Work

Detailed study of HD 219134: A benchmark K dwarf with a compact planetary system

Year: 2026

Type: article

Abstract: Space-based missions such as CoRoT, , and TESS have revolutionised asteroseismology and strengthened its synergies with exoplanet science. With PLATO and ARIEL on the horizon, these synergies will play an even more central role. Kepler We revisit the characterisation of the nearby K dwarf HD 219134 using advanced seismic diagnostics. Our goals are to investigate the reported tension between asteroseismic and interferometric radii, update the fundamental parameters of the star, refine the properties of its planetary system, and investigate the coupled rotational, magnetic, and star–planet evolution of the system, including the atmospheric mass‑loss histories of its planets. The stellar characterisation is based on detailed asteroseismic forward modelling complemented by seismic inversions to quantify systematic uncertainties associated with non‑seismic constraints, assess the compatibility of radius measurements, and evaluate the impact of surface modelling on seismic inferences. The revised stellar properties were used as inputs for rotational evolution investigations, stellar wind modelling, and high‑energy irradiation histories. Seismic inversions rule out the most recent interferometric radius determination, whereas asteroseismic and spectroscopic results are compatible with the previous interferometric measurement from 2019. We derive revised stellar mass, radius, and age of 0.779 ± 0.015_ ± 0.006_ , M_⊙, 0.753 ± 0.005_ ± 0.002_ , R_⊙, and 8.92 ± 0.89_ ± 0.19_ Gyr, respectively. The quoted systematic uncertainties reflect contributions from the non-seismic observational constraints only. Literature values for combined uncertainties arising from physical inputs and surface-effect prescriptions are 0.007M_⊙, 0.002R_⊙, and 0.81 Gyr, respectively. Using stellar wind models and a dedicated calibration of the magnetic braking law for low-mass stars, we reconstructed the rotational and angular‑momentum evolution of the host star and find that standard magnetic braking prescriptions remain broadly consistent with the observed present‑day rotation and angular‑momentum loss. Models invoking weakened magnetic braking provide a closer match but challenge commonly adopted scaling relations for the wind-driven angular momentum loss. The reconstructed X‑ray activity history implies early atmospheric stripping of the innermost planets, while the more massive outer planets are expected to have retained at least part of their primordial envelopes. In particular, HD 219134d appears to have undergone only moderate atmospheric erosion over the system lifetime. (stat) (sys) (stat) (sys) (stat) (sys) The available evidence suggests that the apparent radius discrepancy for HD 219134 does not reflect a genuine astrophysical problem but is more likely the result of underestimated uncertainties in previous interferometric analyses. We therefore advocate adopting the asteroseismic radius, which demonstrates remarkable robustness against variations in modelling assumptions and optimisation strategies.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202661326