Seismic Giants in Clusters: How Well Are We Actually Doing?
Abstract
Observations of red giants in open and globular clusters offer an opportunity to check how the ages estimated from global asteroseismology compare to the more fundamental cluster scale. Using a meta-analysis of seismic ages for stars in well-studied clusters we show both a high variance in inferred ages from asteroseismology within each cluster, as well as potential offsets from the cluster predictions. These disparities are significantly larger than what we would expect from intrinsic model uncertainties or model to model systematics. Given the importance of fundamental calibration, we will also describe ongoing work to increase the potential cluster samples using TESS, searching for sufficiently isolated individual giants in a variety of nearby clusters.
Full text
Seismic Giants in Clusters: How Well Are We Actually Doing? Jamie Tayar TASC-9/KASC-16 July 7, 2025 jtayar.github.io
Stellar Ages ●Galactic Archaeologywe want ages for hundreds of thousands or millions of stars across the Milky Way ●10% ages would be particularly valuable ●(Global) asteroseismology gives us ages, but how good are they?
Why Age Calibration? Silva Aguirre+2018 Xiang & Rix 2022 Stokholm+2023 Nataf+ 2024
Red Giant Global Seismology M Mo = ( ν max ν max ,o ) 3 ( Δ ν Δ ν o ) −4 ( Teff Teff ,o ) 1.5 R Ro = ( ν max ν max ,o ) ( Δ ν Δ ν o ) −2 ( Teff Teff ,o ) 0.5 e.g. Kjeldsen & Bedding 1995
Red Giant Global Seismology M Mo = ( ν max ν max ,o ) 3 ( Δ ν Δ ν o ) −4 ( Teff Teff ,o ) 1.5 R Ro = ( ν max ν max ,o ) ( Δ ν Δ ν o ) −2 ( Teff Teff ,o ) 0.5 Solar values calibrated to bring methods into agreement Temperature scale benchmarked to external references e.g. Pinsonneault et al. 2025 (inc. Tayar)
Red Giant Global Seismology M Mo = ( ν max ν max ,o ) 3 ( fΔ ν Δ ν Δ ν o ) −4 ( Teff Teff ,o ) 1.5 R Ro = ( ν max ν max ,o ) ( fΔ ν Δ ν Δ ν o ) −2 ( Teff Teff ,o ) 0.5 e.g. Pinsonneault et al. 2025 (inc. Tayar) Observed Δν doesn’t quite scale as mean density, use models to correct
Red Giant Global Seismology M Mo = ( f ν max ν max ν max ,o ) 3 ( fΔ ν Δ ν Δ ν o ) −4 ( Teff Teff ,o ) 1.5 R Ro = ( f ν max ν max ν max ,o ) ( fΔ ν Δ ν Δ ν o ) −2 ( Teff Teff ,o ) 0.5 e.g. Pinsonneault et al. 2025 (inc. Tayar) Resulting masses and radii are not quite right, use Gaia or clusters to correct this on average
●With Mass, Radius or logg, and composition ●Can look up in a stellar model what the age is supposed to be on the red giant branch Red Giant Global Seismology Artemis Theodoridis
Kepler TESS Theodoridis, Morales, & Tayar (2025, submitted) Artemis Theodoridis Pinsonneault, Zinn, Tayar+ (2025) >100,000 Stars >20,000 Stars
Asteroseismology In Clusters ●Global seismology only ●No additional information & priors ●Analyze stars individually ●Models from the literature Data from Reyes et al. 2025
NGC 6791 ●Original Kepler field ●Included in APOKASC-3 ●Exclude clump stars (mass loss uncertainty, see Yaguang Li’s talk) Data from Pinsonneault et al. 2025 (inc. Tayar)
Global Seismic Age Uncertainty Tayar & Joyce (2025)
Global Seismic Age Uncertainty Tayar & Joyce (2025)
Global Seismic Age Uncertainty Tayar & Joyce (2025) Should there be an fage and if so, is it a function of age and metallicity?
Age-Metallicity distribution
Age-Metallicity distribution Tayar & Joyce (2025)
Age-Metallicity distribution PLATO Tayar & Joyce (2025)
Age-Metallicity distribution PLATO
Clusters in TESS ●900+ cluster giants bright enough to potentially have detectable oscillations in TESS Carli Mankowski
Summary ●Global Asteroseismology for giants in clusters to calibrate the age scale to 10% ●8 clusters, Age: <1 Gyr-13 Gyr, Metallicity: -2.4 to +0.15 ●~30 day observing sectors, 2 years of observations = 70 days/ cluster, 15-120 giants per cluster, 10% age per cluster ●Custom models for consistent cluster and asteroseismic age scales ●Calibrate the correction factor fage to put 100,000+ field giants from TESS, Kepler, K2, Roman, and Plato on the cluster age scale and answer questions about the Milky Way’s Evolution