The DAV star R808 was observed by 13 different telescopes for more than 170 hours in April 2008 on the WET run XCOV26. 25 independent pulsation frequencies were identified by this data set. We assumed 19 $m$ = 0 modes and performed an asteroseismological study on those 19 modes. We evolve grids of DAV star models by \texttt{WDEC} adopting the element diffusion scheme with pure and screened Coulomb potential effect. The core compositions are from white dwarf models evolved by \texttt{MESA}, which are thermal nuclear burning results. Our best fitting model is from the screened Coulomb potential scenario, which has parameters of log($M_{\rm He}/M_{\rm *}$) = -2.4, log($M_{\rm H}/M_{\rm *}$) = -5.2, $T_{\rm eff}$ = 11100\,K, $M_{\rm *}$ = 0.710\,$M_{\odot}$, log$g$ = 8.194, and $σ_{RMS}$ = 2.86\,s. The value of $σ_{RMS}$ is the smallest among the four existing asteroseismological work. The average period spacing is 46.299\,s for $l$ = 1 modes and 25.647\,s for $l$ = 2 modes. The other 6 observed modes can be fitted by $m$ $\neq$ 0 components of some modes for our best fitting model. Fitting the 25 observed modes, we obtain a $σ_{RMS}$ value of 2.59\,s. Considering the period spacings, we also assume, that at least in one case, we detect an $l$ = 2 trapped mode.
Asteroseismology is a powerful tool to detect the inner structure of stars. It is also widely used to study white dwarfs. In this paper, we discuss the asteroseismology work of DAV stars. The detailed period to period fitting method is fully discussed, including the reliability to detect the inner structure of DAV stars. If we assume that all observed modes of some DAV star are the $l$ = 1 ones, the errors of model fitting will be always great. If we assume that the observed modes are composed of $l$ = 1 and 2 modes, the errors of model fitting will be small. However, there will be modes ident…
We present a large bank of chemical profiles and pulsation periods suited for asteroseismological studies of ZZ Ceti (or DAV) variable stars. Our background equilibrium DA white dwarf models are the result of fully evolutionary computations that take into account the complete history of the progenitor stars from the ZAMS. The models are characterized by self-consistent chemical structures from the centre to the surface, and cover a wide range of stellar masses, effective temperatures, and H envelope thicknesses. We present dipole and quadrupole pulsation $g$-mode periods comfortably covering t…
The DAV star, HS0507+0434B, was observed by Fu et al. (2013) in 2007 and from 2009 December to 2010 January. There were a total of six triplets with nearly equal split, which were identified as $l$ = 1 modes caused by rotation. In order to fit the six $l$ = 1 modes, grids of white dwarf models are generated by WDEC. For the core composition profiles, we choose the linear fittings to carbon profile of white dwarf models from MESA, which can be considered as results of real nuclear burning process. Coupled with diffusion equilibrium H/He and He/C mixtures, we make grids of models in WDEC and do …
L19-2 is a DAV star, which has been intermittently observed from 1976 to 2013. Five independent pulsation modes of 350\,s, 192\,s, 143\,s, 118\,s, and 113\,s are identified. The five modes can be used to constrain the fitting models. The rates of period change can be obtained through the O-C method for modes of 192\,s and 113\,s, which can be used to study the evolution effect of DAV stars. Using the \texttt{WDEC} (2018 version), a large sample DAV star models are evolved. The theoretical modes are calculated and used to fit the observed modes. After fine model fittings, we obtain an optimal m…
EC14012-1446 was observed by Handler et al. in April 2004, June 2004, May 2005, and April 2007, and by Provencal et al. in 2008. We review the observations together and obtain 34 independent frequencies. According to the frequency splitting and the asymptotic period spacing law, we identify 6 $l$=1 modes, 4 $l$=2 modes, 5 $l$=3 modes, 10 $l$=1 or 2 modes. Grids of white dwarf models are generated by WDEC with H, He, C, O diffusion in a four-parameter space. The core compositions are directly from white dwarf models generated by MESA. The best-fitting model has $M_{*}$=0.710\,$M_{\odot}$, $T_{\…
We present the results of the asteroseismological analysis of two rich DAVs, G38-29 and R808, recent targets of the Whole Earth Telescope. 20 periods between 413 s and 1089 s were found in G38-29's pulsation spectrum, while R808 is an even richer pulsator, with 24 periods between 404 s and 1144 s. Traditionally, DAVs that have been analyzed asteroseismologically have had fewer than half a dozen modes. Such a large number of modes presents a special challenge to white dwarf asteroseismology, but at the same time has the potential to yield a detailed picture of the interior chemical make-up of D…
We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of fully evolutionary DA white dwarf models that have consistent chemical profiles at the core and the envelope. We found an asteroseismological model for G117-B15A that closely reproduces its observed pulsation periods. Then, we use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to impose a preliminary upper limit to the mass of the axion.
The internal structures of pulsating white dwarfs can be explored only with asteroseismology. Time series photometric observations were made for the pulsating DA white dwarf (ZZ Ceti star) WD~0246+326 during 9 nights in 2014 with a bi-site observation campaign. Eleven frequencies were detected including 1 triplet, 2 doublets, and 4 single modes, which are identified as either $l=1$ or $l=2$ modes with the complementarity of frequencies present in the literature. From the multiplets, the rotation period of \astrobj{WD~0246+326} is derived as $3.78\pm 0.11$ days. The average period spacing of th…
Using the method termed complex asteroseismology, we derive constraints on model atmospheres, in particular, on the NLTE effects. We fit simultaneously pulsational frequencies and the corresponding values of the nonadiabatic complex parameter f for the four βCephei stars: θOph, νEri, γPeg and 12 Lac. The LTE Kurucz models and the BSTAR2006 NLTE models are tested.
Over the last decade, thanks to the successful space missions launched to detect stellar pulsations, Asteroseismology has produced an extraordinary revolution in astrophysics, unveiling a wealth of results on structural properties of stars over a large part of the H-R diagram. Particularly impressive has been the development of Asteroseismology for stars showing solar-like oscillations, which are excited and intrinsically damped in stars with convective envelopes. Here I will review on the modern era of Asteroseismology with emphasis on results obtained for solar-like stars and discuss its pot…
After highlighting the principle and power of asteroseismology for stellar physics, we briefly emphasize some recent progress in this research for various types of stars. We give an overview of high-precision high duty-cycle space photometry of OB-type stars. Further, we update the overview of seismic estimates of stellar parameters of OB dwarfs, with specific emphasis on convective core overshoot. We discuss connections between pulsational, rotational, and magnetic variability of massive stars and end with future prospects for asteroseismology of evolved OB stars.
The properties of the Extreme Horizontal Branch stars are quite well understood, but much uncertainty surrounds the many paths that bring a star to this peculiar configuration. Asteroseismology of pulsating EHB stars has been performed on a number of objects, bringing us to the stage where comparisons of the inferred properties with evolutionary models becomes feasible. In this review I outline our current understanding of the formation and evolution of these stars, with emphasis on recent progress. The aim is to show how the physical parameters derived by asteroseismology can enable the discr…
Hot subdwarf stars are particularly challenging for asteroseismology due to their rapid pulsation periods, intrinsic faintness and relative rarity both in the field and in clusters. These features have ensured that the preferred method of observation up to now has been white-light photometry, and all asteroseismological solutions to date have been made by model fitting of the frequency spectrum. Several attempts have been made to perform asteroseismology using time-resolved spectroscopy on the brightest of these stars, but with modest results. A few attempts at simultaneous multi-color photome…
Asteroseismology has been proven to be a successful tool to unravel details of the internal structure for different types of stars in various stages of their main sequence and post-main sequence evolution. Recently, we found a relation between the detected pulsation properties in a sample of 34 pre-main sequence (pre-MS) delta Scuti stars and the relative phase in their pre-MS evolution. With this we are able to demonstrate that asteroseismology is similarly powerful if applied to stars in the earliest stages of evolution before the onset of hydrogen core burning.
Asteroseismology of massive stars has recently begun a revolution thanks to high-precision time series photometry from space telescopes. This has allowed accurate and robust constraints on interior physical processes, such as mixing and rotation in the near-core region of stars, to be determined across different masses and ages. In this review, I discuss recent advances in our knowledge of massive star interiors made by means of gravity-mode asteroseismology, and highlight some new observational discoveries of variability in some of the most massive stars in our universe.
I review the properties of pulsators located on the upper main sequence in the HR diagram and discuss asteroseismic inferences on the internal structure of stars of spectral type A and B. Special attention is given to the problem of uncertainties in stellar opacities in modelling.
We are entering a golden era for stellar physics driven by satellite and telescope observations of unprecedented quality and scope. New insights on stellar evolution and stellar interiors physics are being made possible by asteroseismology, the study of stars by the observation of natural, resonant oscillations. Asteroseismology is proving to be particularly significant for the study of solar-type and red-giant stars. These stars show rich spectra of solar-like oscillations, which are excited and intrinsically damped by turbulence in the outermost layers of the convective envelopes. In this re…
In this article, we show how asteroseismology and spectropolarimetry allow to probe dynamical processes in massive star interiors. First, we give a summary of the state-of-the-art. Second, we recall the MHD mechanisms that take place in massive stars. Next, we show how asteroseimology gives strong constraints on the internal mixing and transport of angular momentum while spectropolarimetry allows to unravel the role played by magnetic fields.
Many early-type stars have been measured with high angular velocities. In such stars, mode identification is difficult as the effects of fast and differential rotation are not well known. Using fundamental parameters measured by interferometry, the ESTER structure code and the TOP oscillation code, we investigate the oscillation spectrum of Rasalhague (alpha Ophiuchi), for which observations by the MOST satellite found 57 oscillations frequencies. Results do not show a clear identification of the modes and highlight the difficulties of asteroseismology for such stars with a very complex oscill…
Imagine we could do asteroseismology of large samples of OB-type stars by using just one spectrum per target. That would be great! But this is probably a crazy and stupid idea. Or maybe not. Maybe we have the possibility to open a new window to investigate stellar oscillations in massive stars that has been in front of us for many years, but has not attracted very much our attention: the characterization and understanding of the so-called macroturbulent broadening in OB-type stars.
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.
The Kepler mission, launched in March 2009, has revolutionized asteroseismology, providing detailed observations of thousands of stars. This has allowed in-depth analysis of stars ranging from compact hot subdwarfs to red giants, and including the detection of solar-like oscillations in hundreds of stars on or near the main sequence. Here I mainly consider solar-like oscillations in red giants, where Kepler observations are yielding results of a perhaps unexpected richness. In addition to giving a brief overview of the observational and numerical results for these stars, I present a simple ana…
The successful launches of the CoRoT and Kepler space missions have led to the detections of solar-like oscillations in large samples of red-giant stars. The large numbers of red giants with observed oscillations make it possible to investigate the properties of the sample as a whole: ensemble asteroseismology. In this article we summarise ensemble asteroseismology results obtained from data released by the Kepler Science Team (~150,000 field stars) as presented by Hekker et al. (2011b) and for the clusters NGC 6791, NGC 6811 and NGC 6819 (Hekker et al. 2011a) and we discuss the importance of …
To improve our comprehension of the beta Cephei stars, we set up a photometric multi-site campaign on the open cluster NGC 884 (Chi Persei). Thirteen telescopes joined the 2005-2007 campaign which resulted in almost 78000 CCD frames. We present an up-to-date status of the analysis of these data, in which several interesting oscillating stars are pointed out. We end with the future prospects.
Asteroseismology is a powerful way of determining stellar parameters and properties of stars like the Sun. However, main-sequence F-type stars exhibit short mode lifetimes relative to their oscillation frequency, resulting in overlapping radial and quadrupole modes. The goal of this paper is to use the blended modes for asteroseismology in place of the individual separable modes. We used a peak-bagging method to measure the centroids of radial-quadrupole pairs for 66 stars from the \textit{Kepler} LEGACY sample, as well as θ Cyg, HD 49933, HD 181420, and Procyon. We used the relative quadrupol…
Massive stars are important metal factories in the Universe. They have short and energetic lives, and many of them inevitably explode as a supernova and become a neutron star or black hole. In turn, the formation, evolution and explosive deaths of massive stars impact the surrounding interstellar medium and shape the evolution of their host galaxies. Yet the chemical and dynamical evolution of a massive star, including the chemical yield of the ultimate supernova and the remnant mass of the compact object, strongly depend on the interior physics of the progenitor star. We currently lack empiri…
We introduce our PhD project in which we focus on pulsating stars in eclipsing binaries. The combination of high-precision Kepler photometry with high-resolution HERMES spectroscopy allows for detailed descriptions of our sample of target stars. We report here the detection of three false positives by radial velocity measurements.
Classical Cepheids form one of the foundations of modern cosmology and the extragalactic distance scale, however, cosmic microwave background observations measure cosmological parameters and indirectly the Hubble Constant, H0, to unparalleled precision. The coming decade will provide opportunities to measure H0 to 2% uncertainty thanks to the GAIA satellite, JWST, ELTs and other telescopes using Cepheids and other standard candles. In this work, we discuss the upcoming role for variable stars and asteroseismology in calibrating the distance scale and measuring H0 and what problems exist in und…
We present the results of complex seismic modelling of the Slowly Pulsating B-type star HD74560. The star pulsates in five frequencies detected in photometric observations. For all these frequencies, we identify the mode degree, $\ell$. For two of them, found also in spectroscopic data, we are able to derived the empirical values of the complex nonadiabatic parameter $f$. We test effects of chemical composition and opacity data. Our results show that the properties of seismic models of SPB stars differ significantly from those of the more massive $β$ Cephei stars.
We present an asteroseismological study on the two high-gravity pulsating PG1159 (GW Vir or DOV) stars, PG 2131+066 and PG 1707+427, and on the pulsating [WCE] star NGC 1501. We compute adiabatic $g$-mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Msun. These models take into account the complete evolution of progenitor stars, through the thermally pulsing AGB phase, and born-again episode. We constrain the stellar mass of PG 2131+066, PG 1707+427 and NGC 1501 by comparing the observed period spacing with the asymptotic period spacing and wi…
Red-giant stars are proving to be an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions CoRoT and Kepler as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, they would provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. Gaulme et al. (2013) reported the discove…
The success of helioseismology is due to its capability of measuring p-mode oscillations in the Sun. This allows us to extract informations on the internal structure and rotation of the Sun from the surface to the core. Similarly, asteroseismology is the study of the internal structure of the stars as derived from stellar oscillations. In this review we highlight the progress in the observational asteroseismology, including some basic theoretical aspects. In particular, we discuss our contributions to asteroseismology through the study of chemically peculiar stars under the "Nainital-Cape Surv…
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.
Asteroseismology offers the possibility of probing stellar interiors and testing evolutionary and seismic models. Precise photometry and spectroscopy obtained during multi-site campaigns on young open clusters allows discovering rich samples of pulsating stars and using them in a simultaneous seismic modelling called ensemble asteroseismology. The aim of this study is to obtain the age of the open cluster NGC 6910 by means of ensemble asteroseismology of the early-type pulsating members, to derive their stellar parameters, and to classify the excited modes. We used time-series analysis, perfor…
In rapidly rotating stars Coriolis forces and centrifugal deformations modify the properties of oscillations; the Coriolis force is important for low-frequency modes, while the centrifugal deformation affects mainly p-modes. Here, we discuss properties of g- and r-mode oscillations in rotating stars. Predicted frequency spectra of high-order g-modes (and r-modes) excited in rapidly rotating stars show frequency groupings associated with azimuthal order $m$. We compare such properties with observations in rapidly rotating Be stars, and discuss what is learnt from such comparisons.
Simultaneously and coherently studying the large-scale magnetic field and the stellar pulsations of a massive star provides strong complementary diagnostics suitable for detailed stellar modelling. This hybrid method is called magneto-asteroseismology and permits the determination of the internal structure and conditions within magnetic massive pulsators, for example the effect of magnetism on non-standard mixing processes. Here, we overview this technique, its requirements, and list the currently known suitable stars to apply the method.
Context. The details of the C/O core structure in white dwarf stars has mostly remained inaccessible to the technique of asteroseismology, despite several attempts carried out in the past. Aims. We re-assess the potential of asteroseismology for probing the chemical stratification in white dwarf cores, in light of new highly efficient tools recently developed for that purpose. Methods. Using the forward modeling approach and a new parameterization for the core chemical stratification in ZZ Ceti stars, we test several situations typical of the usually limited constraints available, such as smal…
Since few decades, asteroseismology, the study of stellar oscillations, enables us to probe the interiors of stars with great precision. It allows stringent tests of stellar models and can provide accurate radii, masses and ages for individual stars. Of particular interest are the mixed modes that occur in subgiant solar-like stars since they can place very strong constraints on stellar ages. Here we measure the characteristics of the mixed modes, particularly the coupling strength, using a grid of stellar models for stars with masses between 0.9 and 1.5 M_{\odot}. We show that the coupling st…
Asteroseismology of F-type stars has been hindered by an ambiguity in identification of their oscillation modes. The regular mode pattern that makes this task trivial in cooler stars is masked by increased linewidths. The absolute mode frequencies, encapsulated in the asteroseismic variable epsilon, can help solve this impasse because the values of epsilon implied by the two possible mode identifications are distinct. We find that the correct epsilon can be deduced from the effective temperature and the linewidths and we apply these methods to a sample of solar-like oscillators observed with K…
Although playing a key role in the understanding of the supernova phenomenon, the evolution of massive stars still suffers from uncertainties in their structure, even during their "quiet" main sequence phase and later on during their subgiant and helium burning phases. What is the extent of the mixed central region? In the local mixing length theory (LMLT) frame, are there structural differences using Schwarzschild or Ledoux convection criterion? Where are located the convective zone boundaries? Are there intermediate convection zones during MS and post-MS phase, and what is their extent and l…
This is a progress report on the ongoing project dealing with ensemble asteroseismology of B-type stars in young open clusters. The project is aimed at searches for B-type pulsating stars in open clusters, determination of atmospheric parameters for some members and seismic modeling of B-type pulsators. Some results for NGC 457, IC 1805, IC 4996, NGC 6910 and alpha Per open clusters are presented. For the last cluster, BRITE data for five members were used.
We investigate the internal rotation profile of the GW Vir (PG1159-type) star PG 0122+200 by employing an asteroseismological model that closely reproduces the observed periods of this star. We adopt a forward approach and two inversion methods based on the rotational splitting of the pulsation frequencies to explore the properties of the rotation of PG 0122+200. We found evidence for differential rotation in this star.
Most of low- and intermediate-mass stars that populate the Universe will end their lives as white dwarf stars. These ancient stellar remnants have encrypted inside a precious record of the evolutionary history of the progenitor stars, providing a wealth of information about the evolution of stars, star formation, and the age of a variety of stellar populations, such as our Galaxy and open and globular clusters. While some information like surface chemical composition, temperature and gravity of white dwarfs can be inferred from spectroscopy, the internal structure of these compact stars can be…
Yearslong time series of high-precision brightness measurements have been assembled for thousands of stars with telescopes operating in space. Such data have allowed astronomers to measure the physics of stellar interiors via nonradial oscillations, opening a new avenue to study the stars in the Universe. Asteroseismology, the interpretation of the characteristics of oscillation modes in terms of the physical properties of the stellar interior, brought entirely new insights in how stars rotate and how they build up their chemistry throughout their evolution. Data-driven space asteroseismology …
Red-giant stars are emerging as one of the most interesting areas of space asteroseismology. Even a relatively basic analysis leads to the determination of the global parameters of the stars, such as their mass and radius, and the very extensive space-based data now available for a large number of stars allow detailed investigation of the deep interiors of red giants, including distinguishing between stars that do and do not have helium fusion in the core, on the basis of periods of gravity waves partially trapped in the core. Here I review the theoretical background for these new developments…
Observations from the Kepler satellite were recently published for three bright G-type stars, which were monitored during the first 33.5d of science operations. One of these stars, KIC 11026764, exhibits a characteristic pattern of oscillation frequencies suggesting that the star has evolved significantly. We have derived initial estimates of the properties of KIC 11026764 from the oscillation frequencies observed by Kepler, combined with ground-based spectroscopic data. We present preliminary results from detailed modeling of this star, employing a variety of independent codes and analyses th…
Stars do not simply pop up on the main sequence. Before the stars arrive on the zero-age main sequence, they form in the collapses of molecular clouds, gain matter through accretion processes, and compress their cores until hydrogen can burn in full equilibrium. Although this evolutionary phase lasts a relatively short time, it is the imprint of these important physical processes that is often ignored by simplified assumptions. While asteroseismology offers a great tool to investigate these physical processes, studying pre-MS oscillations in turn has the potential to further advance the field.…
We provide a status report on the determination of stellar ages from asteroseismology for stars of various masses and evolutionary stages. The ability to deduce the ages of stars with a relative precision of typically 10 to 20% is a unique opportunity for stellar evolution and also of great value for both galactic and exoplanet studies. Further, a major uncalibrated ingredient that makes stellar evolution models uncertain, is the stellar interior rotation frequency $Ω(r)$ and its evolution during stellar life. We summarize the recent achievements in the derivation of $Ω(r)$ for different types…
At present, a large number of pulsating white dwarf (WD) stars is being discovered either from Earth-based surveys such as the Sloan Digital Sky Survey, or through observations from space (e.g., the Kepler mission). The asteroseismological techniques allow us to infer details of internal chemical stratification, the total mass, and even the stellar rotation profile. In this paper, we first describe the basic properties of WD stars and their pulsations, as well as the different sub-types of these variables known so far. Subsequently, we describe some recent findings about pulsating low-mass WDs…
The results of our six year systematic observational survey on candidate eclipsing binaries with a delta Sct component are briefly presented. A new catalogue for this kind of systems as well as the properties of their delta Sct members are also presented. The comparison between the components-pulsators and the single delta Sct stars shows that both the evolution and the pulsating properties differ significantly. Finally, we introduce the new era of studying stellar pulsations using high accuracy data from Kepler mission and emphasizing the great opportunities that are now opened for a deep kno…
Scientific research is a continuous process, and the speed of future progress can be estimated by the pace of finding explanations for previous research questions. In this observers based view of stellar pulsation and asteroseismology, we start with the earliest observations of variable stars and the techniques used to observe them. The earliest variable stars were large amplitude, radial pulsators but were followed by other classes of pulsating stars. As the field matured, we outline some cornerstones of research into pulsating star research with an emphasis on changes in observational techni…
Our knowledge of the dynamics of stars has undergone a revolution thanks to the simultaneous large amount of high-quality photometric observations collected by space-based asteroseismology and ground-based high-precision spectropolarimetry. They allowed us to probe the internal rotation of stars and their surface magnetism in the whole Hertzsprung-Russell diagram. However, new methods should still be developed to probe the deep magnetic fields in those stars. Our goal is to provide seismic diagnoses that allow us to sound the internal magnetism of stars. Here, we focus on asymptotic low-freque…
Almost 100 years ago Sir Arthur Eddington noted that the interiors of stars were inaccessible to observations. The advent of helio- and asteroseismology has completely changed this assessment. Helioseismology has provided very detailed information about the interior structure and dynamics of the Sun, highlighting remaining issues in our understanding of the solar interior. In the last decade extensive observations of stellar oscillations, in particular from space photometry, have provided very detailed information about the global and internal properties of stars. Here I provide an overview of…
Asteroseismology is the determination of the interior structures of stars by using their oscillations as seismic waves. Simple explanations of the astrophysical background and some basic theoretical considerations needed in this rapidly evolving field are followed by introductions to the most important concepts and methods on the basis of example. Previous and potential applications of asteroseismology are reviewed and future trends are attempted to be foreseen.
Internal stellar magnetic fields are inaccessible to direct observations and little is known about their amplitude, geometry and evolution. We demonstrate that strong magnetic fields in the cores of red giant stars can be identified with asteroseismology. The fields can manifest themselves via depressed dipole stellar oscillation modes, which arises from a magnetic greenhouse effect that scatters and traps oscillation mode energy within the core of the star. The Kepler satellite has observed a few dozen red giants with depressed dipole modes which we interpret as stars with strongly magnetized…
Asteroseismology is a unique tool to explore the internal structure of stars through both observational and theoretical research. The internal structure of pulsating hydrogen shell white dwarfs (ZZ Ceti stars) detected by asteroseismology is regarded as the representative of all DA white dwarfs. Observations for KUV~08368+4026, which locates in the middle of the ZZ Ceti instability strip, have been carried out in 1999 and from 2009 to 2012 with either single-site runs or multisite campaigns. Time-series photometric data of about 300 hours were collected in total. Through data reduction and ana…
In massive stars, rotation and oscillatory waves can have a tight interplay. In order to assess the importance of additional angular momentum transport mechanisms other than rotation, we compare the asteroseismic properties of a uniformly rotating model and a differentially rotating one. Accordingly, we employ the observed period spacing of 36 dipole g-modes in the Kepler $\sim3.2$ M$_\odot$ target KIC 7760680 to discriminate between these two models. We favor the uniformly rotating model, which fully satisfies all observational constraints. Therefore, efficient angular momentum transport by a…
