Nav: Home

Stars shrouded in iron dust

January 23, 2019

Stars with masses between one and eight times the mass of the Sun evolve along the asymptotic giant branch (AGB) before ending their lives as white dwarfs. It is during this rapid but crucial phase when the stars expand to huge dimensions and cool down, losing a major fraction of their mass due to the strong stellar winds. The low temperature and high density of the winds provide ideal conditions for the condensation of dust grains in their circumstellar envelopes.

The dust produced by the stars in their AGB phase and expelled into the interstellar medium is important for the lives of the galaxies, because this is an essential component for the formation of new stars, and also of planets. That is why characterising the type of dust (solid state organic components, or inorganic components) and the quantity of dust produced by these giant stars is very interesting to the astronomical community.

The journal The Astrophysical Journal Letters today is publishing a study which has answers to the puzzles of a peculiar group of massive AGB stars situated in the Large Magellanic Cloud. Comparing the infrared observations made with the Spitzer Space Telescope (and predictions for the future James Webb Space Telescope) with the theoretical models developed by this group, they have discovered that these stars have masses around 5 solar masses, were formed around 100 million years ago, and are poor in metals (such as iron, magnesium and silicon). Unexpectedly they have discovered that the infrared spectral energy distributions can be reproduced only if iron dust is the principal dust component of their circumstellar envelopes. This is uncommon around massive AGB stars. Before it was known that they mainly produced silicates, large quantities of dust rich in oxygen and silicon, as well as magnesium. But this finding is even more surprising if we consider the metal poor environment of the stars under study.

We have characterized for the first time this class of stars with unique spectral properties. The low metallicity of these giant stars is the essential ingredient which gives peculiar conditions permitting the formation of large quantities of iron dust" explains Ester Marini, the first author of the article and a doctoral student at the Roma Tre University. She adds "In fact, in metal poor environments the complex nucleosynthesis within massive AGB stars is so advanced that it burns up almost all the magnesium and oxygen, necessary to form other types of dust, such as the silicates".

Under these particular conditions iron dust becomes the main component of the dust formed by these stars. "This result is an important confirmation of the theory of iron dust in metal poor environments, already hinted at in independent observational evidence" says the IAC researcher Aníbal García Hernández, a co-author of the work, and one of the initiators of the fruitful collaboration between the IAC and the Osservatorio Astronomico di Roma (OAR-INAF) on these type of giant AGB stars.

"The arrival of the James Webb Space Telescope (JWST) will open up new possibilities for investigating this case in depth", comments Flavia Dell'Agli, a postdoctoral researcher at the IAC, and second author of the article. She adds "That future telescope will greatly enhance the number of resolved extragalactic AGB stars" and that the MIRI instrument on the JWST will be "ideal for identifying this class of stars in other galaxies of the Local Group".
-end-


Instituto de Astrofísica de Canarias (IAC)

Related Iron Articles:

How nitrogen-fixing bacteria sense iron
New research reveals how nitrogen-fixing bacteria sense iron - an essential but deadly micronutrient.
Getting to the root of how plants tolerate too much iron
Salk scientists have found a major genetic regulator of iron tolerance, a gene called GSNOR.
Stressed plants must have iron under control
When land plants' nutrient availability dwindles, they have to respond to this stress.
Is a great iron fertilization experiment already underway?
Using a new, highly sensitive tracer for human-derived iron falling on the ocean, researchers led by the USF College of Marine Science say we have underestimated the iron we add to the ocean compared to natural sources.
High on iron? It stops anaemia but has a downside
A global study looking at the role that iron plays in 900 diseases has uncovered the impact of both low and high iron levels -- and the news is mixed.
Gold for iron nanocubes
Hybrid Au/Fe nanoparticles can grow in an unprecedentedly complex structure with a single-step fabrication method.
BU finds iron may not improve fertility
A new study led by Boston University School of Public Health (BUSPH) researchers finds that there is no consistent association between consuming iron and becoming pregnant.
Study confirms banded iron formations originated from oxidized iron
A new study by University of Alberta scientists shows that banded iron formations originated from oxidized iron, confirming the relevance and accuracy of existing models -- a finding of great importance to the geological community.
Iron volcanoes may have erupted on metal asteroids
Metallic asteroids are thought to have started out as blobs of molten iron floating in space.
study looks to iron from microbes for climate help
Distributing iron particles produced by bacteria could 'fertilize' microscopic ocean plants and ultimately lower atmospheric carbon levels, according to a new paper in Frontiers.
More Iron News and Iron Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#544 Prosperity Without Growth
The societies we live in are organised around growth, objects, and driving forward a constantly expanding economy as benchmarks of success and prosperity. But this growing consumption at all costs is at odds with our understanding of what our planet can support. How do we lower the environmental impact of economic activity? How do we redefine success and prosperity separate from GDP, which politicians and governments have focused on for decades? We speak with ecological economist Tim Jackson, Professor of Sustainable Development at the University of Surrey, Director of the Centre for the Understanding of Sustainable Propserity, and author of...
Now Playing: Radiolab

An Announcement from Radiolab