AlphaGalileo is a service for the media.
Journalists should register for free access to embargoed
news and press office contact information.
Please register view details
Please register to view contact details
Please log in or register to view articles older than 3 months
This item is under embargo and is only visible to journalists
Bookmark this item in My Area
This item is bookmarked
Add comments to this news release
Stars like our Sun eject large amounts of gas and dust into space, containing various elements and compounds. Asymptotic giant branch -- AGB -- phase stars, near their end of life, are particularly significant sources of such substances in our galaxy.
Formation of dust around AGB stars has been considered to play an important role in triggering acceleration of stellar wind, but the detailed mechanism of this acceleration has not been well explained.
And there is yet another conundrum. In space, silicon is ten times more abundant than aluminum. However, many oxygen-rich AGB stars are rich in aluminum oxide dust -- the major carrier of aluminum -- but poor in silicate dust -- the carrier of silicon, which has puzzled researchers: why is aluminum oxide dust so abundant around oxygen-rich AGB stars?
In a paper published in Science Advances, a research team led by Aki Takigawa of Kyoto University have utilized the Atacama Large Millimeter/submillimeter Array -- ALMA, as the high spatial-resolution radio interferometer in Chile is known -- to obtain detailed images of gas molecules forming dust surrounding an AGB star.
"Previously, there was a limit to how well we could observe dust forming regions close to stars," explains Takigawa. "Now, thanks to the high spatial resolution of ALMA, we can obtain images of gases in these regions in finer detail. So we pointed ALMA toward an aluminum oxide-rich AGB star, W Hydrae."
Gas molecules aluminum monoxide and silicon monoxide -- AlO and SiO -- eventually form aluminum oxide and silicate dust. The team observed that AlO was distributed within three stellar radii of W Hydrae, which was surprisingly similar to the previously-observed dust distribution.
Meanwhile, SiO was detected beyond five stellar radii, and moreover 70% remained gaseous, without forming into dust.
"These results indicate that as aluminum oxide grows and accumulates near a star, the addition of a small amount of silicate dust may trigger wind acceleration," elaborates Takigawa. "This decreases gas density, suppressing further silicate dust formation."
"This may explain the presence of aluminum-oxide-rich but silicate-poor AGB stars."
These new results shed light not only on the dynamics of gas and dust surrounding stars, but also on the importance of studying both together. The team plans to continue using ALMA to elucidate gas and dust dynamics in the universe.
The research team members are:
Aki Takigawa (Kyoto University), Takafumi, Kamizuka (The University of Tokyo), Shogo Tachibana (The University of Tokyo), Issei Yamamura (Japan Aerospace Exploration Agency/SOKENDAI)
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
Takigawa et al. "Dust formation and wind acceleration around the aluminum oxide–rich AGB star W Hydrae" in Science Advances in November 2017.
This item has been withdrawn. Registered users can contact the publishing organisation for further details by logging in