final products
• Spectrophotometric analysis of the 5200A region for peculiar and normal stars
• Search of X-ray emission from roAp stars: The case of gamma Equulei