The glory of a nearby star

August 01, 2001

Optical light from a hot stellar corona detected with the VLT

The solar corona is a beautiful sight during total solar eclipses. It is the uppermost region of the extended solar atmosphere and consists of a very hot (over 1 million degrees), tenuous plasma of highly ionised elements that emit strong X-ray radiation. There is also a much weaker coronal emission in the optical part of the spectrum.

The Sun is a normal star and X-ray observations from rockets and orbiting X-ray telescopes have shown that many other stars also possess coronae. But due to observational limits of the telescopes available so far, the much fainter optical emission from stellar coronae had never been detected.

Now, however, an optical coronal line from iron ions that have lost 12 electrons (Fe XIII) has for the first time been observed in a star other than the Sun. The object, a cool star named CN Leonis, is located at a distance of 8 light-years. This impressive observational feat was performed with the UV-Visual Echelle Spectrograph (UVES) on the VLT 8.2-m KUEYEN telescope at the ESO Paranal Observatory, within a programme by German astronomer Juergen Schmitt and his collaborators at the University of Hamburg Observatory.

The possibility to observe stellar coronae with ground-based telescopes opens up new and exciting research opportunities, including the detailed study of stellar cycles, similar to the 11-year solar period.
The full text of ESO Press Release 17/01 on this subject, with 4 photos and all weblinks, is available at:


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