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Stellar models are one of the backbones of modern astronomy. Recent advances in observational astronomy - through asteroseismology, precision photometry, high-resolution spectroscopy, and large-scale surveys - are placing stellar models under greater quantitative scrutiny than ever. The model limitations are being exposed and the next generation of stellar models is needed as soon as possible. Here we review the evolution and importance of core helium burning stars and then discuss a range of methods, both theoretical and observational, that we are using to advance the models. Known observationally as SdB, red clump, horizontal branch, and second clump stars, core helium burning stars are numerous and relatively luminous and therefore contribute disproportionately to distant/extragalactic emission. Our best models of these stars are very uncertain, and poorly constrained by observations. These uncertainties propagate to the later phases of stellar evolution, undermining the accuracy of models of supernova explosions and red giants - both vital to the chemical evolution of the Universe. |
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