arXiv subjects

Patrick Eggenberger

Publications and source records attributed to Patrick Eggenberger.

At least 19 recordsLinked to original sources

arXiv2026

Coexisting Tayler instability-driven dynamos in radiative zones: New dynamo solution and its impacts on stellar physics

Recent asteroseismic observations constitute a great challenge for rotating stellar evolution models, which predict overly fast internal rotation rates when only hydrodynamic processes are included. This suggests the absence of one or several unidentified angular momentum (AM) transport processes in these models. Transport by large-scale and strong magnetic fields in the radiative zone is a promising candidate to explain the observations. While these fields might be characterised by a fossil origin, the Tayler-Spruit dynamo constitutes a primary mechanism to form the necessary magnetic fields. Despite recent numerical studies, this mechanism remains poorly known. Motivated by this scenario, we investigated the Tayler-Spruit dynamo through a new set of 3D numerical simulations. We modelled the radiative zone as a Boussinesq stably stratified fluid whose differential rotation is maintained by a volumetric body force. Here, we report, for the first time, the coexistence of two dynamo solutions, which mainly differ by the magnetic field location (near the equator and the polar axis). While the equatorial dynamo is driven by an instability sharing both characteristics of the magnetorotational and Tayler instabilities, we focus mainly on the newly identified polar dynamo, which is driven by the standard Tayler instability. We show that this dynamo can still operate and transport AM efficiently in a strong stratification regime, with a Brunt-Väisälä frequency that is 130 times larger than the rotation rate. We extracted new scaling laws for the magnetic field, AM transport, and the minimum shear to trigger the dynamo. Finally, we were able to roughly constrain the signature of the generated magnetic fields on asteroseismic modes propagating in main sequence and evolved stars.

astro-ph.SR↗

arXiv2026

The Beauty of k2: Probing Stellar Interiors Using Apsidal Motion. I. The Benchmark Massive Binary HD 152248

Over the last decades, several independent studies have shown the need for large convective boundary mixing (CBM) and convective core sizes in massive stars to reproduce a variety of their observed properties. Yet, stars more massive than 20Msun lack a quantitative prescription for CBM as well as an unequivocal constraint on the internal mixing mechanisms acting in them. We use the apsidal motion observed in the twin binary HD152248 - linked to the internal stellar structure constants k2 of the stars - to constrain massive stars' internal density stratification and CBM. We build GENEC stellar models assuming two different angular momentum transports: purely hydrodynamic (hydro) and magneto-diffusive (magnetic). We confront single- and binary-star models to assess the impact of tidal locking on the star's evolution. We investigate the impact of CBM (overshooting), metallicity, initial helium abundance and mass, mass-loss rate, and mixing length parameter on the evolution of stellar parameters. We highlight that k2 from the models are systematically larger than observed ones, the so-called k2-discrepancy. Models predict stars with too low a density contrast between their core and external layers. Both hydro and magnetic models require large step-overshoot of 1.2 to reproduce stellar parameters, including k2. Other parameters have almost no impact. Given the efficiency of tides to synchronise systems, the assumption of pseudo-synchronisation is sound for this system. It sets an upper limit on the misalignment angle of stellar rotation axes of ~50°. Even with such unexpected large angles, the k2-discrepancy is not solved. Even if the mass-loss rate was underestimated by a factor two, it would have no impact on stellar parameters evolution, including k2. It demonstrates that the apsidal motion is a powerful, robust means to probe stellar interiors.

astro-ph.SR↗

arXiv2026

On the origin of the rotation of massive stars

We explore the origin of the rotation rates of massive stars. Contrary to their low-mass siblings, most massive stars do not have detectable magnetic fields, so that star-disk interaction models used for the formation of rotating low-mass stars do not apply. We investigate whether the magnetic fields of protostellar jets present in the parent molecular cloud prevent the protostar from reaching the critical angular velocity. Starting from the gravitational collapse of a molecular cloud, we run two two-dimensional radiation-gravito-magnetohydroynamical simulations to study the formation of an accretion disk and the launching of magnetically-driven protostellar outflows (of particular interest is the formation of a magnetocentrifugal jet originating from the protostar and inner disk). We then study the angular momentum transfer from the disk and jet onto the protostar. Finally, we compute one-dimensional stellar evolution models of the pre-main sequence including our results from the disk-jet simulations and follow the angular momentum redistribution within the structure of the protostar. We find that the angular momentum transported outwards by the magnetically-driven protostellar outflows is sufficient for keeping the protostar below the critical speed at all times. Moreover, we are able to link the strength of the jet, and thus the rotation rate at the end of the accretion epoch, to the initial conditions for star formation. Our results show that the jet strength produces a variety of stellar rotation rates, suggesting that protostellar jets fix the rotation rate of massive stars.

astro-ph.SR↗

arXiv2026

Confirmation of the hot super-Neptune TOI-672 b with NIRPS and HARPS and Insights into the Neptunian desert around M dwarfs

The Neptunian desert is a distinct lack of Neptune-sized planets at short orbital periods, purportedly carved by photoevaporation and tidal circularization following high-eccentricity migration. Constraining these processes and how they vary across different host-star spectral types requires the detailed characterization of planets in the desert and around its boundaries. In this study, we confirm the planetary nature of a massive super-Neptune identified by TESS around the M0 dwarf TOI-672. We analyse photometry from TESS and ExTrA and precise radial velocity measurements taken with the recently commissioned Near-InfraRed Planet Searcher (NIRPS) and HARPS spectrographs. We measure the planetary orbital period, radius, and mass of 3.634 days, 5.31 +0.24 -0.26 Rearth, and 50.9 +4.5 -4.4 Mearth, respectively. Our findings place TOI-672 b within the Neptunian ridge, a pile-up of planets from 3--5 days at the Neptunian desert boundary. We then use a novel approach to determine the desert boundaries in period-radius space and instellation-radius space, and, for the first time, compare the Neptunian desert boundaries for planets orbiting FGK versus M dwarf stars. We determine that the boundary ridge shifts slightly inward from 3.3 +- 1.4 days for FGK host stars to 2.2 +- 1.0 days for M dwarf host stars; these values do not statistically significantly differ from each other, and the shift to shorter periods for M dwarf planets is smaller than theoretical photoevaporation models predict. We also find that TOI-672 b is a single-planet system within the sensitivity limits of our RV and TTV datasets.

astro-ph.EP↗

arXiv2026

Chemical evolution of close massive binaries -- tidally-enhanced or tidally-suppressed mixing?

One of the largest source of uncertainties in the predictions of stellar models comes from the internal transport mechanisms. In close massive binaries, previous theoretical studies suggest that tides systematically boost chemical mixing. However, observations do not reveal any clear period-nitrogen enrichment trend, challenging these predictions. In addition, comprehensive examinations of the interplay between tidal interactions, angular momentum and chemicals transport have so far been scarce. We investigate the interplay between tidal interactions and rotational mixing, and the impact of the angular moment transport (AMT) assumptions. We examine whether tidal interactions enhance or suppress chemical mixing by computing grids of genec binary models with various AMT treatments. In order to independently assess the role of tidal interactions, we systematically compute model variations of single stars with identical initial conditions. Our investigations reveal that tides can either enhance or suppress mixing relative to single-star models, and that the outcome is highly sensitive to the AMT assumptions. We identify a key contrast between the two types of computed models: in close systems subject to tides, magnetic models predict that the mixing efficiency is mostly determined by the orbital configuration, whereas in hydrodynamic models it also depends on the assumed initial velocity. As a result, hydro models may display non-monotonic period-enrichment trends, or even period-enrichment correlations. These results highlight the importance of the AMT assumptions in modeling binaries with tidal interactions. The sensitivity of the predictions of hydro models to initial conditions extends the size of the period-enrichment parameter space they cover, allowing them to accommodate for peculiar observed systems, i.e., with mild enrichment at short periods, or high enrichment at longer periods.

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arXiv2026

TOI-3862 b: A dense super-Neptune deep in the hot Neptune desert

The structure and evolution of close-in exoplanets are shaped by atmospheric loss and migration processes, which give rise to key population features such as the hot Neptune desert, ridge, and savanna - regions of the period-radius space whose boundaries offer critical insights into planetary formation and survival. As part of the KESPRINT collaboration, we selected the TESS transiting planet candidate TOI-3862.01 for radial velocity follow-up to confirm its planetary nature and characterize its mass and bulk properties. This planet candidate is of particular interest due to its position in the middle of the hot Neptune desert, making it a valuable probe for testing theories of planet migration and atmospheric loss. We confirmed the planetary nature and determined the mass of TOI-3862.01 (hereinafter TOI-3862b) by performing a joint fit with both transit and radial velocity data, precisely characterizing the bulk properties of this planet. TOI-3862b is a super-Neptune on a 1.56-day orbit around a Sun-like star with an effective temperature of 5300$\pm$50K. It has a mass of 53.7$_{-2.9}^{+2.8}$ M$_{\oplus}$ and a radius of 5.53$\pm$0.18 R$_{\oplus}$, corresponding to a density of 1.7$\pm$0.2 g/cm^3. This places it among the rare population of hot and dense super-Neptune desert planets. TOI-3862b, residing deep in the hot Neptune desert, represents a rare occurrence in an otherwise sparsely populated region, offering a valuable opportunity to probe the processes that may allow planets to survive in such environments.

astro-ph.EP↗

arXiv2025

Precise mass and radius determination for two new and one known Neptune-sized planets around G Dwarf hosts

As part of the KESPRINT collaboration, we present the discovery and characterization of three exoplanets in the sub-Neptune to super-Neptune regime, spanning key regions of the exo-Neptunian landscape. TOI-1472c and TOI-1648b are newly discovered sub-Neptunes, while TOI-1472b is a previously known super-Neptune for which we provide an improved mass measurement. These planets have orbital periods of 6--15 days and radii of 2.5--4.1 R$_\oplus$, probing regions where planet formation and atmospheric evolution remain poorly understood. We combine TESS transit photometry with ground-based radial velocities to determine precise masses, radii, and orbital properties. TOI-1472b has a mass of $18.0^{+0.84}_{-0.85}$ M$_\oplus$ and a radius of $4.06 \pm 0.10$ R$_\oplus$, TOI-1472c has a mass of $21.1^{+0.96}_{-0.99}$ M$_\oplus$ and a radius of $3.33 \pm 0.08$ R$_\oplus$, and TOI-1648b has a mass of $7.4^{+1.1}_{-1.3}$ M$_\oplus$ and a radius of $2.54^{+0.14}_{-0.12}$ R$_\oplus$. The planets exhibit a range of eccentricities (0.041--0.178), indicating diverse evolutionary histories. TOI-1648b, with a high Transmission Spectroscopy Metric (TSM $\sim$59), is a promising target for atmospheric characterization. Together, these three planets provide precise constraints on the structure, composition, and dynamical evolution of small to intermediate-sized exoplanets, enriching our understanding of the exo-Neptunian landscape.

astro-ph.EP↗

arXiv2025

The impact of rotational mixing in intermediate-age star clusters with extended main-sequence turn-offs and extended red clumps

The extended main-sequence turn-offs (eMSTOs) and extended red clumps (eRCs) observed in intermediate-age star clusters challenge the traditional understanding of clusters as simple stellar populations. Recently, eMSTOs have been interpreted as signatures of stellar rotation. In this work, we test the effectiveness of rotational mixing in shaping the color-magnitude diagram (CMD) of star clusters. We computed a set of separate single-age synthetic stellar populations, referred to as "Base Stellar Populations" (BSPs), including stellar rotation. These BSPs were generated from two grids of stellar models that share the same input physics but differ in the efficiency of rotational mixing. We used an optimization algorithm to determine the best combination of BSPs to fit the CMDs of two star clusters: the Small Magellanic Cloud cluster NGC 419 and the Milky Way cluster NGC 1817. The synthetic clusters with weak rotational mixing provide the best fit to both the eMSTO and eRC features for both clusters, and are consistent with the luminosities and asteroseismic masses we derived for eRC stars in NGC 1817. In contrast, synthetic clusters with strong rotational mixing result in overly bright post-main-sequence stars, inconsistent with observations. This suggests that, for intermediate-mass stars, the influence of rotational mixing of chemical elements on stellar evolution cannot be so strong as to significantly increase the post-main-sequence luminosity. A simple test suggests that accounting for self-extinction by decretion discs in equator-on fast rotators could influence inferred rotation distributions and help reconcile the projected rotational velocity discrepancy across the eMSTO between models and observations.

astro-ph.SR↗

arXiv2025

Helioseismic inference of the solar radiative opacity

The Sun is the most studied of all stars, and thus constitutes a benchmark for stellar models. However, our vision of the Sun is still incomplete, as illustrated by the current debate on its chemical composition. The problem reaches far beyond chemical abundances and is intimately linked to microscopic and macroscopic physical ingredients of solar models such as radiative opacity, for which experimental results have been recently measured that still await theoretical explanations. We present opacity profiles derived from helioseismic inferences and compare them with detailed theoretical computations of individual element contributions using three different opacity computation codes, in a complementary way to experimental results. We find that our seismic opacity is about 10% higher than theoretical values used in current solar models around 2 million degrees, but lower by 35% than some recent available theoretical values. Using the Sun as a laboratory of fundamental physics, we show that quantitative comparisons between various opacity tables are required to understand the origin of the discrepancies between reported helioseismic, theoretical and experimental opacity values.

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↗

arXiv2024

Towards a holistic magnetic braking model -- II: explaining several long-term internal- and surface-spin properties of solar-like stars and the Sun

We extend our model of magnetic braking (MB), driven by an $α-Ω$ dynamo mechanism, from fully convective M-dwarfs (FCMDs) to explain the surface and internal spin $P_\mathrm{spin}$ evolution of partly convective dwarfs (PCDs) starting from the disc-dispersal stage to the main-sequence turnoff. In our model, the spin of the core is governed by shear at the core-envelope boundary while the spin of the envelope is governed by MB and shear. We show that (1) the most massive FCMDs experience a stronger spin-down than PCDs and less massive FCMDs, (2) the stalled spin-down and enhanced activity of K-dwarfs and the pileup of G-dwarfs older than a few Gyr are stellar-structure- and MB-dependent, and weakly dependent on core-envelope coupling effects, (3) our expression of the core-envelope convergence time-scale $τ_\mathrm{converge}(M_\ast,\,P_\mathrm{spin})$ between a few 10 to 100~Myr strongly depends on stellar structure but weakly on MB strength and shear, such that fast and massive rotators achieve corotation earlier, (4) our estimates of the surface magnetic fields are in general agreement with observations and our wind mass loss evolution explains the weak winds from the solar analog $π^1$ UMa and (5) with our model the massive young Sun hypothesis as a solution to the faint young Sun problem can likely be ruled out, because the maximum mass lost by winds from our Sun with our model is about an order of magnitude smaller than required to solve the problem.

astro-ph.SR↗

arXiv2024

A method for non-linear inversion of the stellar structure applied to gravity-mode pulsators

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

astro-ph.SR↗

arXiv2024

Angular momentum transport near convective-core boundaries of Gamma Doradus stars

Recent asteroseismic studies have revealed that the convective core of $γ$ Doradus stars rotates faster than their radiative interior. We study the development of differential rotation near the convective core to test angular momentum transport processes that are typically adopted in stellar evolution models. Models that only include the advection of angular momentum by meridional circulation and shear instabilities cannot reproduce current rotational constraints, irrespective of the initial conditions. The latest formulation of internal magnetic fields based on the Tayler instability is indeed able to reproduce the internal rotation rate of post-main sequence stars, however, it appears too efficient during the main sequence and has thus been disfavoured. A less efficient version of the same transport process can simultaneously reproduce the rotation rate of the convective core, the rotation rate in radiative regions as probed by gravity-modes, and the surface rotational velocities of $γ$ Doradus stars. Our work suggests that there are additional physical processes apart from internal magnetic fields at work in the stellar interiors of post-main sequence stars.

astro-ph.SR↗

arXiv2023

Impact of different approaches for computing rotating stellar models I. The solar metallicity case

The physics of stellar rotation plays a crucial role in the evolution of stars, their final fate and the properties of compact remnants. Diverse approaches have been adopted to incorporate the effects of rotation in stellar evolution models. This study seeks to explore the consequences of these various prescriptions for rotation on essential outputs of massive star models. We compute a grid of 15 and 60 M$_{\odot}$ stellar evolution models with the Geneva Stellar Evolution Code (GENEC), accounting for both hydrodynamical and magnetic instabilities induced by rotation. In both the 15 and 60 M$_{\odot}$ models, the choice of the vertical and horizontal diffusion coefficients for the non magnetic models strongly impacts the evolution of the chemical structure, but has a weak impact on the angular momentum transport and the rotational velocity of the core. In the 15 M$_{\odot}$ models, the choice of diffusion coefficient impacts the convective core size during the core H-burning phase, whether the model begins core He-burning as a blue or red supergiant and the core mass at the end of He-burning. In the 60 M$_{\odot}$ models, the evolution is dominated by mass loss and is less affected by the choice of diffusion coefficient. In the magnetic models, magnetic instability dominates the angular momentum transport and such models are found to be less mixed when compared to their rotating non-magnetic counterparts. Stellar models with the same initial mass, chemical composition, and rotation may exhibit diverse characteristics depending on the physics applied. By conducting thorough comparisons with observational features, we can ascertain which method(s) produce the most accurate results in different cases.

astro-ph.SR↗

arXiv2023

Dynamical tides in binaries: Inconsistencies in the implementation of Zahn's prescription

Binary evolution codes are essential tools to help in understanding the evolution of binary systems. They contain a great deal of physics, for example stellar evolution, stellar interactions, mass transfer, tides, orbital evolution. Since many of these processes are difficult to account for in detail, we often rely on prescriptions obtained in earlier studies. We highlight that the impact of the dynamical tides with radiative damping has been implemented inconsistently with respect to its original theoretical formulation in many studies. We derive a new analytical solution for the evolution toward synchronization in the case of circular orbits and propose turnkey equations for the case of eccentric orbits that can be used in population synthesis studies. We compare the strength of the tidal torque obtained with this new formula with respect to that obtained with the formula generally used in literature by studying how the evolution toward synchronization of main sequence stellar models is affected. We conclude that by using an incorrect formula for the tidal torque, as has been done in many binary codes, the strength of the dynamical tides with radiative damping is over- or underestimated depending on whether the star is close to or far from synchronization.

astro-ph.SR↗

arXiv2023

Physiological complexity of EEG as a proxy for dementia risk prediction: a review and preliminary cross-section analysis

The aim of this work is to give the readers a review (perspective) of prior work on this kind of complexity-based detection from resting-state EEG and present our preliminary cross-section analysis results on how EEG complexity of supposedly healthy senior persons can serve as an early warning to clinicians. Together with the use of wearables for health, this approach to early detection can be done out of clinical setting improving the chances of increasing the quality of life in seniors.

q-bio.NC↗

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↗