0 5 10 15 20 25 30 (∫+ 1) mod ¢∫[µHz] 300 350 400 450 500 550 ∫[µHz] l=0 l=1 l=2 Uncorrected Surface-Corrected Introduction •Asteroseismic analyses of metal-poor stars enhanced in α-elements (C, O, Ne, Mg…) are vital for studying the formation of our Galaxy’s Halo. •Most previous analyses of metal-poor, α-enhanced stars rely on the global asteroseismic scaling relations, which are scaled to the Sun. •Previous work comparing results from individual frequency modeling with scaling relation estimates indicates that scaling relation results diverge for low-metallicity stars. •Ad-hoc prescriptions like that of M. Salaris, ApJ, 1993 are often used to model α-enhanced stars, but their effects on asteroseismic modeling have not yet been explored in detail. The Sample •Our sample of 8 stars are all metal poor ([Fe/H] ≲ 1.5) and enhanced in α-elements (0.15 ≲ [α /Fe] ≲ 0.4). Some of the stars in our sample have previously been analyzed using asteroseismology. •We obtain the observed oscillation mode frequencies from either literature sources, or by applying peakbagging tools to photometric data from TESS. Asteroseismic modeling is robust to different ways of accounting for [α/Fe]. Individual-frequency modeling results diverge from scaling-relation estimates at low metallicity. Detailed Asteroseismic Modeling of 8 α-element Enhanced Metal Poor Stars Christopher J. Lindsay, Joel Ong, Sarbani Basu My Website α–Enhanced versus Salaris Correction Modeling Methods •For each target star, we calculate MESA stellar models, varying the initial mass, helium abundance, metallicity, and mixing length. To determine the quality of a model’s fit, the GYRE-calculated mode frequencies are compared with the observed frequencies. The spectroscopic observables (Teff, Luminosity, and [Fe/H]) are also compared with observations. •The best fit model for each target is found using an optimization procedure which employs the differential evolution algorithm from P. Mier 2017. •We model each star two ways: •1. α-enhanced, where the abundances and opacity tables used during the model calculations are α-enhanced, based on the observed [α /Fe]. •2. Salaris-corrected, where the models are calculated using a solar-scaled metal mixture, but the observed [Fe/H] is altered according to the observed [α /Fe] following M. Salaris, ApJ, 1993. Results •We determine stellar parameters (mass, radius, age, initial abundances) for each of the 8 stars in our sample. •Comparing α-enhanced and Salariscorrected modeling results, we find that the asteroseismic mass, radius, and age results are consistent between treatments. •Contrasting results from individual mode modeling with those based on asteroseismic scaling relations, we find that masses derived from global asteroseismic parameters are significantly overestimated relative to our detailed modeling. •This may indicate a breakdown of the νmax scaling relation for metal-poor stars, consistent with recent findings. 11 2 2 1 Target Star Source of Asteroseismic Data KIC 8144907 D. Huber+ ( ApJ, 2024) KIC 4671239 J. Larsen+ (A&A, 2025) ν Indi W. Chaplin+ (Nature, 2020) & This Work KIC 7341231 S. Deheuvels+ (ApJ, 2012) HD 140283 M. Lundkvist+ (In Prep) HD 175305 C. Lindsay, Hon, Ong+ ( ApJ, In Review) HD 128279 C. Lindsay, Hon, Ong+ ( ApJ, In Review) TIC 300085386 C. Lindsay, Grunblatt, Hon+ (In Prep) Mass [MØ] 2.48 2.56 2.64 2.72 2.80 Radius Radius [RØ] 0.72 0.78 0.84 0.90 0.96 Mass 6 9 12 15 18 Age 2.48 2.56 2.64 2.72 2.80 Radius 6 9 12 15 18 Age Age [Gyr] Methods Example (KIC 7341241) 0 5 10 15 20 25 (∫+ 1) mod ¢∫[µHz] 300 350 400 450 500 550 ∫[µHz] l=0 l=1 l=2 Uncorrected Surface-Corrected α-enhanced best fit Salaris-corrected best fit Comparison with Scaling Relation Results •We compare the observed νmax to the scalingrelation νmax implied by the best fit mass, radius, and Teff results to quantify the best-fit model deviations from the νmax scaling relation. See S. Sharma+ (ApJ, 2016), Y. Li+ (ApJ, 2024), D. Huber+ (ApJ, 2024), and J. Larsen+ (A&A, 2025) for additional studies of low metallicity stars and the νmax scaling relation. °2.50 °2.25 °2.00 °1.75 °1.50 °1.25 Observed [Fe/H] 1.00 1.05 1.10 1.15 1.20 f∫max Æ-enhanced Results °2.50 °2.25 °2.00 °1.75 °1.50 °1.25 Observed [Fe/H] 1.00 1.05 1.10 1.15 1.20 f∫max Salaris-Corrected Results My Email:
[email protected] 4500475050005250550057506000 TeÆ[K] °0.50 °0.25 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 Luminosity [LØ] Uncorrected Salaris Corrected Æ-Enhanced 2 3 4 5 6 7 Æ-Enhanced Radius Result [RØ] 2 3 4 5 6 7 Salaris-Corrected Radius Result [RØ] 0.75 0.80 0.85 0.90 Æ-Enhanced Mass Result [MØ] 0.65 0.70 0.75 0.80 0.85 0.90 Salaris-Corrected Mass Result [MØ] y=x KIC 8144907 KIC 4671239 ∫Indi HD 140283 KIC 7341231 HD 175305 HD 128279 TIC 300085386 8 10 12 14 Æ-Enhanced Age Result [Gyr] 8 10 12 14 16 Salaris-Corrected Age Result [Gyr] 0 5 10 15 20 25 ∫mod ¢∫ 250 300 350 400 450 ∫/µHz PBJam `=1 PBJam `=0,2 Chaplin+ `=1 Chaplin+ `=0,2 As TESS data continuously becomes available, we have been able to detect more mode frequencies for ν Indi.
