OV CEP (OV Cephei). Polaris, the bright second magnitude star at the end of the handle of the Ursa Minor's Little Dipper, sits in rather lonely splendor, its nearet rivals the Dipper's front bowl stars, Kochab and Pherkad. Surrounding it, however, lies a host of fainter naked-eye stars that beg to be examined (among them 2 and 24 UMi and HR 286, the latter closely accompanying Polaris in its journey around the north celestial pole), if only because from most of the Earth's northern hemisphere they are perpetually on stage. As a collection, they also give a sense of the distribution of the qualities of the naked eye stars. Also among the polar stars are a couple contrasting variables. One -- Polaris itself -- is famed and intensively observed. The other, OV Cephei (the star, though close to the pole, actually across the border into Cepheus), is hardly noted at all and not in the least well examined (revealing how little we really know of the several thousand stars visible to the unaided eye).
pole Polaris (the jewel in a small semicircle of faint telescopic stars called the "Engagement Ring") is centered in a six-degree-wide field of view that shows a variety of other "polar stars." Lamdba Ursae Minoris is the reddish star up and to the right of Polaris, while Yildun (Delta UMi) is the brighter of the two stars at the upper right corner. Roughly between Lambda and Polaris lies the North Celestial Pole, around which they all seem to revolve. The star immediately down and to the right of Polaris is HR 286. OV Cephei is the reddish star at the far left edge just above center.

See the full-resolution image and more on polar stars in the Polar Project.
OV has the distinction of being a red class M (M2) giant, its central hydrogen fusion shut down. From a distance of 500 light years, it shines to us at but fifth magnitude (5.07), which with correction for infrared light radiated from its 3700 Kelvin surface yields a luminosity of 850 times that of the Sun, a radius of 70 solar (85 percent the size of Mercury's orbit), and a mass about 1.5 solar. Only 70 light years from Polaris, our Pole Star would shine in OV's sky at minus second magnitude, brighter than Sirius appears to us. As befits a true red giant, the star is either near or just past the point at which it will fire (or has fired) its core helium to fuse to carbon and oxygen. The double letter combo reveals that OV is a variable star. However, the nature of its variability is unknown, even the degree of the variability uncertain. In the blue part of the spectrum, where photography once ruled, it varies by but a tenth of a magnitude over an unknown period. Over an interval of half a day, the star jitters by about one percent. OV Cephei, however, is significant in that it shows serious evidence for mixing the by-products of nuclear fusion from the deep core to the stellar surface. All the chemical elements come in a variety of isotopes, nuclei that have different numbers of attached neutral neutrons. The amount of carbon-13 (carbon with 7 neutrons) is about a tenth that of ordinary carbon-12 (with 6 neutrons), 10 or so times that found in the Sun. The change is proof that deep inside the star, hydrogen has fused to helium through the so-called "carbon cycle," in which carbon is used as a nuclear catalyst in the creation of stellar energy.
Written by Jim Kaler. Return to STARS.