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The first adiabatic exponent profile, noted $\Gamma_1$, computed along adiabatic coordinates $(T, \rho)$ is in the focus of our study. Under conditions of almost fully ionized hydrogen and helium, the $\Gamma_1$ profile is quite sensitive to heavy elements ionization. $\Gamma_1$ decreases in regions where an element is partially ionized. The recent helioseismic structural inversion is obtained with an accuracy better than $10^{-4}$ in the most of the adiabatic convective zone that allows to study ionization variations. The aim is to determine the major heavy elements content in the solar convective zone. The method of our research is synthesis of the $\Gamma_1$ profile which is based on a linear combination of the contributions of individual heavy elements. The idea of the approach was proposed and justified by Baturin et al. (Astron. Astrophys., 660, A125, 2022). We find the best approximation of the inverted profile $\Gamma_1$ adjusting the abundances of major elements (C, N, O, Ne), meanwhile the abundances of elements heavier than neon are fixed. We synthesize the theoretical $\Gamma_1$ profile using the SAHA-S equation of state, and are able to reproduce the inverted profiles with an accuracy of $(1-2)\cdot 10^{-5}$. Total mass fraction of heavy elements found by this method is $Z=0.0148\pm 0.0004$. The oxygen logarithmic abundance is $8.70\pm 0.03$, carbon $8.44\pm 0.04$, nitrogen $8.12\pm 0.08$, and neon $8.17\pm 0.09$. The obtained estimations of oxygen and carbon agree with spectroscopic abundances by Asplund et al. (Astron. Astrophys., 653, A141, 2021)., Comment: Accepted for publication in Solar Physics

The present-day abundance of beryllium in the solar atmosphere provides clues about mixing mechanisms within stellar interiors. However, abundance determinations based on the Be II 313.107 nm line are prone to systematic errors due to imperfect model spectra. These errors arise from missing continuous opacity in the UV, a significant unidentified blend at 313.102 nm, departures from local thermodynamic equilibrium (LTE), and microturbulence and macroturbulence fudge parameters associated with one-dimensional (1D) hydrostatic model atmospheres. Although these factors have been discussed in the literature, no study has yet accounted for all of them simultaneously. To address this, we present 3D non-LTE calculations for neutral and ionised beryllium in the Sun. We used these models to derive the present-day solar beryllium abundance, calibrating the missing opacity on high resolution solar irradiance data and the unidentified blend on the centre-to-limb variation. We find a surface abundance of 1.21 $\pm$ 0.05 dex, which is significantly lower than the value of 1.38 dex that has been commonly adopted since 2004. Taking the initial abundance via CI chondrites, our result implies that beryllium has been depleted from the surface by an extra 0.11 $\pm$ 0.06 dex, or 22 $\pm$ 11%, on top of any effects of atomic diffusion. This is in tension with standard solar models, which predict negligible depletion, as well as with contemporary solar models that have extra mixing calibrated on the abundances of helium and lithium, which predict excessive depletion. These discrepancies highlight the need for further improvements to the physics in solar and stellar models., Comment: 14 pages, 9 figures; accepted for publication in Astronomy & Astrophysics

Grids of stellar evolution models with rotation using the Geneva stellar evolution code (Genec) have been published for a wide range of metallicities. We introduce the last remaining grid of Genec models, with a metallicity of $Z=10^{-5}$. We study the impact of this extremely metal-poor initial composition on various aspects of stellar evolution, and compare it to the results from previous grids at other metallicities. We provide electronic tables that can be used to interpolate between stellar evolution tracks and for population synthesis. Using the same physics as in the previous papers of this series, we computed a grid of stellar evolution models with Genec spanning masses between 1.7 and 500 $M_\odot$, with and without rotation, at a metallicity of $Z=10^{-5}$. Due to the extremely low metallicity of the models, mass-loss processes are negligible for all except the most massive stars. For most properties (such as evolutionary tracks in the Hertzsprung-Russell diagram, lifetimes, and final fates), the present models fit neatly between those previously computed at surrounding metallicities. However, specific to this metallicity is the very large production of primary nitrogen in moderately rotating stars, which is linked to the interplay between the hydrogen- and helium-burning regions. The stars in the present grid are interesting candidates as sources of nitrogen-enrichment in the early Universe. Indeed, they may have formed very early on from material previously enriched by the massive short-lived Population III stars, and as such constitute a very important piece in the puzzle that is the history of the Universe., Comment: Accepted in A&A. 20 pages, 14 figures, 3 tables

PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.

The measurement of the internal rotation of post-main sequence stars using data from space-based photometry missions has demonstrated the need for an efficient angular momentum transport in stellar interiors. So far, no clear solution has emerged and explaining the observed trends remain a challenge for stellar modellers. We aim at constraining both the shape of the internal rotation profile of six Kepler subgiants studied in details in 2014 and the properties of the missing angular momentum transport process acting in stellar interiors from MCMC inversions of the internal rotation. We apply a new MCMC inversion technique to existing Kepler subgiant targets and test various shapes of the internal rotation profile of all six original subgiants observed in 2014. We also constrain the limitations on the number of free parameters that can be used in the MCMC inversion, showing the limitations in the amount of information in the seismic data. First, we show that large-scale fossil magnetic fields are not able to explain the internal rotation of subgiants, similarly to what was determined from detailed studies of Kepler red giants. We are also able to constrain the location of the transition in the internal rotation profile for the most evolved stars in the available set of subgiants. We find that some of them exhibit a transition located close to the border of the helium core while one clearly does not. We conclude that it might be possible that various processes might be at play to explain our observations, but that revealing the physical nature of the angular momentum process will require a consistent detailed modelling of all subgiants available, particularly the least evolved. In addition, increasing the number of stars for which such inferences are possible (e.g. with the future PLATO mission) is paramount given the key role they play in validating transport process candidates., Comment: Accepted for publication in Astronomy and Astrophysics

We present a method for a non-linear asteroseismic inversion suitable for gravity-mode pulsators and apply it to slowly pulsating B-type (SPB) stars. Our inversion method is based on the iterative improvement of a parameterised static stellar structure model, which in turn is based on constraints from the observed oscillation periods. We present tests to demonstrate that the method is successful in recovering the properties of artificial targets both inside and outside the parameter space. We also present a test of our method on the well-studied SPB star KIC 7760680. We believe that this method is promising for carrying out detailed analyses of observations of SPB and $\gamma$ Dor stars and will provide complementary information to evolutionary models., Comment: Accepted in A&A

Due to the high quality constraints available for the Sun, we can carry out combined analyses using neutrino, spectroscopic and helioseismic observations. Such studies lay the ground for future improvements of key physical components of solar and stellar models, such as the equation of state, radiative opacities or prescriptions for macroscopic transport processes of chemicals which are then used to study other stars in the Universe. We study the existing degeneracies in solar models using the recent high-metallicity spectroscopic abundances by comparing them to helioseismic and neutrino data and discuss how their properties are impacted by changes in various physical ingredients. We carry out a detailed study of solar models computed with a high-metallicity composition from the literature based on averaged-3D models that was claimed to solve the solar problem. The properties of the solar models are significantly affected by using the recent OPLIB opacities and the inclusion of macroscopic transport. The properties of the standard solar models computed using the OPAL opacities are similar to those using the OP opacities. We show that a modifying the temperature gradient just below the base of the convective zone is required to erase the discrepancies in solar models, particularly in the presence of macroscopic mixing. This can be simulated by a local increase of opacity of a few percent. We conclude that the existing degeneracies and issues in solar modelling are not erased by an increase in the solar metallicity in contradiction to was suggested in recent papers. Therefore, standard solar models cannot be used as an argument for a high metallicity composition. While further work is required to improve solar models, we note that direct helioseismic inversions indicate a low metallicity in the convective envelope, in agreement with spectroscopic analyses based on full 3D models., Comment: Accepted for publication in Astronomy and Astrophysics, version before language editing

*Context*. In the framework of the PLATO mission, to be launched in late 2026, seismic inversion techniques will play a key role in the mission precision requirements of the stellar mass, radius, and age. It is therefore relevant to discuss the challenges of the automation of seismic inversions, which were originally developed for individual modelling.\\ *Aims*. We tested the performance of our newly developed quality assessment procedure of seismic inversions, which was designed in the perspective of a pipeline implementation.\\ *Methods*. We applied our assessment procedure on a testing set composed of 26 reference models. We divided our testing set into two categories, calibrator targets whose inversion behaviour is well known from the literature and targets for which we assessed manually the quality of the inversion. We then compared the results of our assessment procedure with our expectations as a human modeller for three types of inversions, the mean density inversion, the acoustic radius inversion, and the central entropy inversion.\\ *Results*. We found that our quality assessment procedure performs as well as a human modeller. The mean density inversion and the acoustic radius inversion are suited for a large-scale application, but not the central entropy inversion, at least in its current form.\\ *Conclusions*. Our assessment procedure showed promising results for a pipeline implementation. It is based on by-products of the inversion and therefore requires few numerical resources to assess quickly the quality of an inversion result., Comment: Accepted for publication in Astronomy & Astrophysics

We present evolutionary models of massive, accreting population III stars with constant and variable accretion rates until the end of silicon burning, with final masses of 1000 - 3000 Msol. In all our models, after the core-hydrogen-burning phase, the star expands towards the red side of the Hertzsprung-Russell diagram is where it spends the rest of its evolution. During core helium burning, the models exhibit an outer convective envelope as well as many large intermediate convective zones.These intermediate zones allow for strong internal mixing to occur which enriches the surface in helium. The effect of increasing metallicity at a constant accretion rate of 10^{-3} Msol/yr shows an increase in the lifetime, final mass and distribution of helium in the envelope. Our fiducial model with mass of 3000 Msol has a final surface helium abundance of 0.74 and 9% of its total mass or 50% of the core mass, has a value of Gamma1 < 4/3 at the end of core silicon burning. If the collapse of the core is accompanied by the ejection of the envelope above the carbon-oxygen core, this could have a significant impact on the chemical evolution of the surroundings and subsequent stellar generations. The model has a final log(N/O) ~ 0.45, above the lower limit in the recently detected high-redshift galaxy GN-z11. We discuss the impact of a single 3000 Msol star on chemical, mechanical and radiative feedback, and present directions for future work., Comment: Accepted for publication in A&A

Context. The metal mass fraction of the Sun Z is a key constraint in solar modelling, but its value is still under debate. The standard solar chemical composition of the late 2000s have the ratio of metals to hydrogen Z/X = 0.0181, with a small increase to 0.0187 in 2021, as inferred from 3D non-LTE spectroscopy. However, more recent work on a horizontally and temporally averaged <3D> model claim Z/X = 0.0225, consistent with the high values of twenty-five years ago based on 1D LTE spectroscopy. Aims. We aim to determine a precise and robust value of the solar metal mass fraction from helioseismic inversions, thus providing independent constraints from spectroscopic methods. Methods. We devise a detailed seismic reconstruction technique of the solar envelope, combining multiple inversions and equations of state to accurately and precisely determine the metal mass fraction value. Results. We show that a low value of the solar metal mass fraction corresponding to Z/X = 0.0187 is favoured by helioseismic constraints and that a higher metal mass fraction corresponding to Z/X = 0.0225 are strongly rejected by helioseismic data. Conclusions. We conclude that direct measurement of the metal mass fraction in the solar envelope favours a low metallicity, in line with the 3D non-LTE spectroscopic determination of 2021. A high metal mass fraction as measured using a <3D> model in 2022 is disfavoured by helioseismology for all modern equations of state used to model the solar convective envelope., Comment: Accepted for publication in A&A, online materials available on demand or on publisher website

Asteroseismic modelling will be part of the pipeline of the PLATO mission and will play a key role in the mission precision requirements on stellar mass, radius and age. It is therefore crucial to compare how current modelling strategies perform, and discuss the limitations and remaining challenges for PLATO, such as the so-called surface effects, the choice of physical ingredients, and stellar activity. In this context, we carried out a systematic study of the impact of surface effects on the estimation of stellar parameters. In this work, we demonstrated how combining a mean density inversion with a fit of frequencies separation ratios can efficiently damp the surface effects and achieve precise and accurate stellar parameters for ten Kepler LEGACY targets, well within the PLATO mission requirements. We applied and compared two modelling approaches, directly fitting the individual frequencies, or coupling a mean density inversion with a fit of the ratios, to six synthetic targets with a patched 3D atmosphere from Sonoi et al. (2015) and ten actual targets from the LEGACY sample. The fit of the individual frequencies is unsurprisingly very sensitive to surface effects and the stellar parameters tend to be biased, which constitutes a fundamental limit to both accuracy and precision. In contrast, coupling a mean density inversion and a fit of the ratios efficiently damps the surface effects, and allows us to get both precise and accurate stellar parameters. The average statistical precision of our selection of LEGACY targets with this second strategy is 1.9% for the mass, 0.7% for the radius, and 4.1% for the age, well within the PLATO requirements. Using the mean density in the constraints significantly improves the precision of the mass, radius and age determinations, on average by 20%, 33%, and 16%, respectively., Comment: Accepted for publication in Astronomy & Astrophysics

Asteroseismology has become a powerful tool to study the internal rotation of stars, and its study allows to constrain the internal AM transport processes and better understand their physical nature. In this context, we compared the rotation rates predicted by asteroseismology and by starspots measurements for four main-sequence stars from the Kepler LEGACY sample, considering different AM transport prescriptions, and investigated if some of these prescriptions could be ruled out. We decoupled the modelling of the structure and of the rotational profile, respectively obtained by an asteroseismic characterization and by using rotating models including a detailed treatment of the AM transport. We then compared the mean asteroseismic rotation rate with the surface rotation rate from starspots measurements for each of the AM transport prescriptions. In the hotter part of the HRD (M > ~ 1.2Msun), combining asteroseismic constraints from splittings of pressure modes and surface rotation rates does not allow to conclude on the need for an efficient AM transport in addition to the sole transport by meridional circulation and shear instability. Both prescriptions are indeed consistent with the quasi-solid rotation measured by Benomar et al. (2015) and Nielsen et al. (2017). In the colder part of the HRD, the situation is different due to the efficient braking of the stellar surface by magnetised winds. We find a clear disagreement between the rotational properties of models including only hydrodynamic processes and asteroseismic constraints, while models with magnetic fields correctly reproduce the observations, similarly to the solar case. This shows the existence of a mass regime corresponding to main-sequence stars around ~ 6000 - 6200 K for which it is difficult to constrain the AM transport processes, unlike for hotter, Gamma Dor stars or colder, less massive solar analogs., Comment: Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor

The transition between convective and radiative stellar regions is still not fully understood. The sharp variations in sound speed located in these transition regions give rise to a signature in specific seismic indicators, opening the possibility to constrain the physics of convection to radiation transition. Among those seismic indicators, the ratios of the small to large frequency separation for $l=0$ and $1$ modes ($r_{010}$) were shown to be particularly efficient to probe these transition regions. Interestingly, in the Kepler Legacy F-type stars, the oscillatory signatures left in the $r_{010}$ ratios by the sharp sound-speed variation have unexpected large amplitudes that still need to be explained. We show that the signature of the bottom of the convective envelope is amplified in the ratios $r_{010}$ by the frequency dependence of the amplitude compared to the signal seen in the frequencies themselves or the second differences. We find that among the different options of physical input investigated here, large amplitude signatures can only be obtained when convective penetration of the surface convective zone into the underlying radiative region is taken into account. In this case and even for amplitudes as large as those observed in F-type stars, the oscillating signature in the ratios can only be detected when the convective envelope is deep enough. This deep extension of the convective envelope causes doubt that the origin of the large amplitudes is due to penetrative convection as it is modelled here or implies that current stellar modelling (without penetrative convection) leads to an underestimation of the size of convective envelopes. In any case, studying the glitch signatures of a large number of oscillating F-type stars opens the possibility to constrain the physics of the stellar interior in these regions., Comment: 19 pages, 12 figures, accepted for publication in A&A

Context. The Sun acts as a cornerstone of stellar physics. Thanks to spectroscopic, helioseismic and neutrino flux observations, we can use the Sun as a laboratory of fundamental physics in extreme conditions. The conclusions we draw are then used to inform and calibrate evolutionary models of all other stars in the Universe. However, solar models are in tension with helioseismic constraints. The debate on the ``solar problem'' has hitherto led to numerous publications discussing potential issues with solar models and abundances. Aims. Using the recently suggested high-metallicity abundances for the Sun, we investigate whether standard solar models, as well as models with macroscopic transport reproducing the solar surface lithium abundances and analyze their properties in terms of helioseismic and neutrino flux observations. Methods. We compute solar evolutionary models and combine spectroscopic and helioseismic constraints as well as neutrino fluxes to investigate the impact of macroscopic transport on these measurements. Results. When high-metallicity solar models are calibrated to reproduce the measured solar lithium depletion, tensions arise with respect to helioseismology and neutrino fluxes. This is yet another demonstration that the solar problem is also linked to the physical prescriptions of solar evolutionary models and not to chemical composition alone. Conclusions. A revision of the physical ingredients of solar models is needed in order to improve our understanding of stellar structure and evolution. The solar problem is not limited to the photospheric abundances if the depletion of light elements is considered. In addition, tighter constraints on the solar beryllium abundance will play a key role in the improvement of solar models., Comment: Accepted for publication in Astronomy and Astrophysics

Context. With the detection of thousands of exoplanets, characterising their dynamical evolution in detail represents a key step in the understanding of their formation. Studying the dissipation of tides occurring both in the host star and in the planets is of great relevance in order to investigate the distribution of the angular momentum occurring among the objects populating the system and to studying the evolution of the orbital parameters. From a theoretical point of view, the dissipation of tides throughout a body may be studied by relying on the so-called phase or time-lag equilibrium tides model in which the reduced tidal quality factor Q'p, or equivalently the product between the love number and the time lag (k2DeltaT), describe how efficiently tides are dissipated within the perturbed body. Constraining these factors by looking at the current configuration of the exoplanetary system is extremely challenging, and simulations accounting for the evolution of the system as a whole might help to shed some light on the mechanisms governing this process. Aims. We aim to constrain the tidal dissipation factors of hot-Jupiter-like planets by studying the orbital evolution of Kepler-91b. Methods. We firstly carried out a detailed asteroseismc characterisation of Kepler-91 and computed a dedicated stellar model using both classical and astereoseismic constraints. We then coupled the evolution of the star to the one of the planets by means of our orbital evolution code and studied the evolution of the system by accounting for tides dissipated both in the planet and in the host star. Results. We found that the maximum value for k2DeltaT (or equivalently the minimum value for Q'p) determining the efficiency of equilibrium tides dissipation occurring within Kepler-91b is 0.4 pm 0.25 s (4.5+5.8 * 10^5)., Comment: accepted for publication in Astronomy & Astrophysics

Solar gravity modes are considered as the {\it Rosetta Stone} for probing and subsequently deciphering the physical properties of the solar inner-most layers. Recent claims of positive detection therefore shed some new light on the long-standing issue of estimating solar gravity mode amplitudes. In this article, our objective is to review the theoretical efforts intended to predict solar gravity mode amplitudes. Because most of these studies assumed analogous driving and damping properties to those for the observed acoustic modes, we also provide a short overview of our current knowledge for these modes in the Sun and solar-type stars (which show solar-like oscillations) before diving into the specific problem of solar gravity modes. Finally, taking recent estimates into account, we conclude and confirm that the low-frequency domain (typically between $10\,\mu$Hz and $100\,\mu$Hz) is certainly more suited to focus on for detecting solar gravity modes. More precisely, around $60\,\mu$Hz, the theoretical estimates are slightly lower than the observational detection threshold as provided by the GOLF (Global Oscillations at Low Frequencies) instrument by about a factor of two only. This is typically within the current uncertainties associated with theoretical estimates and should motivate us for improving our knowledge on turbulence in the whole solar convective region, which is key for improving the accuracy of $g$-mode amplitude estimates. The recent detection of solar inertial modes (Gizon et al. 2021) combined with the continuous development of numerical simulations provide interesting prospects for future studies., Comment: Accepted for publication in Solar Physics

Solar evolutionary models are thus far unable to reproduce spectroscopic, helioseismic, and neutrino constraints consistently, resulting in the so-called solar modeling problem. In parallel, planet formation models predict that the evolving composition of the protosolar disk and, thus, of the gas accreted by the proto-Sun must have been variable. We show that solar evolutionary models that include a realistic planet formation scenario lead to an increased core metallicity of up to 5%, implying that accurate neutrino flux measurements are sensitive to the initial stages of the formation of the Solar System. Models with homogeneous accretion match neutrino constraints to no better than 2.7$\sigma$. In contrast, accretion with a variable composition due to planet formation processes, leading to metal-poor accretion of the last $\sim$4% of the young Sun's total mass, yields solar models within 1.3$\sigma$ of all neutrino constraints. We thus demonstrate that in addition to increased opacities at the base of the convective envelope, the formation history of the Solar System constitutes a key element in resolving the current crisis of solar models., Comment: Accepted for publication in A&A. 10 pages, 7 figures. Supplemental materials are available at https://doi.org/10.5281/zenodo.7156794

HD 129929 is a slowly-rotating $\beta$ Cephei pulsator with a rich spectrum of detected oscillations, including two rotational multiplets. The asteroseismic interpretation revealed the presence of radial differential rotation in this massive star of $\sim$9.35 M . The stellar core is indeed estimated to spin $\sim$3.6 times faster than the surface. The surface rotation was consequently derived as $\sim$2 km/s. This massive star represents an ideal counter-part to the wealth of space-based photometry results for main-sequence and evolved low-mass stars. Those latter have revealed a new, and often unexpected, picture of the angular momentum transport processes acting in stellar interiors. We investigate in a new way the constraints on the internal rotation of HD 129929, focusing on their interpretation for the evolution of the internal rotation during the main sequence of a massive star. We test separately hydrodynamic and magnetic instability transport processes of angular momentum. We used the best asteroseismic model obtained in an earlier work. We calibrated stellar models including rotation, with different transport processes, to reproduce that reference model. We then looked whether one process is favoured to reproduce the rotation profile of HD 129929, based on the fit of the asteroseismic multiplets. The impact of the Tayler magnetic instability on the angular momentum transport predicts a ratio of the core-to-surface rotation rate of only 1.6, while the recently revised prescription of this mechanism predicts solid-body rotation. Both are too low in comparison with the asteroseismic inference. The models with only hydrodynamic processes are in good agreement with the asteroseismic measurements. Strikingly, we can also get a constraint on the profile of rotation on the zero age main sequence: likely, the ratio between the core and surface rotation was at least $\sim$1.7., Comment: 5 pages, 3 figures, accepted for publication as a letter in A&A

The advent of space-based photometry missions in the early 21st century enabled the application to asteroseismic data of advanced inference techniques until then restricted to the field of helioseismology. The high quality of the observations, the discovery of mixed modes in evolved solar-like oscillators and the need for an improvement in the determination of stellar fundamental parameters such as mass, radius and age led to the development of sophisticated modelling tools, amongst which seismic inversions play a key role. In this review, we will discuss the existing inversion techniques for the internal structure of distant stars adapted from helio- to asteroseismology. We will present results obtained for various Kepler targets, their coupling to other existing modelling techniques as well as the limitations of seismic analyses and the perspectives for future developments of these approaches in the context of the current TESS and the future PLATO mission, as well as the exploitation of the mixed modes observed in post-main sequence solar-like oscillators, for which variational formulations might not provide sufficient accuracy., Comment: Accepted for publication in Frontiers in Astronomy and Space Sciences, special topic "Challenges of Asteroseismology in the Era of Space Missions", editors: Javier Pascual Granado, Tiago Campante, Antonio Garc\'ia Hern\'andez, Zhao Guo

With the rapid development of asteroseismology thanks to space-based photometry missions such as CoRoT, Kepler, TESS, and in the future, PLATO, and the use of inversion techniques, quasi-model-independent constraints on the stellar properties can be extracted from a given stellar oscillation spectrum. In this context, inversions based on frequency separation ratios, that are less sensitive to surface effects, appear as a promising technique to constrain the properties of stellar convective cores. We developed an inversion based on frequency separation ratios with the goal of damping the surface effects of the oscillation frequencies. Using this new inversion, we defined a new indicator to constrain the boundary mixing properties of convective cores in solar-like oscillators. We verified our inversion technique by conducting tests in a controlled environment, where the stellar mass and radius are known exactly, and conducted an extensive hare and hounds exercise. The inversion is not affected by surface effects. With the construction of an extensive set of models, favoured and forbidden regions can be highlighted in the parameter space. If the ratios are well fitted, the inversion is unsurprisingly not providing additional information. The indicator coupled with the inversion based on frequency separation ratios seems promising at probing the properties of convective cores, especially for F-type stars exhibiting solar-like oscillations., Comment: Accepted for publication in Astronomy and Astrophysics

Thanks to asteroseismology, constraints on the core rotation rate are available for hundreds of low- and intermediate-mass stars in evolved phases. Current physical processes tested in stellar evolution models cannot reproduce the evolution of these core rotation rates. We investigate the efficiency of the internal angular momentum redistribution in red giants during the hydrogen shell and core-helium burning phases based on the asteroseismic determinations of their core rotation rates. We compute stellar evolution models with rotation and model the transport of angular momentum by the action of a sole dominant diffusive process parametrized by an additional viscosity. We constrain the values of this viscosity to match the mean core rotation rates of red giants and their behaviour with mass and evolution along the red giant branch and in the red clump. For red giants in the hydrogen shell-burning phase the transport of angular momentum must be more efficient in more massive stars. The additional viscosity is found to vary by approximately two orders of magnitude in the mass range M $\sim$ 1 - 2.5 M$_{\odot}$. As stars evolve along the red giant branch, the efficiency of the internal transport of angular momentum must increase for low-mass stars (M $\lesssim$ 2 M$_{\odot}$) and remain approximately constant for slightly higher masses (2.0 M$_{\odot}$ $\lesssim$ M $\lesssim$ 2.5 M$_{\odot}$). In red-clump stars, the additional viscosities must be an order of magnitude higher than in younger red giants of similar mass during the hydrogen shell-burning phase. In combination with previous efforts, we obtain a clear picture of how the physical processes acting in stellar interiors should redistribute angular momentum from the end of the main sequence until the core-helium burning phase for low- and intermediate-mass stars to satisfy the asteroseismic constraints., Comment: 10 pages, 12 figures, 1 table. Accepted for publication in A&A

The possibility of measuring the internal rotation of the Sun and stars thanks to helio- and asteroseismology offers tremendous constraints on hydro- and magnetohydrodynamical processes acting in stellar interiors. Understanding the processes responsible for the transport of angular momentum in stellar interiors is crucial as they will also influence the transport of chemicals and thus the evolution of stars. Here we present some of the key results obtained in both fields and how detailed seismic analyses can provide stringent constraints on the physics of angular momentum transport in the interior of low mass stars and potentially rule out some candidates., Comment: Proceedings of the Sixteenth Marcel Grossman meeting (July 5 - 10 2021, Session on "Rotation in Stellar Evolution")

The advent of space-based photometry observations provided high-quality asteroseismic data for a large number of stars. These observations enabled the adaptation of advanced techniques, until then restricted to helioseismology, to study the best asteroseismic targets. Amongst these, the 16Cyg binary system holds a special place, being the brightest solar twins observed by Kepler. For this system, modellers have access to high-quality asteroseismic, spectroscopic and interferometric data, making it the perfect testbed for the limitations of stellar models. We aim to further constrain the internal structure and fundamental parameters of 16CygA&B using linear seismic inversion techniques of both global indicators and localised corrections of the internal structure. We start from the models defined by detailed modelling in our previous paper and extend our analysis by applying variational inversions to these models. We carried out inversions of so-called seismic indicators and provided local corrections of the internal structure of the two stars. Our results indicate that linear seismic inversions alone are not able to discriminate between standard and non-standard models for 16CygA&B. We confirm the results of our previous studies that used linear inversion techniques, but consider that the differences could be linked to small fundamental parameters variations rather than to a missing process in the models. We confirm the robustness and reliability of the results of the modelling performed in our previous paper. We conclude that non-linear inversions are likely required to further investigate the properties of 16CygA&B from a seismic point of view, but that these inversions should be coupled to analyses of the depletion of light elements such as lithium and beryllium to constrain the macroscopic transport of chemicals and potential non-standard evolutionary paths., Comment: Accepted for publication in Astronomy and Astrophysics

Context: Grids of stellar models, computed with the same physical ingredients, allow one to study the impact of a given physics on a broad range of initial conditions and are a key ingredient for modeling the evolution of galaxies. Aims: We present a grid of single star models for masses between 0.8 and 120 $M_\odot$, with and without rotation for a mass fraction of heavy element Z=0.006, representative of the Large Magellanic Cloud (LMC). Methods: We used the Geneva stellar evolution code. The evolution was computed until the end of the central carbon-burning phase, the early asymptotic giant branch phase, or the core helium-flash for massive, intermediate, and low mass stars, respectively. Results: The outputs of the present stellar models are well framed by the outputs of the two grids obtained by our group for metallicities above and below the one considered here. The models of the present work provide a good fit to the nitrogen surface enrichments observed during the main sequence for stars in the LMC with initial masses around 15 $M_\odot$. They also reproduce the slope of the luminosity function of red supergiants of the LMC well, which is a feature that is sensitive to the time-averaged mass loss rate over the red supergiant phase. The most massive black hole that can be formed from the present models at Z=0.006 is around 55 $M_\odot$. No model in the range of mass considered will enter into the pair-instability supernova regime, while the minimal mass to enter the region of pair pulsation instability is around 60 $M_\odot$ for the rotating models and 85 $M_\odot$ for the nonrotating ones. Conclusions: The present models are of particular interest for comparisons with observations in the LMC and also in the outer regions of the Milky Way. We provide public access to numerical tables that can be used for computing interpolated tracks and for population synthesis studies., Comment: 11 pages, 11 figures, published in A&A

Context. Increasing the number of detected exoplanets is far from anecdotal, especially for long-period planets that require a long duration of observation. More detections imply a better understanding of the statistical properties of exoplanet populations, and detailed modelling of their host stars also enables thorough discussions of star-planet interactions and orbital evolution of planetary systems. Aims. In the context of the discovery of a new planetary system, we aim to perform a complete study of HD 29399 and its companion by means of radial-velocity measurements, seismic characterisation of the host-star, and modelling of the orbital evolution of the system. Methods. High-resolution spectra of HD 29399 were acquired with the CORALIE spectrograph mounted on the 1.2- m Swiss telescope located at La Silla Observatory (Chile) as part of the CASCADES survey. We used the moments of the cross-correlation function profile as well as the photometric variability of the star as diagnostics to distinguish between stellar and planetary-induced signals. To model the host star we combined forward modelling with global and local minimisation approaches and inversion techniques. We also studied the orbital history of the system under the effects of both dynamical and equilibrium tides. Results. We present the detection of a long-period giant planet. Combining these measurements with photometric observations by TESS, we are able to thoroughly model the host star and study the orbital evolution of the system. We derive stellar and planetary masses of $1.17 \pm 0.10~ M_{\odot}$ and $1.59 \pm 0.08 ~M_{Jup}$, respectively, and an age for the system of 6.2 Gyr. We show that neither dynamical nor equilibrium tides have been able to affect the orbital evolution of the planet. Moreover, no engulfment is predicted for the future evolution of the system.

Context. Following the first discovery of a planet orbiting a giant star in 2002, we started the CORALIE radial-velocity search for companions around evolved stars (CASCADES). We present the observations of three stars conducted at the 1.2 m Leonard Euler Swiss telescope at La Silla Observatory, Chile, using the CORALIE spectrograph. Aims. We aim to detect planetary companions to intermediate-mass G- and K- type evolved stars and perform a statistical analysis of this population. We searched for new planetary systems around the stars HD22532 (TIC 200851704), HD64121 (TIC 264770836), and HD69123 (TIC 146264536). Methods. We have followed a volume-limited sample of 641 red giants since 2006 to obtain high-precision radial-velocity measurements. We used the Data & Analysis Center for Exoplanets (DACE) platform to perform a radial-velocity analysis to search for periodic signals in the line profile and activity indices, to distinguish between planetary-induced radial-velocity variations and stellar photospheric jitter, and to search for significant signals in the radial-velocity time series to fit a corresponding Keplerian model. Results. In this paper, we present the survey in detail, and we report on the discovery of the first three planets of the sample around the giant stars HD22532, HD64121, and HD69123., Comment: 20 pages, 18 figures, 7 tables, to be published in Astronomy & Astrophysics

The advent of asteroseismology as the golden path to precisely characterize single stars naturally led to synergies with the field of exoplanetology. Today, the precise determination of stellar masses, radii and ages for exoplanet-host stars is a driving force in the development of dedicated software and techniques to achieve this goal. However, as various approaches exist, it is clear that they all have advantages and inconveniences and that there is a trade-off between accuracy, efficiency, and robustness of the techniques. We aim to compare and discuss various modelling techniques for exoplanet-host red giant stars for which TESS data are available. The results of the seismic modelling are then used to study the dynamical evolution and atmospheric evaporation of the planetary systems. We study, in detail, the robustness, accuracy and precision of various seismic modelling techniques when applied to four exoplanet-host red giants observed by TESS. We discuss the use of global seismic indexes, the use of individual radial frequencies and that of non-radial oscillations. In each case, we discuss the advantages and inconveniences of the modelling technique. We determine precise and accurate masses of exoplanet-host red giant stars orbited by long-period Jupiter-like planets using various modelling techniques. For each target, we also provide a model-independent estimate of the mass from a mean density inversion combined with radii values from Gaia and spectroscopic data. We show that no engulfment or migration is observed for these targets, even if their evolution is extended beyond their estimated seismic ages up the red giant branch., Comment: Accepted for publication in Astronomy and Astrophysics. Part of the CASCADES series of papers

The $\beta$ Cephei pulsators are massive main-sequence stars, presenting low radial-order modes. These modes probe in particular the chemical gradient at the edge of the convective core. They hence give constraints on macroscopic processes, such as hydrodynamic or magnetic instabilities. Yet, it is not clear to what extent the seismic inferences depend on the physics employed for the stellar modelling or on the observational dataset. We investigate the observational constraints which are necessary to provide accurate constraints on the mixing processes in $\beta$ Cephei stars. We explore the importance of the identification of the angular degree of modes. Depending on the quality of the seismic dataset and the classical constraints, we estimate the precision achievable with asteroseismology. We propose a method extending the forward approach classically used to model $\beta$ Cephei stars The probability distributions of the asteroseismic-derived stellar parameters are obtained. With these distributions, we provide a systemic way to estimate the errors of the modelling. A particular effort is made to also include the theoretical uncertainties of the models. We then estimate the accuracy and precision of asteroseismology for $\beta$ Cephei stars in a series of hare and hound exercises. The exercises show that a set of four to five oscillation frequencies with an identified angular degree already leads to accurate inferences on the stellar parameters. Without the identification of the modes, the addition of other classical observational constraints allow to succeed the seismic modelling. When the micro-physics of the star and stellar models used for the modelling differ, the constraints derived on the internal structure remain valid if expressed in terms of acoustic variables. The characterisation of the mixing processes at the boundary of the convective core remain model-dependent., Comment: 17 pages, 14 figures, accepted for publication in A&A

The advent of space-based photometry missions such as CoRoT, Kepler and TESS has sparkled the development of asteroseismology and exoplanetology. The advent of PLATO will further strengthen such multi-disciplinary studies. Testing asteroseismic modelling and its importance for our understanding of planetary systems is crucial. We carried out a detailed modelling of Kepler-93, an exoplanet host star observed by Kepler. This star is particularly interesting as it is very similar to the PLATO benchmark target (G spectral type, ~ 6000K, ~ 1 Msun and ~ 1 Rsun) and provides a real-life testbed for potential procedures to be used for PLATO. We use global and local minimization techniques for the seismic modelling of Kepler-93, varying the ingredients of our stellar models. We compute seismic inversions of the mean density. We use these revised stellar parameters to provide new planetary parameters and simulate the orbital evolution of the system under the effects of tides and atmospheric evaporation. Our fundamental parameters for Kepler-93: mean density = 1.654 +/- 0.004 g/cm3, M = 0.907 +/- 0.023 Msun , R = 0.918 +/- 0.008 Rsun and Age = 6.78 +/- 0.32 Gyr. The uncertainties we report for this benchmark are within the requirements of PLATO. For the exoplanet Kepler-93b, we find Mp = 4.01 +/- 0.67 Mearth, Rp = 1.478 +/- 0.014 Rearth and semi-major axis a = 0.0533 +/- 0.0005 AU. According to our simulations, it seems unlikely that Kepler-93b formed with a mass large enough to be impacted by stellar tides. For the benchmark of PLATO, detailed asteroseismic modelling procedures will be able to provide fundamental stellar parameters within the requirements. We illustrate what synergies can be achieved regarding the orbital evolution and atmospheric evaporation of exoplanets. We note the importance of the high-quality radial velocity follow-up to constrain the formation scenarii of exoplanets., Comment: Accepted for publication in Astronomy and Astrophysics

TOI-849b is one of the few planets populating the hot-Neptune desert and it is the densest Neptune-sized one discovered so far. Its extraordinary proximity to the host star, together with the absence of a massive H/He envelope on top of the $40.8 ~M_{\oplus}$ rocky core calls into question the role played by the host star in the evolution of the system. We aim to study the impact of the host star's rotational history on the evolution of TOI-849b, focussing on the planetary migration due to dynamical tides dissipated in the stellar convective envelope and on the high-energy emission. Rotating stellar models of TOI-849 are coupled to our orbital evolution code to study the evolution of the planetary orbit. The evolution of the planetary atmosphere is studied by means of the JADE code, which uses realistic XUV-fluxes provided by our rotating stellar models. Assuming that the planet was at its present day position ($a=0.01598 \rm AU$) at the protoplanetary disc dispersal, with mass $40.8~ M_{\oplus}$, and considering a broad range of host star initial surface rotation rates ($\Omega_{\rm in}$) in the range $ [3.2, 18]~ \Omega_{\odot}$, we find that only for $\Omega_{\rm in} \leq 5 \Omega_{\odot}$ do we reproduce the current position of the planet, given that for $\Omega_{\rm in}$ larger than $5 \Omega_{\odot}$ its orbit is efficiently deflected by dynamical tides. We tested the impact of increasing the initial mass of the planet on the efficiency of tides, finding that a higher initial mass ($1~M_{\rm Jup}$) does not change the results reported above. Based on these results we computed the evolution of the planetary atmospheres with the JADE code for a large range of initial masses above a core mass of $40.8~M_{\oplus}$, finding that the strong XUV-flux received by the planet is able to remove the entirety of the envelope within the first 50 Myr, even if it formed as a Jupiter-mass planet.

The observations of global stellar oscillations of post main-sequence stars by space-based photometry missions allowed to directly determine their internal rotation. These constraints have pointed towards the existence of angular momentum transport processes unaccounted for in theoretical models. Constraining the properties of their internal rotation thus appears as the golden path to determine the physical nature of these missing dynamical processes. We wish to determine the robustness of a new approach to study the internal rotation of post main-sequence stars, using parametric rotation profiles coupled to a global optimization technique. We test our methodology on Kepler 56, a red giant observed by the Kepler mission. First, we carry out an extensive modelling of the star using global and local minimizations techniques, and seismic inversions. Then, using our best model, we study in details its internal rotation profile, we adopted a Bayesian approach to constrain stellar parametric predetermined rotation profiles using a Monte Carlo Markov Chain analysis of the rotational splittings of mixed modes. Our Monte Carlo Markov Chain analysis of the rotational splittings allows to determine the core and envelope rotation of Kepler 56 as well as give hints about the location of the transition between the slowly rotating envelope and the fast rotating core. We are able to discard a rigid rotation profile in the radiative regions followed by a power-law in the convective zone and show that the data favours a transition located in the radiative region, as predicted by processes originating from a turbulent nature. Our analysis of Kepler 56 indicates that turbulent processes whose transport efficiency is reduced by chemical gradients are favoured, while large scale fossil magnetic fields are disfavoured as a solution to the missing angular momentum transport., Comment: accepted for publication in Astronomy and Astrophysics

Context: The Sun is by far a privileged target for testing stellar models with unique precision. A recent concern appeared with the progress in the solar surface abundances derivation that has led to a decrease of the solar metallicity. While the ancient high-metallicity models were in fair agreement with other solar observational indicators, it is no longer the case for low-metallicity models. Recent collection of data are however promising to shed a new light on it. For instance, the Borexino collaboration released in 2020 the first-ever complete estimate of neutrinos emitted in the CNO cycle. It has reaffirmed the role of the neutrino constraints in the solar modelling process and its associated issues. In parallel, newly claimed detection of solar gravity modes of oscillations offers another opportunity of probing the stratification in the Sun's central layers. Aims: We propose to combine the diagnoses from neutrinos and helioseismology, both from pressure and gravity modes, for assessing the predictions of solar models. We compare in detail the different physical prescriptions currently at disposal for stellar model computations. Results: The CNO neutrino flux confirms 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, although 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 100$\sigma$ to the reported value. Reversely, the family of standard models narrows the expected range of the Sun's period spacing: between $\sim$2150 to $\sim$2190~s. Moreover, we show this indicator can constrain the chemical mixture, opacity, and to a lower extent nuclear reactions in solar models., Comment: 18 pages, 10 figures, accepted for publications in Astronomy and Astrophysics

Tidal interactions and planet evaporation processes impact the evolution of close-in star-planet systems. We study the impact of stellar rotation on these processes. We compute the time evolution of star-planet systems consisting of a planet with initial mass between 0.02 and 2.5 M$_{ Jup}$ (6 and 800 M$_{ Earth}$), in a quasi-circular orbit with an initial orbital distance between 0.01 and 0.10 au, around a solar-type star evolving from the Pre-Main-Sequence (PMS) until the end of the Main-Sequence (MS) phase. We account for the evolution of: the stellar structure, the stellar angular momentum due to tides and magnetic braking, the tidal interactions (equilibrium and dynamical tides in stellar convective zones), the mass-evaporation of the planet, and the secular evolution of the planetary orbit. We consider that at the beginning of the evolution, the proto-planetary disk has fully dissipated and planet formation is complete. Both a rapid initial stellar rotation, and a more efficient angular momentum transport inside the star, in general, contribute toward the enlargement of the domain which is devoid of planets after the PMS phase, in the plane of planet mass vs. orbital distance. Comparisons with the observed distribution of exoplanets orbiting solar mass stars, in the plane of planet mass vs. orbital distance (addressing the "Neptunian desert" feature), show an encouraging agreement with the present simulations, especially since no attempts have been made to fine-tune initial parameters of the models to fit the observations. We also obtain an upper limit for the orbital period of bare-core planets, that agrees with observations of the "radius valley" feature in the plane of planet radius vs. orbital period. The two effects, tides and planet evaporation, should be accounted for simultaneously and in a consistent way, with a detailed model for the evolution of the star., Comment: 15 pages, 13 figures. This manuscript has been accepted for publication in Astronomy & Astrophysics section 10. Planets and planetary systems

Context. Kepler-444 is one of the oldest planetary systems known thus far. Its peculiar configuration consisting of five sub-Earth-sized planets orbiting the companion to a binary stellar system makes its early history puzzling. Moreover, observations of HI-Ly-$\rm \alpha$ variations raise many questions about the potential presence of escaping atmospheres today. Aims. We aim to study the orbital evolution of Kepler-444-d and Kepler-444-e and the impact of atmospheric evaporation on Kepler-444-e. Methods. Rotating stellar models of Kepler-444-A were computed with the Geneva stellar evolution code and coupled to an orbital evolution code, accounting for the effects of dynamical, equilibrium tides and atmospheric evaporation. The impacts of multiple stellar rotational histories and extreme ultraviolet (XUV) luminosity evolutionary tracks are explored. Results. Using detailed rotating stellar models able to reproduce the rotation rate of Kepler-444-A, we find that its observed rotation rate is perfectly in line with what is expected for this old K0-type star, indicating that there is no reason for it to be exceptionally active as would be required to explain the observed HI-Ly-$\rm \alpha$ variations from a stellar origin. We show that given the low planetary mass ($\sim$ 0.03 M$_{\rm \oplus}$) and relatively large orbital distance ($\sim$ 0.06 AU) of Kepler-444-d and e, dynamical tides negligibly affect their orbits, regardless of the stellar rotational history considered. We point out instead how remarkable the impact is of the stellar rotational history on the estimation of the lifetime mass loss for Kepler-444-e. We show that, even in the case of an extremely slow rotating star, it seems unlikely that such a planet could retain a fraction of the initial water-ice content if we assume that it formed with a Ganymede-like composition.

The detection of gravity modes is expected to give us unprecedented insights into the inner dynamics of the Sun. Within this framework, predicting their amplitudes is essential to guide future observational strategies and seismic studies. In this work, we predict the amplitude of low-frequency asymptotic gravity modes generated by penetrative convection at the top of the radiative zone. The result is found to depend critically on the time evolution of the plumes inside the generation region. Using a solar model, we compute the GOLF apparent surface radial velocity of low-degree gravity modes in the frequency range $10~\mu H_z\le \nu \le 100~\mu H_z$. In case of a Gaussian plume time evolution, gravity modes turn out to be undetectable because of too small surface amplitudes. This holds true despite a wide range of values considered for the parameters of the model. In the other limiting case of an exponential time evolution, plumes are expected to drive gravity modes in a much more efficient way because of a much higher temporal coupling between the plumes and the modes than in the Gaussian case. Using reasonable values for the plume parameters based on semi-analytical models, the apparent surface velocities in this case turn out to be one order of magnitude smaller than the 22-years GOLF detection threshold and than the previous estimates considering turbulent pressure as the driving mechanism, with a maximum value of $0.05$ cm s${}^{-1}$ for $\ell =1$ and $\nu\approx 100~\mu H_z$. When accounting for uncertainties on the plume parameters, the apparent surface velocities in the most favorable plausible case become comparable to those predicted with turbulent pressure, and the GOLF observation time required for a detection at $ \nu \approx100~\mu H_z$ and $\ell=1$ is reduced to about 50 yrs., Comment: 18 pages, Accepted for publication in A&A

Spectroscopic studies of Galactic O and B stars show that many stars with masses above 8 M$_{\odot}$ are observed in the HR diagram just beyond the Main-Sequence (MS) band predicted by stellar models computed with a moderate overshooting. This may be an indication that the convective core sizes in stars in the upper part of the HR diagram are larger than predicted by these models. Combining stellar evolution models and spectroscopic parameters derived for a large sample of Galactic O and B stars, including brand new information about their projected rotational velocities, we reexamine the question of the convective core size in MS massive stars. We confirm that for stars more massive than about 8 M$_{\odot}$, the convective core size at the end of the MS phase increases more rapidly with the mass than in models computed with a constant step overshoot chosen to reproduce the main sequence width in the low mass range (around 2 M$_{\odot}$). This conclusion is valid for both the cases of non-rotating models and rotating models either with a moderate or a strong angular momentum transport. The increase of the convective core mass with the mass obtained from the TAMS position is, however, larger than the one deduced from the surface velocity drop for masses above about 15 M$_{\odot}$. Although observations available at the moment cannot decide what is the best choice between the core sizes given by the TAMS and the velocity drop, we discuss different methods to get out of this dilemma. At the moment, comparisons with eclipsing binaries seem to favor the solution given by the velocity drop. While we confirm the need for larger convective cores at higher masses, we find tensions in-between different methods for stars more massive than 15 M$_{\odot}$. The use of single-aged stellar populations (non-interacting binaries or stellar clusters) would be a great asset to resolve this tension., Comment: 13 pages, 8 figures

We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, $N_{\rm eff}^{\rm SM}$, that quantifies the cosmological neutrino-to-photon energy densities. The calculation takes into account neutrino flavour oscillations, finite-temperature effects in the quantum electrodynamics plasma to ${\cal O}(e^3)$, where $e$ is the elementary electric charge, and a full evaluation of the neutrino--neutrino collision integral. We provide furthermore a detailed assessment of the uncertainties in the benchmark $N_{\rm eff}^{\rm SM}$ value, through testing the value's dependence on (i)~optional approximate modelling of the weak collision integrals, (ii)~measurement errors in the physical parameters of the weak sector, and (iii)~numerical convergence, particularly in relation to momentum discretisation. Our new, recommended standard-model benchmark is $N_{\rm eff}^{\rm SM} = 3.0440 \pm 0.0002$, where the nominal uncertainty is attributed predominantly to errors incurred in the numerical solution procedure ($|\delta N_{\rm eff}| \sim10^{-4}$), augmented by measurement errors in the solar mixing angle $\sin^2\theta_{12}$ ($|\delta N_{\rm eff}| \sim10^{-4}$)., Comment: 31 pages, 7 figures. Version accepted for publication in JCAP

The $\alpha$ Cen stellar system is the closest neighbour to our Sun. Its main component is a binary composed of two main-sequence stars, one more massive than the Sun and one less massive. The system's bright magnitude led to a wealth of astronomical observations over a long period, making it an appealing testbed for stellar physics. In particular, detection of stellar pulsations in both $\alpha$ Cen A and B has revealed the potential of asteroseismology for determining its fundamental stellar parameters. Asteroseismic studies have also focused on the presence of a convective core in the A component, but as yet without definitive confirmation. Progress in the determination of solar surface abundances and stellar opacities have yielded new input for stellar theoretical models. We investigate their impact on a reference system such as $\alpha$ Cen AB. We seek to confirm the presence of a convective core in $\alpha$ Cen A by analysing the role of different stellar physics and the potential of asteroseismic inverse methods. We present a new series of asteroseismic calibrations carried out using forward approach modelling and including updated chemical mixture and opacities in the models. We then complement our analysis with help of recent asteroseismic diagnostic tools based on inverse methods developed for solar-like stars. The inclusion of an updated chemical mixture -- that is less metal-rich -- appears to reduce the predicted asteroseismic masses of each component. Neither classical asteroseismic indicators such as frequency ratios, nor asteroseismic inversions favour the presence of a convective core in $\alpha$ Cen A. The quality of the observational seismic dataset is the main limiting factor to settle the issue. Implementing new observing strategies to improve the precision on the pulsation frequencies would certainly refine the outcome of asteroseismology for this binary system., Comment: 16 pages, 8 figures, accepted for publication in Astronomy and Astrophysics

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., Comment: 25 pages, Accepted for publication in Astronomy and Astrophysics

The Sun constitutes an excellent laboratory of fundamental physics. With the advent of helioseismology, we were able to probe its internal layers with unprecedented precision. However, the current state of solar modelling is still stained by tedious issues. One of these problems is related to the disagreement between models computed with recent photospheric abundances and helioseismic constraints. We use solar evolutionary models as initial conditions for reintegrations of their structure using Ledoux discriminant inversions. The resulting models are defined as seismic solar models, satisfying the equations of hydrostatic equilibrium. They will allow us to better constrain the internal structure of the Sun and provide complementary information to that of evolutionary models. These seismic models were computed using various reference models with different equations of state, abundances and opacity tables. We check the robustness of our approach by confirming the good agreement of our seismic models in terms of sound speed, density and entropy proxy inversions as well as frequency-separation ratios of low-degree pressure modes. Our method allows us to determine with an excellent accuracy the Ledoux discriminant profile of the Sun and compute full profiles of this quantity. Our models show an agreement with seismic data of ~0.1% in sound speed, density and entropy proxy as well as with the observed frequency-separation ratios. They surpass all standard and non-standard evolutionary models including ad-hoc changes aiming at reproducing helioseismic constraints. The obtained seismic Ledoux discriminant profile as well as the consistent structure obtained from our procedure paves the way for renewed attempts at constraining the solar modelling problem and the missing physical processes acting in the solar interior by breaking free from the hypotheses of evolutionary models., Comment: Accepted for publication in A&A

The standard cosmological model ($\Lambda$-CDM) predicts that galaxies are built through hierarchical assembly on cosmological timescales$^{1,2}$. The Milky Way, like other disc galaxies, underwent violent mergers and accretion of small satellite galaxies in its early history. Thanks to Gaia-DR2$^3$ and spectroscopic surveys$^4$, the stellar remnants of such mergers have been identified$^{5-7}$. The chronological dating of such events is crucial to uncover the formation and evolution of the Galaxy at high redshift, but it has so far been challenging owing to difficulties in obtaining precise ages for these oldest stars. Here we combine asteroseismology -- the study of stellar oscillations -- with kinematics and chemical abundances, to estimate precise stellar ages ($\sim$ 11%) for a sample of stars observed by the $\mathit{Kepler}$ space mission$^8$. Crucially, this sample includes not only some of the oldest stars that were formed inside the Galaxy, but also stars formed externally and subsequently accreted onto the Milky Way. Leveraging this resolution in age, we provide compelling evidence in favour of models in which the Galaxy had already formed a substantial population of its stars (which now reside mainly in its thick disc) before the in-fall of the satellite galaxy Gaia-Enceladus/Sausage$^{5,6}$ around 10 billions years ago, Comment: Updated with the final version accepted for publication as a Letter in Nature Astronomy (29 pages, 10 figures, 2 tables, including main article and methods section). Improved presentation of results, which have not changed from the previous version

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.

Context: Asteroseismic measurements reveal that an unknown efficient angular momentum (AM) transport mechanism is needed for subgiant and red giant stars. A revised prescription for AM transport by the magnetic Tayler instability has been recently proposed as a possible candidate for such a missing mechanism. Results: The revised prescription for the transport by the Tayler instability leads to low core rotation rates after the main sequence that are in better global agreement with asteroseismic measurements than those predicted by models with purely hydrodynamic processes or with the original Tayler-Spruit dynamo. A detailed comparison with asteroseismic data shows that the rotational properties of at most two of the six subgiants can be correctly reproduced by models accounting for this revised magnetic transport process. This result is obtained independently of the value adopted for the calibration parameter in this prescription. We also find that this transport by the Tayler instability faces difficulties in simultaneously reproducing asteroseismic measurements available for subgiant and red giant stars. The low values of the calibration parameter needed to correctly reproduce the rotational properties of two of the six subgiants lead to core rotation rates during the red giant phase that are too high. Inversely, the higher values of this parameter needed to reproduce the core rotation rates of red giants lead to a very low degree of radial differential rotation before the red giant phase, which is in contradiction with the internal rotation of subgiant stars. Conclusions: In its present form, the revised prescription for the transport by the Tayler instability does not provide a complete solution to the missing AM transport revealed by asteroseismology of evolved stars., Comment: 5 pages, 5 figures, published in A&A

We present a general and model-independent method to obtain an effective Markovian quantum kinetic equation for the expectation value of a slowly evolving scalar field in an adiabatically evolving background from first principles of nonequilibrium quantum field theory. The method requires almost no assumptions about the field's interactions and the composition of the background, except that 1) the coupling constants shall be small enough for perturbation theory to be applicable, 2) there is a clear separation between microphysical time scales and the rate at which bulk properties change, and 3) higher time derivatives of the field remain small. The resulting Markovian equation of motion is expressed in terms of an effective potential and friction coefficients. Motivated by cosmological applications we focus on spatially homogeneous and isotropic systems, but the approach could also be applied to spatial gradients., Comment: 20 pages, 2 figures; version accepted in JCAP

Helioseismology is one of the most successful fields of astrophysics. The observation and characterization of solar oscillation has allowed solar seismologists to study the internal structure and dynamics of the Sun with unprecedented thoroughness. Ground-based networks and dedicated space missions have delivered data of exquisite quality, enabling the development of sophisticated inference techniques. The achievements of the fields count, amongst other, the determination of solar photospheric helium abundance, unacessible to spectroscopic constraints, the precise positioning of the base of the convective zone and the demonstration of the importance of microscopic diffusion in stellar radiative regions. Helioseismology played also a key role in validating the framework used to compute solar and stellar models and played an important role in the so-called solar neutrino problem. In the current era of astrophysics, with the increasing importance of asteroseismology to precisely characterize stars, the Sun still plays a crucial calibration role, acting as a benchmark for stellar models. With the revision of the solar abundances and the current discussions related to radiative opacity computations, the role of the Sun as a laboratory of fundamental physics is undisputable. In this brief review, I will discuss some of the inference techniques developed in the field of helioseismology, dedicated to the exploitation of the solar global oscillation modes., Comment: To appear in the proceedings of the meeting "How Much do we Trust Stellar Models?" held in Li\`ege in Sept 2018

Since the first observations of solar oscillations in 1962, helioseismology has probably been one of the most successful fields of astrophysics. Besides the improvement of observational data, solar seismologists developed sophisticated techniques to infer the internal structure of the Sun. Back in 1990s these comparisons showed a very high agreement between solar models and the Sun. However, the downward revision of the CNO surface abundances in the Sun in 2005, confirmed in 2009, induced a drastic reduction of this agreement leading to the so-called solar modelling problem. More than ten years later, in the era of the space-based photometry missions which have established asteroseismology of solar-like stars as a standard approach to obtain their masses, radii and ages, the solar modelling problem still awaits a solution. We will briefly present the results of new helioseismic inversions, discuss the current uncertainties of solar models and possible solutions to the solar modelling problem. We will also discuss how the solar problem can have significant implications for asteroseismology as a whole by discussing the modelling of the exoplanet-host star Kepler-444, thus impacting the fields requiring a precise and accurate knowledge of stellar masses, radii and ages, such as Galactic archaeology and exoplanetology., Comment: To appear in the proceedings of the conference "Stars and their variability observed from space" held in Vienna in August 2019