Credit:European Space Agency/EPIC team

Schizophrenic Twins

The bright star Castor is a well known to observers; Castor and its "twin" Pollux mark the constellation of Gemini. Many people would be surprised to learn that the optical star Castor is in fact composed of 6 stars. This sextuplet consists of a pair of A-type stars, Castor AB, orbiting each other with a period of 467 years. Around each of these A-type stars orbits another star, an invisible dwarf. Just south of this pair of A-type stars is the star YY Gem, another binary composed of 2 M dwarfs which dance around each other every 19 hours. X-ray astronomers have known for some time that YY Gem and at least one star in the Castor AB system are X-ray sources. A new observation with the EPIC camera on XMM-Newton shows that all 3 binaries are sources of X-rays from gas at temperatures of millions of degrees. Throughout the 25-hour observation of the sextuplet, the EPIC images reveal that all three X-ray sources are variable, indicating giant releases of energy that can evolve in a few minutes or over several hours. But the frequency of the flaring on Castor is quite surprising. At no period during XMM-Newton's observation was the emission constant, perhaps indicating that almost all of the observed X-ray radiation stems from giant eruptions.

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Page Author: Dr. Michael F. Corcoran
Last modified June 30, 2000