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KAPPA DRA (Kappa Draconis). Three stars sit in a little row, thebrightest of them -- Kappa Draconis -- the second star in from theend of the tail ofDraco, the Dragon. At first the three, also known inFlamsteed terms as 4, 5 (Kappa),and 6 Draconis, might look like some sort of odd triple system. The alignment, however, is coincidental, as they have nothing to dowith each other. Yet the contrast is nice, as fourth magnitude(3.88) Kappa is a blue-white class B (B6) giant, whereas the closerof the two, 6 Dra, is a fifth magnitude (4.95) red class M (M4)giant. (4 Dra is a bit warmer fifth magnitude K3 giant). KappaDra, which dominates the trio, has a complex spectral class givenas B6 IIIpe. The "B6" places it in the middle of class B, the"III" means that it is a giant star, the "p" stands for "peculiar,"and the "e" means there are bright emissions at certain wavelengthsin the spectrum (in this case from hydrogen). In short terms,Kappa is a "Be star" much like much brighterGamma Cas, and as such is surrounded by arotating bright disk of radiating matter of its own making. No onequite knows how such disks are created, but they are alwaysassociated with rapidly rotating stars. Moreover, the star isclassed as a "shell star," which implies a thick absorbing disk,one set more or less along the line of sight. The disk, or shell,seems to have a long-term variation of 23 years in addition toother short periods (the disks rather unstable). Kappa Dra shinesto us from a great distance of 500 light years, radiating the lightof 1400Suns from a 14,000 Kelvin surface. The combination tells of a radius 6.4 times that of the Sun. Theminimum (since we do not know the axial tilt) equatorial rotationspeed is argued, one source giving as low as 160 kilometers persecond (80 times solar), another 250. If the former, the starspins in under 2 days (as opposed to 25 days for the Sun), if thelatter in under 1.3 days. The existence of a companion is alsoarguable. From spectral variations, there is a suggestion of onewith a period of 0.89 days, which implies an orbital separation ofonly 0.03 or so Astronomical Units (50 million km). We might befooled, however, as the variations might be the result of rotation,implying a rotation speed of 360 km/sec. On the other hand, thereis a suggestion that the star varies like Sheliak (Beta Lyrae),again implying a companion. Clearly, Kappa Dra is under-studied. Kappa Dra is a hefty 5 solar mass star that has either just endedits core hydrogen fusing stage, or will do so almost immediately. Within only half a million years it will make the transition tobecoming a true red giant that is twice as bright as it is now. While unrelated, the trio near the end of the Dragon's tail arestill pretty close to each other. Ignoring the inevitable errorsof measurement, the red giant 4 Dra is only 50 light years fartheraway, 6 Dra only another 30. From 4 Draconis, our Kappa would bebrilliant, and would shine in a planet's sky (were there one) atmagnitude -1.2, only a little dimmer than we see Sirius.
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