arXiv subjects

Jérôme Bétrisey

Publications and source records attributed to Jérôme Bétrisey.

13 recordsLinked to original sources

arXiv2026

Detailed study of HD 219134: a benchmark K-dwarf with a compact planetary system

Space missions such as CoRoT, Kepler, and TESS have transformed asteroseismology and its synergies with exoplanet science. We revisit the nearby K-dwarf HD 219134 to investigate the tension between asteroseismic and interferometric radii, update its fundamental parameters, and reconstruct the rotational, magnetic, and atmospheric evolution of the system. We combine forward asteroseismic modeling with seismic inversions to assess systematics from non-seismic constraints, radius measurements, and surface modeling. The revised stellar properties are then used for rotational evolution, stellar-wind, and high-energy irradiation calculations. Seismic inversions rule out the most recent interferometric radius, while the asteroseismic and spectroscopic results are compatible with the 2019 interferometric measurement. We obtain $M=0.779\pm0.015_\mathrm{(stat)}\pm0.006_\mathrm{(sys)}\ M_\odot$, $R=0.753\pm0.005_\mathrm{(stat)}\pm0.002_\mathrm{(sys)}\ R_\odot$, and an age of $8.92\pm0.89_\mathrm{(stat)}\pm0.19_\mathrm{(sys)}$ Gyr. These systematics include only non-seismic constraints; literature combined uncertainties from physical inputs and surface effects are $0.007M_\odot$, $0.002R_\odot$, and $0.81$ Gyr. Rotational and wind modelling shows that standard magnetic braking is broadly compatible with the present-day rotation and angular-momentum loss. Weakened braking gives a closer match but challenges standard wind-loss scalings. The inferred X-ray history suggests early stripping of the innermost planets, while the outer planets likely retained part of their primordial envelopes; HD 219134d experienced only moderate erosion. The apparent radius discrepancy likely reflects underestimated uncertainties in previous interferometric analyses rather than an astrophysical inconsistency. We advocate adopting the asteroseismic radius, which is robust to modeling assumptions and optimisation strategies.

astro-ph.EP↗

arXiv2026

Physics-induced impact on the properties of Kepler/K2 solar analogs in the light of PLATO's requirements

Solar analogs are useful laboratories for tests of stellar structure and evolution, particularly in the context of the upcoming PLATO mission. Our study focuses on six seismic solar analogs observed by Kepler and K2. We investigate the impact of the model physical ingredients on these six targets in order to evaluate how well one can satisfy the PLATO precision requirements for stellar parameters with the data quality that is currently available to us. We used as reference values the stellar mass, age, and chemical composition obtained with the Forward and Inverse COmbination (FICO) procedure, based on OPAL opacities and a combination of NACRE II and Solar Fusion II (SFII) nuclear reaction rates. The efficiency of macroscopic transport is calibrated on lithium abundances derived from the analysis of HERMES spectra. From there, we carried out extensive tests of the physical ingredients with the help of a Levenberg-Marquardt local minimisation method using both classical and seismic constraints. In particular, we investigated the impact induced by the use of OPLIB opacities and SFIII nuclear reaction rates on the stellar fundamental properties, as well as the use of various seismic constraints. We quantify the potential differences that changes in the modelling input physics may lead to, and compare their extent with the requirements expected for the PLATO mission (15% in mass, 2% in radius, and 10% in age), providing crucial constraints on the accuracy and robustness with respect to systematics of the determination of fundamental properties for PLATO. For our sample of solar analogs, we are able to accurately retrieve stellar masses within 2.5%. As for stellar ages, we quantify systematics of the order of 10-14% at most, but there are also very promising cases for which deviations remain within 4% depending on the stars and constraints considered.

astro-ph.SR↗

arXiv2026

Minimising magnetic activity effects in PLATO observations: insights from the Sun-as-a-star

Recent studies showed that magnetic activity effects in solar-type stars can substantially bias seismic inferences, particularly age estimates, regardless of modelling strategy or surface treatment. We quantified how magnetic activity effects in the Sun-as-a-star are smoothed by temporal averaging by analysing 182.5-, 365-, 730-, and 1460-day time series from the BiSON network and the GOLF instrument. We estimated the activity-induced systematic uncertainty using two metrics and compared results across baselines to evaluate how the observing window shapes activity-induced biases. Solar-cycle signatures persist even in 1460-day windows. The suppression of magnetic activity effects with increasing baseline is non-monotonic: one- and four-year windows reduce biases far more effectively than shorter baselines in most cases, whereas 730-day windows provide only limited improvement over 365-day ones. Improvements arise from enhanced frequency determination (dominant at 365 days) and from increasingly efficient temporal averaging of the activity cycle (dominant at 1460 days). In contrast, 730-day is an intermediate regime: frequency accuracy has already plateaued and the observing window remains too short to smooth out cycle-related variability. On average, we find that magnetic activity effects decrease by 24%, 12%, 30%, and 38% when transitioning from 182.5 to 365 days, 365 to 730 days, 730 to 1460 days, and 365 to 1460 days for frequency-based fits; the corresponding improvements for ratio-based fits are 13%, 14%, 20%, and 31%. These results indicate that a continuous single-field four-year PLATO observing programme would provide the most effective suppression of magnetic-activity biases for solar analogues, whereas a 2+2-year strategy (in two distinct fields) is significantly more sensitive to magnetic effects, with limited gains between 365- and 730-day windows.

astro-ph.SR↗

arXiv2026

Asteroseismic modelling of main-sequence solar-like stars and Kepler exoplanet host stars with the FICO procedure I. Catalogue of fundamental stellar properties

We present detailed asteroseismic modelling of 95 main-sequence solar-like stars and Kepler exoplanet host stars using the FICO procedure, a three-step method that combines forward and inverse techniques that enables precise inference of fundamental stellar parameters such as mass, radius, age, and mean density. We applied the FICO procedure to a catalogue of stars with high-quality asteroseismic and classical observations, and compared its results against literature values. We also compared its performance with direct frequency fitting using semi-empirical surface corrections. The FICO procedure achieved statistical precisions of 2.3%, 0.82%, 6.9%, and 0.49% in mass, radius, age, and mean density, respectively on average, well within PLATO quality requirements. We reconfirmed that surface-independent methods more effectively mitigate biases inherent to semi-empirical surface corrections, particularly for stars more massive than 1.15 Msun or above 6050 K. Two regimes were identified: near-solar conditions, where both approaches perform similarly, and higher-mass stars, where surface-independent methods consistently outperform direct fitting methods. While our results are consistent with literature values, we observed age biases (~11.5% on average for the Kepler LEGACY sample) that are comparable to the PLATO accuracy requirement of 10% for a Sun-like star, and therefore not negligible in that context. The FICO procedure provides a robust framework for high-precision stellar characterisation in the PLATO era. Its hybrid architecture effectively addresses surface effects, making it a promising tool for the accurate determination of exoplanet host-star properties. Our findings also highlight the importance of carefully selecting and validating the physical assumptions embedded in stellar models, particularly in the context of next-generation space missions such as PLATO.

astro-ph.SR↗

arXiv2025

Frequency separation ratios do not suppress magnetic activity effects in solar-like stars

Magnetic activity effects are typically neglected in asteroseismic modelling of solar-type stars, presuming that these effects can be accounted for in the parametrisation of the surface effects. It was however demonstrated that magnetic activity can have a significant impact on the asteroseismic characterisation using both forward and inverse techniques. We investigated whether frequency separation ratios, which are commonly used to efficiently suppress surface effects, are also able to suppress magnetic activity effects. Based on GOLF and BiSON observations of the Sun-as-a-star, we performed asteroseismic characterisations using frequency separation ratios as constraints to measure the apparent temporal evolution of the stellar parameters and their correlation with the 10.7 cm radio flux. Frequency separation ratios do not suppress the effects of magnetic activity. Both $r_{01}$ and $r_{02}$ ratios exhibit a clear signature of the magnetic activity cycle. Consequently, when these ratios are employed as constraints in asteroseismic modelling, magnetic activity effects are propagated to the stellar characterisation. Additionally, most stellar parameters correlate with the activity cycle, unlike the direct fitting of individual frequencies. Magnetic activity effects significantly impact asteroseismic characterisation, regardless of whether forward modelling or inverse methods are used. Standard techniques to suppress surface effects have proven ineffective against magnetic activity influences and systematic uncertainties of 4.7%, 2.9%, and 1.0% should be considered for the stellar age, mass, and radius, respectively. In preparation for future space-based photometry missions, it is therefore essential to enhance our theoretical understanding of these effects and develop a modelling procedure capable of accounting for or efficiently suppressing them.

astro-ph.SR↗

arXiv2025

The Future of Solar modelling: requirements for a new generation of solar models

Helioseismology and solar modelling have enjoyed a golden era thanks to decades-long surveys from ground-based networks such as for example GONG, BiSON, IRIS and the SOHO and SDO space missions which have provided high-quality helioseismic observations that supplemented photometric, gravitational, size and shape, limb-darkening and spectroscopic constraints as well as measurements of neutrino fluxes. However, the success of solar models is also deeply rooted in progress in fundamental physics (equation of state of the solar plasma, high-quality atomic physics computations and opacities, description of convection and the role of macroscopic transport processes of angular momentum and chemicals, such as for example meridional circulation, internal gravity waves, shear-induced turbulence or even convection. In this paper, we briefly outline some key areas of research that deserve particular attention in solar modelling. We discuss the current uncertainties that need to be addressed, how these limit our predictions from solar models and their impact on stellar evolution in general. We outline potential strategies to mitigate them and how multidisciplinary approaches will be needed in the future to tackle them.

astro-ph.SR↗

arXiv2025

Influence of the magnetic activity cycle on mean density and acoustic radius inversions

Asteroseismic modelling is crucial for upcoming missions like PLATO, CubeSpec, and Roman. Despite significant progress, discrepancies between observations and theoretical predictions introduce biases in stellar characterisation at the precision required by PLATO. Current models typically ignore magnetic activity, assuming its effects are hidden within surface effects. However, recent studies have shown significant impacts of magnetic activity on the Sun's asteroseismic characterisation using forward modelling. Using GOLF and BiSON observations of two full solar activity cycles, we quantified the impact of magnetic activity on solar mean density and acoustic radius inversions. Observations were segmented into yearly overlapping snapshots, each offset by 91.25 days. Inversions were performed for each snapshot to determine mean density and acoustic radius, tracking their temporal evolution and estimating systematic uncertainty due to magnetic activity. We observed a clear imprint of the magnetic activity cycle on solar mean density and acoustic radius through helioseismic inversions, consistent across GOLF and BiSON datasets. This imprint is the largest source of systematic uncertainty in solar asteroseismic characterisation. Including low radial-order modes mitigates these effects more significantly than previously measured for other stellar variables. We recommend asteroseismic values for solar mean density (1.4104 \pm 0.0051 g/cm3) and acoustic radius (3722.0 \pm 4.1 s), averaged over two activity cycles. These values account for major systematic errors, achieving high precision (0.36% for mean density and 0.11% for acoustic radius). These results are promising for high-precision characterisation of Sun-like stars, a better-constrained mean density being able to enhance the precision of stellar radius estimate, which is crucial for exoplanetary system characterisation.

astro-ph.SR↗

arXiv2024

Imprint of the magnetic activity cycle on solar asteroseismic characterisation based on 26 years of GOLF and BiSON data

Building on the success of previous missions, asteroseismic modelling will play a key role in future space-based missions, such as PLATO, CubeSpec, and Roman. Despite remarkable achievements, asteroseismology has revealed significant discrepancies in the physics of theoretical stellar models, which have the potential to bias stellar characterisation at the precision level demanded by PLATO. The current modelling strategies largely overlook magnetic activity, assuming that its effects are masked by filtering the so-called surface effects. Given the presence of activity cycles in multiple solar-like oscillators, and activity variations in a significant fraction of Kepler observations of main-sequence stars (Santos et al. 2019b, 2021, 2023), we measured the impact of magnetic activity on the asteroseismic characterisation of the Sun based on 26.5 years of GOLF and BiSON observations. While magnetic activity is partially absorbed in the treatment of surface effects, we found a discernible imprint of the activity cycle in the determination of the solar age. Notably, this imprint persists across both BiSON and GOLF datasets, with significant variations of up to 6.5% observed between solar minima and maxima. Considering that the Sun exhibits low levels of activity, our study underscores the looming challenge posed by magnetic activity for future photometry missions, and prompts a potential reevaluation of the asteroseismic characterisation of Kepler's most active targets.

astro-ph.SR↗

arXiv2024

Grids of stellar models with rotation VIII: Models from 1.7 to 500 $M_\odot$ at metallicity $Z = 10^{-5}$

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.

astro-ph.SR↗

arXiv2023

Asteroseismic modelling strategies in the PLATO era. II. Automation of seismic inversions and quality assessment procedure

*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.

astro-ph.SR↗

arXiv2023

Asteroseismic modelling strategies in the PLATO era I. Mean density inversions and direct treatment of the seismic information

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.

astro-ph.SR↗

arXiv2023

Testing angular momentum transport processes with asteroseismology of solar-type main-sequence stars

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.

astro-ph.SR↗

arXiv2022

Inversions of stellar structure from asteroseismic data

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.

astro-ph.SR↗