BETA COM (Beta Comae Berenices). The naked-eye sky is dominated by luminous stars, stars that are far brighter than the Sun. Only a few stars like the Sun and fainter sneak through. They simply do not have enough radiative power to be visible unless they are quite close to us. ("Selection effects" like this one, in which Nature shows us "what she wishes," pervade science: the population of microbes far exceeds that of elephants, yet only the elephants are visible without some kind of aid.) It is then quite surprising to find the luminary of a constellation to be a near-solar clone. Fourth magnitude (4.26) Beta Com, with no proper name at all, just barely beats out Diadem (Alpha Comae Berenices) for the honor (such as it is) of being the brightest star within the faint but glorious constellation Coma Berenices (Berenices Hair). Though within the formal constellation boundaries, Beta Com is not a part of the star cluster that makes the constellation's heart, its distance of only 30 light years placing it 1/9 as far as the cluster and half as far as Diadem. At 6000 Kelvin, this class G (G0, alternatively classed as F9.5) star is only slightly warmer than our class G2 (5780 Kelvin) Sun. A hydrogen-fusing dwarf like the Sun, Beta Com is only 37 percent more luminous than is the Sun and but 10 percent larger, the result of 10 percent greater mass. There is some suggestion that the star might have a close companion (detectable only via spectrograph), though such a neighbor is unconfirmed and probably unlikely. How sunlike is Beta Com? It is a bit metal-rich, containing perhaps 7 percent more iron (relative to dominant hydrogen) than the Sun. No planets have yet been spectroscopically detected as they have for several similar stars. A search for a residual dusty disk (one left over from planet formation) around the star has also turned up nothing. Yet the spectrum reveals very sunlike magnetic activity, implying starspots, flares, and all the other trappings of the solar magnetic engine. Indeed, with a rotation period only half that of the Sun, Beta Com is probably more active than the Sun (rotation and up and down convection in the outer stellar layers producing the magnetism). Like the Sun, Beta Com also has a long-term magnetic activity cycle of 16.6 years, about 50 percent longer than the famed 11-year solar cycle. (It may also have a secondary 9.6 year cycle.) If you want to see something of what we would look like at a distance, look to Coma Berenice's brightest star.
Written by Jim Kaler. Return to STARS.