Constraining stellar evolution theory with asteroseismology of γ\gamma Doradus stars using deep learning

The efficiency of the transport of angular momentum and chemical elements inside intermediate-mass stars lacks proper calibration, thereby introducing uncertainties on a star's evolutionary pathway. Improvements require better estimation of stellar masses, evolutionary stages, and internal mixing properties. We aim to develop a neural network approach for asteroseismic modelling and test its capacity to provide stellar masses, ages, and overshooting parameter for a sample of 37 $\gamma$ Doradus stars. Here, our goal is to perform the parameter estimation from modelling of individual periods measured for dipole modes with consecutive radial order. We have trained neural networks to predict theoretical pulsation periods of high-order gravity modes as well as the luminosity, effective temperature, and surface gravity for a given mass, age, overshooting parameter, diffusive envelope mixing, metallicity, and near-core rotation frequency. We have applied our neural networks for Computing Pulsation Periods and Photospheric Observables, C-3PO, to our sample and compute grids of stellar pulsation models for the estimated parameters. We present the near-core rotation rates (from literature) as a function of the inferred stellar age and critical rotation rate. We assess the rotation rates of the sample near the start of the main sequence assuming rigid rotation. Furthermore, we measure the extent of the core overshoot region and find no correlation with mass, age, or rotation. The neural network approach developed in this study allows for the derivation of stellar properties dominant for stellar evolution -- such as mass, age, and extent of core-boundary mixing. It also opens a path for future estimation of mixing profiles throughout the radiative envelope, with the aim to infer those profiles for large samples of $\gamma$ Doradus stars.Comment: 35 pages, 63 figures, accepted for publication in A&

Physical properties of the eclipsing binary KIC 9851944 and analysis of its tidally-perturbed p- and g-mode pulsations

Stars that are both pulsating and eclipsing offer an important opportunity to better understand many of the physical phenomena that occur in stars, because it is possible to measure the pulsation frequencies of stars for which the masses and radii are known precisely and accurately. KIC 9851944 is a double-lined detached eclipsing binary containing two F-stars which show both pressure and gravity mode pulsations. We present an analysis of new high-resolution spectroscopy of the system and high quality light curves from the Kepler and TESS space missions. We determine the masses and effective temperatures of the stars to 0.6% precision, and their radii to 1.0% and 1.5% precision. The secondary component is cooler, but larger and more massive than the primary so is more evolved; both lie inside the {\delta} Scuti and {\gamma} Doradus instability strips. We measure a total of 133 significant pulsation frequencies in the light curve, including 14 multiplets that each contain between 3 and 19 frequencies. We find evidence for tidal perturbations to some of the p- and g-modes, attribute a subset of the frequencies to either the primary or secondary star, and measure a buoyancy radius and near-core rotational frequency for the primary component. KIC 9851944 is mildly metal-rich and MIST isochrones from the MESA evolutionary code agree well with the observed properties of the system for an age of 1.25 Gyr.Comment: 28 pages, 29 figure

Probing the physics in the core boundary layers of the double-lined B-type binary KIC4930889 from its gravito-inertial modes

Stellar evolution models of B-type stars are still uncertain in terms of internal mixing properties, notably in the area between the convective core and the radiative envelope. This impacts age determination of such stars in addition to the computation of chemical yields produced at the end of their life. We investigated the thermal and chemical structure and rotation rate in the near-core boundary layer of the double-lined B-type binary KIC4930889 from its four-year Kepler light curve, ground-based spectroscopy, and Gaia astrometry. We computed grids of 1D stellar structure and evolution models for different mixing profiles and prescriptions of the temperature gradient in the near-core region. We examined the preferred prescription and the near-core rotation rate using 22 prograde dipole modes detected by Kepler photometry. We employed a Mahalanobis distance merit function and considered various nested stellar model grids, rewarding goodness of fit but penalising model complexity. Furthermore, we found a preference for either an exponentially decaying mixing profile in the near-core region or absence of additional near-core mixing, but found no preference for the temperature gradient in this region. The frequency (co)variances of our theoretical predictions are much larger than the errors on the observed frequencies. This forms the main limitation on further constraining the individual parameters of our models. Additionally, non-adiabatic pulsation computations of our best models indicate a need for opacity enhancements to accurately reproduce the observed mode excitation. The eccentric close binary system KIC4930889 proves to be a promising target to investigate additional physics in close binaries by developing new modelling methods with the capacity to include the effect of tidal interactions for full exploitation of all detected oscillation modes.Comment: Accepted for publication in A&A, 20 pages, 14 figures, 10 table

Can we detect deep axisymmetric toroidal magnetic fields in stars?

One of the major discoveries of asteroseismology is the signature of a strong extraction of angular momentum (AM) in the radiative zones of stars across the entire Hertzsprung-Russell diagram, resulting in weak core-to-surface rotation contrasts. Despite all efforts, a consistent AM transport theory, which reproduces both the internal rotation and mixing probed thanks to the seismology of stars, remains one of the major open problems in modern stellar astrophysics. A possible key ingredient to figure out this puzzle is magnetic field with its various possible topologies. Among them, strong axisymmetric toroidal fields, which are subject to the so-called Tayler MHD instability, could play a major role. They could trigger a dynamo action in radiative layers while the resulting magnetic torque allows an efficient transport of AM. But is it possible to detect signatures of these deep toroidal magnetic fields? The only way to answer this question is asteroseismology and the best laboratories of study are intermediate-mass and massive stars because of their external radiative envelope. Since most of these are rapid rotators during their main-sequence, we have to study stellar pulsations propagating in stably stratified, rotating, and potentially strongly magnetised radiative zones. For that, we generalise the traditional approximation of rotation, which provides in its classic version a flexible treatment of the adiabatic propagation of gravito-inertial modes, by taking simultaneously general axisymmetric differential rotation and toroidal magnetic fields into account. Using this new non-perturbative formalism, we derive the asymptotic properties of magneto-gravito-inertial modes and we explore the different possible field configurations. We found that the magnetic effects should be detectable for equatorial fields using high-precision asteroseismic data.Comment: 4 pages, 2 figures. Proceeding of the Annual meeting of the French Society of Astronomy and Astrophysics (SF2A 2022

Asteroseismic modeling of gravity modes in slowly rotating A/F stars with radiative levitation

It has been known for several decades that transport of chemical elements is induced by the process of microscopic atomic diffusion. Yet, the effect of atomic diffusion, including radiative levitation, has hardly been studied in the context of gravity mode pulsations of core-hydrogen burning stars. In this paper, we study the difference in the properties of such modes for models with and without atomic diffusion. We perform asteroseismic modeling of two slowly rotating A- and F-type pulsators, KIC11145123 ($f_{\rm rot} \approx0.010~{\rm d}^{-1}$) and KIC9751996 ($f_{\rm rot} \approx0.0696~{\rm d}^{-1}$), respectively, based on the periods of individual gravity modes. For both stars, we find models whose g-mode periods are in very good agreement with the {\it Kepler\/} asteroseismic data, keeping in mind that the theoretical/numerical precision of present-day stellar evolution models is typically about two orders of magnitude lower than the measurement errors. Using the Akaike Information Criterion (AIC) we have made a comparison between our best models with and without diffusion, and found very strong evidence for signatures of atomic diffusion in the pulsations of KIC11145123. In the case of KIC9751996 the models with atomic diffusion are not able to explain the data as well as the models without it. Furthermore, we compare the observed surface abundances with those predicted by the best fitting models. The observed abundances are inconclusive for KIC9751996, while those of KIC11145123 from the literature can better be explained by a model with atomic diffusion.Comment: Accepted for publication in Ap

Period spacings of γ Doradus pulsators in the Kepler field: Rossby and gravity modes in 82 stars

Rossby modes are the oscillations in a rotating fluid, whose restoring force is the Coriolis force. They provide an additional diagnostic to understand the rotation of stars, which complicates asteroseismic modelling. We report 82 γ Doradus stars for which clear period spacing patterns of both gravity and Rossby modes have been detected. The period spacings of both show a quasi-linear relation with the pulsation period, but the slope is negative for the gravity modes and positive for the Rossby modes. Most Rossby modes have k = −2, m = −1. For only one star, a series of k = −1, m = −1 modes is seen. For each pattern, the mean pulsation period, the mean period spacing, and the slope are measured. We find that the slope correlates with the mean period for Rossby mode patterns. The traditional approximation of rotation is used to measure the near-core rotation rate, assuming the star rotates rigidly. We report the near-core rotation rates, the asymptotic period spacings, and the radial orders of excited modes of these 82 main-sequence stars. The near-core rotation rates lie between 0.6 and 2.3d−1⁠. Six stars show surface rotation modulations, among which only KIC 3341457 shows differential rotation, whilst the other five stars have uniform rotations. The radial orders of excited modes show different distributions for the dipole and quadrupole gravity modes versus the Rossby modes

Constraining the near-core rotation of the gamma Doradus star 43 Cygni using BRITE-Constellation data

Photometric time series of the $\gamma$ Dor star 43 Cyg obtained with the BRITE-Constellation nano-satellites allow us to study its pulsational properties in detail and to constrain its interior structure. We aim to find a g-mode period spacing pattern that allows us to determine the near-core rotation rate of 43 Cyg and redetermine the star's fundamental atmospheric parameters and chemical composition. We conducted a frequency analysis using the 156-days long data set obtained with the BRITE-Toronto satellite and employed a suite of MESA/GYRE models to derive the mode identification, asymptotic period spacing and near-core rotation rate. We also used high-resolution, high signal-to-noise ratio spectroscopic data obtained at the 1.2m Mercator telescope with the HERMES spectrograph to redetermine the fundamental atmospheric parameters and chemical composition of 43 Cyg using the software Spectroscopy Made Easy (SME). We detected 43 intrinsic pulsation frequencies and identified 18 of them to be part of a period spacing pattern consisting of prograde dipole modes with an asymptotic period spacing $\Delta \Pi_{l=1}$ of $2970^{+700}_{-570} \rm s$. The near-core rotation rate was determined to be $f_{\rm rot} = 0.56^{+0.12}_{-0.14}\,\rm d^{-1}$. The atmosphere of 43 Cyg shows solar chemical composition at an effective temperature of 7150 $\pm$ 150 K, a log g of 4.2 $\pm$ 0.6 dex and a projected rotational velocity, $v {\rm sin}i$, of 44 $\pm$ 4 kms$^{-1}$. The morphology of the observed period spacing patterns shows indications of the presence of a significant chemical gradient in the stellar interior.Comment: 9 pages, 8 figures, accepted by A&

Period spacings of γ Doradus pulsators in the Kepler field: detection methods and application to 22 slow rotators

In γ Doradus (γ Dor) stars, the g-mode period spacing shows an approximately linear relation with period. The slope is a new asteroseismic diagnostic, related to the rotation rate and the azimuthal order m. We report two automated methods, the ‘moving-window Fourier transform’ and the ‘cross-correlation’, to detect and measure the period spacings based on 4-yr light curves from the Kepler satellite. The results show that the cross-correlation method performs better at detecting the period spacings and their slopes. In this paper, we apply our method to 22 γ Dor stars with g-mode multiplets split by rotation. The rotation periods are similar to the g-mode period spacings, causing the multiplets to overlap. To clarify the overlapping patterns, we use the échelle diagram and introduce a ‘copy-shift’ diagram to discern and measure the splittings. The first observational relation between slopes and splittings is shown. The slope deviates from zero when the splitting increases, as the theory predicts. We found that what appears to be rotational splittings in two stars is in fact caused by two nearly identical overlapping patterns from binaries

The ESO UVES/FEROS Large Programs of TESS OB pulsators. I. Global stellar parameters from high-resolution spectroscopy

Modern stellar structure and evolution theory experiences a lack of observational calibrations for the interior physics of intermediate- and high-mass stars. This leads to discrepancies between theoretical predictions and observed phenomena mostly related to angular momentum and element transport. Analyses of large samples of massive stars connecting state-of-the-art spectroscopy to asteroseismology may provide clues on how to improve our understanding of their interior structure. We aim to deliver a sample of O- and B-type stars at metallicity regimes of the Milky Way and the Large Magellanic Cloud (LMC) galaxies with accurate atmospheric parameters from high-resolution spectroscopy, along with a detailed investigation of line-profile broadening, for future asteroseismic studies. After describing the general aims of our two Large Programs, we develop dedicated methodology to fit spectral lines and deduce accurate global stellar parameters from high-resolution multi-epoch UVES and FEROS spectroscopy. We use the best available atmosphere models for three regimes covered by our global sample, given its breadth in terms of mass, effective temperature, and evolutionary stage. Aside from accurate atmospheric parameters and locations in the Hertzsprung-Russell diagram, we deliver detailed analyses of macroturbulent line broadening, including estimation of the radial and tangential components. We find that these two components are difficult to disentangle from spectra with signal-to-noise ratios below 250. Future asteroseismic modelling of the deep interior physics of the most promising stars in our sample will improve the existing dearth of such knowledge for large samples of OB stars, including those of low metallicity in the LMC.Comment: Accepted for publication in Astronomy & Astrophysic

The Kepler Smear Campaign: Light curves for 102 Very Bright Stars

We present the first data release of the Kepler Smear Campaign, using collateral 'smear' data obtained in the Kepler four-year mission to reconstruct light curves of 102 stars too bright to have been otherwise targeted. We describe the pipeline developed to extract and calibrate these light curves, and show that we attain photometric precision comparable to stars analyzed by the standard pipeline in the nominal Kepler mission. In this paper, aside from publishing the light curves of these stars, we focus on 66 red giants for which we detect solar-like oscillations, characterizing 33 of these in detail with spectroscopic chemical abundances and asteroseismic masses as benchmark stars. We also classify the whole sample, finding nearly all to be variable, with classical pulsations and binary effects. All source code, light curves, TRES spectra, and asteroseismic and stellar parameters are publicly available as a Kepler legacy sample.Comment: 35 pages, accepted ApJ