We report the characterization and independant detection of K2-60b, as well as the detection and characterization of EPIC 216468514b, two transiting hot gaseous planets from the K2 space mission. We ...confirm the planetary nature of the two systems and determine their fundamental parameters combining the K2 time-series data with FIES@NOT and HARPS-N@TNG spectroscopic observations. K2-60b has a radius of 0.683 +/- 0.037 RJup and a mass of 0.426 +/- 0.037 MJup and orbits a G4V star with an orbital period of 3.00267 +/- 0.00006 days. EPIC 216468514b has a radius of 1.44 +/- 0.15RJup and a mass of 0.84 +/- 0.08 MJup and orbits an F9 IV star every 3.31392 +/- 0.00002 days. K2-60b is among the few planets at the edge of the so-called "desert" of short-period sub Jovian planets. EPIC 216468514b is a highly inflated Jovian planet orbiting an evolved star about to leave the main sequence.
The star EPIC 210894022 has been identified from a light curve acquired through the K2 space mission as possibly orbited by a transiting planet. Our aim is to confirm the planetary nature of the ...object and derive its fundamental parameters. We combine the K2 photometry with reconnaissance spectroscopy and radial velocity (RV) measurements obtained using three separate telescope and spectrograph combinations. The spectroscopic synthesis package SME has been used to derive the stellar photospheric parameters that were used as input to various stellar evolutionary tracks in order to derive the parameters of the system. The planetary transit was also validated to occur on the assumed host star through adaptive imaging and statistical analysis. The star is found to be located in the background of the Hyades cluster at a distance at least 4 times further away from Earth than the cluster itself. The spectrum and the space velocities of EPIC 210894022 strongly suggest it to be a member of the thick disk population. We find that the star is a metal poor (Fe/H=-0.53+/-0.05 dex) and alpha-rich somewhat evolved solar-like object of spectral type G3 with Teff=5730+/-50 K, logg=4.15+/-0.1 (cgs), radius of 1.3+/-0.1 R_Sun, and mass of 0.88+/-0.02 M_Sun. The RV detection together with the imaging confirms with a high level of significance that the transit signature is caused by a super-Earth orbiting the star EPIC 210894022. We measure a mass of 8.6+/-3.9 M_Earth and a radius of 1.9+/-0.2 R_Earth. A second more massive object with a period longer than about 120 days is indicated by a long term linear acceleration. With an age of > 10 Gyrs this system is one of the oldest where planets is hitherto detected. Further studies of this planetary system is important since it contains information about the planetary formation process during a very early epoch of the history of our Galaxy.
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 $M_\star$=$
1.074\pm0.042$, $R_\star$=$ 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.
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space mission during its Campaign 8. It has been recently found to host two small transiting planets, namely, HD3167b, an ultra short ...period (0.96 d) super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit (29.85 d). Here we present an intensive radial velocity follow-up of HD3167 performed with the FIES@NOT, HARPS@ESO-3.6m, and HARPS-N@TNG spectrographs. We revise the system parameters and determine radii, masses, and densities of the two transiting planets by combining the K2 photometry with our spectroscopic data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of ultra-short period planets known to have a rocky terrestrial composition. HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of 2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53) g/cm^3, indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (about 350 km) and the brightness of the host star make HD3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the radial velocity measurements but the currently available data set does not allow us to draw any firm conclusion on the origin of the observed variation.
We confirm the planetary nature of two transiting hot Jupiters discovered by the Kepler spacecraft's K2 extended mission in its Campaign 4, using precise radial velocity measurements from FIES@NOT, ...HARPS-N@TNG, and the coudé spectrograph on the McDonald Observatory 2.7 m telescope. K2-29 b (EPIC 211089792 b) transits a K1V star with a period of \(3.2589263\pm0.0000015\) days; its orbit is slightly eccentric (\(e=0.084_{-0.023}^{+0.032}\)). It has a radius of \(R_P=1.000_{-0.067}^{+0.071}\) \(R_J\) and a mass of \(M_P=0.613_{-0.026}^{+0.027}\) \(M_J\). Its host star exhibits significant rotational variability, and we measure a rotation period of \(P_{\mathrm{rot}}=10.777 \pm 0.031\) days. K2-30 b (EPIC 210957318 b) transits a G6V star with a period of \(4.098503\pm0.000011\) days. It has a radius of \(R_P=1.039_{-0.051}^{+0.050}\) \(R_J\) and a mass of \(M_P=0.579_{-0.027}^{+0.028}\) \(M_J\). The star has a low metallicity for a hot Jupiter host, \(\mathrm{Fe}/\mathrm{H}=-0.15 \pm 0.05\).
We report the discovery of a new ultra-short-period planet and summarize the properties of all such planets for which the mass and radius have been measured. The new planet, EPIC~228732031b, was ...discovered in {\it K2} Campaign 10. It has a radius of 1.81\(^{+0.16}_{-0.12}~R_{\oplus}\) and orbits a G dwarf with a period of 8.9 hours. Radial velocities obtained with Magellan/PFS and TNG/HARPS-N show evidence for stellar activity along with orbital motion. We determined the planetary mass using two different methods: (1) the "floating chunk offset" method, based only on changes in velocity observed on the same night, and (2) a Gaussian process regression based on both the radial-velocity and photometric time series. The results are consistent and lead to a mass measurement of \(6.5 \pm 1.6~M_{\oplus}\), and a mean density of \(6.0^{+3.0}_{-2.7}\)~g~cm\(^{-3}\).
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a 5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open cluster association, which was photometrically ...monitored by K2 during its Campaign 7. We combine the K2 time-series data with ground-based adaptive optics imaging and high resolution spectroscopy to rule out false positive scenarios and determine the main parameters of the system. EPIC 219388192 b has a radius of \(R_\mathrm{b}\)=\(0.937\pm0.042\)~\(\mathrm{R_{Jup}}\) and mass of \(M_\mathrm{b}\)=\(36.50\pm0.09\)~\(\mathrm{M_{Jup}}\), yielding a mean density of \(59.0\pm8.1\)~\(\mathrm{g\,cm^{-3}}\). The host star is nearly a Solar twin with mass \(M_\star\)=\(0.99\pm0.05\)~\(\mathrm{M_{\odot}}\), radius \(R_\star\)=\(1.01\pm0.04\)~\(\mathrm{R_{\odot}}\), effective temperature \(\mathrm{T_{eff}}\)=\(5850\pm85\)~K and iron abundance Fe/H=\(0.03\pm0.08\)~dex. Its age, spectroscopic distance, and reddening are consistent with those of Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the first brown dwarf with precise determinations of mass, radius and age, and serves as benchmark for evolutionary models in the sub-stellar regime.
We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known ...to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood, but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 is an evolved star with a spectroscopically derived stellar radius and mass of \(3.88^{+0.48}_{-0.42}~\mathrm{R_\odot}\) and \(1.53^{+0.13}_{-0.12}~\mathrm{M_\odot}\), respectively, and a very close-in transiting planet, with \(a/R_\star = 3.4\). Radial velocity (RV) follow-up using the HARPS, FIES and PFS instruments leads to a planetary mass of \(50.3^{+9.7}_{-9.4}~\mathrm{M_\oplus}\). In combination with a radius measurement of \(8.3 \pm 1.1~\mathrm{R_\oplus}\), this results in a mean planetary density of \(0.50^{+0.29}_{-0.17}\) g~cm\(^{-3}\). We furthermore discover a long-term RV trend, which may be caused by a long-period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars.
Our aim is to investigate the nature and formation of brown dwarfs by adding a new well-characterised object to the small sample of less than 20 transiting brown dwarfs. One brown dwarf candidate was ...found by the KESPRINT consortium when searching for exoplanets in the K2 space mission Campaign 16 field. We combined the K2 photometric data with a series of multi-colour photometric observations, imaging and radial velocity measurements to rule out false positive scenarios and to determine the fundamental properties of the system. We report the discovery and characterisation of a transiting brown dwarf in a 5.17 day eccentric orbit around the slightly evolved F7V star EPIC 212036875. We find a stellar mass of 1.15+/-0.08 M\(_\odot\), a stellar radius of 1.41+/-0.05 R\(_\odot\), and an age of 5.1+/-0.9 Gyr. The mass and radius of the companion brown dwarf are 51+/-2 MJ and 0.83+/-0.03 RJ, respectively, corresponding to a mean density of 108+15-13 g cm-3. EPIC 212036875 b is a rare object that resides in the brown dwarf desert. In the mass-density diagram for planets, brown dwarfs and stars, we find that all giant planets and brown dwarfs follow the same trend from ~0.3 MJ to the turn-over to hydrogen burning stars at ~73 MJ. EPIC 212036875 b falls close to the theoretical model for mature H/He dominated objects in this diagram as determined by interior structure models, as well as the empirical fit. We argue that EPIC 212036875 b formed via gravitational disc instabilities in the outer part of the disc, followed by a quick migration. Orbital tidal circularisation may have started early in its history for a brief period when the brown dwarf's radius was larger. The lack of spin-orbit synchronisation points to a weak stellar dissipation parameter which implies a circularisation timescale of >23 Gyr, or suggests an interaction between the magnetic and tidal forces of the star and the brown dwarf.
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 \(M_\star\)=\( 1.074\pm0.042\), \(R_\star\)=\( 1.311 ^{+ 0.083} _{ - 0.048} \), 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.
