|
Description
We present an intensive effort to refine the mass and orbit of the enveloped terrestrial planet GJ1214b using 165 radial velocity (RV) measurements taken with the HARPS spectrograph over a period of 10years. We conduct a joint analysis of the RVs with archival Spitzer/IRAC transits and measure a planetary mass and radius of 8.17{+/-}0.43M{Earth} and 2.742-_0.053_^+0.050^R{Earth}. Assuming that GJ1214b is an Earth-like core surrounded by a H/He envelope, we measure an envelope mass fraction of X_env_=5.24_-0.29_^+0.30^%. GJ1214b remains a prime target for secondary eclipse observations of an enveloped terrestrial, the scheduling of which benefits from our constraint on the orbital eccentricity of <0.063 at 95% confidence, which narrows the secondary eclipse window to 2.8hr. By combining GJ1214 with other mid-M-dwarf transiting systems with intensive RV follow up, we calculate the frequency of mid-M-dwarf planetary systems with multiple small planets and find that 90_-21_^+5^% of mid-M dwarfs with a known planet with mass [1,10]M{Earth} and orbital period [0.5,50]days, will host at least one additional planet. We rule out additional planets around GJ1214 down to 3M{Earth} within 10days, such that GJ1214 is a single-planet system within these limits. This result has a 44_-5_^+9^ probability given the prevalence of multiplanet systems around mid-M dwarfs. We also investigate mid-M-dwarf RV systems and show that the probability that all reported RV planet candidates are real planets is <12% at 99% confidence, although this statistical argument is unable to identify the probable false positives.
|
