Disagreement in metallicity dependence of the nu_max scaling factor

Determine the physical origin of the inconsistency between the empirical nu_max scaling-factor f_nu_max inferred from detailed asteroseismic modeling of the very metal-poor red giant KIC 8144907 (which yields f_nu_max greater than 1) and the acoustic cutoff frequency–based prediction by Viani et al. (2018) that f_nu_max is less than 1 in metal-poor stars. Establish how f_nu_max depends on metallicity in the low-metallicity regime and reconcile these approaches to the nu_max scaling relation.

Background

Asteroseismic scaling relations link the frequency of maximum oscillation power (nu_max) to fundamental stellar properties, often using a multiplicative factor f_nu_max to quantify deviations from the simple g–T_eff scaling. Calibrations of these relations at very low metallicity are poorly established and have shown tensions with astrophysical expectations.

In this study, detailed frequency modeling of the very metal-poor star KIC 8144907 yields f_nu_max values slightly greater than unity, indicating an upward deviation from the solar-scaled relation at low metallicity. This contrasts with the findings of Viani et al. (2018), who, based on acoustic cutoff frequency considerations, predicted f_nu_max values less than 1 for metal-poor stars. Understanding and resolving this discrepancy is essential for reliable application of asteroseismic scaling relations to low-metallicity stellar populations.