Beryllium abundances along the evolutionary sequence of the open cluster IC 4651 - New test for hydrodynamical stellar models

TL;DR

This study measures beryllium and lithium abundances in stars of the open cluster IC 4651 to test and refine stellar models involving complex internal mixing processes during stellar evolution.

Contribution

It provides new beryllium abundance data across the entire evolutionary sequence of IC 4651, offering a comprehensive test for advanced hydrodynamical stellar models.

Findings

Beryllium detected in all main sequence and turn-off stars, but not in red giants.

Li and Be dips coincide, with Be depletion being more modest.

Models including rotation, gravity waves, diffusion, and thermohaline mixing reproduce observed features.

Abstract

[abridged] Previous analyses of lithium abundances in main sequence and red giant stars have revealed the action of mixing mechanisms other than convection in stellar interiors. Beryllium abundances in stars with lithium abundance determinations can offer valuable complementary information on the nature of these mechanisms. Our aim is to derive beryllium abundances along the whole evolutionary sequence of an open cluster, IC 4651. These Be abundances are used together with previously determined Li abundances, in the same sample stars, to investigate the mixing mechanisms in a range of stellar masses and evolutionary stages. New beryllium abundances are determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. The careful synthetic modelling of the Be lines region is used to calculate reliable abundances in rapidly rotating stars. The observed behavior of Be and Li is compared to theoretical predictions from stellar models including rotation-induced mixing, internal gravity waves, atomic diffusion, and thermohaline mixing. Beryllium is detected in all the main sequence and turn-off sample stars, both slow- and fast-rotating stars, including the Li-dip stars, but was not detected in the red giants. Confirming previous results, we find that the Li dip is also a Be dip, although the depletion of Be is more modest than that of Li in the corresponding effective temperature range. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions as does the Li dilution. A clear dispersion in the Be abundances is also observed. Theoretical stellar models including the hydrodynamical transport processes mentioned above are able to reproduce well all the observed features.