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Title: ON IRON MONOXIDE NANOPARTICLES AS A CARRIER OF THE MYSTERIOUS 21 μm EMISSION FEATURE IN POST-ASYMPTOTIC GIANT BRANCH STARS

A prominent mysterious emission feature peaking at ∼20.1 μm—historically known as the '21 μm' feature—is seen in over two dozen Galactic and Magellanic Cloud carbon-rich, post-asymptotic giant branch (post-AGB) stars. The nature of its carrier remains unknown since the first detection of the 21 μm feature in 1989. Over a dozen materials have been suggested as possible carrier candidates. However, none of them has been accepted: they either require too much material (compared to what is available in the circumstellar shells around these post-AGB stars), or exhibit additional emission features that are not seen in these 21 μm sources. Recently, iron monoxide (FeO) nanoparticles seem to be a promising carrier candidate as Fe is an abundant element and FeO emits exclusively at ∼21 μm. In this work, using the proto-typical protoplanetary nebula HD 56126 as a test case, we examine FeO nanoparticles as a carrier for the 21 μm feature by modeling their infrared emission, with FeO being stochastically heated by single stellar photons. We find that FeO emits too broad a 21 μm feature to explain that observed and the Fe abundance required to be locked up in FeO exceeds what is available in HD 56126. We therefore concludemore » that FeO nanoparticles are not likely to be responsible for the 21 μm feature.« less
Authors:
;  [1] ;  [2]
  1. Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States)
  2. Department of Astronomy, Beijing Normal University, Beijing 100875 (China)
Publication Date:
OSTI Identifier:
22270613
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; ASYMPTOTIC SOLUTIONS; CARBON; COMPARATIVE EVALUATIONS; COSMIC DUST; ELEMENT ABUNDANCE; GIANT STARS; IRON; IRON OXIDES; MAGELLANIC CLOUDS; NANOSTRUCTURES; NEBULAE; PARTICLES; PHOTONS; PROTOPLANETS; STOCHASTIC PROCESSES