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Abstract: We present a comprehensive abundance analysis of 27 heavy elements in brightgiant stars of the globular clusters M4 and M5 based on high resolution, highsignal-to-noise ratio spectra obtained with the Magellan Clay Telescope. Weconfirm and expand upon previous results for these clusters by showing that 1all elements heavier than, and including, Si have constant abundances withineach cluster, 2 the elements from Ca to Ni have indistinguishablecompositions in M4 and M5, 3 Si, Cu, Zn, and all s-process elements areapproximately 0.3 dex overabundant in M4 relative to M5, and 4 the r-processelements Sm, Eu, Gd, and Th are slightly overabundant in M5 relative to M4. Thecluster-to-cluster abundance differences for Cu and Zn are intriguing,especially in light of their uncertain nucleosynthetic origins. We confirm thatstars other than Type Ia supernovae must produce significant amounts of Cu andZn at or below the clusters- metallicities. If intermediate-mass AGB stars ormassive stars are responsible for the Cu and Zn enhancements in M4, the similarRb-Zr ratios and preliminary Mg isotope ratios in both clusters may beproblematic for either scenario. For the elements from Ba to Hf, we assume thatthe s- and r-process contributions are scaled versions of the solar s- andr-process abundances. We quantify the relative fractions of s- and r-processmaterial for each cluster and show that they provide an excellent fit to theobserved abundances.

Author: David Yong 1, Amanda I. Karakas 1, David L. Lambert 2, Alessandro Chieffi 3, Marco Limongi 4 1 RSAA, Mt Stromlo Observatory, 2 Un

Source: https://arxiv.org/

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