[Paper Review] Stellar evolution with rotation XII: Pre-supernova models

Raphaël Hirschi, G. Meynet+1 more|ArXiv.org|Jun 24, 2004

Stellar, planetary, and galactic studiesPhysics and Astronomy34 references157 citations

TL;DR

This paper presents pre-supernova models of rotating massive stars (12–60 M☉) using an updated version of the Geneva stellar evolution code, incorporating rotationally induced mixing (meridional circulation, secular and dynamical shear instabilities) and an extended α-chain nuclear reaction network. The key finding is that rotation significantly alters pre-supernova structure—especially between 15 and 30 M☉—by increasing core sizes by ~1.5×, shifting progenitor colors from red to blue supergiant, and changing supernova types (Ibc instead of II), primarily due to rotational effects during H and He burning, not late-stage instabilities.

ABSTRACT

We describe the latest developments of the Geneva stellar evolution code in order to model the pre-supernova evolution of rotating massive stars. Rotating and non-rotating stellar models at solar metallicity with masses equal to 12, 15, 20, 25, 40 and 60 solar masses were computed from the ZAMS until the end of the core silicon burning phase. We took into account meridional circulation, secular shear instabilities, horizontal turbulence and dynamical shear instabilities. Most of the differences between the pre-supernova structures obtained from rotating and non-rotating stellar models have their origin in the effects of rotation during the core hydrogen and helium burning phases. The effects of rotation on pre-supernova models are significant between 15 and 30 solar masses. Indeed, rotation increases the core sizes (and the yields) by a factor ~ 1.5. Above 20 solar masses, rotation may change the colour of the supernova progenitors (blue instead of red supergiant) and the supernova type (Ib instead of II). Rotation affects the lower mass limits for radiative core carbon burning, for iron core collapse and for black hole formation. For Wolf-Rayet stars (M > 30 solar masses), the pre-supernova structures are mostly affected by the intensities of the stellar winds and less by rotational mixing. Finally, the core of our rotating WR stars contain enough angular momentum to produce GRBs.

Motivation & Objective

• To extend the Geneva stellar evolution code to model the pre-supernova evolution of rotating massive stars beyond core helium burning.
• To investigate how rotational mixing processes (meridional circulation, secular and dynamical shear instabilities) affect internal structure and angular momentum distribution during advanced burning stages.
• To determine the impact of rotation on pre-supernova core masses, progenitor radii, colors, and supernova types at solar metallicity.
• To compare rotating and non-rotating models to assess the role of rotation in altering core collapse conditions and nucleosynthetic yields.
• To evaluate the lower mass limit for iron core collapse and black hole formation in rotating stars, especially near 12 M☉.

Proposed method

• Extended the nuclear reaction network to include 13 α-chain elements (from 12C to 56Ni), using the method of Arnett & Truran (1969) for stable and rapid integration of abundance evolution.
• Applied Sugimoto’s discretization scheme to stabilize the internal structure equations during advanced evolutionary phases, preventing numerical instabilities.
• Incorporated rotational mixing processes: secular shear, meridional circulation, and dynamical shear instabilities, with dynamical shear acting to smooth angular velocity gradients.
• Used the Schwarzschild criterion for convective stability and 0.1 H_P overshooting in H- and He-burning cores.
• Resolved energy production during Si-burning via the bottleneck reaction between 44Ti and 48Cr, assuming nuclear statistical equilibrium for other heavy elements.
• Computed models from ZAMS to the end of core silicon burning for 12, 15, 20, 25, 40, and 60 M☉ stars at solar metallicity, with and without rotation.

Experimental results

Research questions

• RQ1 How do rotational mixing processes affect the internal angular momentum and chemical structure during the pre-supernova evolution of massive stars?
• RQ2 To what extent do dynamical shear instabilities transport angular momentum or chemical species over long distances in advanced evolutionary stages?
• RQ3 How does rotation alter the core size, progenitor radius, and color of massive stars just before core collapse?
• RQ4 What is the impact of rotation on the lower mass limit for iron core collapse and black hole formation?
• RQ5 How do rotating pre-supernova models compare with non-rotating models in terms of core mass, yields, and supernova type (II vs. Ibc)?

Key findings

• Dynamical shear instabilities primarily smooth sharp angular velocity gradients but do not significantly transport angular momentum or chemical species over long distances.
• Rotation increases core sizes by a factor of ~1.5 in the 15–30 M☉ range, significantly altering yields and progenitor structure.
• For stars between 15 and 30 M☉, rotation can change progenitor morphology from red supergiant to blue supergiant, leading to supernova types Ibc instead of II.
• The effects of rotation on pre-supernova structure are dominated by processes during H and He burning; late-stage instabilities have minimal impact on angular momentum evolution.
• The final angular momentum is well-preserved after core helium burning, allowing reliable estimation of pre-collapse angular momentum.
• Rotating models suggest a lower mass limit for iron core collapse than non-rotating models, with potential collapse possible even at 12 M☉ when rotational mixing is included.