HR 2447 Canis Majoris

(The Planet Project)

cma HR 2447 has not one, but two planets. More unusual, like HR 2877, the planet belong not to an ordinary dwarf, as most do, but to a giant star, one that is in the act of evolving and dying.


The lower circle shows the location of the class K giant star HR 2447, found in the constellation Canis Major. The planets orbit their star with periods of 430 and 2500 days (1.18 and 6.84 years) and average orbital sizes of 1.1 and 3.5 Astronomical Units, the inner one with an eccentricity of about 20 percent. Lower limits to the masses are respectively estimated at 5 and 7 times that of Jupiter.


HR 2447, also called HD 47536, is a fifth magnitude (5.26) class K0 orange giant in Canis Major. Too faint to have a proper or Greek letter name, it is known best by its numbers in the Bright Star(HR) and the Henry Draper (HD) Catalogues. From a distance of 395 light years, it shines with a luminosity of 174 times that of the Sun from a surface with a temperature of 4380 Kelvin. From these values, we infer a radius 22.9 times solar, appropriate for an evolved, helium-fusing giant, and a mass close to that of the Sun. Direct measure of angular diameter leads to a radius of 23.6 times solar, the agreement showing that the stellar parameters are accurate. Our Sun appears half a degree across in our sky. At 1.1 AU, the star would appear over 20 times as big as the Sun, nearly 11 degrees across, twice the angular separation between the front bowl stars of the Big Dipper. Unlike most stars with planets, HR 2447 is metal poor, with an iron content just 20 percent of solar.

HD 47186, the faint smudge at the center of the upper circle, also has a pair of orbiting planets, one of which is a "superearth."
Written by Jim Kaler. Return to The Planet Project or go to STARS.