The Extreme Overabundance of Molybdenum in Two Metal-Poor Stars

TL;DR

This study measures molybdenum levels in five metal-poor stars, revealing extreme overabundance in two, which suggests rare nucleosynthesis events like high-entropy winds in supernovae contributed to their formation.

Contribution

It provides the first detailed molybdenum abundance measurements in metal-poor stars, highlighting rare nucleosynthesis processes responsible for heavy element production.

Findings

Two stars show extremely high molybdenum abundance.

High molybdenum overproduction is confined to a narrow mass range.

Rare nucleosynthesis events likely caused the observed overabundance.

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.