Ground-based observation of emission lines from the corona of a red-dwarf star

All 'solar-like' stars 1 are surrounded by coronae(2), which contain magnet ically confined plasma at temperatures above 10(6) K. (Until now, only the Sun's corona could be observed in the optical-as a shimmering envelope duri ng a total solar eclipse.) As the underlying stellar 'surfaces'-the photosp heres-are much cooler, some non-radiative process must be responsible for h eating the coronae. The heating mechanism is generally thought to be magnet ic in origin, but is not yet understood even for the case of the Sun. Ultra violet emission lines first led to the discovery of the enormous temperatur e of the Sun's corona(3,4), but thermal emission from the coronae of other stars has hitherto been detectable only from space, at X-ray wavelengths. H ere we report the detection of emission from highly ionized iron (Fe XIII a t 3,388.1 Angstrom) in the corona of the red-dwarf star CN Leonis, using a ground-based telescope. The X-ray flux inferred from our data is consistent with previously measured X-ray fluxes, and the non-thermal line width of 1 8.4 kms(-1) indicates great similarities between solar and stellar coronal heating mechanisms. The accessibility and spectral resolution (45,000) of t he ground-based instrument are much better than those of X-ray satellites, so a new window to the study of stellar coronae has been opened.