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Validation and Initial Characterization of the Long-period Planet Kepler-1654 b
Fewer than 20 transiting Kepler planets have periods longer than one year. Our early search of the Kepler light curves revealed one such system, Kepler-1654b (originally KIC 8410697b), which shows exactly two transit events and whose second transit occurred only five days before the failure of the second of two reaction wheels brought the primary Kepler mission to an end. A number of authors have also examined light curves from the Kepler mission searching for long-period planets and identified this candidate. Starting in 2014 September, we began an observational program of imaging, reconnaissance spectroscopy, and precision radial velocity (RV) measurements that confirm with a high degree of confidence that Kepler-1654b is a bona fide transiting planet orbiting a mature G5V star (T eff = 5580 K, [Fe/H] = -0.08) with a semimajor axis of 2.03 au, a period of 1047.84 days, and a radius of 0.82 ±0.02 R Jup. RV measurements using Keck's HIRES spectrometer obtained over 2.5 years set a limit to the planet's mass of <0.5 (3σ) M Jup. The bulk density of the planet is similar to that of Saturn or possibly lower. We assess the suitability of temperate gas giants like Kepler-1654b for transit spectroscopy with the James Webb Space Telescope, as their relatively cold equilibrium temperatures (T pl ∼ 200 K) make them interesting from the standpoint of exoplanet atmospheric physics. Unfortunately, these low temperatures also make the atmospheric scale heights small and thus transmission spectroscopy challenging. Finally, the long time between transits can make scheduling JWST observations difficult - as is the case with Kepler-1654b
The CORALIE survey for southern extrasolar planets: XVIII. Three new massive planets and two low-mass brown dwarfs at greater than 5 AU separation
Context. Since 1998, a planet-search around main sequence stars within 50~pc
in the southern hemisphere has been carried out with the CORALIE spectrograph
at La Silla Observatory. Aims. With an observing time span of more than 20
years, the CORALIE survey is able to detect long term trends in data with
masses and separations large enough to select ideal targets for direct imaging.
Detecting these giant companion candidates will allow us to start bridging the
gap between radial velocity detected exoplanets and directly imaged planets and
brown dwarfs. Methods. Long-term precise Doppler measurements with the CORALIE
spectrograph reveal radial velocity signatures of massive planetary companions
and brown dwarfs on long-period orbits. Results. In this paper we report the
discovery of new companions orbiting HD~181234, HD~13724, HD~25015, HD~92987
and HD~50499. We also report updated orbital parameters for HD~50499b,
HD~92788b and HD~98649b. In addition, we confirm the recent detection of
HD~92788c. The newly reported companions span a period range of 15.6 to 40.4
years and a mass domain of 2.93 to 26.77 , the latter of
which straddles the nominal boundary between planets and brown dwarfs.
Conclusion. We have reported the detection of five new companions and updated
parameters of four known extrasolar planets. We identify at least some of these
companions to be promising candidates for imaging and further characterisation