Mirror principle and the red-giant bump: the battle of entropy in low-mass stars

Abstract

The evolution of low-mass stars into red giants is still poorly understood. During this evolution the core of the star contracts and, simultaneously, the envelope expands -- a process known as the `mirror'. Additionally, there is a short phase where the trend for increasing luminosity is reversed. This is known as the red-giant-branch bump. We explore the underlying physical reasons for these two phenomena by considering the specific entropy distribution in the star and its temporal changes. We find that between the luminosity maximum and luminosity minimum of the bump there is no mirror present and the star is fully contracting. The contraction is halted and the star regains its mirror when the hydrogen-burning shell reaches the mean molecular weight discontinuity. This marks the luminosity minimum of the bump.

arXiv comment10 pages, 11 figures, accepted for publication by MNRAS

References in corpus (10)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• GYRE: An open-source stellar oscillation code based on a new Magnus Multiple Shooting Scheme
• The Red Giant Branch Luminosity Function Bump
• The Red-Giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
• The shape of the Red Giant Branch Bump as a diagnostic of partial mixing processes in low-mass stars
• On the red-giant luminosity bump
• Diagnostics of Stellar Modelling from Spectroscopy and Photometry of Globular Clusters
• Why do low-mass stars become red giants?
• Investigating the Consistency of Stellar Evolution Models with Globular Cluster Observations via the Red Giant Branch Bump

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• Stellar evolution models with entropy-calibrated mixing-length parameter: application to red giants
• A Red Giants' Toy Story
• A Red Giants' Toy Story II: Understanding the Red-Giant Branch Bump
• Dynamical mass of a solar-like oscillator at the main-sequence turnoff from Gaia astrometry & ground-based spectroscopy