Chemical turbulent mixing induced by rotation can affect the internal distribution of mu near the energy-generating core of main-sequence stars, having an effect on the evolutionary tracks similar to that of overshooting. However, this mixing also leads to a smoother chemical composition profile near the edge of the convective core, which is reflected in the behaviour of the buoyancy frequency and, therefore, in the frequencies of gravity modes. We show that for rotational velocities typical of main-sequence B-type pulsating stars, the signature of a rotationally induced mixing significantly perturbs the spectrum of gravity modes and mixed modes, and can be distinguished from that of overshooting. The cases of high-order gravity modes in Slowly Pulsating B stars and of low-order g modes and mixed modes in beta Cephei stars are discussed.
Modeling properly the interface between convective cores and radiative interiors is one the most challenging and important open questions in modern stellar physics. The rapid development of asteroseismology, with the advent of space missions partly dedicated to this discipline, has provided new constraints to progress on this issue. We here give an overview of the information that can be obtained from pressure modes, gravity modes and mixed modes. We also review some of the most recent constraints obtained from space-based asteroseismology on the nature and the amount of mixing beyond convecti…
The size of convective cores remains uncertain, despite its substantial influence on stellar evolution, and thus on stellar ages. The seismic modeling of young subgiants can be used to obtain indirect constraints on the core structure during main sequence, thanks to the high probing potential of mixed modes. We selected the young subgiant KIC10273246, observed by Kepler, based on its mixed-mode properties. We thoroughly modeled this star, with the aim of placing constraints on the size of its main sequence convective core. We first extracted the parameters of the oscillation modes of the star …
Seismic modeling of the Slowly Pulsating B-type star HD182255 yields strong constraints on the radial orders of the two dominant modes. For these frequencies, we derive also the empirical values of the complex nonadiabatic parameter $f$. These two seismic tools, i.e., pulsational frequencies and the associated values of $f$, allow to test available opacity data, chemical composition and overshooting efficiency.
After a brief introduction into the asteroseismic modelling of stars, we provide a compilation of the current seismic estimates of the core overshooting parameter and of the rotational frequency of single and binary massive stars. These important stellar parameters have meanwhile become available for eleven OB-type stars, among which three spectroscopic pulsating binaries and one magnetic pulsator. We highlight the potential of ongoing and future analyses of eclipsing binary pulsators as essential laboraties to test stellar structure and evolution models of single and binary stars.
CHARA Interferometry and TESS Asteroseismology of the Core-Helium Burning Red Giant $κ$ Cyg
Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天文研究所）；Sydney Informatics Hub, Core Research Facilities, University of Sydney（悉尼大学核心研究设施悉尼信息学中心）
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 $γ$ Doradus stars. Here, our goal is to perform the parameter estimation from modelling of individual periods measure…
Saio et al. (2006) have shown that the presence of an intermediate convective zone (ICZ) in post-main sequence models could prevent the propagation of g-modes in the radiative interior and hence avoid the corresponding radiative damping. The development of such a convective region highly depends on the structure of the star in the mu-gradient region surrounding the convective core during the main sequence phase. In particular,the development of this ICZ depends on physical processes such as mass loss, overshooting (Chiosi & Maeder 1986, Chiosi et al. 1992, see also Godart et al., these proceed…
Asteroseismology of non-radial pulsations in Hot B Subdwarfs (sdB stars) offers a unique view into the interior of core-helium-burning stars. Ground-based and space-borne high precision light curves allow for the analysis of pressure and gravity mode pulsations to probe the structure of sdB stars deep into the convective core. As such asteroseismological analysis provides an excellent opportunity to test our understanding of stellar evolution. In light of the newest constraints from asteroseismology of sdB and red clump stars, standard approaches of convective mixing in 1D stellar evolution mo…
Recent investigations have shown that the extended main-sequence turnoffs (eMSTOs) are a common feature of intermediate-age star clusters in the Magellanic Clouds. The eMSTOs are also found in the color-magnitude diagram (CMD) of young-age star clusters. The origin of the eMSTOs is still an open question. Moreover, asteroseismology shows that the value of the overshooting parameter $δ_{\rm ov}$ of the convective core is not fixed for the stars with an approximatelly equal mass. Thus the MSTO of star clusters may be affected by the overshooting of the convective core (OVCC). We calculated the e…
A set of long and nearly continuous observations of alpha Centauri A should allow us to derive an accurate set of asteroseismic constraints to compare to models, and make inferences on the internal structure of our closest stellar neighbour. We intend to improve the knowledge of the interior of alpha Centauri A by determining the nature of its core. We combined the radial velocity time series obtained in May 2001 with three spectrographs in Chile and Australia: CORALIE, UVES, and UCLES. The resulting combined time series has a length of 12.45 days and contains over 10,000 data points and allow…
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^{…
We construct seismic models of the four double-mode radial $δ$ Scuti stars adopting opacities from three databases: OPAL, OP and OPLIB. The aim is to find the models that fit the observed frequencies of the two radial modes and have the effective temperature and luminosity consistent with the observed values. Using the Bayesian analysis based on Monte Carlo simulations, we obtain that only the OPAL seismic models are caught within the observed error box in the HR diagram. Seismic models computed with the OP and OPLIB data are much cooler and less luminous. By including the relative amplitude o…
ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up during the core helium burning and thermally pulsing Asymptotic Giant Branch phases. Through the interpretation of their pulsation periods by means of asteroseismology, details about their origin and evolution can be inferred. The whole pulsation spectrum exhibited by ZZ Ceti stars strongly depends on the inner chemical structure. At present, there are several processes affecting the chemical profiles that are still not accurately determined. We present a study of the impact of the current uncertainties of the white dw…
Frequencies of acoustic and mixed modes in red giant stars are now determined with high precision thanks to the long continuous observations provided by the NASA Kepler mission. Here we consider the eigenfrequencies of nineteen low-luminosity red giant stars selected by Corsaro et al. (2015) for a detailed peak-bagging analysis. Our objective is to obtain stellar parameters by using individual mode frequencies and spectroscopic information. We use a forward modelling technique based on a minimization procedure combining the frequencies of the p modes, the period spacing of the dipolar modes, a…
Hybrid $δ$ Scuti-$γ$ Doradus pulsating stars show acoustic ($p$) oscillation modes typical of $δ$ Scuti variable stars, and gravity ($g$) pulsation modes characteristic of $γ$ Doradus variable stars simultaneously excited. Observations from space missions like MOST, CoRoT, and \emph{Kepler} have revealed a large number of hybrid $δ$ Scuti-$γ$ Doradus pulsators, thus paving the way for a exciting new channel for asteroseismic studies. We perform a detailed asteroseismological modeling of five hybrid $δ$ Scuti-$γ$ Doradus stars. We employ a grid-based modeling approach to sound the internal stru…
The overall evolution of low-mass stars is heavily influenced by the processes occurring in the stellar interior. In particular, mixing processes in convectively unstable zones and overshooting regions affect the resulting observables and main sequence lifetime. We study the effects of different convective boundary definitions and mixing prescriptions in convective cores of low-mass stars, to discriminate the existence, size, and evolutionary stage of the central mixed zone by means of asteroseismology. We implemented the Ledoux criterion for convection in our stellar evolution code, together …
Recent asteroseismic observations by the $\it Kepler$ space mission have revealed the dip fine structure in the period-spacing versus period diagram of rapidly rotating $γ$ Doradus stars. Following the successful reproduction of the dip structure by numerical calculations in previous studies, we present in this paper the physical mechanism of how the dip is formed as a result of the interaction between the gravito-inertial waves in the radiative envelope and the pure inertial waves in the convective core. We analytically describe the wave solutions in both of the radiative envelope and the con…
We aim at studying the theoretical properties of the regular spacings found in the oscillation spectra of delta Scuti stars. We performed a multi-variable analysis covering a wide range of stellar structure and seismic properties and model parameters representative of intermediate-mass, main sequence stars. The work-flow is entirely done using a new Virtual Observatory tool: TOUCAN (the VO gateway for asteroseismic models), which is presented in this paper. A linear relation between the large separation and the mean density is predicted to be found in the low frequency frequency domain (i.e. r…
Our poor understanding of the boundaries of convective cores generates large uncertainties on the extent of these cores and thus on stellar ages. Our aim is to use asteroseismology to consistently measure the extent of convective cores in a sample of main-sequence stars whose masses lie around the mass-limit for having a convective core. We first test and validate a seismic diagnostic that was proposed to probe in a model-dependent way the extent of convective cores using the so-called $r_{010}$ ratios, which are built with $l=0$ and $l=1$ modes. We apply this procedure to 24 low-mass stars ch…
SPB star HD 50230, in fact a hybrid B-type pulsator, has been observed by CoRoT least 137 days. A nearly equidistant period spacing pattern are found among 8 modes which are extracted from the oscillation spectrum with more than 500 frequencies. However, it is thought to be most likely accidental by Szewczuk et al. (2014). In the present work, we analyze the 8 modes in depth with the $χ^2$-matching method. Based on the best fitting model (model MA), we find that they can be well explained as a sequences of consecutive dipolar $(l,~m)=(1,~0)$. The period discrepancies between observations and t…
You're Gonna Need a Bigger Core: Calibrating Massive Star Models against Galactic OB-type Stars
Max Planck Institute for Astrophysics（马克斯·普朗克天体物理研究所）；European Southern Observatory（欧洲南方天文台）；Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉古纳大学）
In the context of the determination of stellar properties using asteroseismology, we study the influence of rotation and convective-core overshooting on the properties of red-giant stars. We used models in order to investigate the effects of these mechanisms on the asymptotic period spacing of gravity modes ($ΔΠ_1$) of red-giant stars that ignite He burning in degenerate conditions (M$\lesssim$2.0 M$_{\odot}$). We also compare the predictions of these models with Kepler observations. For a given $Δν$, $ΔΠ_1$ depends not only on the stellar mass, but also on mixing processes that can affect the…
The goal of stellar evolution theory is to predict the structure of stars throughout their lifetimes. Usually, these predictions can be assessed only indirectly, for example by comparing predicted and observed effective temperatures and luminosities. Thanks now to asteroseismology, which can reveal the internal structure of stars, it becomes possible to compare the predictions from stellar evolution theory to actual stellar structures. In this work, we present an inverse analysis of the oscillation data from the solar-type star KIC 6225718, which was observed by the \emph{Kepler} space observa…
Massive stars are important for the chemical enrichment of the universe. Since internal mixing processes influence their lives, it is very important to place constraints on the corresponding physical parameters, such as core overshooting and the internal rotation profile, so as to calibrate their stellar structure and evolution models. Although asteroseismology has been shown to be able to deliver the most precise constraints so far, the number of detailed seismic studies delivering quantitative results is limited. Our goal is to extend this limited sample with an in-depth case study and provi…
