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Thursday, July 21, 2011

Triple Eclipsing Variable Star System - But Stranger Than That!

Normally, a binary eclipsing variable star system is characterized by a change of aggregate brightness as one star eclipses the other from the vantage point of Earth. Described in the report below however is a triple system with the weird feature that when both of the smaller stars are in front of the larger star, the brightness barely changes. This is due to the fact that despite vastly different sizes, the stars have almost the same surface brightness, and as described below, "just as a white rabbit cannot be seen in snow-fall, the red dwarfs in front of the red giant are also almost invisible"!

From Physorg:

The object, catalogued as HD 181068 and nicknamed `Trinity' by the research team, and is a seventh magnitude star that is almost visible to the naked eye. University of Sydney astronomer Daniel Huber from the School of Physics says: "We found what was a seemingly single star is in reality a complex triple system in which three stars reside in a very special geometry.

The observations we have show mutual eclipses as each of the stars gets behind or in front of the others. The most luminous object is a red around which a close pair of two red dwarfs orbits with a period of 45.5 days." Lead author on the paper Aliz Derekas from the Eotvos University and Konkoly observatory, Budapest, Hungary says: "Thanks to the fortunate viewing angle from Earth, the combined light from the three stars change very characteristically. There are sharp brightness decreases with a period of 0.9 days produced by the mutual eclipses of the close pair of dwarfs, while it takes two days for the close pair to pass in front of or behind the red giant.

"A mind-boggling feature of the variations is that when the red dwarfs are in front of the red giant, their short-period eclipses disappear. This is because the surface brightness of the three stars are actually very similar, and just as a white rabbit cannot be seen in snow-fall, the red dwarfs in front of the red giant are also almost invisible, hence no light is lost when they eclipse each other." 
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