Did Kepler-444 have a long-lived convective core?

With the greater power to infer the state of stellar interiors provided by asteroseismology, it has become possible to study the survi v al of initially conv ectiv e cores within stars during their main-sequence evolution. Standard theories of stellar evolution predict that conv ectiv e cores in subsolar mass stars have lifetimes belo w 1 Gyr . Ho we ver, a recent asteroseismic study of the star Kepler-444 concluded that the initial conv ectiv e core had survived for nearly 8 Gyr . The goal of this paper is to study the conv ectiv e-core evolution of Kepler-444 and to investigate its proposed longevity. We modify the input physics of stellar models to induce longer conv ectiv e-core lifetimes and vary the associated parameter across a dense grid of evolutionary tracks. The observations of metallicity, effective temperature, mean density, and asteroseismic frequency ratios are fitted to the models using the BASTA pipeline. We explore different choices of constraints, from which a long conv ectiv e-core lifetime is only reco v ered for a few specific combinations: mainly from the inclusion of potentially unreliable frequencies and/or excluding the covariances between the frequency ratios, whereas for the classical parameters, the derived luminosity has the largest influence. For all choices of observables, our analysis reliably constrains the conv ectiv e-core lifetime of Kepler-444 to be short, with a median around 0 . 6 Gyr and a 1 a upper bound around 3 . 5 Gyr .

Automated summary

With the advancement of asteroseismology, it has become possible to study the survival of convective cores within stars during their main-sequence evolution. A recent study on the star Kepler-444 found that the convective core had survived for nearly 8 Gyr, contrary to the predictions of standard stellar evolution theories. This paper aims to investigate the convective core evolution of Kepler-444 and determine its proposed longevity by modifying the input physics of stellar models and fitting the observations to the models using the BASTA pipeline. The analysis reliably constraints the convective core lifetime of Kepler-444 to be short, with a median around 0.6 Gyr and an upper bound around 3.5 Gyr.