Aims. We develop a method that provides a comprehensive analysis of the oscillation spectra of solar-like pulsators. We define new seismic indicators that should be as uncorrelated and as precise as possible and should hold detailed information about stellar interiors. This is essential to improve the quality of the results obtained from asteroseismology as it will provide better stellar models which in turn can be used to refine inferences made in exoplanetology and galactic archaeology. Methods. The presented method – WhoSGlAd – relies on Gram-Schmidt’s orthogonalisation process. A Euclidean vector sub-space of functions is defined and the oscillation frequencies are projected over an orthonormal basis in a specific order. This allowed us to obtain independent coefficients that we combined to define independent seismic indicators. Results. The developed method has been shown to be stable and to converge efficiently for solar-like pulsators. Thus, detailed and precise inferences can be obtained on the mass, the age, the chemical composition and the undershooting in the interior of the studied stars. However, attention has to be paid when studying the helium glitch as there seems to be a degeneracy between the influence of the helium abundance and that of the heavy elements on the glitch amplitude. As an example, we analyse the 16CygA (HD 186408) oscillation spectrum to provide an illustration of the capabilities of the method.
Context. The measurement of the apsidal motion in close eccentric massive binary systems provides essential information to probe the internal structure of the stars that compose the system. Aims. Following the determination of the fundamental stellar and binary parameters, we make use of the tidally induced apsidal motion to infer constraints on the internal structure of the stars composing the binary system HD 152219. Methods. The extensive set of spectroscopic, photometric, and radial velocity observations allows us to constrain the fundamental parameters of the stars together with the rate of apsidal motion of the system. Stellar structure and evolution models are further built with the Clés code testing different prescriptions for the internal mixing occurring inside the stars. The effect of stellar rotation axis misalignment with respect to the normal to the orbital plane on our interpretation of the apsidal motion in terms of internal structure constants is investigated.
Context. Apsidal motion in massive eccentric binaries offers precious information about the internal structure of the stars. This is especially true for twin binaries consisting of two nearly identical stars. Aims. We make use of the tidally induced apsidal motion in the twin binary HD 152248 to infer constraints on the internal structure of the O7.5 III-II stars composing this system. Methods. We build stellar evolution models with the code Clés assuming different prescriptions for the internal mixing occurring inside the stars. We identify the models that best reproduce the observationally determined present-day properties of the components of HD 152248, as well as their internal structure constants, and the apsidal motion rate of the system. We analyse the impact on the results of some poorly constrained input parameters in the models, including overshooting, turbulent diffusion, and metallicity. We further build “single” and “binary” GENEC models that account for stellar rotation to investigate the impacts of binarity and rotation. We discuss some effects that could bias our interpretation of the apsidal motion in terms of the internal structure constant. Results. The analysis of the Clés models reveals that reproducing the observed k2 value and rate of apsidal motion simultaneously with the other stellar parameters requires a significant amount of internal mixing (either turbulent diffusion, overshooting, or rotational mixing) or enhanced mass-loss. The results obtained with the GENEC models suggest that a single-star evolution model is sufficient to describe the physics inside this binary system. We suggest that, qualitatively, the high turbulent diffusion required to reproduce the observations could be partly attributed to stellar rotation. We show that higher-order terms in the apsidal motion are negligible. Only a very severe misalignment of the rotation axes with respect to the normal to the orbital plane could significantly impact the rate of apsidal motion, but such a high misalignment is highly unlikely in such a binary system. Conclusions. We infer an age estimate of 5.15 ± 0.13 Myr for the binary system and initial masses of 32.8 ± 0.6 M⊙ for both stars.
Context. Being part of the brightest solar-like stars, and close solar analogues, the 16 Cygni system is of great interest to the scientific community and may provide insight into the past and future evolution of our Sun. It has been observed thoroughly by the Kepler satellite, which provided us with data of an unprecedented quality. Aims. This paper is the first of a series aiming to extensively characterise the system. We test several choices of micro- and macro-physics to highlight their effects on optimal stellar parameters and provide realistic stellar parameter ranges. Methods. We used a recently developed method, WhoSGlAd, that takes the utmost advantage of the whole oscillation spectrum of solar-like stars by simultaneously adjusting the acoustic glitches and the smoothly varying trend. For each choice of input physics, we computed models which account, at best, for a set of seismic indicators that are representative of the stellar structure and are as uncorrelated as possible. The search for optimal models was carried out through a Levenberg-Marquardt minimisation. First, we found individual optimal models for both stars. We then selected the best candidates to fit both stars while imposing a common age and composition. Results. We computed realistic ranges of stellar parameters for individual stars. We also provide two models of the system regarded as a whole. We were not able to build binary models with the whole set of choices of input physics considered for individual stars as our constraints seem too stringent. We may need to include additional parameters to the optimal model search or invoke non-standard physical processes.
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