The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert

The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert
Authors:

Demangeon et al 

Abstract:
To investigate the origin of the features discovered in the exoplanet population, the knowledge of exoplanets' mass and radius with a good precision is essential. In this paper, we report the discovery of three transiting exoplanets by the SuperWASP survey and the SOPHIE spectrograph with mass and radius determined with a precision better than 15 %. WASP-151b and WASP-153b are two hot Saturns with masses, radii, densities and equilibrium temperatures of 0.31^{+0.04}_{-0.03} MJ, 1.13^{+0.03}_{-0.03} RJ, 0.22^{-0.03}_{-0.02} rhoJ and 1, 290^{+20}_{-10} K, and 0.39^{+0.02}_{-0.02} MJ, 1.55^{+0.10}_{-0.08} RJ, 0.11^{+0.02}_{-0.02} rhoJ and 1, 700^{+40}_{-40} K, respectively. Their host stars are early G type stars (with magV ~ 13) and their orbital periods are 4.53 and 3.33 days, respectively. WASP-156b is a Super-Neptune orbiting a K type star (magV = 11.6) . It has a mass of 0.128^{+0.010}_{-0.009} MJ, a radius of 0.51^{+0.02}_{-0.02} RJ, a density of 1.0^{+0.1}_{-0.1} rhoJ, an equilibrium temperature of 970^{+30}_{-20} K and an orbital period of 3.83 days. WASP-151b is slightly inflated, while WASP-153b presents a significant radius anomaly. WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages. We propose that high eccentricity migration could partially explain this behaviour for stars hosting a short period planet. Finally, these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert. Their characteristics support that the ultra-violet irradiation plays an important role in this depletion of planets observed in the exoplanet population.

HATS-43b, HATS-44b, HATS-45b, and HATS-46b: Four Short Period Transiting Giant Planets in the Neptune-Jupiter Mass Range

HATS-43b, HATS-44b, HATS-45b, and HATS-46b: Four Short Period Transiting Giant Planets in the Neptune-Jupiter Mass Range

Authors:

Brahm et al

Abstract:

We report the discovery of four short period extrasolar planets transiting moderately bright stars from photometric measurements of the HATSouth network coupled to additional spectroscopic and photometric follow-up observations. While the planet masses range from 0.26 to 0.90 MJ, the radii are all approximately a Jupiter radii, resulting in a wide range of bulk densities. The orbital period of the planets range from 2.7d to 4.7d, with HATS-43b having an orbit that appears to be marginally non-circular (e= 0.173±0.089). HATS-44 is notable for a high metallicity ([Fe/H]= 0.320±0.071). The host stars spectral types range from late F to early K, and all of them are moderately bright (13.3 less than V less than 14.4), allowing the execution of future detailed follow-up observations. HATS-43b and HATS-46b, with expected transmission signals of 2350 ppm and 1500 ppm, respectively, are particularly well suited targets for atmospheric characterisation via transmission spectroscopy.

LAMOST Reveals Neptune-size Cousins of hot Jupiters, preferentially in "(metal-)rich" and "one-child" Kepler families

LAMOST Reveals Neptune-size Cousins of hot Jupiters, preferentially in "(metal-)rich" and "one-child" Kepler families

Authors:

Dong et al

Abstract:

WWe discover a new population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single transiting planets. We use accurate LAMOST DR4 stellar parameters for main-sequence stars to study the distributions of short-period (1d less than P less than 10d) Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more "puffed up" as compared to that around metal-poor hosts. In two period-radius regimes, planets preferentially reside around metal-rich stars, while there are scantily any planets around metal-poor stars. One is the well-known hot Jupiters, and the other is a new population of Neptune-size planets (2 R_Earth less than R_p less than 6 R_Earth), dubbed as "Hoptunes". Also like hot Jupiters, Hoptunes occur more frequently in systems with single transiting planets than in multiple transiting planetary systems. About 1% of solar-type stars host "Hoptunes", and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a "valley" at approximately Saturn size (in the range of 6 R_Earth less than approximately R_p less than approximately 10 R_Earth), and this "hot-Saturn valley" represents an approximately order-of-magnitude decrease in planet frequency compared to hot Jupiters and Hoptunes. The empirical "kinship" between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.

Ground-based photometry of the 21-day Neptune HD 106315c

Ground-based photometry of the 21-day Neptune HD106315c

Authors:
Lendl et al

Abstract:
Space-based transit surveys such as K2 and TESS allow the detection of small transiting planets with orbital periods beyond 10 days. Few of these warm Neptunes are currently known around stars bright enough to allow for detailed follow-up observations dedicated to their atmospheric characterization. The 21-day period and 3.95 R⊕ planet HD106315c has been discovered based on the observation of two of its transits by K2. We have observed HD106315 using the 1.2m Euler telescope equipped with the EulerCam camera on two instances to confirm the transit using broad band photometry and refine the planetary period. Based on two observed transits of HD106315c, we detect its ∼1 mmag transit and obtain a precise measurement of the planetary ephemerids, which are critical for planning further follow-up observations. We have used the attained precision together with the predicted yield from the TESS mission to evaluate the potential for ground-based confirmation of Neptune-sized planets found by TESS. We find that 1-meter-class telescopes on the ground equipped with precise photometers could substantially contribute to the follow-up of 162 TESS candidates orbiting stars with magnitudes of V≤14. Out of these, 74 planets orbit stars with V≤12 and 12 planets orbit V≤10, which makes these candidates high-priority objects for atmospheric characterization with high-end instrumentation.

Possible formation pathways for the low density Neptune-mass planet HAT-P-26b

Possible formation pathways for the low density Neptune-mass planet HAT-P-26b

Authors:

Ali-Dib et al

Abstract:
We investigate possible pathways for the formation of the low density Neptune-mass planet HAT-P-26b. We use two formation different models based on pebbles and planetesimals accretion, and includes gas accretion, disk migration and simple photoevaporation. The models tracks the oxygen abundance and the properties of the forming planets, that we compare to HAT-P-26b. We find that pebbles accretion can explain this planet more naturally than planetesimals accretion that fails completely unless we artificially enhance the disk metallicity significantly. Pebble accretion models can reproduce HAT-P-26b with either a high initial core mass and low amount of core erosion, or the opposite, with both scenarios being equally plausible. Degeneracy between the formation time and location of the planet implies that more observables are needed to constraint its formation.

HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance

HAT-P-26b: A Neptune-Mass Exoplanet with a Well Constrained Heavy Element Abundance

Authors:

Wakeford et al

Abstract:

A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System, and has served as a cornerstone of planet formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 microns, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H2O absorption bands with a maximum base-to-peak amplitude of 525ppm in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b's atmospheric heavy element content [4.8 (-4.0 +21.5) times solar]. This likely indicates that HAT-P-26b's atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals.

An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres

An Observational Diagnostic for Distinguishing Between Clouds and Haze in Hot Exoplanet Atmospheres

Authors:

Kempton et al

Abstract:

The nature of aerosols in hot exoplanet atmospheres is one of the primary vexing questions facing the exoplanet field. The complex chemistry, multiple formation pathways, and lack of easily identifiable spectral features associated with aerosols make it especially challenging to constrain their key properties. We propose a transmission spectroscopy technique to identify the primary aerosol formation mechanism for the most highly irradiated hot Jupiters. The technique is based on the expectation that the two key types of aerosols -- photochemically generated hazes and equilibrium condensate clouds -- are expected to form and persist in different regions of a highly irradiated planet's atmosphere. Haze can only be produced on the permanent daysides of tidally-locked hot Jupiters, and will be carried downwind by atmospheric dynamics to the evening terminator (seen as the trailing limb during transit). Clouds can only form in cooler regions on the night side and morning terminator (seen as the leading limb during transit) of the most highly irradiated giant planets. Because opposite limbs are expected to be impacted by different types of aerosols, ingress and egress spectra, which primarily probe opposing sides of the planet, will reveal the dominant aerosol formation mechanism. In either case, we typically expect the adjacent hemisphere to retain clear skies. Using this diagnostic, we find that observations with JWST and potentially with HST should be able to distinguish between clouds and haze for currently known highly irradiated hot Jupiters.

K2-98 b: A 32 Earth Mass Neptune-sized Exoplanet in a 10-day orbit around an F8 star

K2-98 b: A 32-M⊕ Neptune-sized planet in a 10-day orbit transiting an F8 star

Authors:

Barragán et al

Abstract:

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⋆=1.074±0.042, R⋆=1.311+0.083−0.048, and age of 5.2+1.2−1.0~Gyr. We derive a planetary mass and radius of Mp=32.2±8.1 and Rp=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 ∼3~Gyr, due to the evolution of the latter towards the red giant branch.

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b

Authors:

Awiphan et al

Abstract:

GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multi-wavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 days or a planet with an orbital period between 2.5 and 4.0 days are excluded. Combined optical and near-infrared transmission spectroscopy favour a H/He dominated haze (mean molecular weight 1.08 ± 0.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b.

EPIC 211391664b: A 32-M⊕ Neptune-sized planet in a 10-day orbit around an F8 star

EPIC 211391664b: A 32-M⊕ Neptune-sized planet in a 10-day orbit transiting an F8 star

Authors:

Barragán et al

Abstract:

We report the discovery of EPIC 211391664b, 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. EPIC 211391664 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with M⋆=1.074±0.042M⊙, R⋆=1.311+0.083−0.048R⊙, and age of 5.2+1.2−1.0~Gyr. We derive a planetary mass and radius of Mp=32.2±8.1M⊕ and Rp=4.3+0.3−0.2R⊕. EPIC 211391664b joins the relatively small group of Neptune-sized planets whose mass and radius have been derived with a precision better than 3-σ. We estimate that the planet will be engulfed by EPIC 211391664 in ∼3~Gyr, due to the evolution of the host star towards the red giant branch.

In Situ and Ex Situ Formation Models of Kepler 11 Planets

In Situ and Ex Situ Formation Models of Kepler 11 Planets

Authors:

D'Angelo et al

Abstract:

We present formation simulations of the six Kepler 11 planets. Models assume either in situ or ex situ assembly, the latter with migration, and are evolved to the estimated age of the system, 8 Gyr. Models combine detailed calculations of both the gaseous envelope and the condensed core structures, including accretion of gas and solids, of the disk's viscous and thermal evolution, including photo-evaporation and disk-planet interactions, and of the planets' evaporative mass loss after disk dispersal. Planet-planet interactions are neglected. Both sets of simulations successfully reproduce measured radii, masses, and orbital distances of the planets, except for the radius of Kepler 11b, which loses its entire gaseous envelope shortly after formation. Gaseous (H+He) envelopes account for < 18% of the planet masses, and between 35 and 60% of the planet radii. In situ models predict a very massive inner disk, whose solids' surface density (sigma_Z) varies from over 1e4 to 1e3 g/cm2 at stellocentric distances 0.1 < r < 0.5 AU. Initial gas densities would be in excess of 1e5 g/cm2 if solids formed locally. Given the high disk temperatures (> 1000 K), planetary interiors can only be composed of metals and highly refractory materials. Sequestration of hydrogen by the core and subsequent outgassing is required to account for the observed radius of Kepler 11b. Ex situ models predict a relatively low-mass disk, whose initial sigma_Z varies from 10 to 5 g/cm2 at 0.5 < r < 7 AU and whose initial gas density ranges from 1e3 to 100 g/cm2. All planetary interiors are expected to be rich in H2O, as core assembly mostly occurs exterior to the ice condensation front. Kepler 11b is expected to have a steam atmosphere, and H2O is likely mixed with H+He in the envelopes of the other planets. Results indicate that Kepler 11g may not be more massive than Kepler 11e.

HD 219828 System has a hot Neptune & Super Jupiter

An extreme planetary system around HD 219828

Authors:

Santos et al

Abstract:

Context.

With about 2000 extrasolar planets confirmed, the results show that planetary systems have a whole range of unexpected properties. This wide diversity provides fundamental clues to the processes of planet formation and evolution.

Aims.

We present a full investigation of the HD 219828 system, a bright metal-rich star for which a hot Neptune has previously been detected.

Methods.

We used a set of HARPS, SOPHIE, and ELODIE radial velocities to search for the existence of orbiting companions to HD 219828. The spectra were used to characterise the star and its chemical abundances, as well as to check for spurious, activity induced signals. A dynamical analysis is also performed to study the stability of the system and to constrain the orbital parameters and planet masses.

Results.

We announce the discovery of a long period (P = 13.1 yr) massive (m sini = 15.1 MJup) companion (HD 219828 c) in a very eccentric orbit (e = 0.81). The same data confirms the existence of a hot Neptune, HD 219828 b, with a minimum mass of 21 M⊕ and a period of 3.83 days. The dynamical analysis shows that the system is stable, and that the equilibrium eccentricity of planet b is close to zero.

Conclusions.

The HD 219828 system is extreme and unique in several aspects. First, ammong all known exoplanet systems it presents an unusually high mass ratio. We also show that systems like HD 219828, with a hot Neptune and a long-period massive companion are more frequent than similar systems with a hot Jupiter instead. This suggests that the formation of hot Neptunes follows a different path than the formation of their hot jovian counterparts. The high mass, long period, and eccentricity of HD 219828 c also make it a good target for Gaia astrometry as well as a potential target for atmospheric characterisation, using direct imaging or high-resolution spectroscopy. Astrometric observations will allow us to derive its real mass and orbital configuration. If a transit of HD 219828 b is detected, we will be able to fully characterise the system, including the relative orbital inclinations. With a clearly known mass, HD 219828 c may become a benchmark object for the range in between giant planets and brown dwarfs.

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ 3470b

Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b

Authors:

Awiphan et al

Abstract:

GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multi-wavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 days or a planet with an orbital period between 2.5 and 4.0 days are excluded. Combined optical and near-infrared transmission spectroscopy favour a H/He dominated haze (mean molecular weight 1.18±0.22) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b.

HD 219828: An extreme planetary system with One long-period super Jupiter to a hot-neptune host star

An extreme planetary system around HD219828. One long-period super Jupiter to a hot-neptune host star

Authors:

Santos et al

Abstract:

With about 2000 extrasolar planets confirmed, the results show that planetary systems have a whole range of unexpected properties. We present a full investigation of the HD219828 system, a bright metal-rich star for which a hot neptune has previously been detected. We used a set of HARPS, SOPHIE, and ELODIE radial velocities to search for the existence of orbiting companions to HD219828. A dynamical analysis is also performed to study the stability of the system and to constrain the orbital parameters and planet masses. We announce the discovery of a long period (P=13.1years) massive (msini=15.1MJup) companion (HD219828c) in a very eccentric orbit (e=0.81). The same data confirms the existence of a hot-neptune, HD219828b, with a minimum mass of 21 MEarth and a period of 3.83days. The dynamical analysis shows that the system is stable. The HD219828 system is extreme and unique in several aspects. First, among all known exoplanet systems it presents an unusually high mass ratio. We also show that systems like HD219828, with a hot neptune and a long-period massive companion are more frequent than similar systems with a hot jupiter instead. This suggests that the formation of hot neptunes follows a different path than the formation of their hot jovian counterparts. The high mass, long period, and eccentricity of HD219828c also make it a good target for Gaia astrometry as well as a potential target for atmospheric characterisation, using direct imaging or high-resolution spectroscopy. Astrometric observations will allow us to derive its real mass and orbital configuration. If a transit of HD219828b is detected, we will be able to fully characterise the system, including the relative orbital inclinations. With a clearly known mass, HD219828c may become a benchmark object for the range in between giant planets and brown dwarfs.

Interaction of the Evaporating Hot Neptune GJ 436b & its Host Star's Stellar Wind

An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ436 b

Authors:

Bourrier et al

Abstract

The warm Neptune GJ436b was observed with HST/STIS at three different epochs in the stellar Ly-alpha line, showing deep, repeated transits caused by a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas. Yet by itself it cannot explain the time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and stellar wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and stellar properties through the direct comparison of simulated and observed spectra. Our simulations match the last two epochs well. The observed sharp early ingresses come from the abrasion of the planetary coma by the stellar wind. Spectra observed during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the stellar wind). We find similar properties at both epochs for the planetary escape rate (2.5x108 g/s), the stellar photoionization rate (2x10−5 /s), the stellar wind bulk velocity (85 km/s), and its kinetic dispersion velocity (10 km/s). We find high velocities for the escaping gas (50-60 km/s) that may indicate MHD waves that dissipate in the upper atmosphere and drive the planetary outflow. In the last epoch the high density of the stellar wind (3x103 /cm3) led to the formation of an exospheric tail mainly composed of neutralized protons. The observations of GJ436 b allow for the first time to clearly separate the contributions of radiation pressure and stellar wind and to probe the regions of the exosphere shaped by each mechanism.

On turbulence driven by axial precession and tidal evolution of the spin–orbit angle of close-in giant planets

On turbulence driven by axial precession and tidal evolution of the spin–orbit angle of close-in giant planets

Author:

Barker

Abstract:

The spin axis of a rotationally deformed planet is forced to precess about its orbital angular momentum vector, due to the tidal gravity of its host star, if these directions are misaligned. This induces internal fluid motions inside the planet that are subject to a hydrodynamic instability. We study the turbulent damping of precessional fluid motions, as a result of this instability, in the simplest local computational model of a giant planet (or star), with and without a weak internal magnetic field. Our aim is to determine the outcome of this instability, and its importance in driving tidal evolution of the spin–orbit angle in precessing planets (and stars). We find that this instability produces turbulent dissipation that is sufficiently strong that it could drive significant tidal evolution of the spin–orbit angle for hot Jupiters with orbital periods shorter than about 10–18 days. If this mechanism acts in isolation, this evolution would be towards alignment or anti-alignment, depending on the initial angle, but the ultimate evolution (if other tidal mechanisms also contribute) is expected to be towards alignment. The turbulent dissipation is proportional to the cube of the precession frequency, so it leads to much slower damping of stellar spin–orbit angles, implying that this instability is unlikely to drive evolution of the spin–orbit angle in stars (either in planetary or close binary systems). We also find that the instability-driven flow can act as a system-scale dynamo, which may play a role in producing magnetic fields in short-period planets.

What *IS* the Radius of hot Neptune Corot-24b?

Identifying the "true" radius of the hot sub-Neptune CoRoT-24b by mass loss modelling

Authors:

Lammer et al

Abstract:

For the hot exoplanets CoRoT-24b and CoRoT-24c, observations have provided transit radii RT of 3.7±0.4 R⊕ and 4.9±0.5 R⊕, and masses of ≤5.7 M⊕ and 28±11 M⊕, respectively. We study their upper atmosphere structure and escape applying an hydrodynamic model. Assuming RT≈ RPL, where RPL is the planetary radius at the pressure of 100 mbar, we obtained for CoRoT-24b unrealistically high thermally-driven hydrodynamic escape rates. This is due to the planet's high temperature and low gravity, independent of the stellar EUV flux. Such high escape rates could last only for less than 100 Myr, while RPL shrinks till the escape rate becomes less than or equal to the maximum possible EUV-driven escape rate. For CoRoT-24b, RPL must be therefore located at ≈1.9−2.2 R⊕ and high altitude hazes/clouds possibly extinct the light at RT. Our analysis constraints also the planet's mass to be 5−5.7 M⊕. For CoRoT-24c, RPL and RT lie too close together to be distinguished in the same way. Similar differences between RPL and RT may be present also for other hot, low-density sub-Neptunes.

Probing HAT-P-11b's Exoatmosphere

Characterizing Exoplanet Atmospheres: From Light-curve Observations to Radiative-transfer Modeling

Authors:

Cubillos et al

Abstract:

Multi-wavelength transit and secondary-eclipse light-curve observations are some of the most powerful techniques to probe the thermo-chemical properties of exoplanets. Although the large planet-to-star brightness contrast and few available spectral bands produce data with low signal-to-noise ratios, a Bayesian approach can robustly reveal what constraints we can set, without over-interpreting the data. Here I performed an end-to-end analysis of transiting exoplanet data. I analyzed space-telescope data for three planets to characterize their atmospheres and refine their orbits, investigated correlated noise estimators, and contributed to the development of the respective data-analysis pipelines. Chapters 2 and 3 describe the Photometry for Orbits, Eclipses and Transits (POET) pipeline to model Spitzer Space Telescope light curves, applied to secondary-eclipse observations of the Jupiter-sized planets WASP-8b and TrES-1. Chapter 4 studies commonly used correlated-noise estimators for exoplanet light-curve modeling, time averaging, residual permutations, and wavelet likelihood, and assesses their applicability and limitations to estimate parameters uncertainties. Chapter 5 describes the open-source Bayesian Atmospheric Radiative Transfer (BART) code to characterize exoplanet atmospheres. BART combines a thermochemical-equilibrium code, a one-dimensional line-by-line radiative-transfer code, and the Multi-core Markov-chain Monte Carlo statistical module to constrains the atmospheric temperature and chemical-abundance profiles of exoplanets. I applied the BART code to the Hubble and Spitzer Space Telescope transit observations of the Neptune-sized planet HAT-P-11b. BART finds an atmosphere enhanced in heavy elements, constraining the water abundance to ~100 times that of the solar abundance.

EPIC 201637175b is Disintegrating; Ultra Short Period Planets in K2 are Half as Common in the Kepler Mission

Ultra Short Period Planets in K2: SuPerPiG Results for Campaigns 0-5

Authors:

Adams et al

Abstract:

We analyzed data from Campaigns 0-5 of the K2 mission and report 19 ultra-short period candidate planets with orbital periods of less than 1 day (nine of which have not been previously reported). The planet candidates range from 0.7-16 Earth radii and periods of 4.2-23.5 hours. One candidate (EPIC 203533312, Kp=12.5) is among the shortest-period planet candidates discovered to date, and, if confirmed as a planet, must have a density of at least rho=8.9 g/cm^3 in order to not be tidally disrupted. Four candidates have nominal radius values in the sub-Jovian desert (3-11 R_E, period under 1.5 days) where theoretical models do not favor their long-term stability; the only confirmed planet in this range is in fact thought to be disintegrating (EPIC 201637175). In addition to the planet candidates, we report on EPIC 211152484, which has intermittent transits that are only visible during about half of the observing campaign, and whose true nature is unclear. Based on an assessment of our survey's completeness, we estimate an occurrence rate for ultra short period planets among K2 target stars that is about half that estimated from the Kepler sample, raising questions as to whether the K2 systems are intrinsically different from the Kepler systems, possibly as a result of their different galactic location.

K2-33b: a 10 Million Year Old hot Neptune in a 5.4 day Orbit

A Neptune-sized transiting planet closely orbiting a 5–10-million-year-old star

Authors:

David et al

Abstract:

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 star’s life. Fully formed planets are frequently detected on short orbital periods around mature stars. Some theories suggest that the in situ formation of planets close to their host stars is unlikely and that the existence of such planets is therefore evidence of large-scale migration. Other theories posit that planet assembly at small orbital separations may be common. Here we report a newly born, transiting planet orbiting its star with a period of 5.4 days. The planet is 50 per cent larger than Neptune, and its mass is less than 3.6 times that of Jupiter (at 99.7 per cent confidence), with a true mass likely to be similar to that of Neptune. The star is 5–10 million years old and has a tenuous dust disk extending outward from about twice the Earth–Sun separation, in addition to the fully formed planet located at less than one-twentieth of the Earth–Sun separation.