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Journal ArticleDOI

Asteroseismic modelling of the solar-type subgiant star $\beta$ Hydri

TL;DR: In this article, the authors search for the best model of the solar-type star \beta Hyi, based on up-to-date non-seismic and seismic data.
Abstract: Comparing models and data of pulsating stars is a powerful way to understand the stellar structure better.\beta Hyi is an evolved solar-type pulsator with mixed modes in its frequency spectrum, making it very interesting for asteroseismic studies.The goal of this work is to search for the best model of the solar-type star \beta Hyi, based on up-to-date non-seismic and seismic data.We present a revised list of frequencies for 33 modes, which we produced by analysing the power spectrum of the published observations again using a new weighting scheme that minimises the daily sidelobes.We ran several grids of evolutionary models with different input parameters and different physics, using the stellar evolutionary code ASTEC.For the models that are inside the observed error box of \beta Hyi, we computed their frequencies with the pulsation code ADIPLS.We used two approaches to find the model that oscillates with the frequencies that are closest to the observed frequencies of \beta Hyi:(i)we assume that the best model is the one that reproduces the star's interior based on the radial oscillation frequencies alone, to which we have applied the correction for the near-surface effects;(ii)we assume that the best model is the one that produces the lowest value of the chi-square (\chi2), i.e. that minimises the difference between the observed frequencies of all available modes and the model predictions, after all model frequencies are corrected for near-surface effects.We show that after applying this correction to the frequencies of the best models, we can reproduce the observed modes well, including the mixed modes.The model that gives the lowest value of the \chi2 is a post-main-sequence model with a mass of 1.04 MSun and a metallicity slightly lower than that of the Sun.Our results underscore the importance of having individual frequencies to constrain the properties of the stellar model.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the scaling relation between the large frequency separation, {Delta}{nu}, and mean stellar density is investigated, and model evolutionary tracks for several asteroseismic diagrams are presented.
Abstract: With the success of the Kepler and CoRoT missions, the number of stars with detected solar-like oscillations has increased by several orders of magnitude; for the first time we are able to perform large-scale ensemble asteroseismology of these stars. In preparation for this golden age of asteroseismology we have computed expected values of various asteroseismic observables from models of varying mass and metallicity. The relationships between these asteroseismic observables, such as the separations between mode frequencies, are able to significantly constrain estimates of the ages and masses of these stars. We investigate the scaling relation between the large frequency separation, {Delta}{nu}, and mean stellar density. Furthermore we present model evolutionary tracks for several asteroseismic diagrams. We have extended the so-called C-D diagram beyond the main sequence to the subgiants and the red giant branch. We also consider another asteroseismic diagram, the {epsilon} diagram, which is more sensitive to variations in stellar properties at the subgiant stages and can aid in determining the correct mode identification. The recent discovery of gravity-mode period spacings in red giants forms the basis for a third asteroseismic diagram. We compare the evolutionary model tracks in these asteroseismic diagrams with results from pre-Kepler studies of solar-likemore » oscillations and early results from Kepler.« less

267 citations


Cites methods from "Asteroseismic modelling of the sola..."

  • ...Masses for β Hyi and η Boo have been estimated from models by Brandão et al. (2011) and Di Mauro et al. (2003), respectively....

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Journal ArticleDOI
TL;DR: In this article, the authors presented an analysis of three months of nearly uninterrupted photometry of 16 Cyg A and B from the Kepler space telescope, and derived the properties of each star independently using the Asteroseismic Modeling Portal, fitting the individual oscillation frequencies and other observational constraints simultaneously.
Abstract: The evolved solar-type stars 16 Cyg A and B have long been studied as solar analogs, yielding a glimpse into the future of our own Sun. The orbital period of the binary system is too long to provide meaningful dynamical constraints on the stellar properties, but asteroseismology can help because the stars are among the brightest in the Kepler field. We present an analysis of three months of nearly uninterrupted photometry of 16 Cyg A and B from the Kepler space telescope. We extract a total of 46 and 41 oscillation frequencies for the two components, respectively, including a clear detection of octupole (l = 3) modes in both stars. We derive the properties of each star independently using the Asteroseismic Modeling Portal, fitting the individual oscillation frequencies and other observational constraints simultaneously. We evaluate the systematic uncertainties from an ensemble of results generated by a variety of stellar evolution codes and fitting methods. The optimal models derived by fitting each component individually yield a common age (t = 6.8 ± 0.4 Gyr) and initial composition (Z i = 0.024 ± 0.002, Y i = 0.25 ± 0.01) within the uncertainties, as expected for the components of a binary system, bolstering our confidence in the reliability of asteroseismic techniques. The longer data sets that will ultimately become available will allow future studies of differential rotation, convection zone depths, and long-term changes due to stellar activity cycles.

195 citations


Cites background from "Asteroseismic modelling of the sola..."

  • ...…Sco (Bazot et al. 2011) provide some context for the Sun observed as a star, while solar analogs like κ1 Cet, β Hyi, and α Cen A & B (Walker et al. 2007; Brandão et al. 2011; Bedding et al. 2004; Kjeldsen et al. 2005) help calibrate stellar evolution for stars that are younger, older, and more or…...

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Journal ArticleDOI
TL;DR: In this article, the authors considered different sets of observational constraints (Hertzsprung-Russell data, metallicity, various sets of seismic constraints) and determined the age, mass and properties of HD 52265 inferred from stellar models, and quantified the impact of the model input physics and free parameters.
Abstract: Context. In the context of the space missions CoRoT, Kepler, Gaia, TESS, and PLATO, precise and accurate stellar ages, masses, and radii are of paramount importance. For instance, they are crucial for constraining scenarii of planetary formation and evolution. Aims. We aim at quantifying how detailed stellar modelling can improve the accuracy and precision on age and mass of individual stars. To that end, we adopt a multifaceted approach where we carefully examine how the number of observational constraints as well as the uncertainties on observations and on model input physics affect the results of age-dating and weighing. Methods. We modelled in detail the exoplanet host-star HD 52265, a main-sequence, solar-like oscillator that CoRoT observed for four months. We considered different sets of observational constraints (Hertzsprung-Russell data, metallicity, various sets of seismic constraints). For each case, we determined the age, mass, and properties of HD 52265 inferred from stellar models, and we quantified the impact of the model input physics and free parameters. We also compared model ages with ages derived by empirical methods or Hertzsprung-Russell diagram inversion. Results. For our case study HD 52265, our seismic analysis provides an age A = 2.10−2.54 Gyr, a mass M = 1.14−1.32 M� ,a nd a radius R = 1.30−1.34 R� , which corresponds to age, mass, and radius uncertainties of ∼10, ∼7, and ∼1.5 per cent, respectively. These uncertainties account for observational errors and current state-of-the-art stellar model uncertainties. Our seismic study also provides constraints on surface convection properties through the mixing-length, which we find to be 12−15 per cent lower than the solar value. On the other hand, because of helium-mass degeneracy, the initial helium abundance is determined modulo the mass value. Finally, we evaluate the seismic mass of the exoplanet to be Mp sini = 1.17−1.26 MJupiter, much more precise than what can be derived by Hertzsprung-Russell diagram inversion. Conclusions. We demonstrate that asteroseismology allows us to substantially improve the age accuracy that can be achieved with other methods. We emphasize that the knowledge of the mean properties of stellar oscillations – such as the large frequency separation – is not enough to derive accurate ages. We need precise individual frequencies to narrow the age scatter that is a result of the model input physics uncertainties. Further progress is required to better constrain the physics at work in stars and the stars helium content. Our results emphasize the importance of precise classical stellar parameters and oscillation frequencies such as will be obtained by the Gaia and PLATO missions.

178 citations

Journal ArticleDOI
TL;DR: In this article, the authors used previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type Kepler targets, and found that fitting the individual frequencies typically doubled the precision of the asterosityismic radius, mass, and age compared to grid-based modeling of the global oscillation properties, and improved the radius and mass by about a factor of three over empirical scaling relations.
Abstract: Recently the number of main-sequence and subgiant stars exhibiting solar-like oscillations that are resolved into individual mode frequencies has increased dramatically. While only a few such data sets were available for detailed modeling just a decade ago, the Kepler mission has produced suitable observations for hundreds of new targets. This rapid expansion in observational capacity has been accompanied by a shift in analysis and modeling strategies to yield uniform sets of derived stellar properties more quickly and easily. We use previously published asteroseismic and spectroscopic data sets to provide a uniform analysis of 42 solar-type Kepler targets from the Asteroseismic Modeling Portal. We find that fitting the individual frequencies typically doubles the precision of the asteroseismic radius, mass, and age compared to grid-based modeling of the global oscillation properties, and improves the precision of the radius and mass by about a factor of three over empirical scaling relations. We demonstrate the utility of the derived properties with several applications.

174 citations

Journal ArticleDOI
TL;DR: In this paper, the first detection of a convective core in a Kepler field main-sequence star was made, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists.
Abstract: Using asteroseismic data and stellar evolution models we make the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence life time is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

156 citations

References
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Journal ArticleDOI
TL;DR: In this article, a new reduction of the Hipparcos data was published, which claimed accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalog.
Abstract: Context. A new reduction of the astrometric data as produced by the Hipparcos mission has been published, claiming accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalog ue. Aims. The new Hipparcos astrometric catalogue is checked for the quality of the data and the consistency of the formal errors as well as the possible presence of error correlations. The differences with the earlier publication are explained. Methods. The internal errors are followed through the reduction proc ess, and the external errors are investigated on the basis of a comparison with radio observations of a small selection of stars, and the distribution of negative parallaxes. Error co rrelation levels are investigated and the reduction by more than a factor 10 as obtained in the new catalogue is explained. Results. The formal errors on the parallaxes for the new catalogue are confirmed. The presence of a small amount of additional noise , though unlikely, cannot be ruled out. Conclusions. The new reduction of the Hipparcos astrometric data provides an improvement by a factor 2.2 in the total weight compared to the catalogue published in 1997, and provides much improved data for a wide range of studies on stellar luminosities and local galactic kinematics.

4,203 citations


"Asteroseismic modelling of the sola..." refers background or methods in this paper

  • ...The radius was obtained by combining the interferometric angular diameter of the star,θ = 2.257±0.019 mas (North et al. 2007), with the revisedHipparcosparallax, πp = 134.07± 0.11 mas (van Leeuwen 2007)....

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  • ...To compute the luminosity of β Hyi we used the same value for the bolometric flux as North et al. (2007),Fbol = (2.019± 0.05) × 109 W m−2 (Blackwell & Lynas-Gray 1998, the uncertainty onFbol is from di Benedetto 1998) and the revisedHipparcos parallax (van Leeuwen 2007)....

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  • ...Also, the Hipparcosparallax ofβ Hyi has been improved from an uncertainty of 0.4% (Perryman & ESA 1997) to 0.08% (van Leeuwen 2007)....

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01 Jul 2009

3,896 citations

Journal ArticleDOI
TL;DR: The updated OPAL Rosseland mean opacities for Population I stars have been presented in this paper, where the main opacity changes are increases of as much as 20% for population I stars due to the explicit inclusion of 19 metals (compared to 12 metals in the earlier calculations).
Abstract: The reexamination of astrophysical opacities has eliminated gross discrepancies between a variety of observations and theoretical calculations; thus allowing for more detailed tests of stellar models. A number of such studies indicate that model results are sensitive to modest changes in the opacity. Consequently, it is desirable to update available opacity databases with recent improvements in physics, refinements of element abundance, and other such factors affecting the results. Updated OPAL Rosseland mean opacities are presented. The new results have incorporated improvements in the physics and numerical procedures as well as corrections. The main opacity changes are increases of as much as 20{percent} for Population I stars due to the explicit inclusion of 19 metals (compared to 12 metals in the earlier calculations) with the other modifications introducing opacity changes smaller than 10{percent}. In addition, the temperature and density range covered by the updated opacity tables has been extended. As before, the tables allow accurate interpolation in density and temperature as well as hydrogen, helium, carbon, oxygen, and metal mass fractions. Although a specific metal composition is emphasized, opacity tables for different metal distributions can be made readily available. The updated opacities are compared to other work. {copyright} {ital 1996 Themore » American Astronomical Society.}« less

2,869 citations


"Asteroseismic modelling of the sola..." refers methods in this paper

  • ...In the computation we used the OPAL 2005 equation of state tables (see Rogers & Nayfonov 2002), OPAL opacities (Iglesias & Rogers 1996) complemented by low-temperature opacities from Ferguson et al. (2005), the solar mixture from Grevesse & Noels (1993), and the NACRE nuclear reaction rates (Angulo…...

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Journal ArticleDOI
TL;DR: In this paper, the corresponding Maxwellian-averaged thermonuclear reaction rates of relevance in astrophysical plasmas at temperatures in the range from 10(6) K to 10(10) K were calculated.

1,874 citations


"Asteroseismic modelling of the sola..." refers methods in this paper

  • ...…we used the OPAL 2005 equation of state tables (see Rogers & Nayfonov 2002), OPAL opacities (Iglesias & Rogers 1996) complemented by low-temperature opacities from Ferguson et al. (2005), the solar mixture from Grevesse & Noels (1993), and the NACRE nuclear reaction rates (Angulo et al. 1999)....

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Journal ArticleDOI
TL;DR: In this paper, the authors presented a new table for low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson, which includes more grain species and updated optical constants.
Abstract: Previous computations of low-temperature Rosseland and Planck mean opacities from Alexander & Ferguson areupdatedandexpanded.Thenewcomputationsincludeamorecompleteequationofstate(EOS)withmoregrain species and updated optical constants. Grains are now explicitly included in thermal equilibrium in the EOS calculation, which allows for a much wider range of grain compositions to be accurately included than was previously the case. The inclusion of high-temperature condensates such as Al2O3 and CaTiO3 significantly affects the total opacityoveranarrowrangeoftemperaturesbeforetheappearanceofthefirstsilicategrains.Thenewopacitytables are tabulated for temperatures ranging from 30,000 to 500 K with gas densities from 10 � 4 to 10 � 19 gc m � 3 .C omparisons with previous Rosseland mean opacity calculations are discussed. At high temperatures, the agreement with OPAL and Opacity Project is quite good. Comparisons at lower temperatures are more divergent as a result of differences in molecular and grain physics included in different calculations. The computation of Planck mean opacities performed with the opacity sampling method is shown to require a very large number of opacity sampling wavelength points; previously published results obtained with fewer wavelength points are shown to be significantly in error. Methods for requesting or obtaining the new tables are provided. Subject heading gs: atomic data — equation of state — methods: numerical — molecular data

1,273 citations