Rusty old stars: a source of the missing interstellar iron?

McDonald, I., Sloan, G. C., Zijlstra, A. A., Matsunaga, N., Matsuura, M. ORCID: https://orcid.org/0000-0002-5529-5593, Kraemer, K. E., Bernard-Salas, J. and Markwick, A. J. 2010. Rusty old stars: a source of the missing interstellar iron? The Astrophysical Journal Letters 717 (2) , L92–L97. 10.1088/2041-8205/717/2/l92

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Abstract

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 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 μm 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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Publisher:	American Astronomical Society
ISSN:	2041-8205
Date of Acceptance:	19 May 2010
Last Modified:	14 May 2024 13:15
URI:	https://orca.cardiff.ac.uk/id/eprint/168068

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