TY - JOUR
T1 - Pushing the boundaries of asteroseismic individual frequency modelling
T2 - Unveiling two evolved very low-metallicity red giants
AU - Larsen, J. R.
AU - Rørsted, J. L.
AU - Aguirre Børsen-Koch, V.
AU - Lundkvist, M. S.
AU - Christensen-Dalsgaard, J.
AU - Winther, M. L.
AU - Stokholm, A.
AU - Li, Y.
AU - Slumstrup, D.
AU - Kjeldsen, H.
AU - Corsaro, E.
AU - Benomar, O.
AU - Dhanpal, S.
AU - Weiss, A.
AU - Mosser, B.
AU - Hekker, S.
AU - Stello, D.
AU - Korn, A. J.
AU - Jendreieck, A.
AU - Elsworth, Y.
AU - Handberg, R.
AU - Kallinger, T.
AU - Jiang, C.
AU - Ruchti, G.
N1 - Publisher Copyright:
© The Authors 2025.
PY - 2025/5/1
Y1 - 2025/5/1
N2 - Context. Metal-poor stars play a crucial role in understanding the nature and evolution of the first stellar generation in the Galaxy. Previously, asteroseismic characterisation of red-giant stars has relied on constraints from the global asteroseismic parameters and not the full spectrum of individual oscillation modes. Using the latter, we present for the first time the characterisation of two evolved very metal-poor stars including the detail-rich mixed-mode patterns. Aims. We will demonstrate that incorporating individual frequencies into grid-based modelling of red-giant stars enhances its precision, enabling detailed studies of these ancient stars and allowing us to infer the stellar properties of two very metal-poor [Fe/H] ∼ -2.5 dex Kepler stars: KIC 4671239 and KIC 7693833. Methods. Recent developments in both observational and theoretical asteroseismology have allowed for detailed studies of the complex oscillation pattern of evolved giants. In this work, we employ Kepler timeseries and surface properties from high-resolution spectroscopic data within a grid-based modelling approach to asteroseismically characterise KIC 4671239 and KIC 7693833 using the BAyesian STellar Algorithm, BASTA. Results. Both stars show agreement between constraints from seismic and classical observables, an overlap unrecoverable when purely considering the global asteroseismic parameters. KIC 4671239 and KIC 7693833 were determined to have masses of 0.78-0.03+0.04 and 0.83-0.01+0.03-0.01 M⊙ with ages of 12.1-1.5+1.6 and 10.3-1.4+0.6 Gyr, respectively. Particularly, for KIC 4671239 the rich spectrum of model frequencies closely matches the observed. Conclusions. A discrepancy between the observed and modelled νmax of ∼10% was found, indicating a metallicity dependence of the νmax scaling relation. For metal-poor populations, this results in overestimations of the stellar masses and wrongful age inferences. Utilising the full spectra of individual oscillation modes lets us circumvent the dependence on the asteroseismic scaling relations through direct constraints on the stars themselves. This allows us to push the boundaries of state-of-the-art detailed modelling of evolved stars at metallicities far different from solar.
AB - Context. Metal-poor stars play a crucial role in understanding the nature and evolution of the first stellar generation in the Galaxy. Previously, asteroseismic characterisation of red-giant stars has relied on constraints from the global asteroseismic parameters and not the full spectrum of individual oscillation modes. Using the latter, we present for the first time the characterisation of two evolved very metal-poor stars including the detail-rich mixed-mode patterns. Aims. We will demonstrate that incorporating individual frequencies into grid-based modelling of red-giant stars enhances its precision, enabling detailed studies of these ancient stars and allowing us to infer the stellar properties of two very metal-poor [Fe/H] ∼ -2.5 dex Kepler stars: KIC 4671239 and KIC 7693833. Methods. Recent developments in both observational and theoretical asteroseismology have allowed for detailed studies of the complex oscillation pattern of evolved giants. In this work, we employ Kepler timeseries and surface properties from high-resolution spectroscopic data within a grid-based modelling approach to asteroseismically characterise KIC 4671239 and KIC 7693833 using the BAyesian STellar Algorithm, BASTA. Results. Both stars show agreement between constraints from seismic and classical observables, an overlap unrecoverable when purely considering the global asteroseismic parameters. KIC 4671239 and KIC 7693833 were determined to have masses of 0.78-0.03+0.04 and 0.83-0.01+0.03-0.01 M⊙ with ages of 12.1-1.5+1.6 and 10.3-1.4+0.6 Gyr, respectively. Particularly, for KIC 4671239 the rich spectrum of model frequencies closely matches the observed. Conclusions. A discrepancy between the observed and modelled νmax of ∼10% was found, indicating a metallicity dependence of the νmax scaling relation. For metal-poor populations, this results in overestimations of the stellar masses and wrongful age inferences. Utilising the full spectra of individual oscillation modes lets us circumvent the dependence on the asteroseismic scaling relations through direct constraints on the stars themselves. This allows us to push the boundaries of state-of-the-art detailed modelling of evolved stars at metallicities far different from solar.
KW - Asteroseismology
KW - Stars: evolution
KW - Stars: individual: KIC 4671239
KW - Stars: individual: KIC 7693833
KW - Stars: oscillations
UR - http://www.scopus.com/inward/record.url?scp=105005535697&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202453554
DO - 10.1051/0004-6361/202453554
M3 - Journal article
AN - SCOPUS:105005535697
SN - 0004-6361
VL - 697
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A153
ER -