The Extrasolar Planet ɛ Eridani b Orbit and Mass

Details The Extrasolar Planet ɛ Eridani b Orbit and Mass The Extrasolar Planet ɛ Eridani b Orbit and Mass

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.1009b&link_type=abstract

American Astronomical Society, DPS meeting #38, #10.09; Bulletin of the American Astronomical Society, Vol. 38, p.1294

Astronomy and Astrophysics

Astronomy

Scientific paper

Hubble Space Telescope (HST) Fine Guidance Sensor astrometric observations of the nearby (3.22 pc), K2 V star epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Due to the long period of the companion, epsilon Eridani b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocity coverage now spans 1980.8 -2006.3. We obtain a perturbation period, P = 6.85 ± 0.03 yr, semi-major 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 (Greaves et al. 2005), demonstrating dust disk and exoplanet co-planarity for the first time. Co-planarity is an expected consequence of planet formation theories. Assuming a primary mass M* = 0.83 MΟ, we obtain a companion mass M = 1.55 ± 0.24MJup. Given the relatively young age of epsilon Eridani ( 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 epsilon Eridani b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly the object responsible for one prominent feature of the dust morphology, the inner cavity. We gratefully acknowledge NASA Grants GO-09167, -09347, -09969, -10610, and 10989.

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