K2-56b/BD+20594b is a High Density Subneptune/MegaEarth

DISCOVERY AND VALIDATION OF A HIGH-DENSITY SUB-NEPTUNE FROM THE K2 MISSION

Authors:

Espinoza et al

Abstract:

We report the discovery of K2-56b, a high-density sub-Neptune exoplanet, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission, ground-based radial velocity (RV) follow-up from HARPS and high-resolution lucky and adaptive optics imaging obtained using AstraLux and MagAO, respectively. The host star is a bright (V = 11.04, K s = 9.37), slightly metal-poor ([Fe/H] = −0.15 ± 0.05 dex) solar analogue located at ${152.1}_{-7.4}^{+9.7}$ pc from Earth, for which we find a radius of ${R}_{* }={0.928}_{-0.040}^{+0.055}{R}_{\odot }$ and a mass of ${M}_{* }={0.961}_{-0.029}^{+0.032}{M}_{\odot }$. A joint analysis of the K2 photometry and HARPS RVs reveal that the planet is in a ≈42 day orbit around its host star, has a radius of ${2.23}_{-0.11}^{+0.14}{R}_{\oplus }$, and a mass of ${16.3}_{-6.1}^{+6.0}{M}_{\oplus }$. Although the data at hand put the planet in the region of the mass–radius diagram where we could expect planets with a pure rock (i.e., magnesium silicate) composition using two-layer models (i.e., between rock/iron and rock/ice compositions), we discuss more realistic three-layer composition models which can explain the high density of the discovered exoplanet. The fact that the planet lies in the boundary between "possibly rocky" and "non-rocky" exoplanets makes it an interesting planet for future RV follow-up.

previous preprint.

EPIC 212521166b: a new MegaEarth With 2.6 Earth Radius & 18.3 Earth Mass

EPIC212521166 b: a Neptune-mass planet with Earth-like density

Authors:

Osborn et al

Abstract:

We report the discovery of the exoplanet EPIC212521166 b from K2 photometry orbiting on a 13.8637d period around an old, metal-poor K3 dwarf star. A joint analysis of K2 photometry and high-precision RVs from HARPS reveals it to have a radius of 2.6±0.1R⊕ and a mass of 18.3±2.8M⊕, making it the most massive planet with a sub-Neptune radius (i.e. mini-Neptune) yet found. When accounting for compression, the resulting Earth-like density is best fit by a 0.2M⊕ hydrogen atmosphere over an 18M⊕ Earth-like core, although the planet could also have significant water content. At 0.1AU, even taking into account the old stellar age of 8±3 Gyr, the planet is unlikely to have been significantly affected by EUV evaporation or tides. However the planet likely disc-migrated to its current position making the lack of a thick H2 atmosphere puzzling. With a V-band magnitude of 11.9 it is particularly amenable to follow-up observations, making EPIC-1166 b a rare and extremely important planetary system.

vA 50: A Neptune Radius, Potentially 1.2 Jupiter Mass Exoplanet (MegaEarth?) Confirmed by K2 Mission

New Pleiades Eclipsing Binaries and a Hyades Transiting System Identified by K2

Authors:

David et al

Abstract:

We present the discovery in Kepler's K2 mission observations and our follow-up radial velocity observations from Keck/HIRES for four eclipsing binary (EB) star systems in the young benchmark Pleiades cluster. Based on our modeling results, we announce two new low mass (Mtotless than 0.6M⊙) EBs among Pleiades members (HCG 76 and MHO 9) and we report on two previously known Pleiades binaries that are also found to be EB systems (HII 2407 and HD 23642). We measured the masses of the binary HCG 76 to ≲2.5% precision, and the radii to ≲4.5% precision, which together with the precise effective temperatures yield an independent Pleiades distance of 132±5 pc. We discuss another EB towards the Pleiades that is a possible but unlikely Pleiades cluster member (AK II 465). The two new confirmed Pleiades systems extend the mass range of Pleiades EB components to 0.2-2 M⊙. Our initial measurements of the fundamental stellar parameters for the Pleiades EBs are discussed in the context of the current stellar models and the nominal cluster isochrone, finding good agreement with the stellar models of Baraffe et al. (2015) at the nominal Pleiades age of 120 Myr.

Finally, in the Hyades, we report a new low mass eclipsing system (vA 50) that was concurrently discovered and studied by Mann et al. (2016). We confirm that the eclipse is likely caused by a Neptune-sized transiting planet, and with the additional radial velocity constraints presented here we improve the constraint on the maximum mass of the planet to be ≲1.2 MJup.

BD+20594b: a Neptune Sized MegaEarth

A Neptune-sized Exoplanet Consistent with a Pure Rock Composition

Authors:

Espinoza et al

Abstract:

We report the discovery of BD+20594b, a Neptune-sized exoplanet consistent with a pure rock composition, made using photometry from Campaign 4 of the two-wheeled Kepler (K2) mission. The host star is a bright (V=11.04, Ks=9.37), slightly metal poor ([Fe/H]=−0.15±0.05 dex) solar analogue located at 152.1+9.7−7.4 pc from Earth, for which we find a radius of R∗=0.928+0.055−0.040R⊙ and a mass of M∗=0.961+0.032−0.029M⊙. A joint analysis of the K2 photometry and HARPS radial velocities reveal that the planet is in a ≈42 day orbit around its host star, has a radius of 2.23+0.14−0.11R⊕, and a mass of 16.3+6.0−6.1M⊕. The data at hand are most consistent with a pure rock composition with a low volatile content, potentially making it a rare exception among Neptune-sized exoplanets discovered so far.

HATS-17b: A Transiting Hot Giant Planet With .77 Jupiter Radius and 1.34 Jupiter Mass ie the Density of Aluminum

HATS-17b: A Transiting Compact Warm Jupiter in a 16.3 Days Circular Orbit

Authors:

Brahm et al

Abstract:

We report the discovery of HATS-17b, the first transiting warm Jupiter of the HATSouth network. HATS-17b transits its bright (V=12.4) G-type (M⋆=1.131 ± 0.030 M⊙, R⋆=1.091+0.070−0.046 R⋆) metal-rich ([Fe/H]=+0.3 dex) host star in a circular orbit with a period of P=16.2546 days. HATS-17b has a very compact radius of 0.777 ± 0.056 RJ given its Jupiter-like mass of 1.338 ± 0.065 MJ. Up to 50% of the mass of HATS-17b may be composed of heavy elements in order to explain its high density with current models of planetary structure. HATS-17b is the longest period transiting planet discovered to date by a ground-based photometric survey, and is one of the brightest transiting warm Jupiter systems known. The brightness of HATS-17b will allow detailed follow-up observations to characterize the orbital geometry of the system and the atmosphere of the planet.

Hot MegaEarth WASP-14b Parameter Refinement

WASP-14 b: transit timing analysis of 19 light curves

Authors:

Raetz et al

Abstract:

Although WASP-14 b is one of the most massive and densest exoplanets on a tight and eccentric orbit, it has never been a target of photometric follow-up monitoring or dedicated observing campaigns. We report on new photometric transit observations of WASP-14 b obtained within the framework of Transit Timing Variations @ Young Exoplanet Transit Initiative (TTV@YETI). We collected 19 light curves of 13 individual transit events using six telescopes located in five observatories distributed in Europe and Asia. From light-curve modelling, we determined the planetary, stellar, and geometrical properties of the system and found them in agreement with the values from the discovery paper. A test of the robustness of the transit times revealed that in case of a non-reproducible transit shape the uncertainties may be underestimated even with a wavelet-based error estimation methods. For the timing analysis, we included two publicly available transit times from 2007 and 2009. The long observation period of seven years (2007–2013) allowed us to refine the transit ephemeris. We derived an orbital period 1.2 s longer and 10 times more precise than the one given in the discovery paper. We found no significant periodic signal in the timing-residuals and, hence, no evidence for TTV in the system.

KOI-372b: a Giant Exoplanet 17% Denser Than Earth

KOI-372: a young extrasolar system with two giant planets on wide and eccentric orbits

Authors:

Mancini et al

Abstract:

We confirm the planetary nature of KOI-372b (aka Kepler object of interest K00372.01), a giant transiting exoplanet orbiting a solar-analog G2V star. The mass of KOI-372b and the eccentricity of its orbit were accurately derived thanks to a series of precise radial velocity measurements obtained with the CAFE spectrograph mounted on the CAHA 2.2-m telescope. A simultaneous fit of the radial-velocity data and Kepler photometry revealed that KOI-372b is a dense Jupiter-like planet with a mass of Mp=3.25 Mjup and a radius of Rp=0.882 Rjup. KOI-372b is moving on a quite eccentric orbit, e=0.172, making a complete revolution around its parent star in 125.6 days. The semi-major axis of the orbit is 0.4937 au, implying that the planet is close to its habitable zone (roughly 0.5 au from it). By analysing the mid-transit times of the 12 transit events of KOI-372b recorded by the Kepler spacecraft, we found a clear transit time variation, which is attributable to the presence of a planet c in a wider orbit. We estimated that KOI-372c has a mass between 0.13 and 0.31 Mjup, also revolving on an eccentric orbit (e=0.17-0.24) in roughly 460 days, at a mean distance of 1.2 au from the host star, within the boundaries of its habitable zone. The analysis of the CAFE spectra revealed a relatively high photospheric lithium content, A(Li)=2.48 dex, suggesting that the parent star is relatively young. From a gyrochronological analysis, we estimate that the age of this planetary system is 1.0 Gyr.

EPIC201505350: Two Planet System with a hot Neptune and a Giant Rocky Exoplanet in a 3:2 Orbital Resonance

One of the closest planet pairs to the 3:2 Mean Motion Resonance, confirmed with K2 observations and Transit Timing Variations: EPIC201505350

Authors:

Armstrong et al

Abstract:

The K2 mission has recently begun to discover new and diverse planetary systems. In December 2014 Campaign 1 data from the mission was released, providing high-precision photometry for ~22000 objects over an 80 day timespan. We searched these data with the aim of detecting further important new objects. Our search through two separate pipelines led to the independent discovery of EPIC201505350, a two-planet system of Neptune sized objects (4.2 and 7.2 R⊕), orbiting a K dwarf extremely close to the 3:2 mean motion resonance. The two planets each show transits, sometimes simultaneously due to their proximity to resonance and alignment of conjunctions. We obtain further ground based photometry of the larger planet with the NITES telescope, demonstrating the presence of large transit timing variations (TTVs) of over an hour. These TTVs allows us to confirm the planetary nature of the system, and place a limit on the mass of the outer planet of 386M⊕.