2 HER (2 Herculis). While all stars are of interest (and for the moment ignoring stars like the Sun whose planets might harbor life), those at the extremes perhaps draw a bit more attention. At the hot end we find the blue, hydrogen-fusing dwarfs (and sometimes giants and even supergiants) of class O. At the other end are the cool reddish stars of class M. Though M dwarfs actually dominate the Galaxy, they are all so faint that even if close, none is visible to the naked eye. So we look then to the much more luminous class M giants and supergiants like Mira, Betelgeuse, Antares, Gamma Crucis, and the like. And while they dot the sky, they are not all that common either. Tucked into far northwestern Hercules between Bootes and Draco is another, Flamsteed's number 2, a class M (M3) giant that lies not quite a degree north of Chi Herculis (Flamsteed's number 1) in a tight triangle that includes 4 Herculis. Just fifth magnitude as a 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 by interstellar dust, which is ignored. Factoring in a large amount of infrared light from the cool, 3400 Kelvin, surface, we find a total radiance of 2680 times that of the Sun. But don't take that too seriously, as the star is so neglected that there is no actual measure of temperature, which is just estimated from the class. Temperature and radius then tell of a large star 150 times bigger than the Sun, one that in our Solar System would come out almost to the orbit of Venus. The various uncertainties make an evaluation of mass difficult to determine, as stars with a range of masses have similar characteristics. The best guess is that 2 Her hovers at around 2 to 2.5 or so solar masses. The evolutionary status is even more difficult to evaluate. It could be enlarging, brightening, and cooling with a dead helium core, dimming with a helium core fusing to carbon and oxygen, or brightening for the second time with a dead carbon/oxygen core. Nobody knows. The star is listed as a low level variable that changes by just 0.014 magnitude over a 10.2 day period, not surprising at all for one that large. It's also listed as a weak "semi-barium star." True barium stars are giants that have been contaminated with heavy elements from evolving companions that are now white dwarfs. Even though it has been sought with sophisticated equipment, no companion to 2 Her has ever been detected, and most likely the assignment is spurious, all rather appropriate for a star that also just missed being Flamsteed's number 1.

Written by Jim Kaler 8/16/13. Return to STARS.