q CAR (q Carinae). Carina (the Keel of the Ship Argo) has so many bright stars that even those of third magnitude had to be given Roman letters by Nicolas de Lacaille (the great explorer of the southern celestial hemisphere) after he ran out of Greek ones. They include the p's and q's of earlier stellar tales, the two linked by their similarity as seen in old typefaces. Those of Carina, which form part of the constellation's outline and are just under two degrees apart, could hardly be more different, p Car (magnitude 3.32) a hot blue-white B4 emission-line hydrogen-fusing dwarf (or core-quiet subgiant) 483 light years away, q Car an orange class K (K3) bright giant of magnitude 3.40 considerably farther at 659 light years (plus or minus 12). Were there no interstellar dust in the way (fat chance in the middle of the Milky Way), q car would appear 0.61 magnitudes brighter and reach almost second magnitude. After figuring in infrared radiation from its 4400 Kelvin surface, q Car is found to shine with a luminosity of 4660 times that of the Sun, 89 percent that of p Car. However, as an evolved cool giant, q Car wins the radius prize, having swollen to 117 times the solar radius, 16 times the size of q Car, 55 percent bigger than the orbit of Mercury. The mass is uncertain. If on its way toward core helium fusion the star weighs in at 8 solar masses (at the lower edge of supernova production), while if helium fusion has already begun it's more like 6.5 Suns. Most likely the star will slough off its outer layers, its core becoming a massive white dwarf. Pretty much the same fate is in store for p Car. Not unusual among giants, q Car seems irregularly variable, shifting erratically between magnitudes 3.36 and 3.42. Measures of the iron content relative to hydrogen range from solar to three times that in the Sun, and is thus really unknown. Two faint thirteenth magnitude "companions" lie at 16 and 26 seconds of arc away from the primary star. If real, they must be low mass M dwarfs that respectively are at least 3399 and 5200 away and take more than 65,000 and 130,000 to make a circuit of their much brighter mate. Given the density of faint stars in the Milky Way, and that each has been observed only at one point in time, companionship seems highly unlikely; both are probably just line of sight coincidences. If q Car were in the northern hemisphere, far more would be known about it. From q Car, p Car would first magnitude, while from p Car, q would reach magnitude zero.

Written by Jim Kaler 2/28/14. Return to STARS.