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Zeta Lupi

Northeastward along the Milky Way from Alpha Centauri lies Zeta Lupi, a third magnitude star in the constellation of Lupus the Wolf. Zeta Lupi is the southernmost of the stars that mark out the body of the Wolf, lying close to the constellation's southern borders with Norma and Centaurus, and is generally taken to represent the Wolf's hindquarters. From here, the Wolf's tail is seen as extending back northwards, marked by the stars Kakkab (or Alpha Lupi) and Beta Lupi.

Zeta Lupi is a double star, and almost certainly a binary, with the primary being a yellow-orange giant late in its evolution. This primary star, designated Zeta Lupi A, has consumed its original reserves of hydrogen, and its core is now fusing the helium created during the earlier phase of its existence.

Near Zeta Lupi A is another star, designated Zeta Lupi B. This is apparently a binary companion of the yellow giant, though the two are so distant from one another that this status has yet to be definitively confirmed. Zeta Lupi B is a pale yellow dwarf star, much less massive than Zeta Lupi A. Indeed, Zeta Lupi B is somewhat comparable to the Sun, though rather larger and more energetic. If Zeta Lupi B is indeed a binary companion of the A star, then it follows an orbit some 2,600 AU from the main star (or about ninety times the distance from the Sun to Neptune). Pursuing such an immense orbit, the dwarf will take tens of thousands of years to complete a single circuit of the giant, explaining why identifying it as a definite binary companion is so difficult.


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