| 1. |
- Guenther, E. W., et al.
(author)
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K2-106, a system containing a metal-rich planet and a planet of lower density
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608, s. 93-
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Journal article (peer-reviewed)abstract
- Planets in the mass range from 2 to 15 M_Earth are very diverse. Some of them have low densities, while others are very dense. By measuring the masses and radii, the mean densities, structure, and composition of the planets are constrained. These parameters also give us important information about their formation and evolution, and about possible processes for atmospheric loss.We determined the masses, radii, and mean densities for the two transiting planets orbiting K2-106. The inner planet has an ultra-short period of 0.57 days. The period of the outer planet is 13.3 days. Although the two planets have similar masses, their densities are very different. For K2-106b we derive Mb=8.36-0.94+0.96 M_Earh, Rb=1.52+/-0.16 R_Earth, and a high density of 13.1-3.6+5.4 g/cm^3. For K2-106c, we find Mc=5.8-3.0+3.3 M_Earth, Rc=2.50-0.26+0.27 R_Earth and a relatively low density of 2.0-1.1+1.6 g/cm^3.Since the system contains two planets of almost the same mass, but different distances from the host star, it is an excellent laboratory to study atmospheric escape. In agreement with the theory of atmospheric-loss processes, it is likely that the outer planet has a hydrogen-dominated atmosphere. The mass and radius of the inner planet is in agreement with theoretical models predicting an iron core containing 80+20-30% of its mass. Such a high metal content is surprising, particularly given that the star has an ordinary (solar) metal abundance. We discuss various possible formation scenarios for this unusual planet.
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| 2. |
- Dai, F., et al.
(author)
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The Discovery and Mass Measurement of a New Ultra-short-period Planet: K2-131
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 154:6, s. 226-
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Journal article (peer-reviewed)abstract
- 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 K2 Campaign 10. It has a radius of 1.81-0.12+0.16 R_Earth and orbits a G dwarf with a period of 8.9 hr. 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+/- 1.6 M_Earth and a mean density of 6.0-2.7+3.0 g cm‑3.
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| 3. |
- Smith, A. M. S., et al.
(author)
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K2-99: a subgiant hosting a transiting warm Jupiter in an eccentric orbit and a long-period companion
- 2017
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In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 464:3, s. 2708-2716
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Journal article (peer-reviewed)abstract
- We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19 +/- 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 +/- 0.05) subgiant, with mass 1.60(+0.14) (-0.10) M (circle dot) and radius 3.1 +/- 0.1 R-circle dot. The planet has a mass of 0.97 +/- 0.09 M-Jup and a radius 1.29 +/- 0.05 R-Jup. A measured systemic radial acceleration of -2.12 +/- 0.04 ms(- 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.
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| 4. |
- Eigmüller, P., et al.
(author)
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K2-60b and K2-107b. A Sub-Jovian and a Jovian Planet from the K2 Mission
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 153:3
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Journal article (peer-reviewed)abstract
- We report the characterization and independent detection of K2-60b, as well as the detection and characterization of K2-107b, 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 R Jup and a mass of 0.426 ± 0.037 M Jup and orbits a G4 V star with an orbital period of 3.00267 ± 0.00006 days. K2-107b has a radius of 1.44 ± 0.15 R Jup and a mass of 0.84 ± 0.08 M Jup 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. K2-107b is a highly inflated Jovian planet orbiting an evolved star about to leave the main sequence.
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| 5. |
- Fridlund, Malcolm, 1952, et al.
(author)
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K2-111 b - A short period super-Earth transiting a metal poor, evolved old star
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 604, s. A16-
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Journal article (peer-reviewed)abstract
- Context. From a light curve acquired through the K2 space mission, the star K2-111(EPIC 210894022) has been identified as possibly orbited by a transiting planet. Aims: Our aim is to confirm the planetary nature of the object and derive its fundamental parameters. Methods: We analyse the light curve variations during the planetary transit using packages developed specifically for exoplanetary transits. Reconnaissance spectroscopy and radial velocity observations have been 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. Results: 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 K2-111 strongly suggest it to be a member of the thick disk population. The co-added high-resolution spectra show that that it is a metal poor ([Fe/H] = - 0.53 ± 0.05 dex) and α-rich somewhat evolved solar-like star of spectral type G3. We find Teff = 5730 ± 50 K, log g⋆ = 4.15 ± 0.1 cgs, and derive a radius of R⋆ = 1.3 ± 0.1 R⊙ and a mass of M⋆ = 0.88 ± 0.02 M⊙. The currently available radial velocity data confirms a super-Earth class planet with a mass of 8.6 ± 3.9 M⊕ and a radius of 1.9 ± 0.2 R⊕. A second more massive object with a period longer than about 120 days is indicated by a long-term radial velocity drift. Conclusions: The radial velocity detection together with the imaging confirms with a high level of significance that the transit signature is caused by a planet orbiting the star K2-111. This planet is also confirmed in the radial velocity data. A second more massive object (planet, brown dwarf, or star) has been detected in the radial velocity signature. With an age of ≳10 Gyr this system is one of the oldest where planets are hitherto detected. Further studies of this planetary system are important since it contains information about the planetary formation process during a very early epoch of the history of our Galaxy.
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| 6. |
- Nespral, D., et al.
(author)
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Mass determination of K2-19b and K2-19c from radial velocities and transit timing variations
- 2017
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601, s. Article Number: A128-
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Journal article (peer-reviewed)abstract
- We present radial velocity follow-up observations of K2-19, a compact planetary system hosting three planets, of which the two larger ones, K2-19b and K2-19c, are close to the 3: 2 mean motion resonance. An analysis considering only the radial velocity measurements detects K2-19b, the larger and more massive planet in the system, with a mass of 54.8 +/- 7.5 M-circle plus and provides a marginal detection of K2-19c, with a mass of M-c = 5.9(-4.3)(+7.6) M-circle plus. We also used the TRADES code to simultaneously model both our RV measurements and the existing transit timing measurements. We derived a mass of 54.4 +/- 8.9 M-circle plus for K2-19b and of 7.5(-1.4)(+3.0) M-circle plus for K2-19c. For K2-19b, these masses are consistent with a previous determination that was principally based on a photodynamical analysis of the K2-19 light curve. Differences remain mainly in the mass determination of the more lightweight planet, driven likely by the limited precision of the RV measurements and possibly some as yet unrecognized systematics.
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| 7. |
- Niraula, P., et al.
(author)
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Three Super-Earths Transiting the Nearby Star GJ 9827
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 154:6, s. 266-
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Journal article (peer-reviewed)abstract
- We report on the discovery of three transiting planets around GJ 9827. The planets have radii of 1.75 ± 0.18, 1.36 ± 0.14, and 2.11_-0.21^+0.22 R⊕, and periods of 1.20896, 3.6480, and 6.2014 days, respectively. The detection was made in Campaign 12 observations as part of our K2 survey of nearby stars. GJ 9827 is a V = 10.39 mag K6V star at a distance of 30.3 ± 1.6 parsecs and the nearest star to be found hosting planets by Kepler and K2. The radial velocity follow-up, high-resolution imaging, and detection of multiple transiting objects near commensurability drastically reduce the false positive probability. The orbital periods of GJ 9827 b, c, and d planets are very close to the 1:3:5 mean motion resonance. Our preliminary analysis shows that GJ 9827 planets are excellent candidates for atmospheric observations. Besides, the planetary radii span both sides of the rocky and gaseous divide, hence the system will be an asset in expanding our understanding of the threshold.
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| 8. |
- Nowak, G., et al.
(author)
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EPIC 219388192b-An Inhabitant of the Brown Dwarf Desert in the Ruprecht 147 Open Cluster
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 153:3
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Journal article (peer-reviewed)abstract
- We report the discovery of EPIC 219388192b, 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 219388192b has a radius of R-b= 0.937 +/- 0.032 R-Jup and mass of M-b= 36.84 +/- 0.97 M-Jup, yielding a mean density of 59.6 +/- 7.6 g cm(- 3). The host star is nearly a solar twin with mass M-star = 1.01 +/- 0.04 Me, radius R-star = 1.01 +/- 0.03 R-circle dot, effective temperature T-eff = 5850 +/- 85 K, and iron abundance [Fe/ H]. = 0.03 +/- 0.08 dex. Its age, spectroscopic distance, and reddening are consistent with those of Ruprecht 147, corroborating its cluster membership. EPIC 219388192b is the first mature brown dwarf with precise determinations of mass, radius, and age, and serves as benchmark for evolutionary models in the substellar regime.
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| 9. |
- Gandolfi, Davide, et al.
(author)
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The Transiting Multi-planet System HD 3167: A 5.7 M ⊕ Super-Earth and an 8.3 M ⊕ Mini-Neptune
- 2017
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In: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 154:3, s. 123-
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Journal article (peer-reviewed)abstract
- HD 3167 is a bright (V = 8.9 mag) K0 V star observed by NASA’s K2 space mission during its Campaign 8. It has recently been found to host two small transiting planets, namely, HD 3167b, an ultra-short-period (0.96 days) super-Earth, and HD 3167c, a mini-Neptune on a relatively long-period orbit (29.85 days). Here we present an intensive radial velocity (RV) follow-up of HD 3167 performed with the FIES@NOT, HARPS@ESO-3.6 m, 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 M⊕, a radius of 1.574 ± 0.054 R⊕, and a mean density of {8.00}-0.98+1.10 g cm^-3, HD 3167b joins the small group of ultra-short-period planets known to have rocky terrestrial compositions. HD 3167c has a mass of 8.33-1.85+1.79 M⊕ and a radius of 2.74}-0.100+0.106 R⊕, yielding a mean density of 2.21-0.53+0.56 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 (∼350 km) and the brightness of the host star make HD 3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the RV measurements but the currently available data set does not allow us to draw any firm conclusions on the origin of the observed variation.
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