Giant star expels multiple dust shells, astronomers find

ScienceDaily (Sep. 27, 2011) — An international team led by KU Leuven astronomer Leen Decin discovered not less than a dozen cold dust arcs around the giant star CW Leo. The team used the sensitive PACS instrument on board the Herschel Space Observatory to detect for the first time arcs of dust far away from the star. CW Leo has expelled these shells of dust in different epochs in its life. The faintest shell we can see now was, according to the team, expelled about 16,000 years ago. In the mean time it has drifted away from the star over more than 7,000 billion kilometers.

Episodes

"Until recently, the environment of giant stars seemed homogeneous, but more and more observations indicate that this is not true," says Leen Decin. "These new Herschel images confirm that in a stunning way. We have detected a dozen arcs, puffed out by the star in the course of its life. The faintest shell we found is already at a distance of 7,000 billion kilometers from the star."

The different shells were ejected by the star with intervals of 500 to 1,700 years. The astronomers in the team believe such shells, even fainter, are also present further out, up to the violent bow shock where the expelled material of the star collides with the interstellar medium. The oldest shells have probably disappeared in the bow shock already.

Our own Sun too will turn into a red giant star, about five billion years from now, when it will inflate and condensate dust in the outer, cooling layers of its atmosphere. The episodes in CW Leo's history help astronomers understand the future of our own Sun.

Cold

Since the different shells have been travelling far away from the star by now, they are also very cold, about -248°C. The PACS instrument onboard the Herschel Space Telescope was especially designed to make images of the far-infrared light emitted by dust that cold. Thanks to the Belgian participation in the building of the PACS instrument, the team got priority access to the space telescope. Christoffel Waelkens, Co-principal investigator of the PACS instrument consortium is proud of yet another discovery by Herschel: "We had a lot of ideas for science with Herschel, but we also hoped that Herschel would surprise us with unexpected results. It has been a continuous delight since the first observations: at every opportunity nature proves to have more imagination than we have, but still presents us the phenomena so that we can understand them."

Digging in the data

Making the rings visible in the Herschel images was not trivial. Pierre Royer, instrument expert in the PACS team of the Institute of Astronomy at KU Leuven, clarifies: "The work of constantly refining the instrumental calibration and improving the data-analysis techniques really becomes rewarding when it comes to push the instrument to its limits, allowing for cutting-edge science." Also after the Herschel Launch in 2009 the PACS instrument team, including 7 scientists and engineers at KU Leuven, continued to refine the initial calibration and data analysis software.

Publication

The team published the results in the October 2011 issue of the journal Astronomy & Astrophysics.

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Katholieke Universiteit Leuven.

Journal Reference:

L. Decin, P. Royer, N. L. J. Cox, B. Vandenbussche, R. Ottensamer, J. A. D. L. Blommaert, M. A. T. Groenewegen, M. J. Barlow, T. Lim, F. Kerschbaum, T. Posch, C. Waelkens. Discovery of multiple dust shells beyond 1?arcmin in the circumstellar envelope of IRC +10216 usingHerschel/PACS. Astronomy & Astrophysics, 2011; 534: A1 DOI: 10.1051/0004-6361/201117360

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Researchers discover superatoms with magnetic shells

ScienceDaily (June 9, 2011) — A team of Virginia Commonwealth University scientists has discovered a new class of 'superatoms' -- a stable cluster of atoms that can mimic different elements of the periodic table -- with unusual magnetic characteristics.

The superatom contains magnetized magnesium atoms, an element traditionally considered as non-magnetic. The metallic character of magnesium along with infused magnetism may one day be used to create molecular electronic devices for the next generation of faster processors, larger memory storage and quantum computers.

In a study published online in the Early Edition of the Proceedings of the National Academy of Sciences, the team reports that the newly discovered cluster consisting of one iron and eight magnesium atoms acts like a tiny magnet that derives its magnetic strength from the iron and magnesium atoms. The combined unit matches the magnetic strength of a single iron atom while preferentially allowing electrons of specific spin orientation to be distributed throughout the cluster.

Through an elaborate series of theoretical studies, Shiv N. Khanna, Ph.D., a Commonwealth professor in the VCU Department of Physics, and his team examined the electronic and magnetic properties of clusters having one iron atom surrounded by multiple magnesium atoms. The team included instructor J. Ulises Reveles and Victor M. Medel, a post-doctoral associate, both from VCU; A. W. Castleman Jr., Ph.D., the Evan Pugh Professor of Chemistry and Physics, and Eberly Distinguished chair in Science in the Department of Chemistry at Penn State University; and Prasenjit Sen and Vikas Chauhan from the Harish-Chandra Research Institute in Allahabad, India.

"Our research opens a new way of infusing magnetic character in otherwise non-magnetic elements through controlled association with a single magnetic atom. An important objective was to discover what combination of atoms would lead to a species that is stable as we put multiple units together," said Khanna.

"The combination of magnetic and conducting attributes was also desirable. Magnesium is a good conductor of electricity and, hence, the superatom combines the benefit of magnetic character along with ease of conduction through its outer skin," he said.

The team found that when the cluster had eight magnesium atoms it acquired extra stability due to filled electronic shells that were far separated from the unfilled shells. An atom is in a stable configuration when its outermost shell is full and far separated from unfilled shells, as found in inert gas atoms. Khanna said that such phenomena commonly occur with paired electrons which are non-magnetic, but in this study the magnetic electronic shell showed stability.

According to Khanna, the new cluster had a magnetic moment of four Bohr magnetons, which is almost twice that of an iron atom in solid iron magnets. A magnetic moment is a measure of the magnetic strength of the cluster. Although the periodic table has more than one hundred elements, there are only nine elements that exhibit magnetic character in solid form.

"A combination such as the one we have created here can lead to significant developments in the area of "molecular electronics" where such devices allow the flow of electrons with particular spin orientation desired for applications such as quantum computers. These molecular devices are also expected to help make denser integrated devices, higher data processing, and other benefits," said Reveles.

Khanna and his team are conducting preliminary studies on the assemblies of the new superatoms and have made some promising observations that may have applications in spintronics. Spintronics is a process using electron spin to synthesize new devices for memory and data processing.

This research was supported by the U.S. Department of Energy.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Virginia Commonwealth University.

Journal Reference:

Victor M. Medel, Jose Ulises Reveles, Shiv N. Khanna, Vikas Chauhan, Prasenjit Sen, A. Welford Castleman. Hund's rule in superatoms with transition metal impurities. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1100129108

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here