Probing core overshooting using subgiant asteroseismology: The case of KIC10273246

Noll, A.; Deheuvels, S.; Ballot, J.

doi:10.1051/0004-6361/202040055

Cited by 30 publications

(23 citation statements)

References 69 publications

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“…Asteroesismology of stars oscillating in p modes and in g modes with 1.3 ≤ M ≤ 24 M has revealed the need for a wide range of convective boundary mixing efficiencies to reproduce observed pulsation frequencies (Briquet et al 2007;Handler 2013;Moravveji et al 2016;Schmid & Aerts 2016;Szewczuk & Daszyńska-Daszkiewicz 2018;Mombarg et al 2019;Pedersen et al 2021). Additionally, asteroseismology of stars pulsating in p modes (pressure waves) between 1.15-1.5 M has revealed the need for a range of convective mixing efficiencies to reproduce observed frequencies (Deheuvels et al 2010;Deheuvels & Michel 2011;Silva Aguirre et al 2011;Salmon et al 2012;Angelou et al 2020;Viani & Basu 2020;Noll et al 2021). Similar to binaries and clusters, the modelling of pulsation frequencies (for both p and g modes) is not sensitive to the efficiency of a single mixing mechanism.…”

Section: Asteroseismologymentioning

confidence: 99%

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Johnston

2021

Preprint

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Context. Internal chemical mixing in intermediate-and high-mass stars represents an immense uncertainty in stellar evolution models. In addition to extending the main-sequence lifetime, chemical mixing also appreciably increases the mass of the stellar core. Several studies have made attempts to calibrate the efficiency of different convective boundary mixing mechanisms, with sometimes seemingly conflicting results. Aims. We aim to demonstrate that stellar models regularly under-predict the masses of convective stellar cores. Methods. We gather convective core mass and fractional core hydrogen content inferences from numerous independent binary and asteroseismic studies, and compare them to stellar evolution models computed with the MESA stellar evolution code. Results. We demonstrate that core mass inferences from the literature are ubiquitously more massive than predicted by stellar evolution models without or with little convective boundary mixing. Conclusions. Independent of the form of internal mixing, stellar models require an efficient mixing mechanism that produces more massive cores throughout the main sequence to reproduce high-precision observations. This has implications for the post-main sequence evolution of all stars which have a well developed convective core on the main sequence.

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Section: Asteroseismologymentioning

confidence: 99%

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Johnston

2021

Preprint

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“…However, stars with a mass greater than ∼ 1.2M have a convective core, and the overshooting may therefore impact the inferred age. For example, Noll et al (2021) demonstrated in the specific case of the KIC10273246 subgiant that models with a finite amount of overshooting are in better agreement with observed data that models without overshooting. Including the effect of overshooting will thus be mandatory in more quantitative studies that will follow the preliminary exploratory work presented here.…”

Section: Period Spacing ∆πmentioning

confidence: 61%

Asteroseismology of evolved stars with EGGMiMoSA I. Theoretical mixed-mode patterns from the subgiant to the RGB phase

Farnir,

Pinçon,

Dupret

et al. 2021

Preprint

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Context. In the context of an ever increasing amount of highly precise data, thanks to the numerous space-borne missions, came a revolution in stellar physics. This data allowed asteroseismology to thrive and improve our general knowledge of stars. Important results were obtained about giant stars owing to the presence of 'mixed modes' in their oscillation spectra. These modes carry information about the whole stellar interior, enabling the comprehensive characterisation of their structure. Aims. The current study is part of a series of papers that provide a technique to coherently and robustly analyse the mixed-modes frequency spectra and characterise the stellar structure of stars on both the subgiant branch and red-giant branch (RGB). In this paper we aim at defining seismic indicators, relevant of the stellar structure, as well as studying their evolution along a grid of models. Methods. The proposed method, EGGMiMoSA, relies on the asymptotic description of mixed modes. It defines appropriate initial guesses for the parameters of the asymptotic formulation and uses a Levenberg-Marquardt minimisation scheme in order to adjust the complex mixed-modes pattern in a fast and robust way. Results. We are able to follow the evolution of the mixed-modes parameters along a grid of models from the subgiant phase to the RGB bump, therefore extending previous works. We show the impact of the stellar mass and composition on the evolution of these parameters. We observe that the evolution of the period spacing ∆π1, pressure offset p, gravity offset g , and coupling factor q as a function of the large frequency separation ∆ν is little affected by the chemical composition and that it follows two different regimes depending on the evolutionary stage. On the subgiant branch, the stellar models display a moderate core-envelope density contrast. Therefore, the evolution of ∆π1, p, g , and q significantly changes with the stellar mass. Furthermore, we demonstrate that, for a given metallicity and with proper measurements of the period spacing ∆π1 and large frequency separation ∆ν, we may unambiguously constrain the stellar mass, radius and age of a subgiant star. Conversely, as the star reaches the red-giant branch, the core-envelope density contrast becomes very large. Consequently, the evolution of p, g and q as a function of ∆ν becomes independent of the stellar mass. This is also true for ∆π1 in stars with masses 1.8M because of core electron degeneracy. This degeneracy in ∆π1 is lifted for higher masses, again allowing for a precise measurement of the stellar age. Overall, our computations qualitatively agree with previous observed and theoretical studies. Conclusions. The method provides automated measurements of the adjusted parameters along a grid of models and opens the way to the precise seismic characterisation of both subgiants and red giants. In the following papers of the series, we will explore further refinements to the technique as well as its application to observed stars.

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“…As stars transition off the main sequence, they exhibit strong radial differential rotation compared to the relatively flat solar profile exemplified in main-sequence stars (Howe 2009). Subgiants early in their transition off the main-sequence demonstrate solid body rotation (Deheuvels et al 2020;Noll et al 2021). However, later into their post-main-sequence evolution, the cores of more evolved subgiants, and low-luminosity RGB stars rotate much faster than their envelope.…”

Section: Introductionmentioning

confidence: 99%

What can rotational splittings of low-luminosity subgiants actually tell us about the rotation profile?

Wilson¹,

Casey²,

Mandel³

et al. 2021

Preprint

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Context. Inversions of the rotation profile using rotationally induced splittings of low-luminosity subgiant stars suggest that angular momentum transport mechanisms must be 1-2 orders of magnitude more efficient than theory predicts. The lack of precise high resolution of measurements of the rotation profile limits our understanding of the physical mechanism inducing excess angular momentum transport. Rotational inversions are limited to some positions in a star and are restricted in accuracy and resolution by the number of observed splittings, the specific modes of the splittings that are observed, and their associated uncertainties. For example, state-of-the-art observations of rotational splittings of low-luminosity subgiants are limited to low degree = 1 and 2 modes, offering only limited precision measures of the core and surface rotation rates, not the shape of the rotation profile between these positions. Aims. We study the feasibility of making precise constraints to the rotation profile between the core and surface and the possibility of differentiating between rotation profile shapes using the observed rotational splittings of low-luminosity subgiant KIC 12508433. Methods. We use qualitative assumptions of extreme angular momentum transport mechanisms to prescribe the shape of the five synthetic profiles with the same core and surface rotation rates. We calculate the expected rotational splittings given these five profiles and analyse the differences between them. Markov chain Monte Carlo integration of the synthetic profiles using their associated splittings highlights the limited differentiability between rotation profiles that can currently be made. Results. Despite significant changes to the shape of the rotation profile, the rotational splittings deviate on a scale much smaller than the precision of splittings in current observations. We also find degeneracy between the surface rotation rate and position of strong differential rotation gradient of the inverted profiles. Conclusions. Constraining the physical mechanism contributing to more efficient angular momentum transport during the lowluminosity subgiant phase through the shape of the profile is impossible with current observations of = 1 and 2 rotationally split modes. We speculate that population inference using only the core and surface rotation rates from rotational splittings of a series of stars beginning to ascend the subgiant branch provides an alternative path to understanding the excess angular momentum transport.

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Probing core overshooting using subgiant asteroseismology: The case of KIC10273246

Cited by 30 publications

References 69 publications

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

One size does not fit all: Evidence for a range of mixing efficiencies in stellar evolution calculations

Asteroseismology of evolved stars with EGGMiMoSA I. Theoretical mixed-mode patterns from the subgiant to the RGB phase

What can rotational splittings of low-luminosity subgiants actually tell us about the rotation profile?

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