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2 HER (2 Herculis). While all stars are of interest (and for themoment ignoring stars like the Sun whose planets might harborlife), those at the extremes perhaps draw a bit more attention. Atthe hot end we find the blue, hydrogen-fusingdwarfs (and sometimesgiants and evensupergiants) of class O. Atthe other end are the cool reddish stars of class M. Though Mdwarfs actually dominate theGalaxy, they are all so faintthat even if close, none is visible to the naked eye. So we lookthen to the much more luminous class M giants and supergiants likeMira,Betelgeuse,Antares,GammaCrucis, and the like. And while they dot the sky, they are notall that common either. Tucked into far northwesternHercules betweenBootes andDraco is another,Flamsteed's number 2, a class M(M3) giant that lies not quite a degree north ofChi Herculis (Flamsteed's number 1) in atight triangle that includes 4 Herculis. Just fifth magnitude asa result of a hefty distance of 654 light years (give or take 21),2 Herculis is actually quite luminous. In spite of its distance,there is little evidence of dimming byinterstellar dust, which is ignored. Factoring in a large amount ofinfrared light from the cool,3400 Kelvin, surface, we find a total radiance of 2680 times thatof theSun. But don't take that tooseriously, as the star is so neglected that there is no actualmeasure of temperature, which is just estimated from the class. Temperature and radius then tell of a large star 150 times biggerthan the Sun, one that in our Solar System would come out almost tothe orbit of Venus. The various uncertainties make an evaluationof mass difficult to determine, as stars with a range of masseshave similar characteristics. The best guess is that 2 Her hoversat around 2 to 2.5 or so solar masses. The evolutionary status iseven more difficult to evaluate. It could be enlarging,brightening, and cooling with a dead helium core, dimming with ahelium core fusing to carbon and oxygen, or brightening for thesecond time with a dead carbon/oxygen core. Nobody knows. Thestar is listed as a low level variable that changes by just 0.014magnitude over a 10.2 day period, not surprising at all for onethat large. It's also listed as a weak "semi-barium star." Truebarium stars are giants that have been contaminated with heavyelements from evolvingcompanions that are nowwhite dwarfs. Even thoughit has been sought with sophisticated equipment, no companion to 2Her has ever been detected, and most likely the assignment isspurious, all rather appropriate for a star that also just missedbeing Flamsteed's number 1.
Written byJim Kaler 8/16/13. Return toSTARS.
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