2006/10/09 by G. Fritz Benedict, G. F. Benedict, B. McArthur +19 · 9 citations
Physics and Astronomy · #Astro and Planetary Science #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/508323
published as Astron.J.132:2206-2218,2006
arxiv created 2006/10/09 · openalex publication_date 2006/10/11 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
Hubble Space Telescope ( HST ) observations of the nearby (3.22 pc) K2 V star Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, Eri b, we extend our astrometric coverage to a total of 14.94 yr (including the 3 yr span of the HST data) by including lower precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8-2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semimajor axis α = 1.88 ± 0.20 mas, and inclination i = 30 1 ± 3 8. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M * = 0.83 M ⊙ , we obtain a companion mass M = 1.55 M J ± 0.24 M J . Given the relatively young age of Eri (∼800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct-imaging attempts. We predict the next periastron at 2007.3 with a total separation ρ = 0 3 at position angle P.A. = -27°. Orbit orientation and geometry dictate that Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 yr indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 yr, possibly responsible for one feature of the dust morphology, the inner cavity.