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Smallest Planet Yet Found Circling a Main Sequence Star (other than our sun)

By SpaceRef Editor
October 18, 2005
Filed under , ,
Smallest Planet Yet Found Circling a Main Sequence Star (other than our sun)

Astrophysics, abstract

From: Eugenio Rivera [view email]
Date (v1): Tue, 18 Oct 2005 01:16:36 GMT (578kb)
Date (revised v2): Tue, 18 Oct 2005 22:21:41 GMT (574kb)

A ~ 7.5 Earth-Mass Planet Orbiting the Nearby Star, GJ 876

E. J. Rivera,
J. J. Lissauer,
R. P. Butler,
G. W. Marcy,
S. S. Vogt,
D. A. Fischer,
T. M. Brown,
G. Laughlin,
G. W. Henry

Comments: 49 pages, 16 figures, 1 electronic table available upon request

High precision, high cadence radial velocity monitoring over the past 8 years
at the W. M. Keck Observatory reveals evidence for a third planet orbiting the
nearby (4.69 pc) dM4 star GJ 876. The residuals of three-body Newtonian fits,
which include GJ 876 and Jupiter mass companions b and c, show significant
power at a periodicity of 1.9379 days. Self-consistently fitting the radial
velocity data with a model that includes an additional body with this period
significantly improves the quality of the fit. These four-body (three-planet)
Newtonian fits find that the minimum mass of companion “d” is m sin i = 5.89
+- 0.54 Earth masses and that its orbital period is 1.93776 (+- 7×10^-5) days.
Assuming coplanar orbits, an inclination of the GJ 876 planetary system to the
plane of the sky of ~ 50 degrees gives the best fit. This inclination yields a
mass for companion d of m = 7.53 +- 0.70 Earth masses, making it by far the
lowest mass companion yet found around a main sequence star other than our Sun.
Precise photometric observations at Fairborn Observatory confirm low-level
brightness variability in GJ 876 and provide the first explicit determination
of the star’s 96.7-day rotation period. Even higher precision short-term
photometric measurements obtained at Las Campanas imply that planet d does not
transit GJ 876.

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