Abstract: 
The post-main sequence evolution of low-mass stars into red-giant stars is of fundamental interest for understanding stellar evolution, as well as for the study of galactic evolution. Yet at the same time it remains an enigma. Of particular interest are two phenomena seen in this evolutionary progression. Firstly, there is the expansion of the envelope and simultaneous contraction of the inner regions of low-mass stars in the subgiant phase and up to the tip of the red-giant branch (RGB), known as the mirror phenomenon. During this time mass shells in the envelope move outwards and mass shells in the inner regions move inwards. Secondly, there is the red-giant-branch bump (RGBB) which is the phase where the trend in increasing luminosity reverses for a short time before it increases again, causing a zig-zag in the evolutionary track. In this talk, I will present the results as presented by Hekker et al. 2020 whom looked at these phenomena from the perspective of the entropy and proposed a toy model to further understand the cause of the RGBB.

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