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

Determining the metallicity of the solar envelope using seismic inversion techniques

peer reviewedThe solar metallicity issue is a long-lasting problem of astrophysics, impacting multi- ple fields and still subject to debate and uncertainties. While spectroscopy has mostly been used to determine the solar heavy elements abundance, helioseismologists at- tempted providing a seismic determination of the metallicity in the solar convective enveloppe. However, the puzzle remains since two independent groups prodived two radically different values for this crucial astrophysical parameter. We aim at provid- ing an independent seismic measurement of the solar metallicity in the convective enveloppe. Our main goal is to help provide new information to break the current stalemate amongst seismic determinations of the solar heavy element abundance. We start by presenting the kernels, the inversion technique and the target function of the inversion we have developed. We then test our approach in multiple hare-and-hounds exercises to assess its reliability and accuracy. We then apply our technique to solar data using calibrated solar models and determine an interval of seismic measurements for the solar metallicity. We show that our inversion can indeed be used to estimate the solar metallicity thanks to our hare-and-hounds exercises. However, we also show that further dependencies in the physical ingredients of solar models lead to a low accuracy. Nevertheless, using various physical ingredients for our solar models, we determine metallicity values between 0.008 and 0.014

Hybrid gamma Doradus/delta Scuti Stars: Comparison Between Observations and Theory

Gamma Doradus are F-type stars pulsating with high order g-modes. Their instability strip (IS) overlaps the red edge of the delta Scuti one. This observation has led to search for objects in this region of the HR diagram showing p and g-modes simultaneously. The existence of such hybrid pulsators has recently been confirmed (Handler 2009) and the number of candidates is increasing (Matthews 2007). From a theoretical point of view, non-adiabatic computations including a time-dependent treatment of convection (TDC) predict the existence of gamma Dor/delta Sct hybrid pulsators (Dupret et al. 2004; Grigahcene et al. 2006). Our aim is to confront the properties of the observed hybrid candidates with the theoretical predictions from non-adiabatic computations of non-radial pulsations including the convection-pulsation interaction.Comment: 3 pages, 3 figures, Poster at "Stellar Pulsation: challenges for theory and observation", Santa Fe, June 200

Sondage stellaire sismique intégral : Une application préliminaire de Whosglad au système 16 Cigni

We present a first application of Whosglad method to the components A and B of the 16 Cygni system. The method was developed to provide a comprehensive analysis of stellar oscillation spectra. It defines new seismic indicators which are as uncorrelated and precise as possible and hold detailed information about stellar interiors. Such indicators, as illustrated in the present paper, may be used to generate stellar models via forward seismic modeling. Finally, seismic constraints retrieved by the method provide realistic stellar parameters.Thèse de doctorat : New seismic probing method for solar-type stars, red subgiants and g pulsator

Sondage stellaire sismique intégral

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 archeology. Method: The presented method – WhoSGlAd – relies on Gram-Schmidt’s orthogonalisation process. A Euclidean vector subspace of functions is defined and the oscillation frequencies are projected over an orthonormal basis in a specific order. This allows the obtention of independent coefficients that we combine 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.Thèse de doctorat : New seismic probing method for solar-type stars, red subgiants and g pulsator

The IACOB project. IV. New predictions for high-degree non-radial mode instability domains in massive stars and their connection with macroturbulent broadening

Context. Asteroseismology is a powerful tool to access the internal structure of stars. Apart from the important impact of theoretical developments, progress in this field has been commonly associated with the analysis of time-resolved observations. Recently, the so-called macroturbulent broadening has been proposed as a complementary and less expensive way - in terms of observational time - to investigate pulsations in massive stars. Aims: We assess to what extent this ubiquitous non-rotational broadening component which shapes the line profiles of O stars and B supergiants is a spectroscopic signature of pulsation modes driven by a heat mechanism. Methods: We compute stellar main-sequence and post-main-sequence models from 3 to 70 M[SUB]⊙[/SUB] with the ATON stellar evolution code, and determine the instability domains for heat-driven modes for degrees ℓ = 1-20 using the adiabatic and non-adiabatic codes LOSC and MAD. We use the observational material compiled in the framework of the IACOB project to investigate possible correlations between the single snapshot line-broadening properties of a sample of ≈260 O and B-type stars and their location inside or outside the various predicted instability domains. Results: We present an homogeneous prediction for the non-radial instability domains of massive stars for degree ℓ up to 20. We provide a global picture of what to expect from an observational point of view in terms of the frequency range of excited modes, and we investigate the behavior of the instabilities with respect to stellar evolution and the degree of the mode. Furthermore, our pulsational stability analysis, once compared to the empirical results, indicates that stellar oscillations originated by a heat mechanism cannot explain alone the occurrence of the large non-rotational line-broadening component commonly detected in the O star and B supergiant domain. Based on observations made with the Nordic Optical Telescope, operated by NOTSA, and the Mercator Telescope, operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias

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

The internal rotation of the Sun and its link to the solar Li and He surface abundances

peer reviewedThe Sun serves as a natural reference for the modelling of the various physical processes at work in stellar interiors. Helioseismology results, which inform us on the characterization of the interior of the Sun (such as, for example, the helium abundance in its envelope), are, however, at odds with heavy element abundances. Moreover, the solar internal rotation and surface abundance of lithium have always been challenging to explain. We present results of solar models that account for transport of angular momentum and chemicals by both hydrodynamic and magnetic instabilities. We show that these transport processes reconcile the internal rotation of the Sun, its surface lithium abundance, and the helioseismic determination of the envelope helium abundance. We also show that the efficiency of the transport of chemicals required to account for the solar surface lithium abundance also predicts the correct value of helium, independently from a specific transport process. © 2022, The Author(s), under exclusive licence to Springer Nature Limited

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

Good Vibrations: Sismologie d'étoiles de masse faible avec WhoSGlAd et EGGMiMoSA

Since most of the information we receive from outer space is carried by stellar light, it comes as a necessity to properly characterise them. With the advent of space missions, it becomes possible to do so, thanks to the gathering of data of unprecedented quality. The past CoRoT and Kepler missions provided the stellar scientists with a wealth of data such that it allowed for the asteroseismology, the study of stellar pulsations and their link with the stellar structure, to thrive. This enabled to provide a detailed characterisation of distant solar-like stars and to pinpoint the shortcomings of current models. However, to provide precise inferences from observed oscillation spectra, it is necessary to have methods which are able to take the most advantage of the exquisite precision of the data. Both of the methods I develop are tailor-made for such needs. The first method, WhoSGlAd, accounts for the oscillations of main-sequence solar-like stars and the acoustic glitches they may exhibit. Acoustic glitches are an oscillating feature in the spectrum caused by a sharp feature in the stellar structure. The adjustment is done in such a way that the fitting parameters are completely independent and the computations are extremely fast. The parameters are then combined to build seismic indicators relevant of the stellar structure as little correlated as possible. Those are then used as constraints to stellar models. The second method, EGGMiMoSA, aims at providing a precise adjustment of the complex behaviour displayed by the mixed-modes oscillation spectra of sugbiant and red giant stars. Mixed-modes constitute a unique opportunity to probe the stellar interior from the surface to the core of the star. Again, the objective of the method is to define seismic indicators relevant of the stellar structure in order to constrain stellar models. During the present seminar, I will introduce both techniques and several results obtained via their use.Thèse de doctorat : New seismic probing method for solar-type stars, red subgiants and g pulsator