Asteroseismic modelling of the metal-poor star<i>τ</i>Ceti

Tang, Yanke; Gai, Ning

doi:10.1051/0004-6361/201014886

Cited by 15 publications

(13 citation statements)

References 63 publications

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“…This relation has been extensively used during the last 10 years (e.g. Tang and Gai 2011;Mathur et al 2012). Of course, it assumes that the mode inertia varies slowly with frequency, that is the case for main-sequence stars.…”

Section: Modelling a Star And Surface Effectsmentioning

confidence: 99%

Asteroseismology of solar-type stars

García

Ballot

2019

Living Rev Sol Phys

154

100

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Until the last few decades, investigations of stellar interiors had been restricted to theoretical studies only constrained by observations of their global properties and external characteristics. However, in the last 30 years the field has been revolutionized by the ability to perform seismic investigations of stellar interiors. This revolution begun with the Sun, where helioseismology has been yielding information competing with what can be inferred about the Earth’s interior from geoseismology. The last two decades have witnessed the advent of asteroseismology of solar-like stars, thanks to a dramatic development of new observing facilities providing the first reliable results on the interiors of distant stars. The coming years will see a huge development in this field. In this review we focus on solar-type stars, i.e., cool main-sequence stars where oscillations are stochastically excited by surface convection. After a short introduction and a historical overview of the discipline, we review the observational techniques generally used, and we describe the theory behind stellar oscillations in cool main-sequence stars. We continue with a complete description of the normal mode analyses through which it is possible to extract the physical information about the structure and dynamics of the stars. We then summarize the lessons that we have learned and discuss unsolved issues and questions that are still unanswered.

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Section: Modelling a Star And Surface Effectsmentioning

confidence: 99%

Asteroseismology of solar-type stars

García

Ballot

2019

Living Rev Sol Phys

154

100

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“…4 and Table 4. Kjeldsen et al (2008) propose b = 4.90 in the case of the Sun, and many studies have adopted this value for other stars (e.g., Christensen-Dalsgaard et al 2010;Dogan et al 2010Dogan et al , 2013Metcalfe et al 2010;Tang & Gai 2011;Brandão et al 2011;Van Eylen et al 2012;Gilliland et al 2013;Gruberbauer et al 2013). When b is fixed, a simple fit provides the value of a (Kjeldsen et al 2008).…”

Section: Parameters Across the T Eff -G Planementioning

confidence: 99%

Surface-effect corrections for solar-like oscillations using 3D hydrodynamical simulations

Sonoi

Samadi

Belkacem

et al. 2015

A&A

114

246

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Context. The CoRoT and Kepler space-borne missions have provided us with a wealth of high-quality observational data that allows for seismic inferences of stellar interiors. This requires the computation of precise and accurate theoretical frequencies, but imperfect modeling of the uppermost stellar layers introduces systematic errors. To overcome this problem, an empirical correction has been introduced by Kjeldsen et al. (2008, ApJ, 683, L175) and is now commonly used for seismic inferences. Nevertheless, we still lack a physical justification allowing for the quantification of the surface-effect corrections. Aims. Our aim is to constrain the surface-effect corrections across the Hertzsprung-Russell (HR) diagram using a set of 3D hydrodynamical simulations. Methods. We used a grid of these simulations computed with the CO 5 BOLD code to model the outer layers of solar-like stars. Upper layers of the corresponding 1D standard models were then replaced by the layers obtained from the horizontally averaged 3D models. The frequency differences between these patched models and the 1D standard models were then calculated using the adiabatic approximation and allowed us to constrain the Kjeldsen et al. power law, as well as a Lorentzian formulation. Results. We find that the surface effects on modal frequencies depend significantly on both the effective temperature and the surface gravity. We further provide the variation in the parameters related to the surface-effect corrections using their power law as well as a Lorentzian formulation. Scaling relations between these parameters and the elevation (related to the Mach number) is also provided. The Lorentzian formulation is shown to be more robust for the whole frequency spectrum, while the power law is not suitable for the frequency shifts in the frequency range above ν max . Finally, we show that, owing to turbulent pressure, the elevation of the uppermost layers modifies the location of the hydrogen ionization zone and consequently introduces glitches in the surface effects for models with high (low) effective temperature (surface gravity). Conclusions. Surface-effect corrections vary significantly across the HR diagram. Therefore, empirical relations like those by Kjeldsen et al. must not be calibrated on the Sun but should instead be constrained using realistic physical modeling as provided by 3D hydrodynamical simulations.

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“…This scaled powerlaw approach has been adopted widely (e.g. Tang & Gai 2011;Mathur et al 2012;Deheuvels et al 2012). However, the fit overpredicts the magnitude of the surface effect at lower frequencies (see Figs.…”

Section: Introductionmentioning

confidence: 99%

A new correction of stellar oscillation frequencies for near-surface effects

Ball

Gizon

2014

A&A

221

337

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Context. Space-based observations of solar-like oscillations present an opportunity to constrain stellar models using individual mode frequencies. However, current stellar models are inaccurate near the surface, which introduces a systematic difference that must be corrected. Aims. We introduce and evaluate two parametrizations of the surface corrections based on formulae given by Gough (1990, LNP, 367, 283). The first we call a cubic term proportional to ν 3 /I and the second has an additional inverse term proportional to ν −1 /I, where ν and I are the frequency and inertia of an oscillation mode. Methods. We first show that these formulae accurately correct model frequencies of two different solar models (Model S and a calibrated MESA model) when compared to observed BiSON frequencies. In particular, even the cubic form alone fits significantly better than a power law. We then incorporate the parametrizations into a modelling pipeline that simultaneously fits the surface effects and the underlying stellar model parameters. We apply this pipeline to synthetic observations of a Sun-like stellar model, solar observations degraded to typical asteroseismic uncertainties, and observations of the well-studied CoRoT target HD 52265. For comparison, we also run the pipeline with the scaled power-law correction proposed by Kjeldsen et al. (2008, ApJ, 683, L175). Results. The fits to synthetic and degraded solar data show that the method is unbiased and produces best-fit parameters that are consistent with the input models and known parameters of the Sun. Our results for HD 52265 are consistent with previous modelling efforts and the magnitude of the surface correction is similar to that of the Sun. The fit using a scaled power-law correction is significantly worse but yields consistent parameters, suggesting that HD 52265 is sufficiently Sun-like for the same power-law to be applicable. Conclusions. We find that the cubic term alone is suitable for asteroseismic applications and it is easy to implement in an existing pipeline. It reproduces the frequency dependence of the surface correction better than a power-law fit, both when comparing calibrated solar models to BiSON observations and when fitting stellar models using the individual frequencies. This parametrization is thus a useful new way to correct model frequencies so that observations of individual mode frequencies can be exploited.

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Asteroseismic modelling of the metal-poor starτCeti

Cited by 15 publications

References 63 publications

Asteroseismology of solar-type stars

Asteroseismology of solar-type stars

Surface-effect corrections for solar-like oscillations using 3D hydrodynamical simulations

A new correction of stellar oscillation frequencies for near-surface effects

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