Gravity-mode period spacings (DPi_1) of red giants probe the stellar core directly, constraining its structure, mass and evolutionary state. Their measurement requires resolving narrow, densely spaced mixed modes and has so far relied on the four-year baseline of Kepler. Recovering DPi_1 from the much shorter (~80-day) baselines typical of K2 remains largely unexplored at the ensemble scale. We develop an automated machine-learning technique to measure global asteroseismic parameters and gravity-mode period spacings for red giants from single-campaign K2 photometry. Two deep residual neural networks take the full-resolution power spectrum of an ~80-day light curve as input, without background fitting or mode identification, and return a probability distribution for each parameter, yielding a point estimate and asymmetric uncertainties. They are trained on ~8 million synthetic spectra and evaluated on held-out synthetics, on Kepler data degraded to K2-like resolution, and on K2 observations. On Kepler data at K2-like resolution, numax and Dnu are recovered for 96% and 91% of stars with robust dispersions of 3.6% and 1.2%; DPi_1 for 22%, with a dispersion of 0.9%. Applied to 18,704 K2 red giants, the inferred numax and Dnu agree with catalogue values to 5.8% and 1.9%, the additional scatter arising from known K2 artefacts. Among the 2,059 young red giants we obtain DPi_1 for 232 stars with a median fractional uncertainty of 1.3%, following the same Dnu-DPi_1 sequence as the Kepler sample although the training set carries no imprint of that relation. We show that numax, Dnu and - for a subset of young red giants - DPi_1 can be recovered from a single ~80-day K2 campaign within an automated, probabilistic machine-learning framework. This approach can also be extended to short-baseline samples from TESS and, in future, Roman and PLATO.
A Seismic Technique for Obtaining White Dwarf Fundamental Parameters from Mean Period Spacings and Astrometry
Queens College（皇后学院）；City University of New York Graduate Center（纽约市立大学研究生院）；American Museum of Natural History（美国自然历史博物馆）；Penn State Wilkes-Barre（宾夕法尼亚州立大学威尔克斯-巴里分校）
Gravity-mode period spacings as seismic diagnostic for a sample of gamma Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy
The space missions CoRoT and Kepler have provided photometric data of unprecedented quality for asteroseismology. A very rich oscillation pattern has been discovered for red giants, including mixed modes that are used to decipher the red giants interiors. They carry information on the radiative core of red giant stars and bring strong constraints on stellar evolution. Since more than 15,000 red giant light curves have been observed by Kepler, we have developed a simple and efficient method for automatically characterizing the mixed-mode pattern and measuring the asymptotic period spacing. With…
KIC8264293 is a fast rotating B-type pulsator observed by Kepler satellite. Its photometric variability is mainly due to pulsations in high-order g modes. Besides, we detected a weak H$α$ emission. Thus, the second source of variability is the fluctuation in a disk around the star. The pulsational spectrum of KIC8264293 reveals a frequency grouping and period spacing pattern. Here, we present the thorough seismic analysis of the star based on these features. Taking into account the position of the star in the HR diagram and fitting the 14 frequencies that form the period spacing we constrain t…
We report the discovery of the hottest hybrid B--type pulsator, KIC\,3240411, that exhibits the period spacing in the low--frequency range. This pattern is associated with asymptotic properties of high-order gravity (g) modes. Our seismic modelling made simultaneously with the mode identification shows that dipole axisymmetric modes best fit the observations. Evolutionary models are computed with MESA code and pulsational models with the linear non-adiabatic code employing the traditional approximation to include the effects of rotation. The problem of mode excitation is discussed. We confirm …
Pulsating binary stars are ideal targets for testing the theory of stellar structure and evolution. Fundamental parameters can be derived to high precision from binary modelling and provide crucial constraints for seismic modelling. High-order gravity modes are sensitive to the conditions near the convective core and therefore allow for a determination of parameters describing interior physics, especially the convective-core overshooting parameter. KIC\,10080943 is a binary system that contains two gravity- and pressure-mode hybrid pulsators. A detailed observational study has provided fundame…
Despite their importance in stellar evolution, little is known about magnetic fields in the interior of stars. The recent seismic detection of magnetic fields in the core of several red giant stars has given measurements of their strength and information on their topology. We revisit the puzzling case of hydrogen-shell burning giants that show deviations from the expected regular period spacing of gravity modes. These stars also tend to have a too low measured period spacing compared to their counterparts. We here show that these two features are well accounted for by strong magnetic fields in…
Seismic evidence for non-synchronization in two close sdB+dM binaries from Kepler photometry
本文报道了密近双星中两颗脉动sdB星的扩展测光。对于这两种情况，我们使用脉动频率的旋转分裂来表明sdB分量旋转得太慢而不能同步旋转。我们使用双星潮汐相互作用的理论，把限制的质量比是独立的径向速度曲线的基础上的估计。伴星的质量低于0.26 M \odot。脉动频谱显示出高泛音g模式脉动的特征。其中一颗恒星KIC 11179657有一个清晰的g模式序列，周期间隔相等，还有几个周期偏离了这一趋势。KIC 02991403显示了一个类似的序列，但有更多的模式，不适合简单的模式。
The detection of mixed modes in red giants with space missions CoRoT and Kepler has revealed their deep internal structure. These modes allow us to characterize the pattern of pressure modes (through the measurement of their asymptotic frequency separation $Δν$) and the pattern of gravity modes (through the determination of their asymptotic period spacing $ΔΠ_1$). It has been shown that red giant branch (RGB) stars regroup on a well-defined sequence in the $Δν$-$ΔΠ_1$ plane. Our first goal is to theoretically explain the features of this sequence and understand how it can be used to probe the …
Asteroseismic Modeling of 1,153 Kepler Red Giant Branch Stars: Improved Stellar Parameters with Gravity-Mode Period Spacings and Luminosity Constraints
CONTEXT. Gamma Doradus stars (hereafter gamma Dor stars) are known to exhibit gravity- and/or gravito-intertial modes that probe the inner stellar region near the convective core boundary. The non-equidistant spacing of the pulsation periods is an observational signature of the stars' evolution and current internal structure and is heavily influenced by rotation. AIMS. We aim to constrain the near-core rotation rates for a sample of gamma Dor stars, for which we have detected period spacing patterns. METHODS. We combined the asymptotic period spacing with the traditional approximation of stell…
When a star evolves into a red giant, the enhanced coupling between core-based gravity modes and envelope-based pressure modes forms mixed modes, allowing its deep interior to be probed by asteroseismology. The ability to obtain information about stellar interiors is important for constraining theories of stellar structure and evolution, for which the origin of various discrepancies between prediction and observation are still under debate. Ongoing speculation surrounds the possibility that some red giant stars may harbour strong (dynamically significant) magnetic fields in their cores, but in…
Seismic data obtained with the space photometric CoRoT and Kepler instruments have led to a unprecendently precise characterization -- in terms of masses and ages -- of a large sample of post main sequence stars (low mass subgiant and red giants). The high quality of the collected seismic data and the subsequent theoretical work for interpreting them brought up a series of issues which revealed that our knowledge of the internal properties of red giant stars remains quite limited. Two such important issues are discussed here, namely mixing beyond the convective core of helium burning red giant…
We have developed a new automated method intended to perform the simultaneous - and thus more consistent - measurement of both the seismic indices characterizing the oscillations and the parameters characterizing the granulation signature of red-giant stars. This method, called MLEUP, takes advantage of the Maximum Likelihood Estimate (MLE) algorithm combined with the parametrized representation of red giant pulsation spectra following the Universal Pattern (UP). Its performances have been tested on Monte Carlo simulations for observation conditions representative of CoRoT and Kepler data. The…
We present photometric and spectroscopic analyses of gravity (g-mode) long-period pulsating hot subdwarf B (sdB) stars. We perform a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with {\it TESS} aiming at the global comparison of the observations with the model predictions based on our stellar evolution computations coupled with the adiabatic pulsation computations. We apply standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. We calculate the mean period spacing for $l = 1$ and $l = 2…
Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
上下文从CoRoT和开普勒飞行任务中获得的大量红巨星样本的星震约束条件为对恒星星族的地震特性进行各种统计研究铺平了道路。目标。我们使用第一个详细的光谱研究19颗CoRoT红巨星（Morel et al 2014）比较理论恒星演化模型与疏散星团NGC 6633和场星的观测。方法.为了探索旋转诱导的混合和热盐不稳定性的影响，我们比较表面碳同位素比和锂的丰度与恒星演化预测。这些化学物质对红巨星分支上的额外混合很敏感。结果我们估计质量，半径和距离为每个明星使用地震的约束。我们注意到依巴谷和地震距离是不同的。然而，由于不确定性，这可能并不重要。虽然星团成员的地震距离是自洽的，但它们比依巴谷距离稍大。这是一个应该在其他地方考虑的问题。包括热盐不稳定性和旋转引起的混合，以及地震确定的质量模型可以解释红巨星目标的化学性质。然而，有了这些恒星样本，我们无法对当前的恒星模型进行严格的测试。对模型物理学的更严格的限制将需要测量核心和表面的旋转速率，以及重力主导的混合模式的周期间隔。如开普勒所提供或柏拉图所预期的那样，大量具有较长时间序列的恒星将有助于集合星震学。
With four years of nearly-continuous photometry from Kepler, we are finally in a good position to apply asteroseismology to $γ$ Doradus stars. In particular several analyses have demonstrated the possibility to detect non-uniform period spacings, which have been predicted to be directly related to rotation. In the present work, we define a new seismic diagnostic for rotation in $γ$ Doradus stars that are too rapidly rotating to present rotational splittings. Based on the non uniformity of their period spacings, we define the observable $Σ$ as the slope of the period spacing when plotted as a f…
We revisit the Tidally Excited Oscillations (TEOs) in the A-type, main-sequence, eccentric binary KOI-54, the prototype of heartbeat stars. Although the linear tidal response of the star is a series of orbital-harmonic frequencies which are not stellar eigenfrequencies, we show that the non-linearly excited non-orbital-harmonic TEOs are eigenmodes. By carefully choosing the modes which satisfy the mode-coupling selection rules, a period spacing ($ΔP$) pattern of quadrupole gravity modes ($ΔP \approx 2520-2535$ sec) can be discerned in the Fourier spectrum, with a detection significance level o…
KIC 10553698A is a hot pulsating subdwarf B (sdB) star observed by the Kepler satellite. It exhibits dipole (l = 1) and quadrupole (l = 2) gravity modes with a clear period spacing structure. The seismic properties of the KIC 10553698A provide a test of stellar evolution models, and offer a unique opportunity to determine mixing processes. We consider mixing due to convective overshooting beyond the boundary of the helium burning core. Very small overshooting ( f = 10^{-6} ) results in a progressive increase in the size of convective core. However, moderate ( f = 10^{-2} ) and small ( f = 10^{…
Owing to their simplicity and ease of application, seismic scaling relations are widely used to determine the properties of stars exhibiting solar-like oscillations, such as solar twins and red giants. So far, no seismic scaling relations for determining the ages of red giant stars have been developed. Such relations would be desirable for galactic archaeology, which uses stellar ages to map the history of the Milky Way. The ages of red giants must instead be estimated with reference to grids of theoretical stellar models, which can be computationally intensive. Here I present an exhaustive se…
Independent of stellar modelling, global seismic parameters of red giants provide unique information on the individual stellar properties as well as on stellar evolution. They allow us to measure key stellar parameters, such as the stellar mass and radius, or to derive the distance of field stars. Furthermore, oscillations with a mixed character directly probe the physical conditions in the stellar core. Here, we explain how very precise seismic indices are obtained, and how they can be used for monitoring stellar evolution and performing Galactic archeology.
The advent of asteroseismology as the golden path to precisely characterize single stars naturally led to synergies with the field of exoplanetology. Today, the precise determination of stellar masses, radii and ages for exoplanet-host stars is a driving force in the development of dedicated software and techniques to achieve this goal. However, as various approaches exist, it is clear that they all have advantages and inconveniences and that there is a trade-off between accuracy, efficiency, and robustness of the techniques. We aim to compare and discuss various modelling techniques for exopl…
Context. While rotation has a major impact on stellar structure and evolution, its effects are not well understood. Thanks to high- quality and long timebase photometric observations obtained with recent space missions, we are now able to study stellar rotation more precisely. Aims. We aim to constrain radial differential rotation profiles in gamma Doradus (gamma Dor) stars, and to develop new theoretical seismic diagnosis for such stars with rapid and potentially non-uniform rotation. Methods. We derive a new asymptotic description which accounts for the impact of weak differential near-core …
First-ascent red giants with masses below about $2\,M_\odot$ ignite helium in their degenerate core as a flash. Stellar evolution codes predict that the He flash consists of a series of consecutive subflashes. The detection of mixed modes in red giants from space missions CoRoT and Kepler has opened new opportunities to search for stars in this evolution stage. During a subflash, the He burning shell is convective, which splits the cavity of gravity modes in two. We here investigate how this additional cavity modifies the oscillation spectrum of the star. We calculate the asymptotic mode frequ…
In this study, we explore the evolution of lithium in giant stars based on data assembled from the literature on asteroseismology and Li abundances for giants. Our final sample of 187 giants consists of 44 red giant branch (RGB), 140 core He-burning (CHeB) and three giants with an unclassified evolutionary phase. For all 187 stars, the seismic parameters $ν\rm_{max}$ (frequency of maximum oscillation power) and $Δν$ (large frequency spacing) are available, while $ΔΠ\rm_{1}$ (the asymptotic gravity-mode period spacing) is available for a subset of 64. For some of the CHeB giants, mass estimates…
Red clump stars are fundamental distance indicators in astrophysics, although theoretical stellar models predict a dependence of absolute magnitudes with ages. This effect is particularly strong below 2 Gyr, but even above this limit a mild age dependence is still expected. We use seismically identified red clump stars in the Kepler field for which we have reliable distances, masses and ages from the SAGA survey to first explore this effect. By excluding red clump stars with masses larger than 1.6 Msun (corresponding to ages younger than 2 Gyr), we derive robust calibrations linking intrinsic …
Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities
In recent years the global seismic scaling relations for the frequency of maximum power and for the large frequency separation have caught the attention of various fields of astrophysics. With the exquisite photometry of \textit{Kepler}, the uncertainties in the seismic observables are small enough to estimate masses and radii with a precision of only a few per cent. Even though this seems to work quite well for main-sequence stars, there is empirical evidence, mainly from studies of eclipsing binary systems, that the seismic scaling relations overestimate the mass and radius of red giants by …
