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6 TRI (6 Trianguli). Fifth magnitude 6 Trianguli seems like ananonymous star with an anonymous name within a small constellation. But wait. It has a bit of a history, as it was once the chief starof a modern subdivision of ancientTriangulum (the Triangle) called "Triangulum Minus" (the "Smaller Triangle") made up inthe late 1600s of what we now call 6, 10, and 12 Trianguli. IfTriangulum Minus had survived the test of time, 6 Tri would now be"Alpha Trianguli Minoris." But it didn't, and it isn't. So 6 Triwill have to do. Oddly, the star is sometimes also called IotaTri, probably by mistake as there is no such designation listed inthe catalogues. Much more important, 6 Tri is a peculiar quadruplestar, a double-double in the mold ofMizar, whose parameters remain somewhatconfused. At a distance of 305 light years, it is classed as acombination fifth magnitude G5giant plus a fainter (magnitude6.44) F5 dwarf, the two stars separated by 3.8 seconds of arc. It's not clear if the stated magnitude of 6 Tri of 4.94 is for thecombination of the two or for the brighter G giant alone. Assumingthe latter case here, the combination has a magnitude of 4.7. TheG giant (6 Tri A) is itself double, the companion another F5 dwarf(6 Tri Ab) going around the G giant (which becomes 6 Tri Aa, itstemperature around 5000 Kelvin) with a period of 14.732 days. Estimated luminosities of 65 and 32Sunssuggest masses of 2.7 and 2.3 solar, leading to an average orbitalseparation of just 0.2 AU, half Mercury's distance from the Sun. The lesser of the visual pair, 6 Tri B, is also double, consistingof (best guess) a pair of mid class F stars that orbit in only 2.24days. Luminosities of 18 and 9 solar suggest masses of 1.7 and 1.5times that of the Sun and a very close separation of 0.05 AU, notmuch bigger than the stellar radii. The visual pair, at least 355AU apart, would then orbit with a period of at least 2300 years. The pairs are so close, however, that they affect each othergravitationally. Six Tri Aa and Ab rotate with the same periodswith which they revolve, thus (like Moon to Earth) keeping one facetoward each other. (Six Tri Ba and Bb certainly do as well). Thetidal locking has spun up the rotation of the giant star, whichthen helps produce a strong magnetic dynamo and activity (includingspots) much like those seen on the Sun, only exaggerated. Suchdoubles are called "RS Canum Venaticorum stars" after theprototype, and includeEpsilon UrsaeMinoris andLambda Andromedae. Asa result of its spottedness and rotation, 6 Tri varies by about atenth of a magnitude in its brightness, which gives it thevariable star name TZ Tri. Combinations such as these are quite hard to study, as it isdifficult to separate the light from the various components, 6 Triin particular a real challenge.
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