Angular momentum transport near convective-core boundaries of Gamma Doradus stars

Galactic archaeology largely relies on precise ages of distant evolved stars in the Milky Way. Nowadays, asteroseismology can deliver ages for many red giants observed with high-cadence, high-precision photometric space missions such as CoRoT Kepler K2, TESS, and soon PLATO. Our aim is to quantify the age uncertainties of currently slowly rotating red giants due to the cumulative effect of their fast rotation during core-hydrogen burning: their rotation in earlier evolutionary phases caused mixing of elements, resulting in heavier helium cores and the prolongation of their main-sequence lifetime. These rotational effects are usually ignored when age-dating red giants, despite our knowledge of fast rotation for stars with $M 1.3$\,M$_ odot$. We used a sample of F-type gravito-inertial pulsators ($ stars) with precise asteroseismic estimates of their internal rotation rate from Kepler\/ asteroseismology and with luminosity estimates from Gaia . For this sample, which includes stars rotating from nearly zero to about 60\,<!PCT!> of the critical rate, we computed the cumulative effect on the age in their post-main-sequence evolution caused by rotational mixing on the main sequence. We used stellar model grids with different physical prescriptions that mimic rotational mixing to assess systematic uncertainties on the age. With respect to non-rotating models, the sample of stars, as red giant progenitors reveals age differences up to 5\,<!PCT!> by the time they start hydrogen-shell burning when relying on the theory of rotationally induced diffusive mixing as included in the MIST isochrones. Using rotational mixing based on an advective-diffusive approach that includes meridional circulation leads to an age shift of 20\,<!PCT!> by the time of the tip of the red giant branch. The age-dating of red giants is affected by the cumulative effect of rotational mixing during the main sequence. Such rotationally induced age shifts should be taken into account in addition to other effects if the aim is to perform Galactic archaeological studies at the highest precision.

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The asteroseismic imprints of mass transfer

Wagg,

Johnston,

Bellinger

et al. 2024

A&A

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We present new simulations investigating the impact of mass transfer on the asteroseismic signals of slowly pulsating B stars. We used MESA to simulate the evolution of a binary star system and GYRE to compute the asteroseismic properties of the accretor star. We show that, compared to a single star of the same final mass, a star that has undergone accretion (of non-enriched material) has a significantly different internal structure, which is evident in both the hydrogen abundance profile and the Brunt–Väisälä frequency profile. These differences result in significant changes in the observed period spacing patterns, implying that one may use this as a diagnostic to test whether a star's core has been rejuvenated as a result of accretion. We show that it is essential to consider the full multimodal posterior distributions when fitting stellar properties of mass-gainers to avoid drawing misleading conclusions. Even with these considerations, stellar ages will be significantly underestimated when assuming single star evolution for a mass-gainer. We find that future detectors with improved uncertainties would rule out single star models with the correct mass and central hydrogen fraction. Our proof of principle analysis demonstrates the need to further investigate the impact of binary interactions on stellar asteroseismic signals for a wide range of parameters, such as the initial mass, the amount of mass transferred, and the age of the accretor star at the onset of mass transfer.

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Angular momentum transport near convective-core boundaries of Gamma Doradus stars

Cited by 5 publications

References 24 publications

Mixing processes in stars

Mixing processes in stars

Age uncertainties of red giants due to cumulative rotational mixing of progenitors calibrated by asteroseismology

The asteroseismic imprints of mass transfer

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