Inference from adiabatic analysis of solar-like oscillations in Red giants

The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way to seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes, highlighting how their detection allows a deeper insight into the properties of the internal structure of red giants. In our study we consider models of red giants in different evolutionary stages, as well as of different masses and chemical composition. We describe how the large and small separations computed with radial modes and with non-radial modes mostly trapped in the envelope depend on the stellar global parameters and evolutionary state, and we compare our theoretical predictions and first KEPLER data.Finally, we find that the properties of dipole modes constitute a promising seismic diagnostic of the evolutionary state of red-giant stars.Comment: 6 pages, 5 figures. Proceedings of IV Helas International Conference: "Seismological Challenges for Stellar Structure", Lanzarote (Canary Islands, Spain), 1-5 February 201

Application of time-dependent convection models to the photometric mode identification in gamma Doradus stars

We apply the Time-Dependent Convection (TDC) treatment of Gabriel \cite{Gabriel1996} and Grigahcène et al. \cite{Grigahcene} to the photometric mode identification in gamma Dor stars. Comparison of our theoretical results with the observed amplitudes and phases of the star gamma Dor is presented. This comparison makes the identification of the degree l of its pulsation modes possible and shows that our TDC models better agree with observations than Frozen Convection (FC) models

Thorough analysis of input physics in CESAM and CLES codes

This contribution is not about the quality of the agreement between stellar models computed by CESAM and CLES codes, but more interesting, on what ESTA-Task~1 run has taught us about these codes and about the input physics they use. We also quantify the effects of different implementations of the same physics on the seismic properties of the stellar models, that in fact is the main aim of ESTA experiments.Comment: 11 pages, 12 fig. Accepted for publication in ApSS CoRoT/ESTA Volu

Upward Revision of the Individual Masses in Α Cen: Implications for the Evolutionary State of the System

The recent upward revisions of the individual masses of the components of the binary system α Centauri (Pourbaix D., this meeting) led us to perform new calibrations of the system. The possibility of the onset a convective core in α Cen A is discussed together with its implications on the p-mode oscillation frequencies

Grids of Stellar Models and Frequencies with CLES + LOSC

We present a grid of stellar models, obtained with the CLES evolution code, following the specification of ESTA-Task1, and the corresponfing seismic properties, computed with the LOSC code. We provide a complete description of the corresponding files that will be available on the ESTA web-pages.Comment: 8 pages, accepted for publication in Astrophys. Space Sci. (CoRoT/ESTA Volume

Influence of non-adiabatic temperature variations on line profile variations of slowly rotating beta Cephei stars and SPBs. II. Simulations of line profile time series

We investigate to what extent non-adiabatic temperature variations at the surface of slowly rotating non-radially pulsating beta Cephei stars and slowly pulsating B stars affect silicon line profile variations. We use the non-adiabatic amplitudes of the effective temperature and gravity variation presented in Dupret et al. (\cite{Dupret02}), together with a Kurucz intensity grid, to compute time series of line profile variations. Our simulations point out that the line shapes do not change significantly due to temperature variations. We find equivalent width variations of at most two percent of the mean equivalent width. We confront our results with observational equivalent width variations and with photometrically obtained effective temperature variations. Based on observations obtained with the Swiss photometric telescope and with the ESO/CAT telescope, at La Silla in Chile

Standard solar models: Perspectives from updated solar neutrino fluxes and gravity-mode period spacing

Context. Thanks to the vast and exquisite set of observations that have been made available for the Sun, our star is by far an ideal target for testing stellar models with a unique precision. A recent issue under consideration in the field is related to the progress in the solar surface abundances derivation that has led to a decrease of the solar metallicity. While the former high-metallicity models were in fair agreement with other observational indicators from helioseismology and solar neutrino fluxes, it is no longer the case for low-metallicity models. This issue has become known as ’the solar problem’. Recent data are, however, promising to shed a new light on it. For instance, in 2020, the Borexino collaboration released the first-ever complete estimate of neutrinos emitted in the CNO cycle, which has reaffirmed the role of the neutrino constraints in the solar modelling process and their potential in exploring related issues. In parallel, a newly claimed detection of solar gravity modes of oscillation offers another opportunity for probing the stratification in the Sun’s central layers. Aims. We propose combining the diagnoses from neutrinos and helioseismology, both from pressure and gravity modes, in assessing the predictions of solar models. We compare in detail the different physical prescriptions currently at our disposal with regard to stellar model computations. Methods. We built a series of solar standard models based on a variation of the different physical ingredients directly affecting the core structure: opacity, chemical mixture, nuclear reactions rates. We compare the predictions of these models to their observational counterparts for the neutrinos fluxes, gravity-mode period spacing, and low-degree pressure mode frequency ratios. Results. The CNO neutrino flux confirms previous findings, exhibiting a preference for high-metallicity models. Nevertheless, we found that mild modification of the nuclear screening factors can re-match low-metallicity model predictions to observed fluxes, al- though it does not restore the agreement with the helioseismic frequency ratios. Neither the high-metallicity or low-metallicity models are able to reproduce the gravity-mode period spacing. The disagreement is huge, more than 100σ to the observed value. Reversely, the family of standard models narrows the expected range of the Sun’s period spacing: between ∼2150 to ∼2190 s. Moreover, we show this indicator can constrain the chemical mixture, opacity, and – to a lower extent – nuclear reactions in solar models

Asteroseismic probing of low mass solar-like stars throughout their evolution with new techniques

In this oral contribution we present two new techniques that aim at precisely probing the stellar structure of low-mass solar-like stars. These two methods, that focus on different evolution stages (i.e. the main-sequence stars, subgiants and red giants), provide reliable, accurate, fast and efficient means to tightly constrain the stellar structure through the definition of robust seismic indicators, which we proved to be excellent structural proxies. Indeed, they allow to precisely infer stellar masses, radii, ages and surface helium contents. This is particularly relevant to the field of exoplanetary science, as a precise determination of exoplanetary masses and radii relies on precise stellar properties. We will first present the potential of the WhoSGlAd method (Farnir et al. 2019) to accurately, and automatically, constrain the stellar structure of large samples of main-sequence stars, which is necessary in the context of the PLATO mission (Rauer et al. 2014). By building almost uncorrelated indicators defined to hold precise structural information, this method proposes a brand new approach to the adjustment of the oscillation spectra that these stars display. We will then present a new method to coherently account for the spectra of both sub-giant and red-giant stars, the EGGMiMoSA method (Farnir et al. 2021, submitted). Relying on the asymptotic description of mixed-modes (Shibahashi 1979, Mosser et al. 2012, Takata 2016), this is the first method that is able to follow the evolution of relevant seismic indicators during these phases, namely the period spacing, frequency separation, coupling factor and the pressure and gravity offsets, and therefore constrain the masses, radii and ages of these evolved stars. In addition, this method reliably provides measurements for these indicators in an automated fashion, which is a great opportunity for the broad characterisation of the large amount of data the PLATO mission is expected to generate. Finally, the combination of these two techniques, which are extremely fast, and their seismic indicators with large scales model search algorithms, such as AIMS (Rendle et al. 2019), could efficiently and robustly provide stellar masses, radii, ages and surface helium abundances for most of the stars observed by the PLATO spacecraft

Investigating surface correction relations for RGB stars

State-of-the-art stellar structure and evolution codes fail to adequately describe turbulent convection. For stars with convective envelopes, such as red giants, this leads to an incomplete depiction of the surface layers. As a result, the predicted stellar oscillation frequencies are haunted by systematic errors, the so-called surface effect. Different empirically and theoretically motivated correction relations have been proposed to deal with this issue. In this paper, we compare the performance of these surface correction relations for red giant branch stars. For this purpose, we apply the different surface correction relations in asteroseismic analyses of eclipsing binaries and open clusters. In accordance with previous studies of main-sequence stars, we find that the use of different surface correction relations biases the derived global stellar properties, including stellar age, mass, and distance estimates. We furthermore demonstrate that the different relations lead to the same systematic errors for two different open clusters. Our results overall discourage from the use of surface correction relations that rely on reference stars to calibrate free parameters. Due to the demonstrated systematic biasing of the results, the use of appropriate surface correction relations is imperative to any asteroseismic analysis of red giants. Accurate mass, age, and distance estimates for red giants are fundamental when addressing questions that deal with the chemo-dynamical evolution of the Milky Way galaxy. In this way, our results also have implications for fields, such as galactic archaeology, that draw on findings from stellar physics