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 XMM-Newton Home > Gallery Home > Stars > Normal Stars > Alpha Centauri A+B

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).

The image above can be displayed at full size and may be downloaded by clicking the image above.

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: 02-Jun-2015 by