Rapidly rotating Population III stellar models as a source of primary nitrogen

¹ Department of Astronomy, University of Geneva, Chemin Pegasi 51, 1290 Versoix, Switzerland
e-mail: sofia.tsiatsiou@unige.ch
² Department of Physics and Astronomy, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556, USA
³ Astronomical Institute, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
⁴ Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium
⁵ Astrophysics Group, Keele University, Keele, Staffordshire ST5 5BG, UK
⁶ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁷ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁸ Department of Astronomy, University of Texas, Austin, TX 78712, USA
⁹ Independent Researcher, Ireland
¹⁰ Independent Researcher, The Netherlands

Received: 3 January 2024
Accepted: 20 April 2024

Abstract

Context. The first stars might have been fast rotators. This would have important consequences for their radiative, mechanical, and chemical feedback.

Aims. We discuss the impact of fast initial rotation on the evolution of massive Population III models and on their nitrogen and oxygen stellar yields.

Methods. We explore the evolution of Population III stars with initial masses in the range of 9 M_⊙ ≤ M_ini ≤ 120 M_⊙, starting with an initial rotation on the zero-age main sequence equal to 70% of the critical one.

Results. We find that with the physics of rotation considered here, our rapidly rotating Population III stellar models do not follow a homogeneous evolution. They lose very little mass in the case in which mechanical winds are switched on when the surface rotation becomes equal to or larger than the critical velocity. The impact on the ionising flux appears to be modest when compared to moderately rotating models. Fast rotation favours, in models with initial masses above ∼20 M_⊙, the appearance of a very extended intermediate convective zone around the H-burning shell during the core He-burning phase. This shell has important consequences for the sizes of the He- and CO-cores, and thus impacts the final fate of stars. Moreover, it has a strong impact on nucleosynthesis, boosting the production of primary ¹⁴N.

Conclusions. Fast initial rotation significantly impacts the chemical feedback of Population III stars. Observations of extremely metal-poor stars and/or starbursting regions are essential to provide constraints on the properties of the first stars.