The mu Arae planetary system: Radial velocities and astrometry

TL;DR

This study refines the orbital parameters of the mu Arae exoplanetary system using combined radial velocity and astrometry data, revealing system stability issues and biases in astrometric measurements.

Contribution

It provides improved orbital elements for known planets and analyzes astrometric data to assess companion masses and system stability.

Findings

Refined orbital elements for four known planets.

No astrometric evidence for additional companions.

Indications of dynamical instability caused by planet d.

Abstract

With Hubble Space Telescope Fine Guidance Sensor astrometry and published and previously unpublished radial velocity measures we explore the exoplanetary system mu Arae.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 uncover a bias towards small inclinations (more face-on than edge-on). This bias remains unexplained by either 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 mu Arae system dynamically unstable on a timescale of 10^5 years, in broad agreement with previous work.