Xi Aquilae

(The Planet Project)

Aquila A one-time class B (on the cool side) dwarf, now a standard evolving K giant, Xi Aquilae has a massive jupiter-like planet.


The circle shows the location of the evolved class K star Xi Aquilae (in Aquila, the Eagle). The planet, Xi Aql b, carrying a mass of at least 2.2 Jupiters, orbits on a circular path with a radius of 0.68 Astronomical Units (about Venus's distance from the Sun) over a period of 137 days (0.37 years). The period is shorter than that of Venus's 225 days because the star (see below) is more massive than the Sun.


Lying immediately southeast of Altair, Xi Aquilae is one of the easiest planet-holding stars to find. At a distance of 184 light years, give or take just 2, and with a coolish temperature of 4780 Kelvin, this class K (K0) giant shines with the light of 48 Suns, giving it a radius of 10.2 times solar and a mass of 2.2 Suns. Now quietly fusing helium to carbon in its deep core, this class K (K0) giant was once a class B9 or so dwarf, and as such represents a stand-in for these hotter stars needed because their more diffuse spectra more or less defy planet detection. Any planets much closer than Xi Aql b would have been, or will be, destroyed by the star's growth as a giant. With an iron content 2/3 that of the Sun, the star runs contrary to the usual rule of planet-holding stars to be metal-rich.
Written 3/09/11 by Jim Kaler. Return to The Planet Project or go to STARS.