The corona of HD 223460 (HR 9024)

European Space Agency, ESTEC – Postbus 299, 2200 AG Noordwijk, The Netherlands

Corresponding author: pgondoin@rssd.esa.int

Received: 13 December 2002
Accepted: 19 June 2003

Abstract

HD 223460 (HR 9024), 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 and triplet lines of helium-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 223460 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 30%. A hypothesis is that the interaction of these structures themselves induces a flaring activity on a small scale not visible in the EPIC light curves that is responsible for heating HD 223460 plasma to coronal temperatures of  K. The intense X-ray activity of HD 223460 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.