Search

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 (Bétrisey et al. 2023, in press). 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. This high precision is very promising for PLATO and leaves some margin for other unaccounted systematics such as the choice of the physical ingredients of the stellar models or the effects of stellar activity., {"references":["Bétrisey, J., Buldgen, G., Reese, D. R., et al. 2023a, arXiv e-prints, arXiv:2306.04509"]}

With the advent of space-based missions such as CoRoT, Kepler, and TESS, asteroseismology has become a powerful tool to study the internal rotation of stars. The rotation depends on the efficiency of the angular momentum (AM) transport inside the star, and its study allows to constrain the internal AM transport processes, as well as improve our understanding of their physical nature. In this context, we compared the rotation rates predicted by asteroseismology and by starspots measurements for four main-sequence F-type stars from the Kepler LEGACY sample, considering different AM transport prescriptions, and investigated if some of these prescriptions could be ruled out. Due to the slow rotation of these stars, 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 and coherent 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 HR diagram (M_star > ~ 1.2M_sun at solar metallicity), 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 HR diagram, 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 F-type stars for which it is difficult to constrain the AM transport processes, unlike for hotter, Gamma Dor stars or colder, less massive solar analogs., {"references":["Benomar, O. et al. 2015, MNRAS, 452, 2654","Bétrisey, J. et al. 2022, A&A, 659, A56","Bétrisey, J. et al. 2023, A&A, 673, L11","Eggenberger, P. et al. 2008, Ap&SS, 316, 43","Eggenberger, P. et al. 2019, A&A, 621, A66","Fuller, J. et al. 2019, MNRAS, 485, 3661","Garraffo, C. et al. 2018, ApJ, 862, 90","Kraft, R. P. 1967, ApJ, 150, 551","Matt, S. P. et al. 2015, ApJ, 799, L23","Ledoux, P. 1951, ApJ, 114, 373","Nielsen, M. B. et al. 2017, A&A, 603, A6","Schou, J. et al. 1994, ApJ, 433, 389"]}

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 accreted gas by the proto-Sun must have been variable. In this talk, we show that solar evolutionary models including 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. We demonstrate that in addition to macroscopic transport and increased opacities at the base of the convective envelope, the formation history of the Solar System constitutes a key element to resolve the current crisis of solar models., {"references":["Adachi, I., Hayashi, C., & Nakazawa, K. 1976, Progress of Theoretical Physics, 56, 1756.","Agostini, M., Altenmüller, K., Appel, S., Atroshchenko, V., Bagdasarian, Z., et al. 2018, Nature, 562, 505.","Appel, S., Bagdasarian, Z., Basilico, D., Bellini, G., Benziger, J., et al. 2022, Phys. Rev. Lett., 129, 252701.","Asplund, M., Amarsi, A. M., & Grevesse, N. 2021, A&A, 653, A141.","Asplund, M., Grevesse, N., Sauval, A. J., & Scott, P. 2009, ARA&A, 47, 481.","Ayukov, S. V. & Baturin, V. A. 2017, Astronomy Reports, 61, 901.","Bahcall, J. N., Serenelli, A. M., & Basu, S. 2006, ApJS, 165, 400.","Bahcall, J. N. & Ulmer, A. 1996, Phys. Rev. D., 53, 4202.","Bailey, J. E., Nagayama, T., Loisel, G. P., Rochau, G. A., Blancard, C., et al. 2015, Nature, 517, 56.","Basu, S., Chaplin, W. J., Elsworth, Y., New, R., & Serenelli, A. M. 2009, ApJ, 699, 1403.","Borexino Collaboration, M., Agostini, Altenmüller, K., Appel, S., Atroshchenko, V., Bagdasarian, Z., et al. 2020, Nature, 587, 577.","Buldgen, G., Eggenberger, P., Noels, A., Scuflaire, R., Amarsi, A. M., et al. 2023, A&A, 669, L9.","Buldgen, G., Salmon, S. J. A. J., Noels, A., Scuflaire, R., Montalban, J., et al. 2019, A&A, 621, A33.","Christensen-Dalsgaard, J., Dappen,W., Ajukov, S. V., Anderson, E. R., Antia, H. M., et al. 1996, Science, 272, 1286.","Christensen-Dalsgaard, J., di Mauro, M. P., Houdek, G., & Pijpers, F. 2009, A&A, 494, 205.","Eggenberger, P., Buldgen, G., Salmon, S. J. A. J., Noels, A., Grevesse, N., et al. 2022, Nature Astronomy, 6, 788.","Gough, D. O. 2019, MNRAS, 485, L114.","Grevesse, N. & Sauval, A. J. 1998, SSRv, 85, 161.","Guillot, T., Fletcher, L. N., Helled, R., Ikoma, M., Line, M. R., et al. 2022, arXiv e-prints, arXiv:2205.04100.","Guillot, T., Ida, S., & Ormel, C. W. 2014, A&A, 572, A72.","Haxton, W. C. & Serenelli, A. M. 2008, ApJ, 687, 678.","Hillenbrand, L. A. 2009, In IAU Symposium, edited by E. E. Mamajek, D. R. Soderblom, & R. F. G. Wyse, IAU Symposium, vol. 258, pp. 81–94.","Kobayashi, H. & Tanaka, H. 2021, ApJ, 922, 16.","Kruijer, T. S., Burkhardt, C., Budde, G., & Kleine, T. 2017, Proceedings of the National Academy of Science, 114, 6712.","Kunitomo, M. & Guillot, T. 2021, A&A, 655, A51.","Kunitomo, M., Guillot, T., & Buldgen, G. 2022, A&A, 667, L2.","Kunitomo, M., Guillot, T., Ida, S., & Takeuchi, T. 2018, A&A, 618, A132.","Kunitomo, M., Guillot, T., Takeuchi, T., & Ida, S. 2017, A&A, 599, A49.","Magg, E., Bergemann, M., Serenelli, A., Bautista, M., Plez, B., et al. 2022, A&A, 661, A140.","Meléndez, J., Asplund, M., Gustafsson, B., & Yong, D. 2009, ApJL, 704, L66.","Montalban, J., Miglio, A., Theado, S., Noels, A., & Grevesse, N. 2006, Communications in Asteroseismology, 147, 80.","Murphy, S. J. & Paunzen, E. 2017, MNRAS, 466, 546.","Nelder, J. A. & Mead, R. 1965, The computer journal, 7, 308.","Orebi Gann, G. D., Zuber, K., Bemmerer, D., & Serenelli, A. 2021, Annual Review of Nuclear and Particle Science, 71, 491.","Paxton, B., Bildsten, L., Dotter, A., Herwig, F., Lesaffre, P., et al. 2011, ApJS, 192, 3.","Paxton, B., Cantiello, M., Arras, P., Bildsten, L., Brown, E. F. et al. 2013, ApJS, 208, 4.","Paxton, B., Marchant, P., Schwab, J., Bauer, E. B., Bildsten, L., et al. 2015, ApJS, 220, 15.","Paxton, B., Schwab, J., Bauer, E. B., Bildsten, L., Blinnikov, S., et al. 2018, ApJS, 234, 34.","Paxton, B., Smolec, R., Schwab, J., Gautschy, A., Bildsten, L., et al. 2019, ApJS, 243, 10.","Serenelli, A. M., Basu, S., Ferguson, J.W., & Asplund, M. 2009, ApJL, 705, L123.","Serenelli, A. M., Haxton, W. C., & Peña-Garay, C. 2011, ApJ, 743, 24.","Spina, L., Sharma, P., Meléndez, J., Bedell, M., Casey, A. R., et al. 2021, Nature Astronomy, 5, 1163.","Villante, F. L. 2010, ApJ, 724, 98.","Vinyoles, N., Serenelli, A. M., Villante, F. L., Basu, S.,","Bergström, J., et al. 2017, ApJ, 835, 202.","Zhang, Q.-S., Li, Y., & Christensen-Dalsgaard, J. 2019, ApJ, 881, 103."]}

The Sun is the most observed star in the Universe. Thanks to this privileged status, it plays a key calibrator role for stellar physics, acting as a laboratory to test fundamental physical ingredients used in theoretical computations. Therefore, any refinement of the recipe of solar models will impact the ingredients for all models of solar-type stars. Following the revision of the solar abundances by Asplund and collaborators in 2005, confirmed in 2009, 2015 and 2021, the standard recipe of solar models has been put under question regarding both microscopic and macroscopic ingredients. In this work, we will present results of new generations of both solar evolutionary and seismic models. We will show how evolutionary models taking into account the effects of rotation and magnetic fields can reproduce both the internal rotation, the lithium surface abundance and the helium abundance in the convective zone of the Sun. Furthermore, we will present a new approach to compute seismic solar models from iterative Ledoux discriminant inversions. We will show how such seismic models can be used to gain insights on the temperature gradient close to the base of the convective zone, where the robustness of opacity tables has been questioned. Combining both approaches will thus provide us with key constraints on the required revision of physical ingredients to solve the long lasting solar modeling problem that followed the abundance revision in the early 2000s., {"references":["Antia, H. M. 1996, A&A, 307, 609.","Asplund, M., Amarsi, A. M., & Grevesse, N. 2021, A&A, 653, A141.","Asplund, M., Grevesse, N., Sauval, A. J., & Scott, P. 2009, ARA&A, 47, 481.","Ayukov, S. V. & Baturin, V. A. 2017, Astronomy Reports, 61, 901.","Baglin, A., Auvergne, M., Barge, P., Deleuil, M., Michel, E., et al. 2009, In IAU Symposium, edited by F. Pont, D. Sas- selov, & M. J. Holman, IAU Symposium, vol. 253, pp. 71–81.","Bailey, J. 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This paper presents the analysis of lock gates submitted to ship impacts. This problem is generally approached in two different ways: firstly, by the use of an equivalent static method, in which the impact is modeled by a quasi-static force, or by the use of dynamic numerical simulations, during which the progress of the ship and the temporal evolution of the impact force is taken into account. The second approach requires extensive calculation and modeling efforts, which are generally prohibitive in the early design stage.A simplified analytical method is presented to evaluate the resistance of such structures when impacted by a ship. The principle is based in the super-element method, firstly evaluating the resistance of the lock gate in local deformation mode, assuming crushing only of certain structural elements in a limited zone, located in the close vicinity of the impact. Secondly, the entire resistance of the lock gate is calculated, considering the global deformation mode, assuming a bending of the entire structure.The scientific objective is to extend this approach to lock gates which cannot currently be treated with this method, in particular those where the layout of the stiffening elements can be highly irregular. This implies to study thoroughly the global deformation modes of the structure and the plastic mechanisms involved in the energy dissipation, in order to predict a correct displacement field and resistance force.

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

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

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 ± 0.10 M⊙ and 1.59 ± 0.08 MJup, 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.

The advent of space-based photometry missions, such as CoRoT, Kepler and TESS, has favoured a rapid development of asteroseismology and its synergies with exoplanetology. Such multi-disciplinary studies will further develop in the future with the PLATO mission. A detailed characterization of the host star can significantly improve our understanding of exoplanetary systems. In this context, we focused on Kepler-93, whose high-quality data and stellar properties make it a PLATO benchmark target. We carried out a detailed stellar modelling using global and local minimization techniques, also considering various changes of the physical ingredients. Our analysis was completed by inversion techniques to provide a more robust mean density estimate and test the impact of surface effects. The revised stellar parameters allowed us to update the planetary parameters of Kepler-93b and simulate its orbital evolution under the effects of tides and atmospheric evaporation. We found that a detailed asteroseismic modelling will be able to meet the PLATO standards for such a solar-like star (Bétrisey et al. 2022)., {"references":["Ballard, S. et al. 2014, ApJ, 790, 12","Bellinger, E. P. et al. 2016, ApJ, 830, 31","Bellinger, E. P. et al. 2019, A&A, 622, A130","Bétrisey, J. et al. 2022, A&A, 659, A56","Borucki, W. J. et al. 2011, ApJ, 736, 19","Dressing, C. D. et al. 2015, ApJ, 800, 135","Huber, D. et al. 2013, ApJ, 767, 127","Marcy, G. W. et al. 2014, ApJS, 210, 20","Silva Aguirre, V. et al. 2015, MNRAS, 452, 2127","Roxburgh, I. W. 1985, Sol. Phys., 100, 21"]}

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., Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor

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

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

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., Accepted for publication in Astronomy and Astrophysics

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

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

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

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

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

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., {"references":["Farnir et al. (2019,2020,2021)","Tassoul (1980)","Gough (1986)","Roxburgh & Vorontsov (2003)","Deheuvels et al. (2016)","Buldgen et al. (2021 in prep.)","Grosjean (2015)","Mosser et al. (2014)"]}

In the last decade, astonishing progresses were achieved in asteroseismology thanks to the high-quality data from the space-based missions CoRoT, Kepler and TESS and the field will further prosper with the future PLATO mission. This high precision is however limited by the “so-called” surface effects of solar-like oscillations. Despite several attempts (Kjeldsen et al. 2008, Ball & Gizon 2014, Sonoi et al. 2015, Ball et al. 2016), current approaches remain empirical and constitute a weakness in stellar modelling and inversion techniques. As illustrated in Buldgen et al. (2019) and Bétrisey et al. (2021, submitted), their actual implementation shows biases on the estimated stellar parameters. For this reason, we developed a new indicator based on the inversion of frequency ratios instead of individual frequencies as it is currently done. This approach is motivated by the works of Roxburgh & Voronsov (2003) and Oti et al. (2005) who pointed out that these frequency ratios and their corresponding kernels are not sensitive to surface regions. In contrast, they are sensitive to deeper stellar layers. Therefore, our new indicator seems promising to better probe central stellar regions of intermediate-mass stars., {"references":["Ball, W.H. & Gizon, L., 2014, A&A, 568, A123","Ball, W.H. et al., 2016, A&A, 592, A159","Bétrisey, J. et al., 2021 (submitted to A&A)","Buldgen, G. et al., 2015, A&A, 583, A62","Buldgen, G. et al., 2019, A&A, 630, A126","Dziembowski, W.A. et al., 1990, MNRAS, 244, 542","Kjeldsen, H. et al., 2008, ApJ Letters, 683, L175","Oti, F. et al., 2005, MNRAS, 356, 671","Roxburgh, I.W. & Voronsov, S.V., 2003, A&A, 411, 215","Sonoi, T. et al., 2015, A&A, 583, A112"]}

Thanks to the space-based photometry missions CoRoT and Kepler, we now benefit from a wealth of seismic data for stars other than the sun. In the future, K2, Tess and Plato will provide further observations. The quality of this data may allow kernel-based linear structural inversion techniques to be used for stars other than the sun. To understand the limitations of this approach, we analyse the validity of the linear assumption used in these inversion techniques. We inspect various structural pairs and see how they are affected by structural changes. We show that uncertainties in radius strongly affect structural pairs of nondimensional variables, and that various other effects might come into play. Amongst these, the importance of micro-physics give the most striking example of how uncertainties in stellar models impact the verification of the linear relations. We also point out that including seismic constraints in the forward modelling fit helps with satisfying the linear relations., Comment: To appear in the proceedings of the Astrofluid 2016 Conference

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., accepted for publication in Astronomy and Astrophysics

Context. 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⊕ rocky core, calls into question the role played by the host star in the evolution of the system. Aims. We aim to study the impact of the host star’s rotational history on the evolution of TOI-849b, particularly focussing on the planetary migration due to dynamical tides dissipated in the stellar convective envelope, and on the high-energy stellar emission. Methods. 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 X-ray and extreme-ultraviolet (XUV) fluxes provided by our rotating stellar models. Results. Assuming that the planet was at its present-day position (ain = 0.01598 AU) at the protoplanetary disc dispersal, with mass 40.8 M⊕, and considering a broad range of host star initial surface rotation rates (Ωin ∈ [3.2, 18] Ω⊙), we find that only for Ωin ≤ 5 Ω⊙ do we reproduce the current position of the planet, given that for Ωin > 5 Ω⊙ its orbit is efficiently deflected by dynamical tides within the first ∼40 Myr of evolution. We also simulated the evolution of the orbit for values of ain ≠ 0.01598 AU for each of the considered rotational histories, confirming that the only combination suited to reproduce the current position of the planet is given by ain = 0.01598 AU and Ωin ≤ 5 Ω⊙. We tested the impact of increasing the initial mass of the planet on the efficiency of tides, finding that a higher initial mass (Min = 1 MJup) 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⊕, 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.

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-Lyαvariations 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 X-ray 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-Lyαvariations from a stellar origin. We show that given the low planetary mass (~0.03 M⊕) and relatively large orbital distance (~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 $��$ 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 $��$ 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 $��$ 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 $��$ 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., 17 pages, 14 figures, accepted for publication in A&A

We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, Neff 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 O(e3), 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 Neff 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 Neff SM 3.0440 ±0.0002, where the nominal uncertainty is attributed predominantly to errors incurred in the numerical solution procedure (|δ Neff| ∼10-4), augmented by measurement errors in the solar mixing angle sin2θ 12 (|δ Neff| ∼10-4).

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., 20 pages, 2 figures; version accepted in JCAP

The $��$ 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 $��$ 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 $��$ Cen AB. We seek to confirm the presence of a convective core in $��$ 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 $��$ 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., 16 pages, 8 figures, accepted for publication in Astronomy and Astrophysics

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

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., 20 pages, 18 figures, 7 tables, to be published in Astronomy & Astrophysics

An offshore wind farm can be located close to traffic lanes of commercial and passenger ships, which may lead to possible collision. The work presented in this paper aims to understand both the crushing behaviour and the nacelle dynamics of a monopile offshore wind turbine when impacted by a ship. Another objective was to deeply investigate the influence of various parameters like ship impact velocity and location, wind direction, soil stiffness and deformability of the striking ship. First, nonlinear numerical simulations of ship - Offshore Wind Turbine (OWT) collisions have been carried out with a rigid striking ship for a better understanding of the OWT's structural behaviour during collision. Different configurations for the wind turbine's structure have been used in order to highlight the modifications in behaviour induced by changing the soil conditions or the loading scenario. The resulting resistant force and internal energies have been compared as well as the tower top (nacelle) displacements and accelerations. Then, another series of simulations have been performed with a deformable ship in order to investigate the influence of the deformability of the striking ship on the OWT's behaviour. It was shown that a slight variation of the impact velocity can lead to consequences ranging from minor damage of the OWT to collapse. Furthermore, the behaviour of the OWT during collision is highly sensitive to wind loads as it was shown that in some cases the OWT can collapse for an impact velocity of only 3 m/s and, in the worst case, can fall directly on the ship. The results obtained showed that it is important to account for the soil flexibility when performing collision simulations because considering the monopile as being clamped at the base would lead to an overestimation of the plastic deformation of the collided structure. Moreover, when the OWT is collided by a deformable striking ship, the deformations of the OWT are 2 times smaller comparing to the deformations caused by impact with a rigid ship and the structure can withstand collisions without collapsing with an impact velocity up to 6 m/s.

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

The Sun is the most studied of stars and a laboratory of fundamental physics. However, the understanding of our star is stained by the solar modelling problem which can stem from various causes. We combine inversions of sound speed, an entropy proxy and the Ledoux discriminant with the position of the base of the convective zone and the photospheric helium abundance to test combinations of ingredients such as equation of state, abundance and opacity tables. We study the potential of the inversions to constrain ad-hoc opacity modifications and additional mixing in the Sun. We show that they provide constraints on these modifications to the ingredients and that the solar problem likely occurs from various sources and using phase shifts with our approach is the next step to take., Comment: To appear in the proceedings of the PHOST meeting held in Banyuls, France

The theory of stellar evolution plays a central role in astrophysics as stellar models are used to infer properties for Galactic and Extragalactic stellar populations as well as exoplanetary systems. However, despite decades of experience, stellar models still face major issues linked to transport processes of chemicals and angular momentum. This review will focus on some of the processes responsible for the most sizable uncertainties in stellar models such as for example convection, rotation and mass loss. The presentation will discuss their implementation, their impact on theoretical predictions and how various observational constraints can help us gain insight on the physics inside stars and face the current challenges of the theory of stellar evolution., Comment: To appear in the proceedings of the PHOST conference held in Banyuls, France

Context. The CoRoT and Kepler missions have paved the way for synergies between exoplanetology and asteroseismology. The use of seismic data helps providing stringent constraints on the stellar properties which directly impact the results of planetary studies. Amongst the most interesting planetary systems discovered by Kepler, Kepler-444 is unique by the quality of its seismic and classical stellar constraints. Its magnitude, age and the presence of 5 small-sized planets orbiting this target makes it an exceptional testbed for exoplanetology. Aims. We aim at providing a detailed characterization of Kepler-444, focusing on the dependency of the results on variations of key ingredients of the theoretical stellar models. This thorough study will serve as a basis for future investigations of the planetary evolution of the system orbiting Kepler-444. Methods. We use local and global minimization techniques to study the internal structure of the exoplanet-host star Kepler-444. We combine seismic observations from the Kepler mission, Gaia DR2 data and revised spectroscopic parameters to precisely constrain its internal structure and evolution. Results. We provide updated robust and precise determinations of the fundamental parameters of Kepler-444 and demonstrate that this low-mass star bore a convective core during a significant portion of its life on the main-sequence. Using seismic data, we are able to estimate the lifetime of the convective core to approximately 8 Gyr out of the 11 Gyr of the evolution of Kepler-444. The revised stellar parameters found by our thorough study are M = 0.754 +- 0.03M_Sun , R = 0.753 +- 0.01R_Sun , Age = 11 +- 1 Gy., Comment: Accepted for publication in Astronomy and Astrophysics

Since the first observations of solar oscillations, helioseismology has been one of the most successful fields of astrophysics. Data of high quality were obtained through the implementation of networks of ground-based observatories such as the GONG project or the BiSON network, coupled with space-based telescopes such as SOHO and SDO missions. Besides the improvement of observational data, solar seismologists developed sophisticated techniques to infer the internal structure of the Sun. These methods, then already extensively used in the field of Geophysics, are called inversion techniques. They allowed to determine the position of the solar convective envelope, its helium abundance and the internal radial profiles of thermodynamic quantities. 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 induced a drastic reduction of this agreement leading to the 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 present the results of new helioseismic inversions, discuss the current uncertainties of solar models as well as some possible solutions to the solar problem. We will show how helioseismology can help us grasp what is amiss in our models. We will also show that, far from being an argument about details of solar models, the solar problem has significant implications for seismology of solar-like stars, on the main sequence and beyond, impacting asteroseismology as a whole as well as the fields requiring precise and accurate knowledge of stellar masses, radii and ages, such as Galactic archaeology and exoplanetology., Comment: Accepted for publication in Front. Astron. Space Sci. - Stellar and Solar Physics

Context. The α 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 α 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. Aims. 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 α Cen AB. We seek to confirm the presence of a convective core in α Cen A by analysing the role of different stellar physics and the potential of asteroseismic inverse methods. Methods. First, we present a new series of asteroseismic calibrations of the binary carried out using forward approach modelling and including updated chemical mixture and opacities in the models. We took advantage of the most up-to-date orbital solution as non-seismic constraints. We then complement our analysis with help of recent asteroseismic diagnostic tools based on inverse methods developed for solar-like stars. Results. 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 the frequency ratios, nor asteroseismic inversions favour the presence of a convective core in α 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.

The theory of stellar evolution plays a central role in astrophysics as stellar models are used to infer properties for Galactic and Extragalactic stellar populations as well as exoplanetary systems. However, despite decades of experience, stellar models still face major issues linked to transport processes of chemicals and angular momentum. This review will focus on some of the processes responsible for the most sizable uncertainties in stellar models such as for example convection, rotation and mass loss. The presentation will discuss their implementation, their impact on theoretical predictions and how various observational constraints can help us gain insight on the physics inside stars and face the current challenges of the theory of stellar evolution.

Since the CoRoT and Kepler missions, the availability of high quality seismic spectra for red giants has made them the standard clocks and rulers for Galactic Archeology. With the expected excellent data from the TESS and PLATO missions, red giants will again play a key role in Galactic studies and stellar physics, thanks to the precise masses and radii determined by asteroseismology. The determination of these quantities is often based on so-called scaling laws, which have been used extensively for main-sequence stars. We show how the SOLA inversion technique can provide robust determinations of the mean density of red giants within 1 per cent of the real value, using only radial oscillations. Combined with radii determinations from Gaia of around 2 per cent precision, this approach provides robust, less model-dependent masses with an error lower than 10 per cent. It will improve age determinations, helping to accurately dissect the Galactic structure and history. We present results on artificial data of standard models, models including an extended atmosphere from averaged 3D simulations and non-adiabatic frequency calculations to test surface effects, and on eclipsing binaries. We show that the inversions provide very robust mean density estimates, using at best seismic information. However, we also show that a distinction between red-giant branch and red-clump stars is required to determine a reliable estimate of the mean density. The stability of the inversion enables an implementation in automated pipelines, making it suitable for large samples of stars., Accepted for publication in MNRAS

Context: The observations of solar-like oscillations in evolved stars have brought important constraints on their internal rotation rates. To correctly reproduce these data, an efficient transport mechanism is needed in addition to meridional circulation and shear instability. Aims: We study the efficiency of the transport of angular momentum during the subgiant phase. Results: The precise asteroseismic measurements of both core and surface rotation rates available for the six Kepler targets enable a precise determination of the efficiency of the transport of angular momentum needed for each of these subgiants. These results are found to be insensitive to all the uncertainties related to the modelling of rotational effects before the post-main sequence phase. An interesting exception in this context is the case of young subgiants (typical values of log(g) close to 4), because their rotational properties are sensitive to the degree of radial differential rotation on the main sequence. These young subgiants constitute therefore perfect targets to constrain the transport of angular momentum on the main sequence from asteroseismic observations of evolved stars. As for red giants, we find that the efficiency of the additional transport process increases with the mass of the star during the subgiant phase. However, the efficiency of this undetermined mechanism decreases with evolution during the subgiant phase, contrary to what is found for red giants. Consequently, a transport process with an efficiency that increases with the degree of radial differential rotation cannot account for the core rotation rates of subgiants, while it correctly reproduces the rotation rates of red giant stars. This suggests that the physical nature of the additional mechanism needed for the internal transport of angular momentum may be different in subgiant and red giant stars., Comment: 10 pages, 11 figures, accepted for publication in A&A

Aims: We develop a method that provides a comprehensive analysis of the oscillation spectra of solar-like pulsators. We define new seismic indicators that should be as uncorrelated and as precise as possible and should hold detailed information about stellar interiors. This is essential to improve the quality of the results obtained from asteroseismology as it will provide better stellar models which in turn can be used to refine inferences made in exoplanetology and galactic archaeology. Methods: The presented method - WhoSGlAd - relies on Gram-Schmidt's orthogonalisation process. A Euclidean vector 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., Comment: Accepted for publication in Astronomy and Astrophysics, 20 pages

This paper presents a simplified analytical method to evaluate the resistance of a single plating lock gate impacted by a river barge. The approach is based on the assumption that the gate behavior may be divided into two successive phases. At the beginning of the collision, local crushing of some structural elements occurs concomitantly with small overall elastic motion of the entire gate. Then, when the penetration of the barge into the gate becomes important, a global plastic mechanism develops over the entire structure. In addition to the membrane and bending deformations occurring classically in such collisions, the particular flat shape of the striking barge bow leads to shear deformations near the gate edges. For all these deformation modes, closed-form expressions of the gate resistance are derived for both local and global deformation phases by applying the upper-bound method. These analytical developments are then validated through comparisons with numerical solutions obtained from non-linear finite-element simulations.

This paper presents a meshless method to perform the seismic analysis of a plane lock gate. The approach is based on the analytical derivation of the total hydrodynamic pressure, with due consideration for the gate flexibility. In particular, the flexibility of the gate and the fluid–structure interaction are taken into account in the calculation of the equivalent force that has to be applied on the gate to model the action of the water. To reach this goal, the Rayleigh–Ritz method is first used to determine the modal properties of the dry structure. This is achieved by using mode shapes extracted from the beam theory as generating functions. The results obtained in this way are validated by comparison with numerical solutions. The second step consists in performing the dynamic analysis of the gate by deriving a weak form of the equilibrium equation. Based on the Galerkin method, a matrix formulation is derived and the Newmark integration scheme is used for the evaluation of the pressure during the earthquake. Here again, non-linear finite element simulations including water modeling are carried out to corroborate the analytical developments. In addition, the lumped-mass method is also investigated and a criteria is proposed to check its applicability. Finally, some concluding remarks are given to perform more easily the seismic analysis of lock gates.