The asteroseismic binary KIC 1084173: What does it tell us about core helium-burning red clump star models?
Schimak, Lea S.; Bedding, Tim; Crawford, Courtney; Beck, Paul G.; Huber, Daniel; Li, Yaguang; Montet, Ben; Pedersen, May Gade; Grossmann, Desmond
- Publisher
- Zenodo
- Language
- en
Abstract
Binaries in which both stars are pulsating are rare but extremely valuable. We present the first study of an asteroseismic binary system consisting of a core helium-burning red clump star and a red giant branch star. KIC 10841730 provides ideal conditions to not only estimate mass loss during the tip of the red giant branch but also to test the accuracy of modelling red clump stars. While prior studies have revealed discrepancies in modelled period spacings of mixed modes in red clump stars, other model parameters remain largely untested. We perform a detailed modelling analysis using individual mode frequencies and cover a large parameter space varying mass, metallicity, He-abundance, mixing length, overshooting, mass-loss and explore different methods to correct for surface effects. We find two possible results for the red clump models. One solution requires introducing an unexpected offset of the phase shift in the red clump model, yielding an age consistent with the companion star. Alternatively, we find that excluding the identification of 2-3 questionable radial modes resolves the phase-shift offset issue but results in a higher mass and thus a much younger age for the red clump star, contradicting the age obtained from its companion. We conclude that uncertainties in red clump models affect not only the g-mode period spacings but also the properties of the p modes. We show the power of asteroseismic binaries in validating and constraining stellar models and highlight the need for refining red-clump models.
Full text
The asteroseismic binary KIC 1084173: What does it tell us about core helium-burning red clump star models? Lea Schimak Work in progress… Tim Bedding, Courtney Crawford, Daniel Huber, Paul Beck Yaguang Li, Ben Montet, May Gade Pedersen, Desmond Grossmann 09.07.2025 TASC9/KASC16 Vienna
2 Why KIC 1084173? RGB RC ●Kepler asteroseismic binary (same age!) ●Binary period ~3000d (negligible interaction) ●Consists of a Red Giant Branch (RGB) and a Red Clump (RC) component §Constrain mass loss (RC is less massive than RGB) §Testing RC models
RCRGB 3 Kepler Observations
The difficulties of modelling red clump stars 5 ●Degenerate core àHe-Flash ●Long run time
The difficulties of modelling red clump stars 6 ●Degenerate core àHe-Flash ●Long run time ●Convective core boundary §ΔΠ (Core size) does not match the observations §Options: step/ exponential overshooting, semiconvection, predictive mixing, convective premixing, …
The difficulties of modelling red clump stars 7 ●Degenerate core àHe-Flash ●Long run time ●Convective core boundary §ΔΠ (Core size) does not match the observations §Options: step/ exponential overshooting, semiconvection, predictive mixing, convective premixing, …
●Varied parameters: ●Constraints: ●Only calculated pure p-modes (π-modes) Ong &Basu(2020) Modelling with & 8 §Initial mass §Mass loss §Metallicity §He-abundance §Mixing-length §Overshooting §individual frequencies with surface correction Ball & Gizon (2014); Roxburgh (2016) §Period spacing ΔΠ (RGB only) §Teff & [M/H] §Binary (age & composition)
●Stretched period/frequency échelle diagram to measure π-modes 9 π-modes RCRGB
10 RGB: model vs observation RGB ●Surface correction Ball & Gizon (2014) §Consequence of bad 1D modelling of the surface §Adding a star-and modeldependent correction term
19 RC: model vs observation RC
20 RC-models; An offset in ε? RC
●Future work: §Testing different convective core boundary descriptions §More stars to test (cluster and/or more binaries) ●Takeaways: §Modelling red clump stars is hard and uncertain §Surface corrections depend on their constraints §Asteroseismic binaries are great for diagnosing stellar models 21 Conclusion
