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.