HR 4067 Ursae Majoris

(The Planet Project)

UMa HR 4067 is host not only to a massive "Jupiter," but has a distant class L companion that has such a low mass that it is close to being a brown dwarf.

THE PLANET

The right-hand lower circle shows the location of the class F dwarf HR 4067 Ursae Majoris in the constellation Ursa Major. The bright star in the circle is third magnitude Tania Australis (Mu UMa). Sixth magnitude HR 4067 is tucked in just below and a bit to the right of it, making the star incredibly easy to find. HR 4067 has a massive planet that carries at least 7.99 times the mass of Jupiter. It orbits the star with a period of 256.6 days at an average distance of 0.89 Astronomical Units (134 million kilometers, 83 million miles), 0.89 times the size of Earth's orbit around the Sun. The orbit is highly eccentric, however, and takes the planet from as far as 1.49 AU from its star to as close in as 0.29 AU, the latter only 75 percent the distance of Mercury from the Sun.

THE STAR

HR 4067 Ursae Majoris is a sixth magnitude (5.74) class F7 dwarf in Ursa 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 127 light years, it shines with a luminosity of 6.2 times that of the Sun from a surface at 6230 Kelvin (450 degrees warmer than the Sun), which tells of a star with a radius 2.1 solar, a mass between 1.4 and 1.5 solar, and an age that lies between 1.5 and 3 billion years. The star may be very close to giving up core hydrogen fusion, and has also been classed as a subgiant-dwarf. Like most stars with planets, HR 4067 UMa is rich in metals, its iron abundance (relative to hydrogen) 1.7 times that of the Sun. Its rotation period is 9 days, only a third that of the Sun. The star is also host to a very dim, class L0 red dwarf companion (making HR 4067 a double star) that has a mass between 0.073 and 0.077 solar masses (77 to 80 Jupiters), which is at or just above the line at which stars cease full hydrogen fusion and below which the star would be a brown dwarf. At a distance of at least 2460 AU, the dim companion takes at least 100,000 years to make an orbit. While there is no visual magnitude measurement, such stars hover around absolute magnitude 20 (less than a millionth that of the Sun). From the orbiting planet (at the stated distance), the companion would therefore shine only at fifth magnitude, not much brighter than HR 4067 does from here!

The circle to the left of HR 4067 shows 47 Ursae Majoris, while that toward upper right shows Pi-2 Ursae Majoris (also known as 4 UMa), both of which also support planets.
Written by Jim Kaler. Return to The Planet Project or go to STARS.