Are C-rich ultra iron poor stars also He-rich - Astrophysics > Solar and Stellar AstrophysicsReport as inadecuate

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Abstract: abridged The three most iron poor stars presently known Fe-H equal to-5.96 -5.4 and -4.75 are carbon-rich, they are called C-Rich Ultra-Metal PoorStars CRUMPS. The origin of their peculiar surface abundances is notunderstood. We propose a synthetic view of the different models so far proposedto explain the peculiar abundances observed at the surface of the CRUMP stars.We deduce some expected trends based on nucleosynthetic arguments and look forsignatures allowing to discriminate among models. We discuss the conditions forhaving CRUMP stars which are He-rich, i.e. with a mass fraction of heliumgreater than 0.30 and up to 0.60. We discuss the chemical composition of starsmade of interstellar medium mixed with wind material of very metal poor massivestars, with wind plus supernova ejecta and with material extracted from theenvelope of early AGB stars. Rotating and non-rotating models are considered.CRUMP stars formed from wind material of massive stars mixed with small amountsof pristine interstellar medium are He-rich helium mass fraction between 0.30and 0.60, Li-depleted and present low $^{12}$C-$^{13}$C ratios inferior to 10in number. Such He-rich stars, if discovered, would confirm that the mostmetal poor CRUMPs formed from essentially pure wind-envelope material. Theywould provide the most direct way to probe the nucleosynthetic outputs of thefirst generations of stars. We show that rotation is a key ingredient toexplain the abundance patterns of CRUMPS stars.

Author: Georges Meynet, Raphael Hirschi, Sylvia Ekstrom, Andre Maeder, Cyril Georgy, Patrick Eggenberger, Cristina Chiappini


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