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X-rays from Alpha Centauri - The darkening of the solar twin

Minimum credit line: Image courtesy of Robrade, Jan and ESA. (for details, see Conditions of Use).

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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.

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XMM-Newton; Europe's X-Ray Observatory
Last update: 09-Oct-2013 by