The μ Arae Planetary System: Radial Velocities and Astrometry

With Hubble Space Telescope Fine Guidance Sensor astrometry and published and previously unpublished radial velocity measures, we explore the exoplanetary system μ Arae. Our modeling of the radial velocities results in improved orbital elements for the four previously known components. Our astrometry contains no evidence for any known companion but provides upper limits for three companion masses. A final summary of all past Fine Guidance Sensor exoplanet astrometry results uncovers a bias toward small inclinations (more face-on than edge-on). This bias remains unexplained by small number statistics, modeling technique, Fine Guidance Sensor mechanical issues, or orbit modeling of noise-dominated data. A numerical analysis using our refined orbital elements suggests that planet d renders the μ Arae system dynamically unstable on a timescale of 10⁵ yr, in broad agreement with previous work.