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Register a new userK2-98 b: A 32-M$_oplus$ Neptune-sized planet in a 10-day orbit transiting an F8 star
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We report the discovery of K2-98 b (EPIC 211391664 b), a transiting Neptune-sized planet monitored by the K2 mission during its campaign 5. We combine the K2 time-series data with ground-based photometric and spectroscopic follow-up observations to confirm the planetary nature of the object and derive its mass, radius, and orbital parameters. K2-98 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with $M_star$=$ 1.074pm0.042$, $R_star$=$ 1.311 ^{+ 0.083} _{ - 0.048} $, and age of $5.2_{-1.0}^{+1.2}$~Gyr. We derive a planetary mass and radius of $M_mathrm{p}$=$ 32.2 pm 8.1 $ and $R_mathrm{p}$=$4.3^{+0.3}_{-0.2}$. K2-98 b joins the relatively small group of Neptune-sized planets whose both mass and radius have been derived with a precision better than 25 %. We estimate that the planet will be engulfed by its host star in $sim$3~Gyr, due to the evolution of the latter towards the red giant branch.
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We report on the discovery of K2-141 b (EPIC 246393474 b), an ultra-short-period super-Earth on a 6.7-hour orbit transiting an active K7 V star based on data from K2 campaign 12. We confirmed the planets existence and measured its mass with a series of follow-up observations: seeing-limited MuSCAT imaging, NESSI high-resolution speckle observations, and FIES and HARPS high-precision radial-velocity monitoring. K2-141 b has a mass of $5.31 pm 0.46 $ $M_{oplus}$ and radius of $1.54^{+0.10}_{-0.09}$ $R_{oplus}$, yielding a mean density of $8.00_{ - 1.45 } ^ { + 1.83 }$ $mathrm{g,cm^{-3}}$ and suggesting a rocky-iron composition. Models indicate that iron cannot exceed $sim$70 % of the total mass. With an orbital period of only 6.7 hours, K2-141 b is the shortest-period planet known to date with a precisely determined mass.
We report the discovery from K2 of a transiting terrestrial planet in an ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in only 4.3 hours, the second-shortest orbital period of any known planet, just 4 minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a combination of archival images, AO imaging, RV measurements, and light curve modelling, we show that no plausible eclipsing binary scenario can explain the K2 light curve, and thus confirm the planetary nature of the system. The planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463 +/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.
Theories of the formation and early evolution of planetary systems postulate that planets are born in circumstellar disks, and undergo radial migration during and after dissipation of the dust and gas disk from which they formed. The precise ages of meteorites indicate that planetesimals - the building blocks of planets - are produced within the first million years of a stars life. A prominent question is: how early can one find fully formed planets like those frequently detected on short orbital periods around mature stars? Some theories suggest the in situ formation of planets close to their host stars is unlikely and the existence of such planets is evidence for large scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report on a newly-born, transiting planet orbiting its star every 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times Jupiter (at 99.7 per cent confidence), with a true mass likely to be within a factor of several of Neptunes. The 5-10 million year old star has a tenuous dust disk extending outwards from about 2 times the Earth-Sun separation, in addition to the large planet located at less than one-twentieth the Earth-Sun separation.
We report the discovery of a Neptune-size planet (Rp = 3.0 Re) in the Hyades Cluster. The host star is in a binary system, comprising a K5V star and M7/8V star with a projected separation of 40 AU. The planet orbits the primary star with an orbital period of 17.3 days and a transit duration of 3 hours. The host star is bright (V=11.2, J=9.1) and so may be a good target for precise radial velocity measurements. K2-136A c is the first Neptune-sized planet to be found orbiting in a binary system within an open cluster. The Hyades is the nearest star cluster to the Sun, has an age of 625-750 Myr, and forms one of the fundamental rungs in the distance ladder; understanding the planet population in such a well-studied cluster can help us understand and set constraints on the formation and evolution of planetary systems.
We report the discovery and characterization of HD 89345b (K2-234b; EPIC 248777106b), a Saturn-sized planet orbiting a slightly evolved star. HD 89345 is a bright star ($V = 9.3$ mag) observed by the K2 mission with one-minute time sampling. It exhibits solar-like oscillations. We conducted asteroseismology to determine the parameters of the star, finding the mass and radius to be $1.12^{+0.04}_{-0.01}~M_odot$ and $1.657^{+0.020}_{-0.004}~R_odot$, respectively. The star appears to have recently left the main sequence, based on the inferred age, $9.4^{+0.4}_{-1.3}~mathrm{Gyr}$, and the non-detection of mixed modes. The star hosts a warm Saturn ($P = 11.8$~days, $R_p = 6.86 pm 0.14~R_oplus$). Radial-velocity follow-up observations performed with the FIES, HARPS, and HARPS-N spectrographs show that the planet has a mass of $35.7 pm 3.3~M_oplus$. The data also show that the planets orbit is eccentric ($eapprox 0.2$). An investigation of the rotational splitting of the oscillation frequencies of the star yields no conclusive evidence on the stellar inclination angle. We further obtained Rossiter-McLaughlin observations, which result in a broad posterior of the stellar obliquity. The planet seems to conform to the same patterns that have been observed for other sub-Saturns regarding planet mass and multiplicity, orbital eccentricity, and stellar metallicity.
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