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ALPHA ANT (Alpha Antliae). Little attention is paid this star. Even less would be if it were not the remarkably dim luminary of aneven more obscure constellation,Antlia,the Air Pump. It's hard to fathom that anyone would invent afigure in which the brightest star is on the faint end of fourthmagnitude (4.28), but the nineteenth-century's Abbe Lacaille(Antlia's inventor) did anyway. Physically, Alpha Ant appears asan orange class K (K4) giant placed 365 light years away, which iswhy it appears so dim. It is a bit on the cool side, however, andhas been classed as low as M0, showing that it is not just anotherhelium-burning "clump star" (one of the pack), but is a bitdifferent. There is some indication of the spectroscopic detectionof a binary companion, but that is most likely caused by motions inthe star's atmosphere, as it is somewhat variable, and is alsolosing mass. How variable is not known, as the star has never beenthe subject of a particular study -- in fact it is hardly noted atall,less than one science paper a year mentioning it. Thisisolated star provides a good example astronomers face in dealingwith the problem of stellar evolution, the ageing process. Itsstate of being depends critically on both distance and temperature. The K4 spectral class says 4100 Kelvin, while the single actualmeasure, which probably no more reliable, gives 3990. The problemis in the allowance for low-energy infrared radiation not seen bythe eye, which climbs quickly with dropping temperature. If thehigher temperature is valid, then the luminosity is 480Suns. The formal error in the distance (thedegree to which we are uncertain about it) gives a luminosity rangeof about 15 percent. If the cooler temperature is correct, thenthe star shines with the brightness of 555 Suns (with the samepercentage range). The real problem is that stars with asignificant range of mass all rather look alike during the variousgiant stages, allowing a range of 1.7 to 3 times that of the Sun. One thing is sure, that Alpha Antliae is not at this moment stable. We cannot quite tell, however, if it is brightening with a deadhelium core, dimming with helium core burning to carbon and oxygen,or brightening with a dead carbon core. The most likely scenariois that it is a 2.2 solar mass star that is on its "way up,"brightening for the second time with carbon core and an age ofabout a billion years (supported by its variability). It will turninto a Mira-type variable and then pop its outer envelope to turninto a white dwarf.
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