arXiv subjects

S. N. Breton

Publications and source records attributed to S. N. Breton.

At least 19 recordsLinked to original sources

arXiv2026

Luminaries in the Sky: The TESS LEGACY sample of bright stars. II. In-depth seismic characterisation of 32 naked-eye stars in the PLATO LOP fields

The NASA TESS mission is conducting a nearly full-sky survey, enabling the photometric characterisation of millions of stars. The forthcoming ESA PLATO mission will provide long-duration, high-precision photometry of tens of thousands of bright stars to be characterised through asteroseismology. The TESS Luminaries sample is a catalogue of 196 bright naked-eye (V < 6) main-sequence (MS) and sub-giant (SG) stars exhibiting solar-like oscillations. Among them, the subset located within the PLATO long-duration observation phase (LOP) fields constitutes an exceptional set of targets that will be observable by PLATO from the earliest phases of the mission, making them ideal calibrators during commissioning and the first months of science operations. This paper aims to provide an in-depth asteroseismic characterisation of 32 Luminaries stars that fall within the PLATO LOP fields of view. Individual mode parameters were extracted for the first time for 26 of them. We used three independent seismic pipelines, one of which is similar to the algorithms used in the official PLATO pipeline. Statistical criterion were applied to identify the optimal combination of data calibration, observing cadence, and fitting pipeline for each star. For all stars, we derived large and small separations, the asymptotic phase term, radial mode amplitudes, and mean linewidths per order. Comparisons reveal consistent trends in the seismic parameters, confirming the robustness of our analysis. In SGs, mixed-mode identification differs in the three pipelines, revealing extraction inconsistencies requiring longer datasets to improve our mode identifications. The Luminaries stars located in the PLATO LOP fields constitute a unique sample that will play a crucial role in validating, calibrating, and optimising PLATO's seismic performance.

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arXiv2026

Characterizing six seismic solar analogs observed by Kepler, K2, and HERMES

Solar analogs, stars that closely match the fundamental properties of the Sun, provide key benchmarks for testing stellar structure and evolution across different ages and activity levels. Their detailed characterization helps place the Sun in context within the broader population of solar-like stars. This study presents the characterization of six seismic solar analogs observed by the NASA Kepler and K2 missions. Combining asteroseismic constraints from space-based photometry with high-resolution spectroscopy and \textit{Gaia} astrometry, we derived their fundamental parameters and assessed their resemblance to the Sun. Global seismic properties and individual oscillation modes were extracted from the photometric light curves, while atmospheric parameters were obtained from data collected by the HERMES spectrograph at the Mercator telescope. Stellar modeling using seven independent stellar evolution codes yielded consistent masses, radii, and ages. These stars have masses between 0.91 and 1.04~$\mathrm{M}_\odot$, radii between 0.95 and 1.08~$\mathrm{R}_\odot$, and ages from about 1.8 to 9.1~Gyr, with typical systematic uncertainties of $\pm$ 0.02~$\mathrm{M}_\odot$, $\pm$ 0.01~$\mathrm{R}_\odot$, and $\pm$ 0.7~Gyr, respectively. One star, EPIC~206064678, exhibits properties very similar to those of the Sun, with $M = 1.016 \pm 0.033\,\mathrm{M}_\odot$, $R = 0.990 \pm 0.011\,\mathrm{R}_\odot$, and an age of $5.40 \pm 0.12$\,Gyr. It can therefore be considered a close solar twin, although it is slightly older and more metal-rich ($0.25 \pm 0.07$\,dex). Four targets display binarity signatures and all exhibit very low chromospheric activity. This work broadens the sample of well-characterized seismic solar analogs towards a larger sample of metallicities and ages, providing new references for comparative stellar studies and future asteroseismic investigations.

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arXiv2025

Is convective turbulence the only exciting mechanism of global p modes in the Sun?

In solar-like oscillators, acoustic waves are excited by turbulent motion in the convective envelope and propagate inward, generating a variety of standing pressure modes. When combining together the power of several solar acoustic modes, an excess not compatible with pure stochastic excitation was found in some studies. This could be the signature of a second mode excitation source. With over 27 years of helioseismic data from the Sun as a star observations by the Solar and Heliospheric Observatory (SoHO), we aim to study the variation in mode energy over this period, covering solar Cycles 23, 24, and the beginning of Cycle 25. We focus on the possible sources of high peaks in the mode-energy time series, i.e. instrumental problems or other exciting mechanisms, such as flares or Coronal Mass Ejections. We reconstruct the energy time series for each mode with a sampling time of 1.45 days. By combining the small-time-scale variations in energy for several low-degree modes in the 2090-3710uHz range, we study the correlation between the modes and their compatibility with the hypothesis that modes are only stochastically excited by convection. The observed excitation rate significantly deviates from what would be expected in the case of a purely stochastic excitation. Our results indicate that this energy excess cannot be only attributed to instrumental effects and does not exhibit a cyclic variation. Although high-energy excesses are occasionally associated with observations of flares or CMEs, no consistent pattern could be identified. The excitation is slightly more frequent for modes probing the upper layer of the convective zone. Furthermore, the energy supply rate seems to vary over time with the mean value following a modulation that can match the Quasi-Biennial Oscillation (QBO) observed in other solar indicators, and the variance being anti-correlated with the cycle.

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arXiv2025

Non-transiting exoplanets as a means of understanding star-planet interactions in close-in systems

Previous studies showed evidence of a dearth of close-in exoplanets around fast rotators, which can be explained by the combined action of intense tidal and magnetic interactions between planets and their host star. Detecting more exoplanets experiencing such interactions, with orbits evolving on short timescales, is therefore crucial to improve our understanding of the underlying physical mechanisms. For this purpose, we performed a new search for close-in non-transiting substellar companions in the Kepler data, focusing on orbital periods below 2.3 days. We focused on main-sequence solar-type stars and subgiant stars for which a surface rotation period was measured. For each star, we looked for an excess in the power spectral density of the light curve, which could correspond to the signature of a close-in non-transiting companion. We compared our candidates with existing catalogues to eliminate potential contaminants in our sample, and we visually inspected the phase-folded light curve and its wavelet decomposition. We identify 88 stars exhibiting a signature consistent with the presence of a close non-transiting substellar companion. We show that the objects in our sample are located mostly within the dearth zone, emphasising the importance of performing follow-up of such systems in order to gather observational evidence of star-planet interactions.

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arXiv2024

Solar p-modes excitation rate along the magnetic activity cycle

Magnetic cycles of solar-like stars influence their internal physics. Thus, the frequency, amplitude, excitation rate, and damping of the acoustic oscillation modes (p-modes) vary with the cycle over time. We need to understand the impact of magnetic activity on p-modes in order to characterise precisely stars that will be observed by the ESA PLATO mission, to be launched late 2026 with the objective to find Earth-like planets around solar-type stars. In this work, we investigate the variation of mode excitation in the Sun during Cycles 23, 24 and the beginning of Cycle 25. To do so, we analyse data obtained since 1996 by two instruments onboard the SoHO satellite: the GOLF spectrometer and the VIRGO sunphotometer. We use a method enabling us to reach a better temporal resolution than classical methods. Combining the variations of energy for several modes l=[0-2] in three frequency bands (i.e. [1800, 2450], [2450, 3110], [3110, 3790] μHz), our preliminary results show that more energy is associated to several modes during cycle minima, suggesting that there could be a second source of excitation other than turbulent convection that would excite several modes at a time during solar minima.

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arXiv2024

Measuring stellar surface rotation and activity with the PLATO mission -- I. Strategy and application to simulated light curves

The Planetary Transits and Oscillations of stars mission (PLATO) will allow us to measure surface rotation and monitor photometric activity of tens of thousands of main sequence solar-type and subgiant stars. This paper is the first of a series dedicated to the preparation of the analysis of stellar surface rotation and photospheric activity with the near-future PLATO data. We describe in this work the strategy that will be implemented in the PLATO pipeline to measure stellar surface rotation, photometric activity, and long-term modulations. The algorithms are applied on both noise-free and noisy simulations of solar-type stars, which include activity cycles, latitudinal differential rotation, and spot evolution. PLATO simulated systematics are included in the noisy light curves. We show that surface rotation periods can be recovered with confidence for most of the stars with only six months of observations and that the {recovery rate} of the analysis significantly improves as additional observations are collected. This means that the first PLATO data release will already provide a substantial set of measurements for this quantity, with a significant refinement on their quality as the instrument obtains longer light curves. Measuring the Schwabe-like magnetic activity cycle during the mission will require that the same field be observed over a significant timescale (more than four years). Nevertheless, PLATO will provide a vast and robust sample of solar-type stars with constraints on the activity-cycle length. Such a sample is lacking from previous missions dedicated to space photometry.

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arXiv2024

Kepler main-sequence solar-like stars: surface rotation and magnetic-activity evolution

While the mission's primary goal was focused on exoplanet detection and characterization, Kepler made and continues to make extraordinary advances in stellar physics. Stellar rotation and magnetic activity are no exceptions. Kepler allowed for these properties to be determined for tens of thousands of stars from the main sequence up to the red giant branch. From photometry, this can be achieved by investigating the brightness fluctuations due to active regions, which cause surface inhomogeneities, or through asteroseismology as oscillation modes are sensitive to rotation and magnetic fields. This review summarizes the rotation and magnetic activity properties of the single main-sequence solar-like stars within the Kepler field. We contextualize the Kepler sample by comparing it to known transitions in the stellar rotation and magnetic-activity evolution, such as the convergence to the rotation sequence (from the saturated to the unsaturated regime of magnetic activity) and the Vaughan-Preston gap. While reviewing the publicly available data, we also uncover one interesting finding related to the intermediate-rotation gap seen in Kepler and other surveys. We find evidence for this rotation gap in previous ground-based data for the X-ray luminosity. Understanding the complex evolution and interplay between rotation and magnetic activity in solar-like stars is crucial, as it sheds light on fundamental processes governing stellar evolution, including the evolution of our own Sun.

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arXiv2024

Equilibrium tides and magnetic activity in stars with close-by massive planets. The intriguing case of WASP-18

WASP-18 is an F6V star that hosts a planet with a mass of about 10 Jupiter masses and an orbital period of 0.94 days. In spite of its relatively fast rotation and young age, the star remains undetected in X-rays, thus implying a very low level of magnetic activity. To account for such unexpected properties, we propose a mechanism that modifies the internal stratification and the photospheric magnetic activity of a late-type main sequence star with a close-by massive planet based on the action of the equilibrium tide. We speculate that the horizontal flow produced by the equilibrium tide may interact with the convective plumes in the overshoot layer below the stellar outer convective envelope. The interaction is characterized by a very high Reynolds number leading to the development of turbulent boundary layers at the surface of such structures, whereas turbulent wakes extend over most of the overshoot layer that they straddle. We propose that such a tidally induced turbulence can lead to a reduction of the filling factor of the downdrafts in the overshoot layer. As a consequence, the absolute value of the sub-adiabatic gradient increases in that layer hindering the emergence of magnetic flux tubes responsible for the formation of photospheric starspots. We conjecture that this process is occurring in WASP-18, thus providing a possible mechanism to account for the very low level of magnetic activity observed for such a planet host.

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arXiv2023

Stellar spectral-type (mass) dependence of the dearth of close-in planets around fast-rotating stars. Architecture of Kepler confirmed single-exoplanet systems compared to star-planet evolution models

In 2013 a dearth of close-in planets around fast-rotating host stars was found using statistical tests on Kepler data. The addition of more Kepler and Transiting Exoplanet Survey Satellite (TESS) systems in 2022 filled this region of the diagram of stellar rotation period (Prot) versus the planet orbital period (Porb). We revisited the Prot extraction of Kepler planet-host stars, we classify the stars by their spectral type, and we studied their Prot-Porb relations. We only used confirmed exoplanet systems to minimize biases. In order to learn about the physical processes at work, we used the star-planet evolution code ESPEM (French acronym for Evolution of Planetary Systems and Magnetism) to compute a realistic population synthesis of exoplanet systems and compared them with observations. Because ESPEM works with a single planet orbiting around a single main-sequence star, we limit our study to this population of Kepler observed systems filtering out binaries, evolved stars, and multi-planets. We find in both, observations and simulations, the existence of a dearth in close-in planets orbiting around fast-rotating stars, with a dependence on the stellar spectral type (F, G, and K), which is a proxy of the mass in our sample of stars. There is a change in the edge of the dearth as a function of the spectral type (and mass). It moves towards shorter Prot as temperature (and mass) increases, making the dearth look smaller. Realistic formation hypotheses included in the model and the proper treatment of tidal and magnetic migration are enough to qualitatively explain the dearth of hot planets around fast-rotating stars and the uncovered trend with spectral type.

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arXiv2023

Temporal variation of the photometric magnetic activity for the Sun and Kepler solar-like stars

The photometric time series of solar-like stars can exhibit rotational modulation due to active regions co-rotating with the stellar surface, allowing us to constrain stellar rotation and magnetic activity. In this work we investigate the behavior, particularly the variability, of the photometric magnetic activity of Kepler solar-like stars and compare it with that of the Sun. We adopted the photometric magnetic activity proxy Sph, which was computed with a cadence of 5 x the rotation period, Prot. The average Sph was taken as the mean activity level, and the standard deviation was taken as a measure of the temporal variation of the magnetic activity over the observations. We also analyzed Sun-as-a-star photometric data from VIRGO. Sun-like stars were selected from a very narrow parameter space around the solar properties. We also looked into KIC 8006161 (HD 173701), an active metal-rich G dwarf, and we compared its magnetic activity to that of stars with similar stellar parameters. We find that the amplitude of Sph variability is strongly correlated with its mean value, independent of spectral type. An equivalent relationship has been found for ground-based observations of chromospheric activity emission and magnetic field strength, but in this work we show that photometric Kepler data also present the same behavior. While, depending on the cycle phase, the Sun is among the less active stars, we find that the solar Sph properties are consistent with those observed in Kepler Sun-like stars. KIC 8006161 is, however, among the most active of its peers, which tend to be metal-rich. This results from an underlying relationship between Prot and metallicity and supports the following interpretation of the magnetic activity of KIC 8006161: its strong activity is a consequence of its high metallicity, which affects the depth of the convection zone and, consequently, the efficiency of the dynamo.

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arXiv2023

Multi-campaign Asteroseismic Analysis of eight Solar-like pulsating stars observed by the K2 mission

The NASA K2 mission that succeeded the nominal Kepler mission observed several hundreds of thousands of stars during its operations. While most of the stars were observed in single campaigns of 80 days, some of them were targeted for more than one campaign. We perform an asteroseismic study of a sample of eight solar-like stars observed during K2 Campaigns 6 and 17. We first extract the light curves for the two campaigns using two different pipelines, EVEREST and Lightkurve. The seismic analysis is done on the combined light curve of C6 and C17 where the gap between them was removed and the two campaigns were stitched together. We determine the global seismic parameters of the solar-like oscillations using two different methods (A2Z pipeline and the apollinaire code). We perform the peak-bagging of the modes to characterize their individual frequencies. By combining the frequencies with the Gaia DR2 effective temperature and luminosity, and metallicity for five of the targets, we determine the fundamental parameters of the targets using the IACgrids based on the MESA code. While the masses and radii of our targets probe a similar parameter space compared to the Kepler solar-like stars with detailed modeling, we find that for a given mass our more evolved stars seem to be older compared to previous seismic stellar ensembles. We calculate the stellar parameters using two different grids of models, incorporating and excluding the treatment of diffusion, and find that the results agree generally within the uncertainties, except for the ages. The seismic radii and the Gaia DR2 radii present an average difference of 4% with a dispersion of 5%. Although the agreement is quite good, the seismic radii are slightly underestimated compared to Gaia DR2 for our stars, the disagreement being greater for the more evolved ones.

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arXiv2022

Deciphering stellar chorus: apollinaire, a Python 3 module for Bayesian peakbagging in helio- and asteroseismology

Since the asteroseismic revolution, availability of efficient and reliable methods to extract stellar-oscillation mode parameters has been one of the keystone of modern stellar physics. In the helio- and asteroseismology fields, these methods are usually referred as peakbagging. We introduce in this paper the apollinaire module, a new Python 3 open-source Markov Chains Monte Carlo (MCMC) framework dedicated to peakbagging. The theoretical framework necessary to understand MCMC peakbagging methods for disk-integrated helio- and asteroseismic observations are extensively described. In particular, we present the models that are used to estimate the posterior probability function in a peakbagging framework. A description of the apollinaire module is then provided. We explain how the module enables stellar background, p-mode global pattern and individual-mode parameters extraction. By taking into account instrumental specificities, stellar inclination angle, rotational splittings, and asymmetries, the module allows fitting a large variety of p-mode models suited for solar as well as stellar data analysis with different instruments. After having been validated through a Monte Carlo fitting trial on synthetic data, the module is benchmarked by comparing its outputs with results obtained with other peakbagging codes. An analysis of the PSD of 89 one-year subseries of GOLF observations is performed. Six stars are also selected from the Kepler LEGACY sample in order to demonstrate the code abilities on asteroseismic data. The parameters we extract with apollinaire are in good agreement with those presented in the literature and demonstrate the precision and reliability of the module.

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arXiv2021

K2-99 revisited: a non-inflated warm Jupiter, and a temperate giant planet on a 522-d orbit around a subgiant

We report new photometric and spectroscopic observations of the K2-99 planetary system. Asteroseismic analysis of the short-cadence light curve from K2's Campaign 17 allows us to refine the stellar properties. We find K2-99 to be significantly smaller than previously thought, with $R_{\star} = 2.55\pm0.02$ $\mathrm{R_\odot}$. The new light curve also contains four transits of K2-99b, which we use to improve our knowledge of the planetary properties. We find the planet to be a non-inflated warm Jupiter, with $R_\mathrm{b} = 1.06 \pm 0.01$ $\mathrm{R_{Jup}}$. Sixty new radial velocity measurements from HARPS, HARPS-N, and HIRES enable the determination of the orbital parameters of K2-99c, which were previously poorly constrained. We find that this outer planet has a minimum mass $M_\mathrm{c} \sin i_\mathrm{c} = 8.4\pm0.2$ $\mathrm{M_{Jup}}$, and an eccentric orbit ($e_\mathrm{c} = 0.210 \pm 0.009$) with a period of $522.2\pm1.4$ d. Upcoming TESS observations in 2022 have a good chance of detecting the transit of this planet, if the mutual inclination between the two planetary orbits is small.

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arXiv2021

No swan song for Sun-as-a-star helioseismology: performances of the Solar-SONG prototype for individual mode characterisation

The GOLF instrument on board SoHO has been in operation for almost 25 years but aging of the instrument has now strongly affected its performance, especially in the low-frequency p-mode region. At the end of the SoHO mission, the ground-based network BiSON will remain the only facility able to perform Sun-integrated helioseismic observations. Therefore, we want to assess the helioseismic performances of an échelle spectrograph like SONG. Indeed, the high precision of such an instrument and the quality of the data acquired for asteroseismic purpose calls for an evaluation of the instrument ability to perform global radial-velocity measurements of the solar disk. Data acquired during the Solar-SONG 2018 observation campaign at the Teide Observatory are used to study mid- and low-frequency p modes. A Solar-SONG time series of 30-day duration is reduced with a combination of the traditional IDL iSONG pipeline and a new Python pipeline described in this paper. A mode fitting method built around a Bayesian approach is then performed on the Solar-SONG and contemporaneous GOLF, BiSON, and HMI data. For this contemporaneous time series, Solar-SONG is able to characterise p modes at a lower frequency than BiSON and GOLF (1750μHz against 1946 and 2157 μHz respectively), while for HMI it is possible to characterise a mode at 1686 μHz. The decrease of GOLF sensitivity is then evaluated through the evolution of its low-frequency p-mode characterisation abilities over the years. [abridged]

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arXiv2021

Detections of solar-like oscillations in dwarfs and subgiants with Kepler DR25 short-cadence data

During the survey phase of the Kepler mission, several thousands of stars were observed in short cadence, allowing the detection of solar-like oscillations in more than 500 main-sequence and sub-giant stars. Later, the Kepler Science Office discovered an issue in the calibration that affected half of the short-cadence data, leading to a new data release (DR25) with improved corrections. We re-analyze the one-month time series of the Kepler survey phase to search for new solar-like oscillations. We study the seismic parameters of 99 stars (46 targets with new reported solar-like oscillations) increasing by around 8% the known sample of solar-like stars with asteroseismic analysis of the short-cadence data from Kepler. We compute the masses and radii using seismic scaling relations and find that this new sample populates the massive stars (above 1.2Ms and up to 2Ms) and subgiant phase. We determine the granulation parameters and amplitude of the modes, which agree with previously derived scaling relations. The stars studied here are slightly fainter than the previously known sample of main-sequence and subgiants with asteroseismic detections. We also study the surface rotation and magnetic activity levels of those stars. Our sample of has similar levels of activity compared to the previously known sample and in the same range as the Sun between the minimum and maximum of its activity cycle. We find that for 7 stars, a possible blend could be the reason for the previous non detection. We compare the radii obtained from the scaling relations with the Gaia ones and find that the Gaia radii are overestimated by 4.4% on average compared to the seismic radii and a decreasing trend with evolutionary stage. We re-analyze the DR25 of the main-sequence and sub-giant stars with solar-like oscillations previously detected and provide their global seismic parameters for a total of 526 stars.

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arXiv2021

Surface rotation and photometric activity for Kepler targets. II. G and F main-sequence stars, and cool subgiant stars

Dark magnetic spots crossing the stellar disc lead to quasi-periodic brightness variations, which allow us to constrain stellar surface rotation and photometric activity. The current work is the second of this series (Santos et al. 2019; Paper I), where we analyze the Kepler long-cadence data of 132,921 main-sequence F and G stars and late subgiant stars. Rotation-period candidates are obtained by combining wavelet analysis with autocorrelation function. Reliable rotation periods are then selected via a machine learning (ML) algorithm (Breton et al. 2021), automatic selection, and complementary visual inspection. The ML training data set comprises 26,521 main-sequence K and M stars from Paper I. To supplement the training, we analyze in the same way as Paper I, i.e. automatic selection and visual inspection, 34,100 additional stars. We finally provide rotation periods Prot and associated photometric activity proxy Sph for 39,592 targets. Hotter stars are generally faster rotators than cooler stars. For main-sequence G stars, Sph spans a wider range of values with increasing effective temperature, while F stars tend to have smaller Sph values in comparison with cooler stars. Overall for G stars, fast rotators are photometrically more active than slow rotators, with Sph saturating at short periods. The combined outcome of the two papers accounts for average Prot and Sph values for 55,232 main-sequence and subgiant FGKM stars (out of 159,442 targets), with 24,182 new Prot detections in comparison with McQuillan et al. (2014). The upper edge of the Prot distribution is located at longer Prot than found previously.

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arXiv2021

A calibration of the Rossby number from asteroseismology

Stellar activity and rotation are tightly related in a dynamo process. Our understanding of this mechanism is mainly limited by our capability of inferring the properties of stellar turbulent convection. In particular, the convective turnover time is a key ingredient through the estimation of the stellar Rossby number, which is the ratio of the rotation period and the convective turnover time. In this work we propose a new calibration of the $(B-V)$ color index dependence of the convective turnover time, hence of the stellar Rossby number. Our new calibration is based on the stellar structure properties inferred through the detailed modeling of solar-like pulsators using asteroseismic observables. We show the impact of this calibration in a stellar activity -- Rossby number diagram by applying it to a sample of about 40,000 stars observed with Kepler and for which photometric activity proxy $S_\mathrm{\!ph}$ and surface rotation periods are available. Additionally, we provide a new calibration of the convective turnover time as function of the $(G_\mathrm{BP}-G_\mathrm{RP})$ color index for allowing applicability in the ESA Gaia photometric passbands.

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arXiv2019

Determining surface rotation periods of solar-like stars observed by the Kepler mission using machine learning techniques

For a solar-like star, the surface rotation evolves with time, allowing in principle to estimate the age of a star from its surface rotation period. Here we are interested in measuring surface rotation periods of solar-like stars observed by the NASA Kepler mission. Different methods have been developed to track rotation signals in Kepler photometric light curves: time-frequency analysis based on wavelet techniques, autocorrelation and composite spectrum. We use the learning abilities of random forest classifiers to take decisions during two crucial steps of the analysis. First, given some input parameters, we discriminate the considered Kepler targets between rotating MS stars, non-rotating MS stars, red giants, binaries and pulsators. We then use a second classifier only on the MS rotating targets to decide the best data-analysis treatment.

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