Water vapor clouds surround bright giant star

Surprising knowledge raises questions about the chemical composition of end-stage stars

Picture of the carbon star CW Leonis with its shell-shaped dust cover. This consists mainly of soot, which is produced in large quantities by the star. In the inner area of ​​the shell, hot steam was discovered by Herschel. Taken with the Very Large Telescope of the European Southern Observatory in Chile. North is up and east is left. © Izan Leao / Federal University of Rio Grande do Norte, Brazil
Read out

With the help of the Herschel satellite telescope, astronomers have detected large amounts of water vapor at a temperature of around 700 degrees Celsius in the shell of the aging carbon star CW Leonis. This surprising finding raises new questions about the chemical composition of stars in their final stages, according to the scientists in the latest issue of Nature.

In the constellation Leo is the red giant star CW Leonis, which produces vast amounts of gas and carbon dust - in total on the order of one earth mass per year. He gives the astronomers puzzles since since 2001 for the first time evidence of water vapor was found in its extensive shell: Since then, the question arises, how water can arise around such an object.

Because a carbon-rich star like this one is usually surrounded by carbon monoxide and not like CW Leonis with oxygenated molecules - like H2O.

Spectroscopic data from Herschel

Thanks to the Herschel satellite of the European Space Agency (ESA), the research team, which also included astronomers working with Franz Kerschbaum from the University of Vienna, for the first time succeeded in clearly demonstrating dozens of water vapor lines in the spectrum of the deep red star.

As the scientists report in Nature, some of the detected spectral lines can only be explained by transitions from highly excited states - which requires temperatures of about 700 degrees Celsius. display

So there must be water vapor in the inner, sooty shell of the carbon star. It may be there by UV radiation by photochemical means. This would require a special lumpy structure of the star's high atmosphere.

Software from Austria

Herschel, who obtained the results, observes the sky in the far infrared and has a light-collecting surface twice that of the Hubble Space Telescope.

At the Institute for Astronomy of the University of Vienna, the software was developed which makes it possible to compress the data sufficiently on board the satellite in order to transfer it to Earth ", says Kerschbaum.

(idw - University of Vienna, 02.09.2010 - DLO)