X-rays from Alpha Centauri - The darkening of the solar twin
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Image courtesy of Robrade, Jan and ESA.
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About this Image
Two EPIC MOS images of Alpha Centauri A+B, taken in March 2003 (left) and Feb. 2005 (right). Alpha Centauri
is the nearest stellar system consisting of a G2V (A) and a K1V (B) star at a distance of about 4 light-years,
the M dwarf Proxima Centauri is not in the field of view.
The separation of Alpha Centauri A+B is in March 2003 around 12",
in Feb. 2005 somewhat above 10".
Alpha Cen B is the X-ray brighter object down right and exhibits a comparable X-ray luminosity in both exposures.
In contrast Alpha Cen A, a star very similar to our Sun, is only visible in the left image.
It has fainted in X-rays by at least an order of magnitude, a behaviour never observed before despite several
observations of the Alpha Centauri system over the last 25 years. Is this an irregular event or do we see a
coronal activity cycle ?
The Sun, a rather inactive star, exhibits a well known activity cycle with a period of 11 years.
While chromospheric activity cycles on low activity stars are established from optical measurements of Ca II emission lines,
X-ray, i.e. coronal, activity cycles are known for very few objects, often correlated with chromospheric activity.
A long-term monitoring program with XMM-Newton of solar-like stars, including Alpha Centauri A+B,
was initiated to put some more light on this topic. No activity cycle was ever detected on a component of Alpha Centauri.
Since also no chromospheric data of Alpha Centauri is available and all previous resolved X-ray observations
(Einstein, ROSAT, Chandra) revealed a similar situation as during the March 2003 XMM-Newton observation,
a definite explanation of this astonishing finding can only be given by future observations.
Investigator(s): Robrade, J., Schmitt, J.H.M.M., Favata, F.
Higher resolution versions of this image may be available, please contact the XMM-Newton HelpDesk.
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