Title: HD 202206 : A Circumbinary Brown Dwarf System,
Abstract: With Hubble Space Telescope Fine Guidance Sensor astrometry and previously
published radial velocity measures we explore the exoplanetary system HD
202206. Our modeling results in a parallax, $\pi_{abs} = 21.96\pm0.12$
milliseconds of arc, a mass for HD 202206 B of M$_B = 0.089^{ +0.007}_{-0.006}$
Msun, and a mass for HD 202206 c of M$_c = 17.9 ^{ +2.9}_{-1.8}$ MJup. HD
202206 is a nearly face-on G+M binary orbited by a brown dwarf. The system
architecture we determine supports past assertions that stability requires a
5:1 mean motion resonance (we find a period ratio, $P_c/P_B = 4.92\pm0.04$) and
coplanarity (we find a mutual inclination, Phi = 6 \arcdeg \pm 2 \arcdeg).