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Register a new userEPIC201702477b: A Long Period Transiting Brown Dwarf from K2
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We report the discovery of EPIC201702477b, a transiting brown dwarf in a long period (40.73691 +/- 0.00037 day) and eccentric (e=0.2281 +/- 0.0026) orbit. This system was initially reported as a planetary candidate based on two transit events seen in K2 Campaign 1 photometry and later validated as an exoplanet. We confirm the transit and refine the ephemeris with two subsequent ground-based detections of the transit using the LCOGT 1m telescope network. We rule out any transit timing variations above the level of 30s. Using high precision radial velocity measurements from HARPS and SOPHIE we identify the transiting companion as a brown dwarf with a mass, radius, and bulk density of 66.9 +/- 1.7 M$_J$, 0.757 +/- 0.065 R$_J$, and 191+/-51 g.cm$^{-3}$ respectively. EPIC201702477b is the smallest radius brown dwarf yet discovered, with a mass just below the H-burning limit. It has the highest density of any planet, substellar mass object or main-sequence star discovered so far. We find evidence in the set of known transiting brown dwarfs for two populations of objects - high mass brown dwarfs and low mass brown dwarfs. The higher-mass population have radii in very close agreement to theoretical models, and show a lower-mass limit around 60 M$_J$. This may be the signature of mass-dependent ejection of systems during the formation process.
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Context: We present the transit and follow-up of a single transit event from Campaign 14 of K2, EPIC248847494b, which has a duration of 54 hours and a 0.18% depth. Aims: Using photometric tools and conducting radial velocity follow-up, we vet and characterise this very strong candidate. Methods: Owing to the long, unknown period, standard follow-up methods needed to be adapted. The transit was fitted using Namaste, and the radial velocity slope was measured and compared to a grid of planet-like orbits with varying masses and periods. These used stellar parameters measured from spectra and the distance as measured by Gaia. Results: Orbiting around a sub-giant star with a radius of 2.70$pm$0.12R$_{rm Sol}$, the planet has a radius of 1.11$_{-0.07}^{+0.07}$R$_{rm Jup}$ and a period of 3650$_{-1130}^{+1280}$ days. The radial velocity measurements constrain the mass to be lower than 13M$_{rm Jup}$, which implies a planet-like object. Conclusions: We have found a planet at 4.5 AU from a single-transit event. After a full radial velocity follow-up campaign, if confirmed, it will be the longest-period transiting planet discovered.
We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12 +0.30 -0.15 Rjup, a mass of 63.3 +- 4.1 Mjup, and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b is either very young or inflated compared to standard evolution models, a situation similar to that of M-dwarfs stars orbiting close to solar-type stars. Spectroscopic constraints and an analysis of the lightcurve favors a spin period between 2.9 and 3.1 days for the central star, compatible with a double-synchronisation of the system.
We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19$pm$ 0.04) orbit around K2-99, an 11th magnitude subgiant in Virgo. We confirm the planetary nature of the companion with radial velocities, and determine that the star is a metal-rich ([Fe/H] = 0.20$pm$0.05) subgiant, with mass $1.60^{+0.14}_{-0.10}~M_odot$ and radius $3.1pm 0.1~R_odot$. The planet has a mass of $0.97pm0.09~M_{rm Jup}$ and a radius $1.29pm0.05~R_{rm Jup}$. A measured systemic radial acceleration of $-2.12pm0.04~{rm m s^{-1} d^{-1}}$ offers compelling evidence for the existence of a third body in the system, perhaps a brown dwarf orbiting with a period of several hundred days.
We report the discovery of K2-287b, a Saturn mass planet orbiting a G-dwarf with a period of $P approx 15$ days. First uncovered as a candidate using K2 campaign 15 data, follow-up photometry and spectroscopy were used to determine a mass of $M_P = 0.317 pm 0.026$ $M_J$, radius $R_P = 0.833 pm 0.013$ $R_J$, period $P = 14.893291 pm 0.000025$ days and eccentricity $e = 0.476 pm 0.026$. The host star is a metal-rich $V=11.410 pm 0.129$ mag G dwarf for which we estimate a mass $M_* = 1.056$ $M_odot$, radius $R_* = 1.07 pm 0.01$ $R_odot$, metallicity [Fe/H] = $0.20 pm 0.05$ and $T_{eff} = 5673 pm 75$ K. This warm eccentric planet with a time-averaged equilibrium temperature of $T_{eq} approx 800$ K adds to the small sample of giant planets orbiting nearby stars whose structure is not expected to be affected by stellar irradiation. Follow-up studies on the K2-287 system could help in constraining theories of migration of planets in close-in orbits.
The Kepler Mission has discovered thousands of exoplanets and revolutionized our understanding of their population. This large, homogeneous catalog of discoveries has enabled rigorous studies of the occurrence rate of exoplanets and planetary systems as a function of their physical properties. However, transit surveys like Kepler are most sensitive to planets with orbital periods much shorter than the orbital periods of Jupiter and Saturn, the most massive planets in our Solar System. To address this deficiency, we perform a fully automated search for long-period exoplanets with only one or two transits in the archival Kepler light curves. When applied to the $sim 40,000$ brightest Sun-like target stars, this search produces 16 long-period exoplanet candidates. Of these candidates, 6 are novel discoveries and 5 are in systems with inner short-period transiting planets. Since our method involves no human intervention, we empirically characterize the detection efficiency of our search. Based on these results, we measure the average occurrence rate of exoplanets smaller than Jupiter with orbital periods in the range 2-25 years to be $2.0pm0.7$ planets per Sun-like star.
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