EDP Sciences
Free access
Volume 413, Number 3, January III 2004
Page(s) 1095 - 1104
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20031575

A&A 413, 1095-1104 (2004)
DOI: 10.1051/0004-6361:20031575

The corona of HD 199178 (V 1794 Cygni)

P. Gondoin

European Space Agency, ESTEC - Postbus 299, 2200 AG Noordwijk, The Netherlands
(Received 20 May 2003 / Accepted 1 October 2003)

HD 199178 (V 1794 Cygni), a chromospherically active late-type giant with a high X-ray luminosity, was observed by the XMM-Newton space observatory. Series of lines of highly ionized Fe and several Lyman lines of hydrogen-like ions are visible in the reflection grating spectra, most notably from O and Ne. Analysis results suggest a scenario where the corona of HD 199178 is dominated by large magnetic structures similar in size to interconnecting loops between solar active regions but significantly hotter. The surface area coverage of these active regions may approach up to a 90%. An hypothesis is that the interaction of these structures themselves induces a flaring activity in a small scale not visible in the EPIC light curves that is responsible for heating HD 199178 plasma to coronal temperatures of $T
\ge 10^{7}$  K. The intense X-ray activity of HD 199178 is related to its evolutionary position at the bottom of the red giant branch. It is anticipated that its rotation will spin-down in the future with the effect of decreasing its helicity related, dynamo driven activity and suppressing large scale magnetic structures in its corona.

Key words: stars: individual: HD 199178 -- stars: activity -- stars: coronae -- stars: evolution -- stars: late-type -- stars: x-ray

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© ESO 2004