The Extreme Overabundance of Molybdenum in Two Metal-Poor Stars

Abstract

We report determinations of the molybdenum abundances in five mildly to extremely metal-poor turnoff stars using five Mo II lines near 2000A. In two of the stars, the abundance of molybdenum is found to be extremely enhanced, as high or higher than the neighboring even-Z elements ruthenium and zirconium. Of the several nucleosynthesis scenarios envisioned for the production of nuclei in this mass range in the oldest stars, a high-entropy wind acting in a core-collapse supernova seems uniquely capable of the twin aspects of a high molybdenum overproduction confined to a narrow mass range. Whatever the details of the nucleosynthesis mechanism, however, this unusual excess suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-Fe heavy elements in these cases, an unexpected result given that both are only moderately metal-poor.

updated in v2, including text missing from the third-to-last paragraph in the published version

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• New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-Poor Stars
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• Stellar abundances and presolar grains trace the nucleosynthetic origin of molybdenum and ruthenium
• High-resolution abundance analysis of HD 140283
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• Diversity of Abundance Patterns of Light Neutron-capture Elements in Very-metal-poor Stars
• Trans-iron Ge, As, Se, and heavier elements in the dwarf metal-poor stars, HD~19445, HD~84937, HD~94028, HD~140283, and HD~160617
• A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283
• Enrichment of the Galactic disc with neutron-capture elements: Mo and Ru
• The Abundance of Lead in Four Metal-Poor Stars
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• New Fe I Level Energies and Line Identifications from Stellar Spectra. III. Initial Results from UV, Optical, and Infrared Spectra
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• The R-Process Alliance: A Nearly Complete R-Process Abundance Template Derived from Ultraviolet Spectroscopy of the R-Process-Enhanced Metal-Poor Star HD 222925