Accession Number:

ADA528580

Title:

Rusty Old Stars: A Source of the Missing Interstellar Iron

Descriptive Note:

Journal article

Corporate Author:

AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE

Report Date:

2010-06-18

Pagination or Media Count:

8.0

Abstract:

Iron, the universes 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 Spitzer Space Telescope 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, FeO is examined as the likely carrier for the 20 urn 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.

Subject Categories:

  • Astrophysics
  • Metallurgy and Metallography

Distribution Statement:

APPROVED FOR PUBLIC RELEASE