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MAIA (20 Tauri). ThePleiades, theSeven Sisters star cluster (one of two naked eye clusters thatbelong toTaurus, the other theHyades), twinkle high in northernhemisphere autumn and winter skies, while shining closer to thehorizon in the skies of southern hemisphere spring and summer. Maia, a proper name, is one of the seven mythical daughters ofAtlas andPleione. Shining at bright third magnitude (3.87) froma distance of 385 light years, she ranks fourth brightest afterAlcyone, Atlas, andElectra. Except forAlcyone (Eta Tauri), the Pleiades' stars carry onlyFlamsteed numbers, Maia number20 in the west-to-east parade of numbered naked-eye stars withinthe celestial Bull. A blue-white class B (B8) giant star, Maiaradiates 660 times more energy than does theSun from a warm surface with a rather uncertaintemperature of 12,600 Kelvin. Its radius of 5 1/2 times that ofthe Sun gives it true giant status, although the giants in thesehotter stars are nowhere near as large as their cooler orangecousins likeArcturus andAldebaran (which lies in front of the Hyades). As a giant, Maia either has shut down its internal hydrogen fusionor will do so very shortly, its mass of a bit over four times thatof the Sun giving the star a destiny as a massive white dwarf. Like the other stars of the cluster, Maia is involved with thePleiades reflection nebula that peaks aroundMerope. Maia appears to be a relativelyslow rotator, and as such has a fairly quiet atmosphere. As aresult, different kinds of atoms drift downward under the pull ofgravity, whereas others are lofted upward by radiation, the effectsmaking Maia one of the "mercury-manganese stars," in which thesetwo and other chemical elements are greatly enhanced (manganese inMaia up by a factor of 160 compared with hydrogen). The star alsohas a bit of a curious history. Fifty years ago, the greatastronomer Otto Struve suggested that Maia was slightly variable,with a period of a few hours. It thence became the prototype of awhole class of "Maia variables" that includedPherkad (Gamma Ursae Minoris) and that werein an otherwise stable realm of temperature and luminosity. Astronomers have argued since then about the reality of the class. Only recently has the issue been put to rest, when the prototype(and some others) were found to be stable and not varying at all(though others in the purported class do vary for other reasons).
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