New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) have revealed a remarkably thin spherical shell around U Antliae, a star located in the southern constellation of Antlia, about 900 light-years away from Earth.
This ALMA image reveals much finer structure in the U Antliae shell than has previously been possible. Image credit: ALMA / ESO / NAOJ / NRAO / F. Kerschbaum.
U Antliae (also known as HD 91793 and HR 4153) is a so-called carbon star — an evolved, cool and luminous star of the asymptotic giant branch type.
Around 2,700 years ago, this star went through a short period of rapid mass loss.
During this period of only a few hundred years, the material making up the shell seen in the new ALMA data was ejected at high speed.
Examination of U Antliae’s shell in further detail shows some evidence of thin, wispy gas clouds known as filamentary substructures.
“Understanding the chemical composition of the shells and atmospheres of stars like U Antliae, and how these shells form by mass loss, is important to properly understand how stars evolve in the early Universe and also how galaxies evolved,” said University of Vienna astronomer Franz Kerschbaum and co-authors.
“Such shells show a rich variety of chemical compounds based on carbon and other elements. They also help to recycle matter, and contribute up to 70% of the dust between stars.”
This image from the Digitized Sky Survey 2 shows U Antliae and its surroundings. Image credit: ESO / Digitized Sky Survey 2 / Davide De Martin.
The new ALMA data are not just a single image; ALMA produces a 3D dataset (a data cube) with each slice being observed at a slightly different wavelength.
“Because of the Doppler effect, this means that different slices of the data cube show images of gas moving at different speeds towards or away from the observer,” Dr. Kerschbaum and colleagues explained.
“U Antliae’s shell is also remarkable as it is very symmetrically round and also remarkably thin.”
“By displaying the different velocities we can cut this cosmic bubble into virtual slices just as we do in computer tomography of a human body.”
The research is published in the journal Astronomy & Astrophysics (arXiv.org preprint).
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F. Kerschbaum et al. 2017. Rings and filaments: The remarkable detached CO shell of U Antliae. A&A 605, A116; doi: 10.1051/0004-6361/201730665
