Hot Jupiters Research Articles

ExoGemS Detection of a Metal Hydride in an Exoplanet Atmosphere at High Spectral Resolution

Exoplanet atmosphere studies are often enriched by synergies with brown dwarf analogs. However, many key molecules commonly seen in brown dwarfs have yet to be confirmed in exoplanet atmospheres. An important example is chromium hydride (CrH), which is often used to probe atmospheric temperatures and classify brown dwarfs into spectral types. Recently, tentative evidence for CrH was reported in the low-resolution transmission spectrum of the hot Jupiter WASP-31b. Here, we present high spectral resolution observations of WASP-31b’s transmission spectrum from GRACES/Gemini North and UVES/Very Large Telescope. We detect CrH at 5.6σ confidence, representing the first metal hydride detection in an exoplanet atmosphere at high spectral resolution. Our findings constitute a critical step in understanding the role of metal hydrides in exoplanet atmospheres.

Revised orbits of the two nearest Jupiters

ABSTRACT With its near-to-mid-infrared high-contrast imaging capabilities, JWST is ushering us into a golden age of directly imaging Jupiter-like planets. As the two closest cold Jupiters, ε Ind A b and ε Eridani b have sufficiently wide orbits and adequate infrared emissions to be detected by JWST. To detect more Jupiter-like planets for direct imaging, we develop a gost-based method to analyse radial velocity data and multiple Gaia data releases simultaneously. Without approximating instantaneous astrometry by catalogue astrometry, this approach enables the use of multiple Gaia data releases for detection of both short-period and long-period planets. We determine a mass of $2.96_{-0.38}^{+0.41}$ MJup and a period of $42.92_{-4.09}^{+6.38}$ yr for ε Ind A b. We also find a mass of $0.76_{-0.11}^{+0.14}$ MJup , a period of $7.36_{-0.05}^{+0.04}$ yr, and an eccentricity of 0.26$_{-0.04}^{+0.04}$ MJup, for ε Eridani b. The eccentricity differs from that given by some previous solutions, probably due to the sensitivity of orbital eccentricity to noise modelling. Our work refines the constraints on orbits and masses of the two nearest Jupiters and demonstrate the feasibility of using multiple Gaia data releases to constrain Jupiter-like planets.

Full spectroscopic model and trihybrid experimental-perturbative-variational line list for ZrO

ABSTRACT Zirconium monoxide (ZrO) absorption lines define rare S-type stars and are currently being sought on exoplanets. Successful detection is dependent on an accurate and comprehensive line list, with existing data not ideal for many applications. Specifically, the Plez et al. line list is near-complete but has insufficient accuracy for high-resolution cross-correlation, while the Sorensen & Bernath data have high accuracy but only consider a small number of spectral bands. This article presents a novel spectroscopic model, variational line list, and trihybrid line list for the main 90Zr16O isotopologue, as well as isotopologue-extrapolated hybrid line lists for the 91Zr16O, 92Zr16O, 93Zr16O, 94Zr16O, and 96Zr16O isotopologues. These were constructed using Duo based on icMRCI-SD/CASSCF ab initio electronic data calculated using molpro, experimental energies obtained from a previous MARVEL data compilation, and perturbative energies from Sorensen & Bernath. The new 90Zr16O ExoMol-style trihybrid line list, ZorrO, comprises 227 118 energies (13 075 experimental) and 47 662 773 transitions up to 30 000 cm −1 (333 nm) between 10 low-lying electronic states (X 1Σ+, a 3Δ, A 1Δ, b 3Π, B 1Π, C 1Σ+, d 3Φ, e 3Π, f 3Δ, and F 1Δ). The inclusion of experimental energy levels in ZorrO means ZrO will be much easier to detect using high-resolution ground-based telescopes in the 12 500–17 500 cm−1 (571–800 nm) spectral region. The inclusion of variational energy levels means that the ZorrO line list has very high completeness and can accurately model molecular absorption cross-sections even at high temperatures. The ZorrO data will hopefully facilitate the first detection of ZrO in the atmosphere of a hot Jupiter exoplanet, or alternatively more conclusively exclude its presence.

Modelling dynamically driven global cloud formation microphysics in the HAT-P-1b atmosphere

ABSTRACT Insight into the formation and global distribution of cloud particles in exoplanet atmospheres continues to be a key problem to tackle going into the JWST era. Understanding microphysical cloud processes and atmospheric feedback mechanisms in three-dimensional (3D) has proven to be a challenging prospect for exoplaneteers. In an effort to address the large computational burden of coupling these models in 3D simulations, we develop an open source, lightweight, and efficient microphysical cloud model for exoplanet atmospheres. ‘Mini-cloud’ is a microphysical based cloud model for exoplanet condensate clouds that can be coupled to contemporary general circulation models (GCMs) and other time-dependent simulations. We couple mini-cloud to the Exo-FMS GCM and use a prime JWST target, the hot Jupiter HAT-P-1b, as a test case for the cloud formation module. After 1000+ of days of integration with mini-cloud, our results show a complex 3D cloud structure with cloud properties relating closely the dynamical and temperature properties of the atmosphere. Current transit and emission spectra data are best fit with a reduced cloud particle number density compared to the nominal simulation, with our simulated JWST NIRISS SOSS spectra showing promising prospects for characterizing the atmosphere in detail. Overall, our study is another small step in first principles 3D exoplanet cloud formation microphysical modelling. We suggest that additional physics not included in the present model, such as coagulation, are required to reduce the number density of particles to appropriately observed levels.

Examining NHD versus QHD in the GCM THOR with non-grey radiative transfer for the hot Jupiter regime

ABSTRACT Global circulation models (GCMs) play an important role in contemporary investigations of exoplanet atmospheres. Different GCMs evolve various sets of dynamical equations, which can result in obtaining different atmospheric properties between models. In this study, we investigate the effect of different dynamical equation sets on the atmospheres of hot Jupiter exoplanets. We compare GCM simulations using the quasi-primitive dynamical equations (QHD) and the deep Navier-Stokes equations (NHD) in the GCM THOR. We utilize a two-stream non-grey ‘picket-fence’ scheme to increase the realism of the radiative transfer calculations. We perform GCM simulations covering a wide parameter range grid of system parameters in the population of exoplanets. Our results show significant differences between simulations with the NHD and QHD equation sets at lower gravity, higher rotation rates, or at higher irradiation temperatures. The chosen parameter range shows the relevance of choosing dynamical equation sets dependent on system and planetary properties. Our results show the climate states of hot Jupiters seem to be very diverse, where exceptions to prograde superrotation can often occur. Overall, our study shows the evolution of different climate states that arise just due to different selections of Navier-Stokes equations and approximations. We show the divergent behaviour of approximations used in GCMs for Earth but applied for non Earth-like planets.

EXPRES. IV. Two Additional Planets Orbiting ρ Coronae Borealis Reveal Uncommon System Architecture

Thousands of exoplanet detections have been made over the last 25 years using Doppler observations, transit photometry, direct imaging, and astrometry. Each of these methods is sensitive to different ranges of orbital separations and planetary radii (or masses). This makes it difficult to fully characterize exoplanet architectures and to place our solar system in context with the wealth of discoveries that have been made. Here, we use the EXtreme PREcision Spectrograph to reveal planets in previously undetectable regions of the mass–period parameter space for the star ρ Coronae Borealis. We add two new planets to the previously known system with one hot Jupiter in a 39 day orbit and a warm super-Neptune in a 102 day orbit. The new detections include a temperate Neptune planet ( M ⊕) in a 281.4 day orbit and a hot super-Earth ( M ⊕) in a 12.95 day orbit. This result shows that details of planetary system architectures have been hiding just below our previous detection limits; this signals an exciting era for the next generation of extreme precision spectrographs.

A Spectroscopic Thermometer: Individual Vibrational Band Spectroscopy with the Example of OH in the Atmosphere of WASP-33b

Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail, by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-33b as an example. We simulate low-resolution spectroscopic data for observations with the JWST's NIRSpec instrument and use high-resolution observational data obtained from the Subaru InfraRed Doppler instrument (IRD). Vibrational band–specific OH cross-section sets are constructed and used in retrievals on the (simulated) low- and (real) high-resolution data. Low-resolution observations are simulated for two WASP-33b emission scenarios: under the assumption of local thermal equilibrium (LTE) and with a toy non-LTE model for vibrational excitation of selected bands. We show that mixing ratios for individual bands can be retrieved with sufficient precision to allow the vibrational population distributions of the forward models to be reconstructed. A fit for the Boltzmann distribution in the LTE case shows that the vibrational temperature is recoverable in this manner. For high-resolution, cross-correlation applications, we apply the individual vibrational band analysis to an IRD spectrum of WASP-33b, applying an “unpeeling” technique. Individual detection significances for the two strongest bands are shown to be in line with Boltzmann-distributed vibrational state populations, consistent with the effective temperature of the WASP-33b atmosphere reported previously. We show the viability of this approach for analyzing the individual vibrational state populations behind observed and simulated spectra, including reconstructing state population distributions.

Tidal dissipation due to the elliptical instability and turbulent viscosity in convection zones in rotating giant planets and stars

ABSTRACT Tidal dissipation in star–planet systems can occur through various mechanisms, among which is the elliptical instability. This acts on elliptically deformed equilibrium tidal flows in rotating fluid planets and stars, and excites inertial waves in convective regions if the dimensionless tidal amplitude (ϵ) is sufficiently large. We study its interaction with turbulent convection, and attempt to constrain the contributions of both elliptical instability and convection to tidal dissipation. For this, we perform an extensive suite of Cartesian hydrodynamical simulations of rotating Rayleigh–Bénard convection in a small patch of a planet. We find that tidal dissipation resulting from the elliptical instability, when it operates, is consistent with ϵ3, as in prior simulations without convection. Convective motions also act as an effective viscosity on large-scale tidal flows, resulting in continuous tidal dissipation (scaling as ϵ2). We derive scaling laws for the effective viscosity using (rotating) mixing-length theory, and find that they predict the turbulent quantities found in our simulations very well. In addition, we examine the reduction of the effective viscosity for fast tides, which we observe to scale with tidal frequency (ω) as ω−2. We evaluate our scaling laws using interior models of Hot Jupiters computed with mesa. We conclude that rotation reduces convective length-scales, velocities, and effective viscosities (though not in the fast tides regime). We estimate that elliptical instability is efficient for the shortest period Hot Jupiters, and that effective viscosity of turbulent convection is negligible in giant planets compared with inertial waves.

TOI-1130: A photodynamical analysis of a hot Jupiter in resonance with an inner low-mass planet

The TOI-1130 is a known planetary system around a K-dwarf consisting of a gas giant planet, TOI-1130 c on an 8.4-day orbit that is accompanied by an inner Neptune-sized planet, TOI-1130 b, with an orbital period of 4.1 days. We collected precise radial velocity (RV) measurements of TOI-1130 with the HARPS and PFS spectrographs as part of our ongoing RV follow-up program. We performed a photodynamical modeling of the HARPS and PFS RVs, along with transit photometry from the Transiting Exoplanet Survey Satellite (TESS) and the TESS Follow-up Observing Program (TFOP). We determined the planet masses and radii of TOI-1130 b and TOI-1130 c to be Mb = 19.28 ± 0.97M⊕ and Rb = 3.56 ± 0.13 R⊕, and Mc = 325.59 ± 5.59M⊕ and Rc = 13.32−1.41+1.55 R⊕, respectively. We have spectroscopically confirmed the existence of TOI-1130 b, which had previously only been validated. We find that the two planets have orbits with small eccentricities in a 2:1 resonant configuration. This is the first known system with a hot Jupiter and an inner lower mass planet locked in a mean-motion resonance. TOI-1130 belongs to the small, yet growing population of hot Jupiters with an inner low-mass planet that poses a challenge to the pathway scenario for hot Jupiter formation. We also detected a linear RV trend that is possibly due to the presence of an outer massive companion.

Volatile-to-sulfur Ratios Can Recover a Gas Giant’s Accretion History

The newfound ability to detect SO2 in exoplanet atmospheres presents an opportunity to measure sulfur abundances and so directly test between competing modes of planet formation. In contrast to carbon and oxygen, whose dominant molecules are frequently observed, sulfur is much less volatile and resides almost exclusively in solid form in protoplanetary disks. This dichotomy leads different models of planet formation to predict different compositions of gas giant planets. Whereas planetesimal-based models predict roughly stellar C/S and O/S ratios, pebble-accretion models more often predict superstellar ratios. To explore the detectability of SO2 in transmission spectra and its ability to diagnose planet formation, we present a grid of atmospheric photochemical models and corresponding synthetic spectra for WASP-39b (where SO2 has been detected). Our 3D grid contains 113 models (spanning 1–100× the solar abundance ratio of C, O, and S) for thermal profiles corresponding to the morning and evening terminators, as well as mean terminator transmission spectra. Our models show that for a WASP-39b-like O/H and C/H enhancement of ∼10× solar, SO2 can only be seen for C/S and O/S ≲ 1.5× solar, and that WASP-39b’s reported SO2 abundance of 1–10 ppm may be more consistent with planetesimal accretion than with pebble-accretion models (although some pebble models also manage to predict similarly low ratios). More extreme C/S and O/S ratios may be detectable in higher-metallicity atmospheres, suggesting that smaller and more metal-rich gas and ice giants may be particularly interesting targets for testing planet formation models. Future studies should explore the dependence of SO2 on a wider array of planetary and stellar parameters, both for the prototypical SO2 planet WASP-39b, as well as for other hot Jupiters and smaller gas giants.

In situ enrichment in heavy elements of hot Jupiters

Context. Radius and mass measurements of short-period giant planets reveal that many of these planets contain a large amount of heavy elements. Although the range of inferred metallicities is broad, planets with more than 100 M⊕ of heavy elements are not rare. This is in sharp contrast with the expectations of the conventional core-accretion model for the origin of giant planets. Aims. The proposed explanations for the heavy-element enrichment of giant planets fall short of explaining the most enriched planets. We look for additional processes that can explain the full envelope of inferred enrichments. Methods. We revisited the dynamics of pebbles and dust in the vicinity of giant planets using analytic estimates and published results on the profile of a gap opened by a giant planet, the radial velocity of the gas with respect to the planet, the Stokes number of particles in the different parts of the disk, and the consequent dust/gas ratio. Although our results are derived in the framework of a viscous α-disk, we also discuss the case of disks driven by angular momentum removal in magnetized winds. Results. When giant planets are far from the star, dust and pebbles are confined to a pressure bump at the outer edge of the planet-induced gap. When the planets reach the inner part of the disk (rp ≪ 2 au), dust instead penetrates into the gap together with the gas. The dust/gas ratio can be enhanced by more than an order of magnitude if the radial drift of dust is not impeded farther out by other barriers. Thus, hot planets undergoing runaway gas accretion can swallow a large amount of dust, acquiring ~100 M⊕ of heavy elements by the time they reach Jupiter masses. Conclusions. Whereas the gas accreted by giant planets in the outer disk is very dust-poor, that accreted by hot planets can be extremely dust-rich. Thus, provided that a large fraction of the atmosphere of hot Jupiters is accreted in situ, a large amount of dust can be accreted as well. We draw a distinction between this process and pebble accretion (i.e., the capture of dust without the accretion of gas), which is ineffective at small stellocentric radii, even for super-Earths. Giant planets farther out in the disk are extremely effective barriers against the flow of pebbles and dust across their gap. Saturn and Jupiter, after locking into a mutual mean motion resonance and reversing their migration, could have accreted small pebble debris.

A Hydrodynamic Study of the Escape of Metal Species and Excited Hydrogen from the Atmosphere of the Hot Jupiter WASP-121b

In the near-UV and optical transmission spectrum of the hot Jupiter WASP-121b, recent observations have detected strong absorption features of Mg, Fe, Ca, and Hα, extending outside of the planet’s Roche lobe. Studying these atomic signatures can directly trace the escaping atmosphere and constrain the energy balance of the upper atmosphere. To understand these features, we introduce a detailed forward model by expanding the capability of a one-dimensional model of the upper atmosphere and hydrodynamic escape to include important processes of atomic metal species. The hydrodynamic model is coupled to a Lyα Monte Carlo radiative transfer calculation to simulate the excited hydrogen population and associated heating/ionization effects. Using this model, we interpret the detected atomic features in the transmission spectrum of WASP-121b and explore the impact of metals and excited hydrogen on its upper atmosphere. We demonstrate the use of multiple absorption lines to impose stronger constraints on the properties of the upper atmosphere than the analysis of a single transmission feature can provide. In addition, the model shows that line broadening due to atmospheric outflow driven by Roche lobe overflow is necessary to explain the observed line widths and highlights the importance of the high mass-loss rate caused by Roche lobe overflow, which requires careful consideration of the structure of the lower and middle atmosphere. We also show that metal species and excited-state hydrogen can play an important role in the thermal and ionization balance of ultrahot Jupiter thermospheres.

X-Ray Activity Variations and Coronal Abundances of the Star–Planet Interaction Candidate HD 179949

We carry out detailed spectral and timing analyses of the Chandra X-ray data of HD 179949, a prototypical example of a star with a close-in giant planet with possible star–planet interaction (SPI) effects. We find a low coronal abundance A(Fe)/AH) ≈ 0.2 relative to the solar photospheric baseline of Anders & Grevesse, and significantly lower than the stellar photosphere as well. We further find low abundances of high first ionization potential (FIP) elements A(O)/A(Fe) ≲ 1, A(Ne)/A(Fe) ≲ 0.1, but with indications of higher abundances of A(N)/A(Fe) ≫ 1, A(Al)/A(Fe) ≲ 10. We estimate a FIP bias for this star in the range ≈ − 0.3 to −0.1, larger than the ≲ −0.5 expected for stars of this type, but similar to stars hosting close-in hot Jupiters. We detect significant intensity variability over timescales ranging from 100 s to 10 ks, and also evidence for spectral variability over timescales of 1–10 ks. We combine the Chandra flux measurements with Swift and XMM-Newton measurements to detect periodicities, and determine that the dominant signal is tied to the stellar polar rotational period, consistent with expectations that the corona is rotational-pole dominated. We also find evidence for periodicity at both the planetary orbital frequency and at its beat frequency with the stellar polar rotational period, suggesting the presence of a magnetic connection between the planet and the stellar pole. If these periodicities represent an SPI signal, it is likely driven by a quasi-continuous form of heating (e.g., magnetic field stretching) rather than sporadic, hot, impulsive flare-like reconnections.

Three Saturn-mass planets transiting F-type stars revealed with TESS and HARPS

While the sample of confirmed exoplanets continues to grow, the population of transiting exoplanets around early-type stars is still limited. These planets allow us to investigate the planet properties and formation pathways over a wide range of stellar masses and study the impact of high irradiation on hot Jupiters orbiting such stars. We report the discovery of TOI-615b, TOI-622b, and TOI-2641b, three Saturn-mass planets transiting main sequence, F-type stars. The planets were identified by the Transiting Exoplanet Survey Satellite (TESS) and confirmed with complementary ground-based and radial velocity observations. TOI-615b is a highly irradiated (~1277 F⊕) and bloated Saturn-mass planet (1.69−0.06+0.05 RJup and 0.43−0.08+0.09 MJup) in a 4.66 day orbit transiting a 6850 K star. TOI-622b has a radius of 0.82−0.03+0.03 RJup and a mass of 0.30−0.08+0.07 MJup in a 6.40 day orbit. Despite its high insolation flux (~600 F⊕), TOI-622b does not show any evidence of radius inflation. TOI-2641b is a 0.39−0.04+0.02 MJup planet in a 4.88 day orbit with a grazing transit (b = 1.04−0.06+0.05) that results in a poorly constrained radius of 1.61−0.64+0.46 RJup. Additionally, TOI-615b is considered attractive for atmospheric studies via transmission spectroscopy with ground-based spectrographs and JWST. Future atmospheric and spin-orbit alignment observations are essential since they can provide information on the atmospheric composition, formation, and migration of exoplanets across various stellar types.

A close-in giant planet escapes engulfment by its star.

When main-sequence stars expand into red giants, they are expected to engulf close-in planets1-5. Until now, the absence of planets with short orbital periods around post-expansion, core-helium-burning red giants6-8 has been interpreted as evidence that short-period planets around Sun-like stars do not survive the giant expansion phase of their host stars9. Here we present the discovery that the giant planet 8 Ursae Minoris b10 orbits a core-helium-burning red giant. At a distance of only 0.5 AU from its host star, the planet would have been engulfed by its host star, which is predicted by standard single-star evolution to have previously expanded to a radius of 0.7 AU. Given the brief lifetime of helium-burning giants, the nearly circular orbit of the planet is challenging to reconcile with scenarios in which the planet survives by having a distant orbit initially. Instead, the planet may have avoided engulfment through a stellar merger that either altered the evolution of the host star or produced 8 Ursae Minoris b as a second-generation planet11. This system shows that core-helium-burning red giants can harbour close planets and provides evidence for the role of non-canonical stellar evolution in the extended survival of late-stage exoplanetary systems.

TOI-3984 A b and TOI-5293 A b: Two Temperate Gas Giants Transiting Mid-M Dwarfs in Wide Binary Systems

We confirm the planetary nature of two gas giants discovered by TESS to transit M dwarfs with stellar companions at wide separations. TOI-3984 A (J = 11.93) is an M4 dwarf hosting a short-period (4.353326 ± 0.000005 days) gas giant (M p = 0.14 ± 0.03 M J and R p = 0.71 ± 0.02 R J) with a wide-separation white dwarf companion. TOI-5293 A (J = 12.47) is an M3 dwarf hosting a short-period (2.930289 ± 0.000004 days) gas giant (M p = 0.54 ± 0.07 M J and R p = 1.06 ± 0.04 R J) with a wide-separation M dwarf companion. We characterize both systems using a combination of ground- and space-based photometry, speckle imaging, and high-precision radial velocities from the Habitable-zone Planet Finder and NEID spectrographs. TOI-3984 A b (T eq = 563 ± 15 K and ) and TOI-5293 A b ( K and TSM = 92 ± 14) are two of the coolest gas giants among the population of hot Jupiter–sized gas planets orbiting M dwarfs and are favorable targets for atmospheric characterization of temperate gas giants and 3D obliquity measurements to probe system architecture and migration scenarios.

Evidence of radius inflation in radiative GCM models of WASP-76b due to the advection of potential temperature

ABSTRACT Understanding the discrepancy between the radii of observed hot Jupiters and standard ‘radiative-convective’ models remains a hotly debated topic in the exoplanet community. One mechanism which has been proposed to bridge this gap, and which has recently come under scrutiny, is the vertical advection of potential temperature from the irradiated outer atmosphere deep into the interior, heating the deep unirradiated atmosphere, warming the internal adiabat, and resulting in radius inflation. Specifically, a recent study which explored the atmosphere of WASP-76b using a 3D non-grey GCM suggested that their models lacked radius inflation, and hence any vertical enthalpy advection. Here we perform additional analysis of these, and related models, focusing on an explicit analysis of vertical enthalpy transport and the resulting heating of the deep atmosphere compared with 1D models. Our results indicate that, after any evolution linked with initialization, all the WASP-76b models considered here exhibit significant vertical enthalpy transport, heating the deep atmosphere significantly when compared with standard 1D models. Furthermore, comparison of a long time-scale (and hence near steady-state) model with a Jupiter-like internal-structure model suggests not only strong radius-inflation, but also that the model radius, 1.98 RJ, may be comparable with observations (1.83 ± 0.06 RJ). We thus conclude that the vertical advection of potential temperature alone is enough to explain the radius inflation of WASP-76b, and potentially other irradiated gas giants, albeit with the proviso that the exact strength of the vertical advection remains sensitive to model parameters, such as the inclusion of deep atmospheric drag.

A hot super-Earth planet in the WASP-84 planetary system

ABSTRACT Hot Jupiters have been perceived as loners devoid of planetary companions in close orbital proximity. However, recent discoveries based on space-borne precise photometry have revealed that at least some fraction of giant planets coexists with low-mass planets in compact orbital architectures. We report detecting a 1.446-d transit-like signal in the photometric time series acquired with the Transiting Exoplanet Survey Satellite (TESS) for the WASP-84 system, which is known to contain a hot Jupiter on a circular 8.5-d orbit. The planet was validated based on TESS photometry, and its signal was distilled in radial velocity measurements. The joint analysis of photometric and Doppler data resulted in a multiplanetary model of the system. With a mass of $15\, \mathrm{ M}_{{\oplus }}$, radius of $2\, \mathrm{ R}_{{\oplus }}$, and orbital distance of 0.024 au, the new planet WASP-84 c was classified as a hot super-Earth with the equilibrium temperature of 1300 K. A growing number of companions to hot Jupiters indicates that a non-negligible part of them must have formed under a quiescent scenario such as disc migration or in situ formation.

Secular dynamics of stellar spin driven by planets inside Kozai–Lidov resonance

Abstract In many exoplanetary systems with ‘hot Jupiters’, it is observed that the spin axes of host stars are highly misaligned to planetary orbital axes. In this study, a possible channel is investigated for producing such a misalignment under a hierarchical three-body system where the evolution of stellar spin is subjected to the gravitational torque induced from the planet inside Kozai–Lidov (KL) resonance. In particular, two special configurations are explored in detail. The first one corresponds to the configuration with planets at KL fixed points, and the second one corresponds to the configurations with planets moving on KL librating cycles. When the planet is located at the KL fixed point, the corresponding Hamiltonian model is of one degree of freedom and there are three branches of libration centres for stellar spin. When the planet is moving on KL cycles, the technique of Poincaré section is taken to reveal global structures of stellar spin in phase space. To understand the complex structures, perturbative treatments are adopted to study rotational dynamics. It shows that analytical structures in phase portraits under the resonant model can agree well with numerical structures arising in Poincaré sections, showing that the complicated dynamics of stellar spin are governed by the primary resonance under the unperturbed Hamiltonian model in combination with the 2:1 (high-order and/or secondary) spin-orbit resonances.

Tidal Evolution of Close-in Exoplanets and Host Stars

Abstract The evolution of exoplanetary systems with a close-in planet is ruled by the tides mutually raised on the two bodies and by the magnetic braking of the host star. This paper deals with consequences of this evolution and some features that can be observed in the distribution of the systems two main periods: the orbital periods and the stars rotational periods. The results of the simulations are compared to plots showing both periods as determined from the light curves of a large number of Kepler objects of interest. These plots show important irregularities as a dearth of systems in some regions and accumulations of hot Jupiters in others. It is shown that the accumulation of short-period hot Jupiters around stars with rotation periods close to 25 days results from the evolution of the systems under the joint action of tides and braking, and requires a relaxation factor for solar-type stars of around 10 s−1.