Netherlands Institute for Space Research (SRON) | 31 Aug 2010
Herschel Finds Water in a Cosmic DesertAstronomers have found water vapour in the atmosphere of a carbon star with the Herschel space observatory. Until now the formation of water vapour in the atmosphere of such a star was deemed impossible. The discovery was made by a team of astronomers led by Leen Decin (University of Amsterdam and Katholieke Universiteit Leuven, Belgium).
When the astronomers discovered the unexpected cloud of water vapour around the old red giant star CW Leonis (IRC+10216) in 2001, they immediately began searching for the source. Stars like IRC+10216 are known as carbon stars and are thought not to make much water. Initially they suspected the star’s heat must be evaporating comets or even dwarf planets to produce the water.
Now, Herschel’s PACS and SPIRE instruments have revealed that the secret ingredient is ultraviolet light, because the water is too hot to have come from the destruction of icy celestial bodies.
NASA JPL-Caltech Herschel | 2010-281 | 01 Sep 2010
Water features in old starsWater Around a Carbon Star
This Herschel image shows IRC+10216, also known as CW Leonis -- a star rich in carbon where astronomers were surprised to find water. This color-coded image shows the star, surrounded by a clumpy envelope of dust, at three infrared wavelengths, taken by Herschel's spectral and photometric imaging receiver (SPIRE) and photodetector array camera and spectrometer (PACS). Blue shows light of 160 microns; green shows 250 microns; and red shows 350 microns.
Credit: ESA/PACS SPIRE Consortia The Herschel infrared space observatory has discovered that ultraviolet starlight is the key ingredient for making water in space. It is the only explanation for why a dying star is surrounded by a gigantic cloud of hot water vapor. Herschel is a European Space Agency mission with important participation from NASA.
Every recipe needs a secret ingredient. When astronomers discovered an unexpected cloud of water vapor around the old star IRC+10216 using NASA's Submillimeter Wave Astronomy Satellite in 2001, they immediately began searching for the source. Stars like IRC+10216 are known as carbon stars and are thought not to make much water. Initially they suspected the star's heat must be evaporating comets or even dwarf planets to produce the water.
Now, Herschel has revealed that the secret ingredient is ultraviolet light, because the water is too hot to have come from the destruction of icy celestial bodies.
"Models predict that there should be no water in the envelopes around stars like this, so astronomers were puzzled about how it got there," said Paul Goldsmith, the NASA project scientist for Herschel at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "These Herschel observations confirm the surprising presence of water vapor in what we thought was an astronomical desert."
This research, which was led by Leen Decin of the Katholieke Universiteit Leuven, Belgium, appears in the Sept. 2 issue of Nature.
Nature 467 7311 | Editor's Summary | 02 Sep 2010
Astrophysics: Unexpected warm water - B GustafssonThe discovery in 2001 of water vapour around the ageing carbon star IRC+10216 was a surprise, because stellar evolution models predicted the virtual absence of water in carbon-rich stars. Several explanations were offered, but with only one water line detected in the spectrum of one carbon-rich evolved star, it was difficult to discriminate between the alternatives. Now observations with the European Space Agency's Herschel satellite have discovered dozens of water lines in the far-infrared and submillimetre spectrum of IRC+10216. These include high-excitation lines with energies corresponding to temperatures of around 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope.
- Nature 467 7311 35 (02 Sep 2010) DOI: 10.1038/467035a
- Nature 467 7311 64 (02 Sep 2010) DOI: 10.1038/nature09344
