Asteroseismology of the young open cluster NGC 2516

II. Constraining cluster age using gravity-mode pulsators

¹ Institute of Astronomy (IvS), Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
² Université Paris-Saclay, Université de Paris, Sorbonne Paris Cité, CEA, CNRS, AIM, F-91191 Gif-sur-Yvette, France
³ Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010 6500 GL, Nijmegen, The Netherlands
⁴ Max-Planck-Institut fũr Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany

^⋆ Corresponding authors: gang.li@kuleuven.be, conny.aerts@kuleuven.be, Joey.Mombarg@cea.fr

Received: 14 July 2025
Accepted: 4 September 2025

Abstract

Context. Although asteroseismology is regarded as the most powerful tool for probing stellar interiors, seismic modelling remains dependent on global stellar parameters such as temperature and luminosity. Stellar clusters offer direct measurements of these parameters by fitting a colour–magnitude diagram. This makes the application of asteroseismology in stellar clusters a valuable approach to advancing the entire field of stellar physics modelling.

Aims. We aimed to develop seismic modelling for gravity-mode pulsators in the open cluster NGC 2516 to determine stellar ages and investigate internal mixing processes.

Methods. We computed 1D stellar evolutionary models using the code called modules for experiments in stellar astrophysics (MESA), which incorporates rotation-induced transport processes. Exponential overshooting in the transition layers between convective and radiative regions was included, and rotation-induced mixing in the radiative envelope. Grids of evolutionary models that covered isochrone-derived mass ranges were computed. The models were evolved up to 300 Myr because of the young age of the cluster (∼100 Myr).

Results. By fitting the frequencies of identified modes of four gravity-mode member pulsators simultaneously, we measured the seismic age of cluster NGC 2516 as 132 ± 8 Myr. This high-precision seismic age estimate deviates by 1σ from the isochronal age derived from public MESA isochrones and stellar tracks (MIST) isochrones for rotating stars. Our findings show that seismic modelling strongly constrains core overshooting, but because the period spacing patterns are smooth, it provides weak constraints on mixing in the radiative envelope of young gravity-mode pulsators. The two most massive gravity-mode pulsators have MIST masses of ∼2.0 M_⊙ while their seismic masses are ∼1.75 M_⊙. We constructed new asteroseismology-calibrated isochrones using input physics identical to that of our seismic model grid. While this resolved the age discrepancy, the mass discrepancy is only partially addressed. The remaining small but persisting mass discrepancy implies a mismatch between the physics in core to surface environments of 1D stellar models and the seismic observables probing these areas of fast-rotating stars.