CUJAM (Omega Herculis). Allowing for some hyperbole, Cujam (ku- yam, out of Latin) has more angles to it than a protractor. Not hard to find in southeastern Hercules, bright fifth magnitude (4.57) Cujam (Omega Herculis) lies between the head of Serpens Caput to the west and northern Ophiuchus to the east. The corrupted proper name, which has various spellings, is perhaps more grammatically served by "Caia." In any case it refers badly to a club (with reference to Hercules) and was affixed during the Renaissance. It's far better to use Bayer's designation of Omega Herculis. The star thus has the dubious honor of holding up the stack of the Greek letter system, which is topped in the constellation by Rasalgethi, Alpha Herculis (which lies a dozen degrees nearly due east of Omega). If that's not enough, as both 24 Herculis and 51 Serpentis, Omega Herculis is one of two dozen stars given dual Flamsteed numbers. While the latter is never now used, it shows the uncertainty of early constellation boundaries (see Zeta Serpentis).

The star itself, a class B (B9p) "peculiar" presumed dwarf 250 light years away (give or take 12), is a match for its name. The "p" refers to a weird chemical composition caused by gravitational settling of some elements and radiative lofting of others, one that is further enhanced by a strong magnetic field. The prototype is Cor Caroli, Alpha-2 Canum Venaticorum in Canes Venatici. Omega Her then becomes an "alpha2 CVn star," one with especially large enhancements of chromium and europium. Iron may be up significantly too. In such a star the enhancements are concentrated into spots near the rotation poles, whose axis is generally inclined to the line of sight. As the spots rotate in and out of view, the stars vary, Omega by a few hundredths of a magnitude over an interval of 2.961 days, which is taken as the rotation period. The projected equatorial rotation speed of 46 kilometers per second, along with radius (see below), gives 3.5 days. The rotation axis would then be inclined to the line of sight by 63 or so degrees. Magnetic fields up to several hundred times that of the Earth have been measured. Distance, a 16 percent correction for dimming by interstellar dust, and a temperature of 9730 Kelvin (to account for ultraviolet light) leads to a luminosity 82 times that of the Sun and a radius 3.2 times solar. Theory then points to a mass of 2.7 Suns and shows that the star is indeed a dwarf, one about two-thirds of the way through its hydrogen fusing lifetime of 450 million years. After Omega Her's gianthood, in which the core will eventually be fused to a mix of carbon and oxygen and the outer layers ejected to make a planetary nebula, Omega Her will expire as a white dwarf with a final mass of about 0.7 times that of the Sun. Three "companions" hover around. Two, an 11th magnitude star (Omega C) 26 seconds of arc away and another at 13th magnitude and 130 seconds (D), are from their motions obvious line of sight coincidences. Eleventh magnitude (11.5) Omega B, however, measured at 1.9 seconds away in 1878 and 0.8 seconds in 2000, may well be real. If so, it's a class K5 dwarf at least 150 Astronomical Units from bright Omega A, and takes at least a thousand years to orbit. Thanks to Latin scholar David Bright for discussion of the name.

Written by Jim Kaler 8/22/13. Return to STARS.