DELTA COL (Delta Columbae). Well below Orion and to the southwest of Canis Major, lies the pretty triangle that makes the modern constellation of Noah's Dove, Columba Noae, now known more simply as Columba. While the two brightest stars, Alpha and Beta Col carry proper names (Phact and Wazn), the rest -- except for runaway Mu Columbae -- are pretty well ignored, including third and fourth ranked fourth magnitude (3.85 and 4.36) Delta and Gamma (yes, out of order) Columbae. Bayer's Delta even suffers the indignity of not being entirely sure what constellation it is in, as it is also known as 3 Canis Majoris, Flamsteed having placed it with Orion's Larger Dog, while the modern constellation boundaries tossed it back to the Dove. As might be expected, the star --the most easterly of Columba's brighter ones -- lies less than a degree below the Dog-Dove border. At a distance of 234 light years (give or take just 6), and with a roughly-determined temperature of 5120 Kelvin, this class G (G7) bright giant shines at a rate of 150 times that of the Sun, from which we can deduce a radius of 16 times solar. Theory then shows that it is a three (3.2 perhaps a bit closer) solar mass star that is quietly fusing helium to carbon and oxygen in its nuclear-burning core, its age about a third of a billion years. The star's metal content relative to hydrogen, about 40 percent that of the Sun, is not that unusual. Emissions from the ionized magnesium atom (visible only from space), show the star to be marginally magnetically active.

A bigger issue is that Delta Col is not alone, but is attended to by a close, spectroscopically- observed companion with an orbital period of 2.38 years. The problem with learning more is that such observations do not give the orbital tilt, so that from them we cannot determine a mass and true orbital radius for Delta Col B, only lower limits. But here, positional astronomy comes to the rescue. Satellite (Hipparcos) data show how the motion of Delta A is being disturbed by orbiting Delta B, which does give the tilt. Combination of all observations coupled to the theoretically-derived mass of Delta A (plus Kepler's Laws) show that the companion has a mass about 0.9 Suns, making it a cool-end class G (G8 or 9) dwarf. The two orbit at an average separation of 2.9 Astronomical Units with a seriously large eccentricity that takes them from as close as 0.9 AU to as far apart as 4.9. Were rather sunlike Delta Col B to have an inhabited planet (seemingly unlikely given gravitational effects of the Delta A), its citizens would see the giant-star primary average nearly three degrees across in their sky (growing at closest distance to almost five). Given the light of two suns, though, one a luminous giant, it seems impossible that anyone could survive. Not quite so, however, for a similar (yet different) giant, Kappa Gem, with a solar-type companion that orbits at a huge distance of 325 AU from its star, where life might be possible. If nothing else, the two show the great diversity found among stellar pairs.
Written by Jim Kaler 2/25/11. Return to STARS.