Asteroseismic investigation of HD 140283: The Methuselah star

TL;DR

HD 140283’s first asteroseismic analysis from TESS data delivers precise constraints on mass, radius, and asteroseismic age for one of the Galaxy’s oldest metal-poor stars. By fitting a densely sampled GARSTEC grid with the Bayesian tool BASTA to six radial and eleven dipolar frequencies, plus Gaia parallax and broad-band colors, the study finds $M=0.75 \pm 0.01\,M_\odot$, $R=2.078^{+0.012}_{-0.011}\,R_\odot$, and $t=14.2 \pm 0.4$ Gyr, with a significant $ν_\mathrm{max}$-scaling deviation in the metal-poor regime ($f_{ν_\mathrm{max}} = 1.14 \pm 0.03$). The seismic age is compatible with the Universe within $1\sigma$, supporting an early formation epoch, while chemical and kinematic evidence points to a halo origin, likely Gaia-Enceladus. The results emphasize the impact of adopting custom abundances and opacities in modelling very old stars and illustrate the power of asteroseismology for age dating in the low-metallicity regime. Future work with additional TESS data and spectroscopy could further refine the physics of metal-poor oscillators and Pop III progenitor constraints.

Abstract

HD 140283 is a well-studied metal-poor subgiant and a Gaia benchmark star, often used for testing stellar models due to its proximity, brightness, and low metallicity ([Fe/H] = -2.3 dex). Here we present the first asteroseismic analysis of HD 140283, providing improved constraints on its fundamental properties. The star was observed by TESS in 20-second cadence during Sector 51. We extracted a custom light curve and performed a frequency analysis, revealing a rich spectrum of solar-like oscillations including mixed modes. These were combined with parameters from the literature to provide constraints on our model inference performed with BASTA. Using a dense grid of models, we find a mass of $0.75 \pm 0.01 \ \mathrm{M}_\odot$, a radius of $2.078 \substack{+0.012\\-0.011} \ \mathrm{R}_\odot$, and an age of $14.2 \pm 0.4$ Gyr, in agreement with the upper limit set by the age of the Universe within $1σ$. The observed frequency of maximum power, $\left(ν_\mathrm{max}\right)_\mathrm{obs} = 611.3 \pm 7.4 \ μ\mathrm{Hz}$, is significantly higher than predicted from standard scaling relations ($\left(ν_\mathrm{max}\right)_\mathrm{mod} = 537.2 \substack{+2.9\\-1.8} \ μ\mathrm{Hz}$), extending known deviations into the metal-poor regime. To our knowledge, the oscillations in HD 140283 have the highest $ν_\mathrm{max}$ of any metal-poor star to date, which will help to advance our understanding of oscillations in metal-poor stars in general. The results demonstrate the value of asteroseismology for precise age determination in old halo stars and taking custom abundances and opacities into account during the modelling is probably important for further improving models of such stars. In addition, a detailed characterisation of metal-poor stars, such as HD 140283, will also help advance our understanding of Population III stars and their impact on future stellar generations.

Figures (12)

• Figure 1: Compilation of literature ages colour-coded by mass for HD 140283 (the result of this work is also given). The circles show age estimates, the squares give age ranges, and the arrows are upper and lower limits. The dashed line at $13.787 \ \mathrm{Gyr}$ indicates the age of the Universe ref:planck2020 and its uncertainty. A table of the references can be found appendix \ref{['sec:app_ages']}.
• Figure 2: Iron abundance vs frequency of maximum power for stars with asteroseismic detections, modified from a similar plot by ref:huber2024. The star shows HD 140283 (this work), while the points are literature values. The black points are from ref:pinsonneault2014, ref:serenelli2017, ref:metsuno2021 and ref:stasik2024. The filled coloured points show stars with modelling of individual frequencies; $\nu$ Indi Bedding2006ref:chaplin2020, KIC 7341231 ref:deheuvels2012, KIC 7693833 and KIC 4671239 Larsen25, KIC 8144907 ref:huber2024, and HD 175305 and HD 128279 ref:lindsay2025, while the open circle shows EPIC 206443679 ref:valentini2019 with modelling of the global seismic parameters.
• Figure 3: Example of a target pixel file for HD 140283. Our custom mask is shown in red.
• Figure 4: Time series of HD 140283. The flux is shown in blue and the measurement uncertainties in orange. The gaps are explained in the text.
• Figure 5: Power spectrum of HD 140283: unsmoothed (grey) and smoothed to 1 $\mu$Hz (black) with the oscillation frequencies clearly seen. The measured frequency of maximum oscillation power is $\nu_\mathrm{max} = 611.3 \pm 7.4 \ \mu\mathrm{Hz}$.