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Internal gravity waves (IGWs) have been shown to contribute to the transport of chemical elements in stars with a convective core and radiative envelope. Recent 2D hydrodynamical simulations of convection in intermediate-mass stars have provided estimates of the chemical mixing efficiency of such waves. The chemical diffusion coefficient from IGW mixing is described by a constant A times the squared wave velocity. The value of A, however, remains unconstrained by such simulations. This work aims at investigating what values A can take in order to reproduce the observed nitrogen surface abundances of the most nitrogen-enriched massive stars. Furthermore, we discuss the prevalence of IGW mixing compared to rotational mixing. We provide an implementation of these mixing profiles predicted from hydrodynamical simulations in the one-dimensional stellar evolution code MESA. We compute evolution tracks for stars between 3 and 30Msun with this new implementation for IGW mixing and study the evolution for the surface abundances of isotopes involved in the CNO cycle, particularly the N14 isotope. We show that this 1D framework predicting the chemical diffusion coefficient from IGW mixing yields consistent morphologies of the mixing profile in comparison with hydrodynamical simulations. We find that the value of A must increase with mass in order to reproduce the most nitrogen-enriched stars. Assuming these calibrated values for A, mixing by IGWs is a potential mechanism to reproduce well-mixed stars without needing rapid rotation. We have provided observational limits on the efficiency of IGW mixing for future theoretical studies. Future asteroseismic modelling efforts taking IGW mixing into account will be able to place additional constraints on the convective core mass, as our models predict that the convective core should be significantly more massive if IGW mixing is indeed efficient., Comment: Accepted for publication in Astronomy & Astrophysics. 12 pages. Full abstract in PDF

Numerical computations of stellar oscillations for models representative of B-type stars predict fewer modes to be excited than observations reveal from modern space-based photometric data. One shortcoming of state-of-the-art evolution models of B-type stars that may cause a lack of excited modes is the absence of microscopic diffusion in most such models. We investigate whether the inclusion of microscopic diffusion in stellar models of B-type stars, notably radiative levitation experienced by isotopes, leads to extra mode driving by the opacity mechanism compared to the case of models that do not include microscopic diffusion. We consider the case of slowly to moderately rotating stars and use non-rotating equilibrium models, while we account for (uniform) rotation in the computations of the pulsation frequencies. We calculate 1D stellar models with and without microscopic diffusion and examine the effect of radiative levitation on mode excitation, for both low-radial order pressure and gravity modes and for high-radial order gravity modes. We find systematically more modes to be excited for the stellar models including microscopic diffusion compared to those without it, in agreement with observational findings of pulsating B-type dwarfs. Furthermore, the models with microscopic diffusion predict that excited modes occur earlier on in the evolution compared to modes without it. In order to maintain realistic surface abundances during the main sequence, we include macroscopic envelope mixing by internal gravity waves. While radiative levitation has so far largely been neglected in stellar evolution computations of B-type stars for computational convenience, it impacts mode excitation predictions for stellar models of such stars. We conclude that the process of radiative levitation is able to reduce the discrepancy between predicted and observed excited pulsation modes in B-type stars., Comment: Paper accepted for publication in Astronomy & Astrophysics (10 pages, 11 figures). Full abstract in PDF

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. Our aim is to quantify age uncertainties of 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 resulting in heavier helium cores and the prolongation of their main sequence. These rotational effects are usually ignored when age-dating red giants, despite our knowledge of fast rotation for stars with $M\ge1.3\,$M$_\odot$. We use a sample of 490 $\gamma$ Doradus pulsators with precise asteroseismic estimates of their internal rotation rate and with luminosity estimates from Gaia. For this sample, which includes stars rotating from nearly 0 to about 60% of the critical rate, we compute the cumulative effect on the age in their post-main sequence evolution caused by rotational mixing on the main sequence. We use stellar model grids with different physical prescriptions mimicking rotational mixing to assess systematic uncertainties on the age. With respect to non-rotating models, the sample of 490 stars, as red giant progenitors, reveals age differences up to 5% 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 including meridional circulation leads to an age shift of 20% by the time of the TRGB. 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. (abridged), Comment: Accepted for publication in A&A, 10+3 pages, 8+2 figures

Context. Asteroseismic studies showed that cores of post main-sequence stars rotate slower than theoretically predicted by stellar models with purely hydrodynamical transport processes. Recent studies on main sequence stars, particularly Gamma Doradus ($\gamma$ Dor) stars, revealed their internal rotation rate for hundreds of stars, offering a counterpart on the main sequence for studies of angular momentum transport. Aims. We investigate whether such a disagreement between observed and predicted internal rotation rates is present in main sequence stars by studying angular momentum transport in $\gamma$ Dor stars. Furthermore, we test whether models of rotating stars with internal magnetic fields can reproduce their rotational properties. Methods. We compute rotating models with the Geneva stellar evolution code taking into account meridional circulation and the shear instability. We also compute models with internal magnetic fields using a general formalism for transport by the Tayler-Spruit dynamo. We then compare these models to observational constraints for $\gamma$ Dor stars that we compiled from the literature, combining so the core rotation rates, projected rotational velocities from spectroscopy, and constraints on their fundamental parameters. Results. We show that combining the different observational constraints available for $\gamma$ Dor stars enable to clearly distinguish the different scenarios for internal angular momentum transport. Stellar models with purely hydrodynamical processes are in disagreement with the data whereas models with internal magnetic fields can reproduce both core and surface constraints simultaneously. Conclusions. Similarly to results obtained for subgiant and red giant stars, angular momentum transport in radiative regions of $\gamma$ Dor stars is highly efficient, in good agreement with predictions of models with internal magnetic fields., Comment: Accepted for publication in Astronomy & Astrophysics. 16 pages, 17 figures, 1 appendix