Hot Jupiters Driven by High-eccentricity Migration in Globular Clusters

Hot Jupiters Driven by High-eccentricity Migration in Globular Clusters

Authors:

Hammers et al

Abstract:

Hot Jupiters (HJs) are short-period giant planets that are observed around $\sim 1 \% $ of solar-type field stars. One possible formation scenario for HJs is high-eccentricity (high-e) migration, in which the planet forms at much larger radii, is excited to high eccentricity by some mechanism, and migrates to its current orbit due to tidal dissipation occurring near periapsis. We consider high-e migration in dense stellar systems such as the cores of globular clusters (GCs), in which encounters with passing stars can excite planets to the high eccentricities needed to initiate migration. We study this process via Monte Carlo simulations of encounters with a star+planet system including the effects of tidal dissipation, using an efficient regularized restricted three-body code. HJs are produced in our simulations over a significant range of the stellar number density ${n}_{\star }$. Assuming the planet is initially on a low-eccentricity orbit with semimajor axis 1 au, for ${n}_{\star }\lesssim {10}^{3}\,{\mathrm{pc}}^{-3}$ the encounter rate is too low to induce orbital migration, whereas for ${n}_{\star }\gtrsim {10}^{6}\,{\mathrm{pc}}^{-3}$ HJ formation is suppressed because the planet is more likely ejected from its host star, tidally disrupted, or transferred to a perturbing star. The fraction of planets that are converted to HJs peaks at $\approx 2 \% $ for intermediate number densities of $\approx 4\times {10}^{4}\,{\mathrm{pc}}^{-3}$. Warm Jupiters, giant planets with periods between 10 and 100 days, are produced in our simulations with an efficiency of up to $\approx 0.5 \% $. Our results suggest that HJs can form through high-e migration induced by stellar encounters in the centers of of dense GCs, but not in their outskirts where the densities are lower.

The Most Eccentric Planet Orbiting a Giant Star

The Pan-Pacific Planet Search. VII. The Most Eccentric Planet Orbiting a Giant Star

Authors:

Wittenmyer et al

Abstract:

Radial velocity observations from three instruments reveal the presence of a 4 M Jup planet candidate orbiting the K giant HD 76920. HD 76920b has an orbital eccentricity of 0.856 ± 0.009, making it the most eccentric planet known to orbit an evolved star. There is no indication that HD 76920 has an unseen binary companion, suggesting a scattering event rather than Kozai oscillations as a probable culprit for the observed eccentricity. The candidate planet currently approaches to about four stellar radii from its host star, and is predicted to be engulfed on a ~100 Myr timescale due to the combined effects of stellar evolution and tidal interactions.

Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32Ab

Possible detection of a bimodal cloud distribution in the atmosphere of HAT-P-32Ab from multi-band photometry

Authors:

Tregloan-Reed et al

Abstract:
We present high-precision photometry of eight separate transit events in the HAT-P-32 planetary system. One transit event was observed simultaneously by two telescopes of which one obtained a simultaneous multi-band light curve in three optical bands, giving a total of 11 transit light curves. Due to the filter selection and in conjunction with using the defocussed photometry technique we were able to obtain an extremely high precision, ground-based transit in the \textit{u}-band (350\,nm), with an rms scatter of ≈1\,mmag. All 11 transits were modelled using \textsc{prism} and \textsc{gemc}, and the physical properties of the system calculated. We find the mass and radius of the host star to be $1.182\pm 0.041\Msun$ and $1.225\pm0.015\Rsun$, respectively. For the planet we find a mass of $0.80\pm 0.14\Mjup$, a radius of $1.807\pm0.022\Rjup$ and a density of $0.126\pm0.023\pjup$. These values are consistent with those found in the literature. We also obtain a new orbital ephemeris for the system T0=BJD/TDB2454420.447187(96)+2.15000800(10)×E. We measured the transmission spectrum of HAT-P-32\,A\,b and compared it to theoretical transmission spectra. Our results indicate a bimodal cloud particle distribution consisting of Rayleigh--like haze and grey absorbing cloud particles within the atmosphere of HAT-P-32\,A\,b.

sdB Pulsating Star V391 Peg's Giant Planet Not Detected

The sdB pulsating star V391 Peg and its putative giant planet revisited after 13 years of time-series photometric data

Authors:

Silvotti et al

Abstract:

V391 Peg (alias HS2201+2610) is a subdwarf B (sdB) pulsating star that shows both p- and g-modes. By studying the arrival times of the p-mode maxima and minima through the O-C method, in a previous article the presence of a planet was inferred with an orbital period of 3.2 yr and a minimum mass of 3.2 M_Jup. Here we present an updated O-C analysis using a larger data set of 1066 hours of photometric time series (~2.5x larger in terms of the number of data points), which covers the period between 1999 and 2012 (compared with 1999-2006 of the previous analysis). Up to the end of 2008, the new O-C diagram of the main pulsation frequency (f1) is compatible with (and improves) the previous two-component solution representing the long-term variation of the pulsation period (parabolic component) and the giant planet (sine wave component). Since 2009, the O-C trend of f1 changes, and the time derivative of the pulsation period (p_dot) passes from positive to negative; the reason of this change of regime is not clear and could be related to nonlinear interactions between different pulsation modes. With the new data, the O-C diagram of the secondary pulsation frequency (f2) continues to show two components (parabola and sine wave), like in the previous analysis. Various solutions are proposed to fit the O-C diagrams of f1 and f2, but in all of them, the sinusoidal components of f1 and f2 differ or at least agree less well than before. The nice agreement found previously was a coincidence due to various small effects that are carefully analysed. Now, with a larger dataset, the presence of a planet is more uncertain and would require confirmation with an independent method. The new data allow us to improve the measurement of p_dot for f1 and f2: using only the data up to the end of 2008, we obtain p_dot_1=(1.34+-0.04)x10**-12 and p_dot_2=(1.62+-0.22)x10**-12

OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System

OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System

Authors:

Han et al

Abstract:

We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find four degenerate triple-lens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about ${M}_{1}\sim 0.7\,{M}_{\odot }$, while the planet is a super Jupiter. In all cases, the system lies in the Galactic disk, about halfway toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low-mass brown dwarf, with relative mass ratios (1:0.03:0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source.

KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion

KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion 

Authors:

Siverd et al

Abstract:

We present the discovery of the giant planet KELT-19Ab, which transits the moderately bright (V∼9.9) A8V star TYC 764-1494-1. We confirm the planetary nature of the companion via a combination of low-precision radial velocities, which limit the mass to MP less than 4.1MJ (3σ), and a clear Doppler tomography signal, which indicates a retrograde projected spin-orbit misalignment of λ=−179.7+3.7−3.8 degrees. Global modeling indicates that the Teff=7500±110K host star has M∗=1.62+0.25−0.20M⊙ and R∗=1.83±0.10R⊙. The planet has a radius of RP=1.91±0.11RJ and receives a stellar insolation flux of ∼3.2×109ergs−1cm−2, leading to an inferred equilibrium temperature of Teq∼1935K assuming zero albedo and complete heat redistribution. With a vsinI∗=84.8±2.0kms−1, the host star is rapidly-rotating. Interestingly, its vsinI∗ is relatively low compared to other stars with similar effective temperatures, and it appears to be enhanced in metallic species such as strontium but deficient in others such as calcium, suggesting that it is likely an Am star. KELT-19A would be the first definitive detection of an Am host of a transiting planet of which we are aware. Adaptive optics observations of the system reveal the existence of a companion with late G9V/early K1V spectral type at a projected separation of ≈160AU. Radial velocity measurements indicate that this companion is bound. Most Am stars are known to have stellar companions, which are often invoked to explain the relatively slow rotation of the primary. In this case, the stellar companion is unlikely to have caused the tidal braking of the primary.

Transmission spectroscopy of the hot Jupiter TrES-3 b: Disproof of an overly large Rayleigh-like feature

Transmission spectroscopy of the hot Jupiter TrES-3 b: Disproof of an overly large Rayleigh-like feature 

Authors:

Mackebrandt et al

Abstract:
Context. Transit events of extrasolar planets offer the opportunity to study the composition of their atmospheres. Previous work on transmission spectroscopy of the close-in gas giant TrES-3 b revealed an increase in absorption towards blue wavelengths of very large amplitude in terms of atmospheric pressure scale heights, too large to be explained by Rayleigh-scattering in the planetary atmosphere. Aims. We present a follow-up study of the optical transmission spectrum of the hot Jupiter TrES-3 b to investigate the strong increase in opacity towards short wavelengths found by a previous study. Furthermore, we aim to estimate the effect of stellar spots on the transmission spectrum. Methods. This work uses previously published long slit spectroscopy transit data of the Gran Telescopio Canarias (GTC) and published broad band observations as well as new observations in different bands from the near-UV to the near-IR, for a homogeneous transit light curve analysis. Additionally, a long-term photometric monitoring of the TrES-3 host star was performed. Results. Our newly analysed GTC spectroscopic transit observations show a slope of much lower amplitude than previous studies. We conclude from our results the previously reported increasing signal towards short wavelengths is not intrinsic to the TrES-3 system. Furthermore, the broad band spectrum favours a flat spectrum. Long-term photometric monitoring rules out a significant modification of the transmission spectrum by unocculted star spots.

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.

A Six-planet System around the Star HD 34445

A Six-planet System around the Star HD 34445 

Authors:

Vogt et al 

Abstract:

We present a new precision radial velocity (RV) data set that reveals a multi-planet system orbiting the G0V star HD 34445. Our 18-year span consists of 333 precision RV observations, 56 of which were previously published and 277 of which are new data from the Keck Observatory, Magellan at Las Campanas Observatory, and the Automated Planet Finder at Lick Observatory. These data indicate the presence of six planet candidates in Keplerian motion about the host star with periods of 1057, 215, 118, 49, 677, and 5700 days, and minimum masses of 0.63, 0.17, 0.1, 0.05, 0.12, and 0.38 M J, respectively. The HD 34445 planetary system, with its high degree of multiplicity, its long orbital periods, and its induced stellar RV half-amplitudes in the range 2 m s−1 lesssim K lesssim 5 m s−1 is fundamentally unlike either our own solar system (in which only Jupiter and Saturn induce significant reflex velocities for the Sun), or the Kepler multiple-transiting systems (which tend to have much more compact orbital configurations).

Chaotic quadruple secular evolution and the production of misaligned exomoons and Warm Jupiters in stellar multiples

Chaotic quadruple secular evolution and the production of misaligned exomoons and Warm Jupiters in stellar multiples 

Authors:

Grishin et al

Abstract:
We study the chaotic and secular evolution of hierarchical quadruple systems in the 3+1 configuration, focusing on the evolution of mutual inclination of the inner binaries as the system undergoes coupled Lidov-Kozai (LK) oscillations. We include short-range forces (SRF; such as those due to tidal and rotational distortions) that control the eccentricity excitation of the inner binary. The evolution of mutual inclination is described, a priori, by two dimensionless parameters, $\pazocal{R}_0$, the ratio between the inner and outer LK time-scales and ϵSRF, the ratio between the SRF precession and the inner LK precession rates. We find that the chaotic zones for the mutual inclination depend mainly on $\pazocal{R}_0$, while ϵSRF controls mainly the range of eccentricity excitation. The mutual inclination evolves chaotically for $1\lesssim \pazocal{R}_0\lesssim 10$, leading to large misalignments. For $0.4 \lesssim \pazocal{R}_0 \lesssim 0.8$, the system could be weakly excited and produce bimodal distribution of mutual inclination angles. Our results can be applied to exomoons-planets in stellar binaries and Warm/Hot Jupiters in stellar triples. Such systems could develop large mutual inclination angles if the inner binary is tight enough, and also high eccentricities, depending of the strength of the short-range forces. Future detections of tilted Warm/Hot Jupiters and exomoons could put our mechanism under observational tests.

The nature of the giant exomoon candidate Kepler-1625 b-i

The nature of the giant exomoon candidate Kepler-1625 b-i 

Authors:

Heller et al

Abstract:
The recent announcement of a Neptune-sized exomoon candidate around the transiting Jupiter-sized object Kepler-1625 b could indicate the presence of a hitherto unknown kind of gas giant moons, if confirmed. Three transits have been observed, allowing radius estimates of both objects. Here we investigate possible mass regimes of the transiting system that could produce the observed signatures and study them in the context of moon formation in the solar system, i.e. via impacts, capture, or in-situ accretion. The radius of Kepler-1625 b suggests it could be anything from a gas giant planet somewhat more massive than Saturn (0.4 M_Jup) to a brown dwarf (BD) (up to 75 M_Jup) or even a very-low-mass star (VLMS) (112 M_Jup ~ 0.11 M_sun). The proposed companion would certainly have a planetary mass. Possible extreme scenarios range from a highly inflated Earth-mass gas satellite to an atmosphere-free water-rock companion of about 180 M_Ear. Furthermore, the planet-moon dynamics during the transits suggest a total system mass of 17.6_{-12.6}^{+19.2} M_Jup. A Neptune-mass exomoon around a giant planet or low-mass BD would not be compatible with the common mass scaling relation of the solar system moons about gas giants. The case of a mini-Neptune around a high-mass BD or a VLMS, however, would be located in a similar region of the satellite-to-host mass ratio diagram as Proxima b, the TRAPPIST-1 system, and LHS 1140 b. The capture of a Neptune-mass object around a 10 M_Jup planet during a close binary encounter is possible in principle. The ejected object, however, would have had to be a super-Earth object, raising further questions of how such a system could have formed. In summary, this exomoon candidate is barely compatible with established moon formation theories. If it can be validated as orbiting a super-Jovian planet, then it would pose an exquisite riddle for formation theorists to solve.

Evidence for Atmospheric Cold-trap Processes in the Noninverted Emission Spectrum of Kepler-13Ab Using HST/WFC3

Evidence for Atmospheric Cold-trap Processes in the Noninverted Emission Spectrum of Kepler-13Ab Using HST/WFC3 

Authors: 

Beatty et al 

Abstract: 

We observed two eclipses of the Kepler-13A planetary system, on UT 2014 April 28 and UT 2014 October 13, in the near-infrared using Wide Field Camera 3 on the Hubble Space Telescope. By using the nearby binary stars Kepler-13BC as a reference, we were able to create a differential light curve for Kepler-13A that had little of the systematics typically present in HST/WFC3 spectrophotometry. We measure a broadband (1.1–1.65 μm) eclipse depth of 734 ± 28 ppm and are able to measure the emission spectrum of the planet at R ≈ 50 with an average precision of 70 ppm. We find that Kepler-13Ab possesses a noninverted, monotonically decreasing vertical temperature profile. We exclude an isothermal profile and an inverted profile at more than 3σ. We also find that the dayside emission of Kepler-13Ab appears generally similar to an isolated M7 brown dwarf at a similar effective temperature. Due to the relatively high mass and surface gravity of Kepler-13Ab, we suggest that the apparent lack of an inversion is due to cold-trap processes in the planet's atmosphere. Using a toy model for where cold traps should inhibit inversions, as well as observations of other planets in this temperature range with measured emission spectra, we argue that with more detailed modeling and more observations we may be able to place useful constraints on the size of condensates on the daysides of hot Jupiters.

Diffusive Tidal Evolution for Migrating hot Jupiters

Diffusive Tidal Evolution for Migrating hot Jupiters

Author:

Wu

Abstract:

I consider a Jovian planet on a highly eccentric orbit around its host star, a situation possibly produced by secular interactions with its planetary or stellar companions. At every periastron passage, tidal interactions lead to an energy exchange between the orbit and the planet's internal oscillations (predominantly an l=2 f-mode). Starting from zero energy, this f-mode can be diffusively excited if the one-kick energy gain is greater than (ωPorb)−1 of the orbital energy. This occurs at a pericentre distance of 4 tidal radii (or 1.6 Roche radius). Furthermore, when the f-mode has a non-negligible initial energy, this diffusive evolution can set in at a much reduced threshold. The first finding is important for stalling the secular migration. The f-mode can absorb orbital energy and decouple the planet from its secular perturbers, parking all migrating jupiters safely outside the zone of tidal disruption. The second finding is important for circularizing the planet's orbit. It allows an excited f-mode to continuously absorb orbital energy even when the one-kick energy is weakening along the path of circularization (due to increasing pericentre distance). So without any explicit dissipation, other than the fact that the f-mode will damp nonlinearly when its amplitude reaches unity, the planet can be transported from a few AU to 0.2 AU in 10^4 yrs. Such a rapid circularization corresponds to an equivalent tidal dissipation factor Q ~ 1, and it explains the observed deficit of super-eccentric Jovian planets. Lastly, the repeated f-mode breaking deposits energy and angular momentum in the outer shells of the planet. This likely alters the planet's thermal structure, but should fall short of ablating it. Overall, this work boosts the case for forming hot Jupiters through high-eccentricity secular migration.

Aerosol Constraints on the Atmosphere of the Hot Saturn-mass planet WASP-49b

Aerosol Constraints on the Atmosphere of the Hot Saturn-mass planet WASP-49b 

Authors:
Cubillos et al

Abstract:
The strong, nearly wavelength-independent absorption cross section of aerosols produces featureless exoplanet transmission spectra, limiting our ability to characterize their atmospheres. Here we show that even in the presence of featureless spectra, we can still characterize certain atmospheric properties. Specifically, we constrain the upper and lower pressure boundaries of aerosol layers, and present plausible composition candidates. We study the case of the bloated Saturn-mass planet WASP-49b, where near-infrared observations reveal a flat transmission spectrum between 0.7 and 1.0 {\microns}. First, we use a hydrodynamic upper-atmosphere code to estimate the pressure reached by the ionizing stellar high-energy photons at 10−8 bar, setting the upper pressure boundary where aerosols could exist. Then, we combine HELIOS and Pyrat Bay radiative-transfer models to constrain the temperature and photospheric pressure of atmospheric aerosols, in a Bayesian framework. For WASP-49b, we constrain the transmission photosphere (hence, the aerosol deck boundaries) to pressures above 10−5 bar (100× solar metallicity), 10−4 bar (solar), and 10−3 bar (0.1× solar) as lower boundary, and below 10−7 bar as upper boundary. Lastly, we compare condensation curves of aerosol compounds with the planet's pressure-temperature profile to identify plausible condensates responsible for the absorption. Under these circumstances, we find as candidates: Na2S (at 100× solar metallicity); Cr and MnS (at solar and 0.1× solar); and forsterite, enstatite, and alabandite (at 0.1× solar).

A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems

A Direct Imaging Survey of Spitzer detected debris disks: Occurrence of giant planets in dusty systems

Authors:

Meshkat et al

Abstract:

We describe a joint high contrast imaging survey for planets at Keck and VLT of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars which do not show infrared excesses. We assumed a double power law distribution in mass and semi-major axis of the form f(m,a) = Cmαaβ, where we adopted power law values and logarithmically flat values for the mass and semi-major axis of planets. We find that the frequency of giant planets with masses 5-20 MJup and separations 10-1000 AU around stars with debris disks is 6.27% (68% confidence interval 3.68 - 9.76%), compared to 0.73% (68% confidence interval 0.20 - 1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples.

Inferring giant planets from ALMA mm continuum and line observations in (transition) disks

Inferring giant planets from ALMA mm continuum and line observations in (transition) disks 

Authors:

Facchini et al

Abstract:
Potential signatures of proto-planets embedded in their natal protoplanetary disk are radial gaps or cavities in the continuum emission in the IR-mm wavelength range. ALMA observations are now probing spatially resolved rotational line emission of CO and other chemical species. These observations can provide complementary information on the mechanism carving the gaps in dust and additional constraints on the purported planet mass. We post-process 2D hydrodynamical simulations of planet-disk models, where the dust densities and grain size distributions are computed with a dust evolution code. The simulations explore different planet masses (1MJ≤Mp≤15MJ) and turbulent parameters. The outputs are post-processed with the thermo-chemical code DALI, accounting for the radially and vertically varying dust properties as in Facchini et al. (2017). We obtain the gas and dust temperature structures, chemical abundances, and synthetic emission maps of both thermal continuum and CO rotational lines. This is the first study combining hydro simulations, dust evolution and chemistry to predict gas emission of disks hosting massive planets. All radial intensity profiles of the CO main isotopologues show a gap at the planet location. The ratio between the location of the gap as seen in CO and the peak in the mm continuum at the pressure maximum outside the orbit of the planet shows a clear dependence on planet mass. Due to the low dust density in the gaps, the dust and gas components can become thermally decoupled, with the gas being colder than the dust. The gaps seen in CO are due to a combination of gas temperature dropping at the location of the planet, and of the underlying surface density profile. In none of the models is a CO cavity observed, only CO gaps, indicating that one single massive planet is not able to explain the CO cavities observed in transition disks.

Observability of Forming Planets and their Circumplanetary Disks I. – Parameter Study for ALMA

Observability of Forming Planets and their Circumplanetary Disks I. – Parameter Study for ALMA
Authors:

Szulágyi et al

Abstract:
We present mock observations of forming planets with ALMA. The possible detections of circumplanetary disks (CPDs) were investigated around planets of Saturn, 1, 3, 5, and 10 Jupiter-masses that are placed at 5.2 AU from their star. The radiative, three dimensional hydrodynamic simulations were then post-processed with RADMC3D and the ALMA Observation Simulator. We found that even though the CPDs are too small to be resolved, they are hot due to the accreting planet in the optically thick limit, therefore the best chance to detect them with continuum observations in this case is at the shortest ALMA wavelengths, such as Band 9 (440 microns). Similar fluxes were found in the case of Saturn and Jupiter-mass planets, as for the 10 MJup gas-giant, due to temperature weighted optical depth effects: when no deep gap is carved, the planet region is blanketed by the optically thick circumstellar disk leading to a less efficient cooling there. A test was made for a 52 AU orbital separation, showed that optically thin CPDs are also detectable in band 7 but they need longer integration times (>5hrs). Comparing the gap profiles of the same simulation at various ALMA bands and the hydro simulation confirmed that they change significantly, first because the gap is wider at longer wavelengths due to decreasing optical depth; second, the beam convolution makes the gap shallower and at least 25% narrower. Therefore, caution has to be made when estimating planet masses based on ALMA continuum observations of gaps.

Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions

Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions 

Authors:

Khodachenko et al 

Abstract:

To shed more light on the nature of the observed Lyα absorption during transits of HD 209458b and to quantify the major mechanisms responsible for the production of fast hydrogen atoms (the so-called energetic neutral atoms, ENAs) around the planet, 2D hydrodynamic multifluid modeling of the expanding planetary upper atmosphere, which is driven by stellar XUV, and its interaction with the stellar wind has been performed. The model self-consistently describes the escaping planetary wind, taking into account the generation of ENAs due to particle acceleration by the radiation pressure and by the charge exchange between the stellar wind protons and planetary atoms. The calculations in a wide range of stellar wind parameters and XUV flux values showed that under typical Sun-like star conditions, the amount of generated ENAs is too small, and the observed absorption at the level of 6%–8% can be attributed only to the non-resonant natural line broadening. For lower XUV fluxes, e.g., during the activity minima, the number of planetary atoms that survive photoionization and give rise to ENAs increases, resulting in up to 10%–15% absorption at the blue wing of the Lyα line, caused by resonant thermal line broadening. A similar asymmetric absorption can be seen under the conditions realized during coronal mass ejections, when sufficiently high stellar wind pressure confines the escaping planetary material within a kind of bowshock around the planet. It was found that the radiation pressure in all considered cases has a negligible contribution to the production of ENAs and the corresponding absorption.

A search for transit timing variations and orbital decay in WASP-46b

A search for transit timing variations and orbital decay in WASP-46b 

Authors:

Petrucci et al

Abstract:

We present 12 new transit observations of the exoplanet WASP-46b obtained with the 1.54-m telescope at Estación Astrofísica de Bosque Alegre (EABA, Argentina) and the 0.40-m Horacio Ghielmetti and 2.15-m Jorge Sahade telescopes at Complejo Astronómico El Leoncito (CASLEO, Argentina). We analyse them together with 37 light curves from the literature to re-determine the physical parameters and search for additional planets via transit timing variations (TTVs). We consider the 31 transits with uncertainties in their mid-transit times (eT0 eT0) less than 1 minute, to perform the first homogeneous study of TTVs for the system, finding a dispersion of σ = 1.66 minutes over a 6 year baseline. Since no periodic variations are found, our interpretation for this relatively high value of σ is that the stellar activity could be affecting the measured mid-transit times. This value of dispersion allows us to rule out the presence of additional bodies with masses larger than 2.3, 4.6, 7, and 9.3 M⊕ M⊕ at the first-order mean-motion resonances 2:1, 3:2, 4:3, and 5:4 with the transiting planet, respectively. Despite the 6 year baseline and a typical light curve precision of 2 × 10−3, we find that we cannot significantly demonstrate a slow decrease of the orbital period of WASP-46b. We place a lower limit of Q⋆ greater than 7 × 103 on the tidal quality factor and determine that an additional 6 year baseline is required to rule out Q⋆ less than 105.

Forming Different Planetary Architectures. I. The Formation Efficiency of Hot Jupiters from High-eccentricity Mechanisms

Forming Different Planetary Architectures. I. The Formation Efficiency of Hot Jupiters from High-eccentricity Mechanisms 

Authors: 

Wang et al 

Abstract: 

Exoplanets discovered over the past decades have provided a new sample of giant exoplanets: hot Jupiters. For lack of enough materials in the current locations of hot Jupiters, they are perceived to form outside the snowline. Then, they migrate to the locations observed through interactions with gas disks or high-eccentricity mechanisms. We examined the efficiencies of different high-eccentricity mechanisms for forming hot Jupiters in near-coplanar multi-planet systems. These mechanisms include planet–planet scattering, the Kozai–Lidov mechanism, coplanar high-eccentricity migration, and secular chaos, as well as other two new mechanisms that we present in this work, which can produce hot Jupiters with high inclinations even in retrograde. We find that the Kozai–Lidov mechanism plays the most important role in producing hot Jupiters among these mechanisms. Secular chaos is not the usual channel for the formation of hot Jupiters due to the lack of an angular momentum deficit within ${10}^{7}{T}_{\mathrm{in}}$ (periods of the inner orbit). According to comparisons between the observations and simulations, we speculate that there are at least two populations of hot Jupiters. One population migrates into the boundary of tidal effects due to interactions with the gas disk, such as ups And b, WASP-47 b, and HIP 14810 b. These systems usually have at least two planets with lower eccentricities, and remain dynamically stable in compact orbital configurations. Another population forms through high-eccentricity mechanisms after the excitation of eccentricity due to dynamical instability. These kinds of hot Jupiters usually have Jupiter-like companions in distant orbits with moderate or high eccentricities.