2010/05/19 by Iain McDonald, I. McDonald, G. C. Sloan +13 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1088/2041-8205/717/2/l92
7 pages. 4 figures, accepted ApJL
arxiv created 2010/05/19 · openalex publication_date 2010/06/18 · arxiv updated 2015/05/19 · openalex created_date 2019/06/27 · openalex updated_date 2026/07/31
Iron, the universe’s most abundant refractory element, is highly depleted in both circumstellar and interstellar environments, meaning it exists in solid form. The nature of this solid is unknown. In this Letter, we provide evidence that metallic iron grains are present around oxygen-rich asymptotic giant branch stars, where it is observationally manifest as a featureless mid-infrared excess. This identification is made using <i>Spitzer Space Telescope</i> observations of evolved globular cluster stars, where iron dust production appears ubiquitous and in some cases can be modeled as the only observed dust product. In this context, F<sub>e</sub>O is examined as the likely carrier for the 20 <i>μ</i>m feature observed in some of these stars.Metallic iron appears to be an important part of the dust condensation sequence at low metallicity, and subsequently plays an influential role in the interstellar medium. We explore the stellar metallicities and luminosities at which iron formation is observed, and how the presence of iron affects the outflow and its chemistry. The conditions under which iron can provide sufficient opacity to drive a wind remain unclear.