Issue |
A&A
Volume 444, Number 2, December III 2005
|
|
---|---|---|
Page(s) | 531 - 538 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20053567 | |
Published online | 25 November 2005 |
The relation between X-ray activity and rotation in intermediate-mass G giants
European Space Agency, ESTEC – Postbus 299, 2200 AG Noordwijk, The Netherlands
Received:
3
June
2005
Accepted:
11
July
2005
I study the relation between X-ray activity and rotation among
intermediate-mass single G giants. The results show evidence that the
quiescent coronal activity of these stars, as measured by their X-ray
surface flux, increases linearly with the angular rotation velocity
and with the inverse of the Rossby number. Even the most rapidly
rotating G giants do not reach the canonical log() ≈ –3 saturation level. The effect of rapid rotation
on these stars could result mainly in an increased coverage of their
surface with magnetic close loop structures. The empirical
activity-rotation relationship accounts for the occurrence of a
maximum of magnetic activity in the atmosphere of intermediate-mass
stars as they evolve off the main-sequence near the bottom of the red
giant branch. Remarkably, the relation between X-ray to bolometric
luminosity ratio and the Rossby number or rotation period for G giants
differs from the power law dependence with an index of about –2 that
is observed for main-sequence stars. Possible implications for the
dynamo generation of magnetic fields on giants are discussed.
Key words: stars: activity / stars: coronae / stars: evolution / stars: late-type / X-rays: stars / stars: magnetic fields
© ESO, 2005
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