Search

We study transits of several 'hot Jupiter' systems, including WASP-12 b, WASP-43 b, WASP-103 b, HAT-P-23 b, KELT-16 b, WD 1856+534 b, and WTS-2 b, with the goal of detecting tidal orbital decay and extending the baselines of transit times. We find no evidence of orbital decay in any of the observed systems except for that of the extensively studied WASP-12 b. Although the orbit of WASP-12 b is unequivocally decaying, we find no evidence for acceleration of said orbital decay, with measured |$\ddot{P} = (-7 \pm 8) \times 10^{-14} \, \rm s^{-1}$|⁠ , against the expected acceleration decay of |$\ddot{P} \approx -10^{-23} \, \rm s^{-1}$|⁠. In the case of WD 1856+534 b, there is a tentative detection of orbital growth with |$\dot{P} = (5.0 \pm 1.5) \times 10^{-10}$|⁠. While statistically significant, we err on the side of caution and wait for longer follow-up observations to consider the measured |$\dot{P}$| real. For most systems, we provide a 95 per cent confidence lower limit on the tidal quality factor, |$Q_\star ^{\prime }$|⁠. The possibility of detecting orbital decay in hot Jupiters via long-term radial velocity (RV) measurements is also explored. We find that |${\sim} 1 \rm \, m \, s^{-1}$| precision in RVs will be required to detect orbital decay of WASP-12 b with only 3 yr of observations. Currently available RV measurements and precision are unable to detect orbital decay in any of the systems studied here. [ABSTRACT FROM AUTHOR]

Ly  |$\alpha$| transits provide an opportunity to test models of atmospheric escape directly. However, translating observations into constraints on the properties of the escaping atmosphere is challenging. The major reason for this is that the observable parts of the outflow often comes from material outside the planet's Hill sphere, where the interaction between the planetary outflow and circumstellar environment is important. As a result, 3D models are required to match observations. Whilst 3D hydrodynamic simulations are able to match observational features qualitatively, they are too computationally expensive to perform a statistical retrieval of properties of the outflow. Here, we develop a model that determines the trajectory, ionization state, and 3D geometry of the outflow as a function of its properties and system parameters. We then couple this model to a ray tracing routine in order to produce synthetic transits. We demonstrate the validity of this approach, reproducing the trajectory of the outflows seen in 3D simulations. We illustrate the use of this model by performing a retrieval on the transit spectrum of GJ 436 b. The bound on planetary outflow velocity and mass-loss rates are consistent with a photoevaporative wind. [ABSTRACT FROM AUTHOR]

Stars do not form in isolation but together with other stars, and often in a clustered environment. Depending on the initial conditions in these environments, such as initial density and substructure, the distances of encounters between stars will differ. These encounters can also affect just-formed exoplanetary systems. Using N -body simulations, we show the effect of a single fly-by on a common type of exoplanetary system: close-in super-Earths/sub-Neptunes with or without a distant giant planet. Even a single encounter can significantly modify the architecture of these exoplanetary systems over their long lifetimes. We test fly-bys with different characteristics, such as distance and mass, and show how they perturb the inner planets long after the encounter, leading to collisions and mutual inclination excitation, which can significantly modify the observed architecture of these systems in transit. We find that our initially four-planet inner systems reduce to three or two inner planets depending on their initial separation and that the mutual inclinations of these remaining planets can be high enough to reduce the number of observable, transiting planets. In our 500 Myr simulations, we show that this reduction in the number of transiting planets due to stellar fly-bys can contribute to the observed excess of single-transit systems. [ABSTRACT FROM AUTHOR]

With the release of a large amount of astronomical data, an increasing number of close-in hot Jupiters have been discovered. Calculating their evolutionary curves using star–planet interaction models presents a challenge. To expedite the generation of evolutionary curves for these close-in hot Jupiter systems, we utilized tidal interaction models established on mesa to create 15 745 samples of star–planet systems and 7500 samples of stars. Additionally, we employed a neural network (Multilayer Perceptron – MLP) to predict the evolutionary curves of the systems, including stellar effective temperature, radius, stellar rotation period, and planetary orbital period. The median relative errors of the predicted evolutionary curves were found to be 0.15 per cent, 0.43 per cent, 2.61 per cent, and 0.57 per cent, respectively. Furthermore, the speed at which we generate evolutionary curves exceeds that of model-generated curves by more than four orders of magnitude. We also extracted features of planetary migration states and utilized lightgbm to classify the samples into six categories for prediction. We found that by combining three types that undergo long-term double synchronization into one label, the classifier effectively recognized these features. Apart from systems experiencing long-term double synchronization, the median relative errors of the predicted evolutionary curves were all below 4 per cent. Our work provides an efficient method to save significant computational resources and time with minimal loss in accuracy. This research also lays the foundation for analysing the evolutionary characteristics of systems under different migration states, aiding in the understanding of the underlying physical mechanisms of such systems. Finally, to a large extent, our approach could replace the calculations of theoretical models. [ABSTRACT FROM AUTHOR]

The numerical simulation of the HD 63433 system is performed with the aim to study upper atmospheres of two mini-Neptunes, planets b and c, interacting with the stellar wind of the parent star. The obtained results demonstrate that both exoplanets form the extended envelopes with strong supersonic outflows. The synthetic absorption profiles in the Ly α line show that under moderate stellar wind conditions, similar to those of the normal solar wind, the energetic neutral atoms contribute to the absorption in the high-velocity blue wing of the line at a level of tens per cent. The absorption in metastable helium He  i (23S) line appears rather weak and below the detection limit by current instruments. An important feature revealed by the simulations is that the tail of escaping atmospheric material of the inner planet disturbs the stellar wind at orbital location of the outer planet and might, therefore, affect its observation in Ly α line. [ABSTRACT FROM AUTHOR]

Over a quarter of white dwarfs have photospheric metal pollution, which is evidence for recent accretion of exoplanetary material. While a wide range of mechanisms have been proposed to account for this pollution, there are currently few observational constraints to differentiate between them. To investigate the driving mechanism, we observe a sample of polluted and non-polluted white dwarfs in wide binary systems with main-sequence stars. Using the companion stars' metallicities as a proxy for the white dwarfs' primordial metallicities, we compare the metallicities of polluted and non-polluted systems. Because there is a well-known correlation between giant planet occurrence and higher metallicity (with a stronger correlation for close-in and eccentric planets), these metallicity distributions can be used to probe the role of gas giants in white dwarf accretion. We find that the metallicity distributions of polluted and non-polluted systems are consistent with the hypothesis that both samples have the same underlying metallicity distribution. However, we note that this result is likely biased by several selection effects. Additionally, we find no significant trend between white dwarf accretion rates and metallicity. These findings suggest that giant planets are not the dominant cause of white dwarf accretion events in binary systems. [ABSTRACT FROM AUTHOR]

Planetary systems in mean motion resonances hold a special place among the planetary population. They allow us to study planet formation in great detail as dissipative processes are thought to have played an important role in their existence. Additionally, planetary masses in bright resonant systems can be independently measured via both radial velocities and transit timing variations. In principle, they also allow us to quickly determine the inclination of all planets in the system since, for the system to be stable, they are likely all in coplanar orbits. To describe the full dynamical state of the system, we also need the stellar obliquity, which provides the orbital alignment of a planet with respect to the spin of its host star and can be measured thanks to the Rossiter–McLaughlin effect. It was recently discovered that HD 110067 harbors a system of six sub-Neptunes in resonant chain orbits. We here analyze an ESPRESSO high-resolution spectroscopic time series of HD 110067 during the transit of planet c. We find the orbit of HD 110067 c to be well aligned, with a sky-projected obliquity of λ =6+24-26 deg. This result indicates that the current architecture of the system was reached through convergent migration without any major disruptive events. Finally, we report transit-timing variation in this system as we find a significant offset of 19 ± 4 min in the center of the transit compared to the published ephemeris. [ABSTRACT FROM AUTHOR]

Context. The high-energy environments of host stars could prove deleterious for their planets. It is crucial to ascertain this contextual information to characterize the atmospheres of terrestrial exoplanets. Aims. We aim to fully characterize a unique triple system, LTT1445, with three known rocky planets around LTT 1445A. Methods. We studied the X-ray irradiation and flaring of this system based on a new 50 ks Chandra observation, which is divided into 10 ks, 10 ks, and 30 ks segments conducted two days apart, and two months apart, respectively. These data were complemented by an archival Chandra observation approximately 1 yr earlier and repeated observations with extended ROentgen Survey with an Imaging Telescope Array (eROSITA), the soft X-ray instrument on the Spectrum-Roentgen-Gamma (SRG) mission. This enabled the investigation of X-ray flux behavior across multiple time scales. With the observed X-ray flux from the exoplanet host star A, we estimated the photo-evaporation mass loss of each exoplanet. With the planet modeling package, VPLanet, we predicted the evolution and anticipated current atmospheric conditions. Results. Our Chandra observations indicate that LTT 1445C is the dominant X-ray source, with additional contribution from LTT 1445B. We find that LTT 1445A, a slowly rotating star, exhibits no significant flare activity in the new Chandra dataset. Comparing the flux incident occuring on the exoplanets, we find that LTT 1445BC components do not pose a greater threat to the planets orbiting LTT 1445A than the emission from A itself. According to the results from the simulation, LTT 1445Ad could have the capacity to retain its water surface. [ABSTRACT FROM AUTHOR]

Context. The Kepler high-precision planetary sample has revealed a 'radius valley' separating compact super-Earths from sub-Neptunes with lower densities. Super-Earths are generally assumed to be rocky planets that were probably born in situ, while the composition and formation of sub-Neptunes remains debated. Numerous statistical studies have explored planetary and stellar properties and their correlations to provide observational clues. However, no conclusive result on the origin of the radius valley or the composition of sub-Neptunes has been derived to date. Aims. To provide more constraints, our aim is to investigate the distributions of the orbital spacing of sub-Neptunes and super-Earth planets in Kepler systems and compare their distributions with theoretical predictions of planet pairs of different formation pathways and compositions in synthetic planetary systems. Methods. Based on the Kepler planetary sample, we derived the distributions of period ratios of sub-Neptune and super-Earth planet pairs. Using synthetic planetary systems generated by the Generation III Bern Model, we also obtained theoretical predictions of period ratio distributions of planet pairs of different compositions and origins. Results. We find that Kepler sub-Neptune pairs show a significant preference to be near first-order mean motion resonances by a factor of 1.7−0.3+0.3. This is smaller than the model predictions for 'water-rich' pairs but larger than that of 'water-poor' pairs by confidence levels of ~2σ. Kepler super-Earth pairs show no significant preference for mean motion resonances from a random distribution. The derived normalised fraction of near first-order resonances of actual Kepler super-Earth pairs is consistent with that of synthetic water-poor planet pairs but significantly (≳3σ) smaller than that of synthetic water-rich planet pairs. Conclusions. The orbital migration has been more important for sub-Neptunes than for super-Earths, suggesting a partial ex situ formation of the former and an origin of the radius valley caused in part by distinct formation pathways. However, the model comparisons also show that sub-Neptunes in Kepler multiple systems are not likely (~2σ) to all be water-rich planets born ex situ but a mixture of the two (in situ and ex situ) pathways. Whereas, Kepler super-Earth planets are predominantly composed of water-poor planets that were born inside the ice line, likely through a series of giant impacts without large-scale migration. [ABSTRACT FROM AUTHOR]

Context. Mercury presents a highly dynamic, small magnetosphere in which magnetic reconnection plays a fundamental role. Aim. We aim to model the global characteristics of magnetic reconnection in the Hermean environment. In particular, we focus on waves observed during the third BepiColombo flyby. Method. In this work, we used two fully kinetic three-dimensional (3D) simulations carried out with the iPIC3D code, which models the interaction of the solar wind with the Hermean magnetosphere. For the simulations, we used southward solar wind conditions that allow for a maximum magnetic coupling between the solar wind and the planet. Results. Our simulations show that a significant wave activity, triggered by magnetic reconnection, develops near the diffusion region in the magnetotail and propagates at large scales in the night-side magnetosphere. We see an increase in electron temperature close to the diffusion region and we specifically observe narrowband whistler waves developing near the reconnection region. These waves propagate nearly parallel to the magnetic field at frequency f ∼ 0.5fce. In addition to the electromagnetic component, these waves also exhibit an electrostatic one. Furthermore, we observe a strong electron temperature anisotropy, suggesting it plays a role as the source of these waves. [ABSTRACT FROM AUTHOR]

Earth-like planets in the habitable zone of low-mass stars undergo strong tidal effects that modify their spin states. These planets are expected to host dense atmospheres that can also play an important role in the spin evolution. On one hand, gravitational tides tend to synchronise the rotation with the orbital mean motion, but on the other hand, thermal atmospheric tides push the rotation away and may lead to asynchronous equilibria. Here, we investigate the complete tidal evolution of Earth-like planets by taking into account the effect of obliquity and eccentric orbits. We adopted an Andrade rheology for the gravitational tides and benchmarked the unknown parameters with the present rotation of Venus. We then applied our model to Earth-like planets, and we show that asynchronous rotation can be expected for planets orbiting stars with masses between 0.4 and 0.9 M⊙ and semi-major axes between 0.2 and 0.7 au. Interestingly, we find that Earth-like planets in the habitable zone of stars with masses ~0.8 M⊙ may end up with an equilibrium rotation of 24 h. We additionally find that these planets can also develop high obliquities, which may help sustain temperate environments. [ABSTRACT FROM AUTHOR]

Aims. WASP-18 is an F6V star that hosts a planet with a mass of ~10 Jupiter masses and an orbital period of ~0.94 days. In spite of its relatively fast rotation and young age, the star remains undetected in X-rays, thus implying a very low level of magnetic activity. To account for such unexpected properties, we propose a mechanism that modifies the internal stratification and the photospheric magnetic activity of a late-type main sequence star with a close-by massive planet based on the action of the equilibrium tide. Methods. We speculate that the horizontal flow produced by the equilibrium tide may interact with the convective plumes in the overshoot layer below the stellar outer convective envelope. The interaction is characterised by a very high Reynolds number (Re ~ 1010), leading to the development of turbulent boundary layers at the surface of such structures, whereas turbulent wakes extend over most of the overshoot layer that they straddle. Results. We propose that such a tidally induced turbulence can lead to a reduction of the filling factor of the downdrafts in the overshoot layer. As a consequence, the absolute value of the sub-adiabatic gradient increases in that layer hindering the emergence of magnetic flux tubes responsible for the formation of photospheric starspots. We conjecture that this process is occurring in WASP-18, thus providing a possible mechanism to account for the very low level of magnetic activity observed for such a planet host. [ABSTRACT FROM AUTHOR]

According to the strange quark matter hypothesis, strange planets may exist, which are planetary mass objects composed of almost equal numbers of up, down, and strange quarks. A strange planet can revolve around its host strange star in a very close-in orbit. When it finally merges with the host, strong gravitational wave emissions will be generated. Here, the gravitational waveforms are derived for the merging process, taking into account the effects of the strange star's magnetic field on the dynamics. Effects of the inclination angle are also considered. Templates of the gravitational waveforms are derived. It is found that the magnetic interactions significantly speed up the merging process. Coalescence events of such strange planetary systems occurring in our Galaxy as well as in local galaxies can be effectively detected by current and future gravitational experiments, which may hopefully provide a new method to test the strange quark matter hypothesis and probe the magnetic field of compact stars. [ABSTRACT FROM AUTHOR]

Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber worlds better endowed with volatiles, being the most common habitable planets. For the subgroup of fast rotators following eccentric orbits, atmospheres suffer radiative forcing and their heat capacity provides a method for gauging atmospheric thickness and surface conditions. We further explore the model presented in a previous paper and apply it to real and hypothetical exoplanets in the habitable zone of various classes of stars, simulating atmospheric and orbital characteristics. For planetary eccentricities e ∼ 0.3, the forcing-induced hypothetical temperature variation would reach ∼80 K for airless planets and ∼10 K for planets with substantial atmospheres. For Kepler-186 f and Kepler-442 b, assuming e ∼ 0.1, temperature variations can reach ∼24 K. We also consider habitable exomoons in circular orbits around gas giants within the habitable zone, which suffer radiative forcing due to their epicyclic motion. We study several combinations of parameters for the characterization of planets (mass, eccentricity, and semimajor axis) and exomoons (mass, orbital radius, albedo, and atmospheric characteristics) for different stellar types. For e ∼ 0.3, exomoon temperature varies up to ∼90 K, while for ∼0.6 variations can reach ∼200 K. Such exomoons may plausibly retain their volatiles by continued volcanic activity fuelled by tidal dissipation. Although currently undetectable, such effects might be within reach of future Extremely Large Telescope-class telescopes and space missions with mid-infrared and coronagraphic capabilities. [ABSTRACT FROM AUTHOR]

We analyse a tilt instability of the orbit of an outer planet in a two-planet circumbinary system that we recently reported. The binary is on an eccentric orbit and the inner circumbinary planet is on a circular polar orbit that causes the binary to undergo apsidal precession. The outer circumbinary planet is initially on a circular or eccentric orbit that is coplanar with respect to the binary. We apply a Hamiltonian in quadrupole order of the binary potential to show that the tilt instability is the result of a secular resonance in which the apsidal precession rate of the binary matches the nodal precession rate of the outer planet. A resonance is possible because the polar inner planet causes the apsidal precession of the binary to be retrograde. The outer planet periodically undergoes large tilt oscillations for which we analytically determine the initial evolution and maximum inclination. Following a typically relatively short adjustment phase, the tilt grows exponentially in time at a characteristic rate that is of order the absolute value of the binary apsidal precession rate. The analytic results agree well with numerical simulations. This instability is analogous to the Kozai–Lidov instability, but applied to a circumbinary object. The instability fails to operate if the binary mass ratio is too extreme. The instability occurs even if the outer planet is instead an object of stellar mass and involves tilt oscillations of the inner binary. [ABSTRACT FROM AUTHOR]

In a gaseous medium, dynamical friction (DF) reaches a maximum when the orbital speed of a (point-like) perturber moving on a circular orbit is close to the sound speed. Therefore, in a quasi-steady state, eccentric orbits of perturbers approaching the sound barrier (from below) should rapidly circularize as they experience the strongest drag at pericentre passage. To investigate this effect, we extend the solution for circular DF in a uniform gaseous medium to eccentric Keplerian orbits. We derive an approximation to the steady-state DF force, which is valid for eccentricities as high as e  = 0.9 in a limited range of Mach number around the transition to supersonic regime. We validate our analytical result with 3D simulations of the gas density response. Although gaseous DF generally dissipates orbital energy, we find that it can be directed along the motion of the perturber near pericentre passage when the eccentricity is e ≳ 0.9. We apply our results to compute the long-time evolution of the orbital parameters. Most trajectories tend to circularize as the perturber moves into the supersonic regime. However, orbits with eccentricities e ≳ 0.8 below the sound barrier experience a slight increase in eccentricity as they loose orbital energy. Possible extensions to our analytical approach are also discussed. [ABSTRACT FROM AUTHOR]

Context. Several studies suggest that the emission properties of a star can be significantly affected by its interaction with a nearby planet through magnetic fields or interaction between their respective winds. However, the actual observability of these effects remains a subject of debate. An illustrative example is the HD 189733A system: certain characteristics of its emissions have been interpreted as indicative of ongoing interactions between the star and its associated planet. Other studies attribute these characteristics to the coronal activity of the star. Aims. In this study we aimed to investigate whether the observed stellar X-ray flare events, which appear to be in phase with the planetary period in the HD 189733A system, could be attributed to the accretion of the planetary wind onto the stellar surface or if they resulted from an interaction between the planetary and stellar winds. Methods. We developed a 3D magnetohydrodynamic model with the PLUTO code that describes the system HD 189733A , including the central host star and its hot Jupiter along with their respective winds. The effects of gravity and the magnetic fields of both the star and the planet are taken into account. Results. Our analysis reveals that, in the cases examined in this study, the accretion scenario is only viable when the stellar magnetic field strength is at 5 G and the planetary magnetic field strength is at 1 G. In this scenario, the Rayleigh-Taylor instabilities lead to the formation of an accretion column that connects the star to the planet. Once formed the accretion column remains stable for the duration of the simulation. The accretion column produces an accretion rate of the order of 1012 g s−1 and shows an average density of about 107 cm−3. In the other case explored, the accretion column does not form because the Rayleigh-Taylor instability is suppressed by the stronger magnetic field intensities assumed for both the star and the planet. We synthesized the emission resulting from the shocked planetary wind and found that the total X-ray emission ranges from 5 × 1023 to 1024 erg s−1. Conclusions. In the case of accretion, the emission originating from the hotspot cannot be distinguished from the coronal activity. Also, the interaction between the planetary and stellar winds cannot be responsible for the X-ray emission, as the total emission produced is about four orders of magnitude lower than the average X-ray luminosity of the star. [ABSTRACT FROM AUTHOR]

Context. Transmission spectroscopy is one of the most powerful techniques used to characterize transiting exoplanets, since it allows for the abundance of the atomic and molecular species in the planetary atmosphere to be measured. However, stellar lines may bias the determination of such abundances if their center-to-limb variations (CLVs) are not properly accounted for. Aims. This paper aims to show that three-dimensional (3D) radiation hydrodynamic models and the assumption of non-local ther-modynamic equilibrium (non-LTE) line formation are required for an accurate modeling of the stellar CLV of the Na I D1 and K I resonance lines on transmission spectra. Methods. We modeled the CLV of the Na I D1 and K I resonance lines in the Sun with 3D non-LTE radiative transfer. The synthetic spectra were compared to solar observations with high spatial and spectral resolution, including new data collected with the CRISP instrument at the Swedish 1-m Solar Telescope between µ = 0.1 and µ = 1.0. Results. Our 3D non-LTE modeling of the Na I D1 resonance line at 5896 Å and the K I 7699 Å resonance line in the Sun is in good agreement with the observed CLV in the solar spectrum. Moreover, the simulated CLV curve for a Jupiter-Sun system inferred with a 3D non-LTE analysis shows significant differences from the one obtained from a 1D atmosphere. The latter does indeed tend to overestimate the amplitude of the transmission curve by a factor that is on the same order of magnitude as a planetary absorption depth (i.e., up to 0.2%). Conclusions. This work highlights the fact that to correctly characterize exoplanetary atmospheres, 3D non-LTE synthetic spectra ought to be used to estimate the stellar CLV effect in transmission spectra of solar-like planet hosts. Moreover, since different spectral lines show different CLV curves for the same geometry of the planet-star system, it is fundamental to model the CLV individually for each line of interest. The work will be extended to other lines and FGK-type stars, allowing for synthetic high-resolution spectra to mitigate the stellar contamination of low-resolution planetary spectra, for example, those drawn from JWST. [ABSTRACT FROM AUTHOR]

We investigate the orbital dynamics of an exosystem consisting of a solar-mass host star, a transiting body, and an Earth-size exoplanet within the framework of the generalized three-body problem. Depending on its mass, the transiting body can either be a super-Jupiter or a brown dwarf. To determine the final states of the Earth-size exoplanet, we conduct a systematic and detailed classification of the available phase space trajectories. Our classification scheme distinguishes between the bounded, escape, and collisional motions of the Earth-size exoplanet. Additionally, for cases of ordered (regular) motion, we further categorize the associated initial conditions based on the geometry of their respective trajectories. These bounded regular trajectories hold significant importance as they provide insights into the regions of phase space where the motion of the Earth-size exoplanet can be dynamically stable. Of particular interest is the identification of initial conditions that result in a bounded exomoon-like orbit of the Earth-size exoplanet around the transiting body. [ABSTRACT FROM AUTHOR]

Understanding atmospheric escape in close-in exoplanets is critical to interpreting their evolution. We map out the parameter space over which photoevaporation and core-powered mass-loss dominate atmospheric escape. Generally, the transition between the two regimes is determined by the location of the Bondi radius (i.e. the sonic point of core-powered outflow) relative to the penetration depth of extreme ultra-violet (XUV) photons. Photoevaporation dominates the loss when the XUV penetration depth lies inside the Bondi radius (R XUV < R B) and core-powered mass-loss when XUV radiation is absorbed higher up in the flow (R B < R XUV). The transition between the two regimes occurs at a roughly constant ratio of the planet's radius to its Bondi radius, with the exact value depending logarithmically on planetary and stellar properties. In general, core-powered mass-loss dominates for lower gravity planets with higher equilibrium temperatures, and photoevaporation dominates for higher gravity planets with lower equilibrium temperatures. However, planets can transition between these two mass-loss regimes during their evolution, and core-powered mass-loss can 'enhance' photoevaporation over a significant region of parameter space. Interestingly, a planet that is ultimately stripped by core-powered mass-loss has likely only ever experienced core-powered mass-loss. In contrast, a planet that is ultimately stripped by photoevaporation could have experienced an early phase of core-powered mass-loss. Applying our results to the observed super-Earth population suggests that it contains significant fractions of planets where each mechanism controlled the final removal of the H/He envelope, although photoevaporation appears to be responsible for the final carving of the exoplanet radius valley. [ABSTRACT FROM AUTHOR]

A planetary system can undergo multiple episodes of intense dynamical activities throughout its life, resulting in the production of star-grazing planetesimals (or exocomets) and pollution of the host star. Such activity is especially pronounced when giant planets interact with other small bodies during the system's evolution. However, due to the chaotic nature of the dynamics, it is difficult to determine the properties of the perturbing planet(s) from the observed planetesimal-disruption activities. In this study, we examine the outcomes of planetesimal-planet scatterings in a general setting. We focus on one-planet systems, and determine the likelihood and time-scale of planetesimal disruption by the host star as a function of the planet properties. We obtain a new analytical expression for the minimum distance a scattering body can reach, extending previous results by considering finite planet eccentricity and non-zero planetesimal mass. Through N -body simulations, we derive the distribution of minimum distances and the likelihood and time-scales of three possible outcomes of planetesimal-planet scatterings: collision with the planet, ejection, and disruption by the star. For planetesimals with negligible mass, we identify four defining dimensionless parameters (the planet eccentricity, planet-to-star mass ratio, planet radius to semimajor axis ratio, and the stellar disruption radius to planet semimajor axis ratio) that enable us to scale the problem and generalize our findings to a wide range of orbital configurations. Using these results, we explore three applications: falling evaporating bodies in the β Pictoris system, white dwarf pollution due to planetesimal disruption and planet engulfment by main-sequence stars. [ABSTRACT FROM AUTHOR]

The link between stellar host properties, be it chemical, physical, dynamical, or galactic in nature, with the presence of planetary companions, has been one that has been repeatedly tested in the literature. Several corroborated work has argued that the correlation between a stellar atmosphere's chemistry and the presence of gas giant companions is primordial in nature, implying that the chemical budget in a protoplanetary disc, and by proxy the eventual stellar host, increases the likelihood of gas giant formation. In this work, we aim to use the power of computer vision to build and test a machine learning classifier capable of discriminating between gas giant host stars and a comparison sample, using spectral data of the host stars in the visible regime. High-resolution spectra are used to preserve any inherent information which may contribute to the classification, and are fed into a stacked ensemble design incorporating several convolutional neural networks. The spectral range is binned such that each is assigned to a first-level voter, with the meta-learner aggregating their votes into a final classification. We contextualize and elaborate on the model design and results presented in a prior proceedings publication, and present an amended architecture incorporating semisupervized learning. Both models achieve relatively strong performance metrics and generalize over the holdout sets well, yet still present signs of overfitting. [ABSTRACT FROM AUTHOR]

The magnetized solar wind drives a current system around Mars that maintains its induced magnetosphere. The solar wind also transfers its energy to the atmospheric ions, causing continuous atmospheric erosion, which has a profound impact on the planet's evolution history. Here, we use Amitis, a Graphics Processing Unit (GPU)-based hybrid plasma model to first reproduce the global pattern of the net electric current and ion currents under an interplanetary magnetic field perpendicular to the solar wind flow direction. The resultant current distribution matches the observations and reveals more details. Using the electric field distribution characterized earlier with the same model, we calculate for the first time the spatial distribution of energy transfer rate to the plasmas in general and to different ion species at Mars. We find out that (1) the solar wind kinetic energy is the dominant energy source that drives Martian induced magnetosphere, (2) the energy flux of the shocked solar wind flows from the magnetic equatorial plane towards the plasma sheet in the induced magnetotail, (3) both the bow shock and the induced magnetospheric boundary are dynamos where plasma energy is transferred to the electromagnetic field, and (4) the planetary ions act as loads and gain energy from the electromagnetic field. The most intense load region is the planetary ion plume. The general pattern of the energy transfer rate revealed in this study is common for induced magnetospheres. Its variabilities with the upstream conditions can provide physical insight into the observed ion escape variabilities. [ABSTRACT FROM AUTHOR]

We report intensive monitoring of the activity variability in the Hα line for 10 Sun-like stars using the 1.88 m reflector at Okayama Branch Office, Subaru Telescope, during the last four years (2019–2022). Our aim was to investigate features of the stellar magnetic activity behavior. We correlated the Hα line variability of each star with the stellar activity levels derived from the Ca  ii H&K line, suggesting its efficiency as a magnetic activity indicator. In analyzing the Hα line variation, we observed that some stars exhibited linear or quadratic trends during the observation period. Among several G- and K-type stars expected to have co-existing activity cycles, we confirmed the 2.9 yr short cycle of ϵ Eri (K2V) from the Hα observations. Additionally, we established upper limits on the Hα variability of β Com (G0V) and κ1 Cet (G5V) concerning their expected shorter cycles. We also detected the possibility of short-term activity cycles in two F-type stars, β Vir (F9V; ∼530 d) and α CMi (F5IV-V; ∼130 d). The cycle in α CMi was observed in only one season of our 4 yr observations, suggesting the temporal absence of the cycle period. However, for stars with planets, we did not observe significant magnetic activity variability likely associated with the planetary orbital period. It is speculated that the impact of Hα variability on radial velocity (RV) measurements may vary with spectral type. [ABSTRACT FROM AUTHOR]

The gas giant Kepler-1658b has been inferred to be spiralling into its sub-giant F-type host star Kepler-1658a (KOI-4). The measured rate of change of its orbital period is |$\stackrel{\bf \centerdot }{\textstyle {P}}_{\rm orb}\, =\, -\, 131^{+20}_{-22}\,\rm {ms\,yr^{ -1}}$|⁠ , which can be explained by tidal dissipation in the star if its modified tidal quality factor is as low as |$Q^{\, \prime }\approx 2.50\times {10}^{4}$|⁠. We explore whether this could plausibly be consistent with theoretical predictions based on applying up-to-date tidal theory in stellar models (varying stellar mass, age, and metallicity) consistent with our newly derived observational constraints. In most of our models matching the combined constraints on the stellar effective temperature and radius, the dissipation in the star is far too weak, capable of providing |$Q^{\, \prime }\gtrsim 10^9$|⁠ , hence contributing negligibly to orbital evolution. Using only constraints on the stellar radius, efficient tidal dissipation sufficient to explain observations is possible due to inertial waves in the convective envelope during the sub-giant phase, providing |$Q^{\, \prime }\sim 10^4$|⁠ , but this period in the evolution is very short-lived (shorter than 102 yr in our models). We show that dissipation in the planet is capable of explaining the observed |$\dot{P}_\mathrm{orb}$| only if the planet rotates non-synchronously. Tidally induced pericentre precession is a viable explanation if the periastron argument is near 3π/2 and the planet's quadrupolar Love number is above 0.26. Further observations constraining the stellar and planetary properties in this system have the exciting potential to test tidal theories in stars and planets. [ABSTRACT FROM AUTHOR]

We extend the study of Papaloizou and Savonije of the tidal interactions of close orbiting giant planets with a central solar-type star to the situation where the spin axis of the central star and the orbital angular momentum are misaligned. We determine the tidal response taking into account the possibility of the excitation of r modes and the effect of tidal forcing due to potential perturbations that have zero frequency in a non-rotating frame. Although there is near resonance with r modes with degree l ′ = 1 and orders m  = ±1, half widths turn out to be sufficiently narrow so that in practice dissipation rates are found to be similar to those produced by non-resonant potential perturbations. We use our results to determine the evolution of the misalignment for the full range of initial inclination angles taking account of the spin-down of the central star due to magnetic braking. Overall we find the rate of tidal evolution to be unimportant for a one Jupiter mass planet with orbital period ∼3.7 d over a main-sequence lifetime. However, it becomes significant for higher mass planets and shorter orbital periods, approximately scaling as the square of the planet mass and the inverse fourth power of the orbital period. [ABSTRACT FROM AUTHOR]

Context. Short-period giant planets (P ≲ 10 days, Mp >0.1 MJ) are frequently found to be solitary compared to other classes of exo-planets. Small inner companions to giant planets with P ≲ 15 days are known only in five compact systems: WASP-47, Kepler-730, WASP-132, TOI-1130, and TOI-2000. Here, we report the confirmation of TOI-5398, the youngest known compact multi-planet system composed of a hot sub-Neptune (TOI-5398 c, Pc = 4.77271 days) orbiting interior to a short-period Saturn (TOI-5398 b, Pb = 10.590547 days) planet, both transiting around a 650 ± 150 Myr G-type star. Aims. As part of the Global Architecture of Planetary Systems (GAPS) Young Object project, we confirmed and characterised this compact system, measuring the radius and mass of both planets, thus constraining their bulk composition. Methods. Using multi-dimensional Gaussian processes, we simultaneously modelled stellar activity and planetary signals from the Transiting Exoplanet Survey Satellite (TESS) Sector 48 light curve and our High Accuracy Radial velocity Planet Searcher (HARPS-N) radial velocity (RV) time series. We confirmed the planetary nature of both planets, TOI-5398 b and TOI-5398 c, and obtained a precise estimation of their stellar parameters. Results. Through the use of astrometric, photometric, and spectroscopic observations, our findings indicate that TOI-5398 is a young, active G dwarf star (650 ± 150 Myr) with a rotational period of Prot = 7.34 days. The transit photometry and RV measurements enabled us to measure both the radius and mass of planets b, Rb = 10.30 ± 0.40 R⊕, Mb = 58.7 ± 5.7 M⊕, and c, Rc = 3.52 ± 0.19 R⊕, Mc = 11.8 ± 4.8 M⊕. TESS observed TOI-5398 during sector 48 and no further observations are planned in the current Extended Mission, making our ground-based light curves crucial for improvement of the ephemeris. With a transmission spectroscopy metric (TSM) value of around 300, TOI-5398 b is the most amenable warm giant (10 < P < 100 days) for JWST atmospheric characterisation. [ABSTRACT FROM AUTHOR]

Context. Stellar activity is the most relevant types of astrophysical noise that affect the discovery and characterization of extrasolar planets. On the other hand, the amplitude of stellar activity could hint at an interaction between the star and a close-in giant planet. Progress has been made in recent years in understanding how to deal with stellar activity and search for observational evidence of star-planet interactions. Aims. The aim of this work is to characterize the chromospheric activity of stars hosting short-period exoplanets by studying the correlations between the chromospheric emission (CE) in the Ca II H&K and the planetary parameters. Methods. We measured CE in the Ca II H&K lines using more than 1900 high-resolution spectra of a sample composed of 76 targets, observed with the HARPS-N spectrograph between 2012 and 2020. We transformed the fluxes into bolometric- and photospheric-corrected chromospheric emission ratios, R′HK. Furthermore, we completed the sample of hosts digging for data in previous works. Stellar parameters Teff, B–V, and V were retrieved homogeneously from the Gaia DR3. Then, M★, R★, and ages were determined from isochrone fitting. We retrieved planetary data from the literature and catalogs. The search for correlations between the log(R′HK) and planetary parameters have been performed through both Spearman's rank and its statistics as well as the more sophisticated Gaussian mixture model method. Results. We found that the distribution of log(R′HK) for the transiting planet hosts is different from the distribution of field main-sequence and sub-giant stars. The log(R′HK) of planetary hosts is correlated with planetary parameters proportional to the planetary radius to the power of n (RPn, indicating a common origin for the correlations. The statistical analysis has also highlighted four clusters of host stars with different behavior in terms of their stellar activity with respect to the planetary surface gravity. Some of the host stars have a value of log(R′HK) that is lower than the basal level of activity for main sequence stars. The planets of these systems are very close to filling their Roche lobe, suggesting that they evaporate through hydrodynamic escape under the strong irradiation of the host star, creating shrouds that absorb the core of the chromospheric resonance lines. [ABSTRACT FROM AUTHOR]

Stars and planets move supersonically in a gaseous medium during planetary engulfment, stellar interactions, and within protoplanetary discs. For a nearly uniform medium, the relevant parameters are the Mach number and the size of the body, R , relative to its accretion radius, R A. Over many decades, numerical and analytical work has characterized the flow, the drag on the body, and the possible suite of instabilities. Only a limited amount of work has treated the stellar boundary as it is in many of these astrophysical settings, a hard sphere at R. Thus, we present new 3D athena++   hydrodynamic calculations for a large range of parameters. For R A ≪ R , the results are as expected for pure hydrodynamics with minimal impact from gravity, which we verify by comparing to experimental wind tunnel data in air. When R A ≈ R , a hydrostatically supported separation bubble forms behind the gravitating body, exerting significant pressure on the sphere and driving a recompression shock, which intersects with the bow shock. For R A ≫ R , the bubble transitions into an isentropic, spherically symmetric halo, as seen in earlier works. These two distinct regimes of flow morphology may be treated separately in terms of their shock stand-off distance and drag coefficients. Most importantly for astrophysical applications, we propose a new formula for the dynamical friction, which depends on the ratio of the shock stand-off distance to R A. That exploration also reveals the minimum size of the simulation domain needed to accurately capture the deflection of incoming streamlines due to gravity. [ABSTRACT FROM AUTHOR]

In many star–planet systems discovered so far, the innermost planet orbits within only a few stellar radii. In these systems, planets could become in situ probes of the extended stellar magnetic field. Because they disturb the field as they move, they are expected to trigger flares in the corona. Potential differences to the energies and morphologies of intrinsic flares are poorly constrained. However, as we expect planet-induced flares to correlate with the planet's orbital period, we can identify them from a clustering of flares in phase with the planet's orbit. We used the excellent phase coverage from Kepler and the Transiting Exoplanet Survey Satellite to find flaring star–planet systems, compile a catalogue of all their flares, and measure how much they cluster in orbital phase. In the 1811 searched systems, we found 25 single stars with three or more flares each. We quantified the significance of the clustering in each system, and compared it against the theoretically expected power of magnetic interaction that leads to planet-induced flaring. Most systems do not show any clustering, consistent with low expected power. Those we expect to show clustering fall on two branches. An inactive one, without any signs of clustering, and a tentative active one, where the clustering becomes more pronounced as the expected power of interaction increases. The flares in HIP 67522 are prominently clustered (p < 0.006). This young hot Jupiter system is the most promising candidate for magnetic star–planet interaction in our sample. [ABSTRACT FROM AUTHOR]

The Neptunian desert is a region in period-radius parameter space with very few Neptune-sized planets at short orbital periods. Amongst these, LTT 9779 b is the only known Neptune with a period shorter than 1 d to retain a significant H–He atmosphere. If the Neptune desert is the result of X-ray/EUV-driven photoevaporation, it is surprising that the atmosphere of LTT 9779 b survived the intense bombardment of high-energy photons from its young host star. However, the star has low measured rotational broadening, which points to the possibility of an anomalously slow spin period and hence a faint X-ray emission history that may have failed to evaporate the planet's atmosphere. We observed LTT 9779 with XMM-Newton and measured an upper limit for its X-ray luminosity that is a factor of 15 lower than expected for its age. We also simulated the evaporation past of LTT 9779 b and found that the survival of its atmosphere to the present day is consistent with an unusually faint XUV irradiation history that matches both the X-ray and rotation velocity measurements. We conclude that the anomalously low X-ray irradiation of the one Neptune seen to survive in Neptunian desert supports the interpretation of the desert as primarily a result of photoevaporation. [ABSTRACT FROM AUTHOR]

Planets orbiting young stars are thought to experience atmospheric evaporation as a result of the host stars' high-magnetic activity. We study the evaporation history and expected future of the three known transiting exoplanets in the young multiplanet system K2-198. Based on spectroscopic and photometric measurements, we estimate an age of the K-dwarf host star between 200 and 500 Myr, and calculate the high-energy environment of these planets using eROSITA X-ray measurements. We find that the innermost planet K2-198c has likely lost its primordial envelope within the first few 10s of Myr regardless of the age at which the star drops out of the saturated X-ray regime. For the two outer planets, a range of initial envelope mass fractions is possible, depending on the not-yet-measured planetary mass and the stars' spin-down history. Regarding the future of the system, we find that the outermost planet K2-198b is stable against photoevaporation for a wide range of planetary masses, while the middle planet K2-198d is only able to retain an atmosphere for a mass range between ∼7 and 18 M⊕. Lower mass planets are too susceptible to mass-loss, and a very thin present-day envelope for higher mass planets is easily lost with the estimated mass-loss rates. Our results support the idea that all three planets started out above the radius valley in the (sub-)Neptune regime and were then transformed into their current states by atmospheric evaporation, but also stress the importance of measuring planetary masses for (young) multiplanet systems before conducting more detailed photoevaporation simulations. [ABSTRACT FROM AUTHOR]

White dwarfs that have accreted planetary materials provide a powerful tool to probe the interiors and formation of exoplanets. In particular, the high Fe/Si ratio of some white dwarf pollutants suggests that they are fragments of bodies that were heated enough to undergo large-scale melting and iron core formation. In the Solar system, this phenomenon is associated with bodies that formed early and so had short-lived radionuclides to power their melting, and/or grew large. However, if the planetary bodies accreted by white dwarfs formed during the (pre)-main sequence lifetime of the host star, they will have potentially been exposed to a second era of heating during the star's giant branches. This work aims to quantify the effect of stellar irradiation during the giant branches on planetary bodies by coupling stellar evolution to thermal and orbital evolution of planetesimals. We find that large-scale melting, sufficient to form an iron core, can be induced by stellar irradiation, but only in close-in small bodies: planetesimals with radii ≲ 30 km originally within ∼2 au orbiting a 1–3 M⊙ host star with solar metallicity. Most of the observed white dwarf pollutants are too massive to be explained by the accretion of these small planetesimals that are melted during the giant branches. Therefore, we conclude that those white dwarfs that have accreted large masses of materials with enhanced or reduced Fe/Si remain an indicator of planetesimal's differentiation shortly after formation, potentially linked to radiogenic heating. [ABSTRACT FROM AUTHOR]

We extend our previous work on the evolution of close binary systems with misaligned orbital and spin angular momenta resulting from non-dissipative tidal interaction to include all physical effects contributing to apsidal motion. In addition to tidal distortion of the primary by the compact secondary, these include relativistic Einstein precession and the rotational distortion of the primary. The influence of the precession of the line of nodes is included. The dependence of the tidal torque on the apsidal angle |$\hat{\varpi }$| couples the apsidal motion to the rate of evolution of the misalignment angle β which is found to oscillate. We provide analytical estimates for the oscillation amplitude Δβ over a wide range of parameter space confirmed by numerical integrations. This is found to be more significant near critical curves on which |${\mathrm{d}}{\hat{\varpi }} /{\mathrm{d}}t=0$| for a specified β. We find that to obtain 0.1 < Δβ < ∼1, the mass ratio q > ∼1, the initial eccentricity should be modest, |$\cos \beta \lt 1/\sqrt{5},$| with cos β < 0 corresponding to retrograde rotation, initially, and the primary rotation rate should be sufficiently large. The extended discussion of apsidal motion and its coupled evolution to the misalignment angle given here has potential applications to close binaries with anomalous apsidal motion as well as transiting exoplanets such as warm Jupiters. [ABSTRACT FROM AUTHOR]

We extend a magnetic braking (MB) model, which has been used earlier to address the evolution of cataclysmic variables, to address the spin period P spin evolution of fully convective M-dwarf (FCMD) stars. The MB mechanism is an α–Ω dynamo, which leads to stellar winds that carry away angular momentum. We model our MB torque such that the FCMDs experience an MB torque, approximately scaling as |$P_\mathrm{spin}^{-1}$| at shorter periods, before transitioning into a Skumanich-type MB torque, scaling as |$P_\mathrm{spin}^{-3}$|⁠. We also implement a parametrized reduction in the wind mass-loss owing to the entrapment of winds in dead zones. We choose a set of initial conditions and vary the two free parameters in our model to find a good match of our spin trajectories with open clusters containing FCMDs such as NGC2547, Pleiades, NGC2516, and Praesepe. We find that our model can explain the long spin periods of field stars and that a spread in spin distribution persists till over 3 Gyr. An advantage of our model is in relating physically motivated estimations of the magnetic field strength and stellar wind to properties of the stellar dynamo, which other models often remain agnostic about. We track the spin dependence of the wind mass-losses, Alfvén radii, and surface magnetic fields and find good agreement with observations. We discuss the implications of our results on the effect of the host FCMD on any orbiting exoplanets and our plans to extend this model to explain solar-like stars in the future. [ABSTRACT FROM AUTHOR]

Very young massive planets are sufficiently luminous by their internal heat of formation to permit detailed studies, including spectroscopy of their atmospheres with large telescopes at sufficient resolution (λ/Δλ ≳ 1000) to identify major constituents to inform models of planet formation and early evolution. We obtained 1–2.4  μ m (YJHK) spectra of the planetary-mass 'b' companion of 2MASS J04372171+2651014, a 1–3 Myr-old M dwarf member of the Taurus star-forming region, and one of the youngest such objects discovered to date. These indicate the presence of CO and possibly H2O and CH4 in the atmosphere, all suggesting a T eff of around 1200 K, characteristic of a L-T transition spectral type and consistent with previous estimates based on its luminosity and age. The absence or attenuation of spectral features at shorter wavelengths suggests the presence of micron-size dust, consistent with the object's red colour. The spectrum of 2M0437b resembles those of the HR 8799 planets, especially the innermost 'b' planet, with the exception of a pronounced flux deficit in the H -band of uncertain origin. [ABSTRACT FROM AUTHOR]

The transiting planet K2-18 b is one of the best candidates for a relatively nearby world harboring biological life. The long-term orbital evolution of this planet is investigated using theoretical and purely numerical techniques for two possible configurations: A single planet orbiting the host star, and a two-planet system including the proposed inner planet close to the 4:1 mean motion rationalization. The emphasis is made on the secular changes of eccentricity and orbital inclination, which are important for the climate stability of the planet. It is demonstrated that the secular orbital dynamics of planet K2-18 b with an internal companion are accurately represented by the periodic eccentricity and inclination exchange on the time scales of a few Kyr. A single planet is not expected to experience fast orbital changes, with the much weaker tidal and rotation-driven perturbations mostly reflecting in a slow periastron and nodal precession. The tidal decay of the orbit is too insignificant on the time scale of the stellar age. However, the conditions for the habitability of a single K2-18 b planet are much improved if, like the Earth, it rotates faster than the mean motion and its rotation angle is tilted by a hypothetical moon. Milanković's cycles of the habitable planet's climate are discussed for both configurations. [ABSTRACT FROM AUTHOR]

The aim of this study is to analyse the Earth habitability with respect to the direct exposition of the Earth atmosphere to the solar wind (SW) along the Sun's evolution on the main sequence including the realistic evolution of the space weather conditions and the Earth magnetic field. The MHD code PLUTO in spherical coordinates is applied to perform parametric studies with respect to the SW dynamic pressure and the interplanetary magnetic field intensity for different Earth magnetic field configurations. Quiet space weather conditions may not impact the Earth habitability. On the other hand, the impact of interplanetary coronal mass ejections (ICME) could lead to the erosion of the primary Earth atmosphere during the Hadean eon. A dipolar field of 30 μ T is strong enough to shield the Earth from the Eo-Archean age as well as 15 and 5 μ T dipolar fields from the Meso-Archean and Meso-Proterozoic, respectively. Multipolar weak field period during the Meso-Proterozoic age may not be a threat for ICME-like space weather conditions if the field intensity is at least 15 μ T and the ratio between the quadrupolar (Q) and dipolar (D) coefficients is |$\frac{Q}{D} \le 0.5$|⁠. By contrast, the Earth habitability in the Phanerozoic eon (including the present time) can be hampered during multipolar low field periods with a strength of 5 μ T and |$\frac{Q}{D} \ge 0.5$| associated with geomagnetic reversals. Consequently, the effect of the SW should be considered as a possible driver of Earth's habitability. [ABSTRACT FROM AUTHOR]

The existence of giant planets on wide orbits (⁠|$\stackrel{\gt }{_\sim }100\rm ~au$|⁠) challenge planet formation theories; the core accretion scenario has difficulty in forming them, whereas the disc instability model forms an overabundance of them that is not seen observations. We perform N -body simulations investigating the effect of close stellar encounters (≤1200 au) on systems hosting wide-orbit giant planets and the extent at which such interactions may disrupt the initial wide-orbit planet population. We find that the effect of an interaction on the orbit of a planet is stronger for high-mass, low-velocity perturbers, as expected. We find that due to just a single encounter there is a |$\sim 17~{{\ \rm per\ cent}}$| chance that the wide-orbit giant planet is liberated in the field, a |$\sim 10~{{\ \rm per\ cent}}$| chance it is scattered significantly outwards, and a |$\sim 6~{{\ \rm per\ cent}}$| chance it is significantly scattered inwards. Moreover, there is a |$\sim 21~{{\ \rm per\ cent}}$| chance that its eccentricity is excited to e > 0.1, making it more prone to disruption in subsequent encounters. The results strongly suggest that the effect of even a single stellar encounter is significant in disrupting the primordial wide-orbit giant planet population; in reality the effect will be even more prominent, as in a young star-forming region more such interactions are expected to occur. We conclude that the low occurrence rate of wide-orbit planets revealed by observational surveys does not exclude the possibility that such planetary systems are initially abundant, and therefore the disc–instability model may be a plausible scenario for their formation. [ABSTRACT FROM AUTHOR]

In this project, we determined the constraints on the modified tidal quality factor, |$Q_{\rm pl}^{\prime }$|⁠ , of gas-giant planets orbiting close to their host stars. We allowed |$Q_{\rm pl}^{\prime }$| to depend on tidal frequency, accounting for the multiple tidal waves with time-dependent frequencies simultaneously present on the planet. We performed our analysis on 78 single-star and single-planet systems, with giant planets and host stars with radiative cores and convective outer shells. We extracted constraints on the frequency-dependent |$Q_{\rm pl}^{\prime }$| for each system separately and combined them to find general constraints on |$Q_{\rm pl}^{\prime }$| required to explain the observed eccentricity envelope while simultaneously allowing the observed eccentricities of all systems to survive to the present-day. Individual systems do not place tight constraints on |$Q_{\rm pl}^{\prime }$|⁠. However, since similar planets must have similar tidal dissipation, we require that a consistent, possibly frequency-dependent, model must apply. Under that assumption, we find that the value of |$\log _{10}Q_{\rm pl}^{\prime }$| for HJs is 5.0 ± 0.5 for the range of tidal period from 0.8 to 7 d. We did not see any clear sign of frequency dependence of |$Q_{\rm pl}^{\prime }$|⁠. [ABSTRACT FROM AUTHOR]

This paper examines the energetics of a convective flow subject to an oscillation with a period |$t_{\rm osc}$| much smaller than the convective time-scale |$t_{\rm conv}$|⁠ , allowing for compressibility and uniform rotation. We show that the energy of the oscillation is exchanged with the kinetic energy of the convective flow at a rate |$D_R$| that couples the Reynolds stress of the oscillation with the convective velocity gradient. For the equilibrium tide and inertial waves, this is the only energy exchange term, whereas for p modes there are also exchanges with the potential and internal energy of the convective flow. Locally, |$\left| D_R \right| \sim u^{\prime 2} / t_{\rm conv}$|⁠ , where |$u^{\prime}$| is the oscillating velocity. If |$t_{\rm conv} \ll t_{\rm osc}$| and assuming mixing length theory, |$\left| D_R \right|$| is |$\left(\lambda_{\rm conv} / \lambda_{\rm osc} \right)^2$| smaller, where |$\lambda_{\rm conv}$| and |$\lambda_{\rm osc}$| are the characteristic scales of convection and the oscillation. Assuming local dissipation, we show that the equilibrium tide lags behind the tidal potential by a phase |$\delta(r) \sim r \omega_{\rm osc} / \left(g(r) t_{\rm conv}(r) \right)$|⁠ , where g is the gravitational acceleration. The equilibrium tide can be described locally as a harmonic oscillator with natural frequency |$\left(g/r \right)^{1/2}$| and subject to a damping force |$-u^{\prime}/t_{\rm conv}$|⁠. Although |$\delta(r)$| varies by orders of magnitude through the flow, it is possible to define an average phase shift |$\overline{\delta }$| which is in good agreement with observations for Jupiter and some of the moons of Saturn. Finally, |$1 / \overline{\delta }$| is shown to be equal to the standard tidal dissipation factor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Red Nova ZTF SLRN-2020 is the third transient event with properties that are compatible with the merger of a planet with a main-sequence (or close to) star on a dynamical time-scale. While the two first transient events occurred in young stellar objects, ZTF SLRN-2020 occurred in an old system. None the less, I show that the three star–planet intermediate luminosity optical transients (ILOTs, also termed Red Novae) occupy the same area in the energy–time diagram of ILOTs. Based on models for ILOTs that are power by stellar binary interaction, I suggest that the planet in ZTF SLRN-2020 launched jets at about its escape speed before it was engulfed by the star. Interestingly, the escape speed from the planet is similar to the orbital speed of the planet. This leads to an outflow with a very low terminal velocity, much below the escape velocity from the star, and in concentration around ≈45° to the equatorial plane. As well, the planet might have lost back some of the accreted mass just before engulfment, forming an accretion disc around the star. This disc might have launched jets during the main outburst of the event. The jets form a bipolar expanding nebula. [ABSTRACT FROM AUTHOR]

Context. White dwarfs are the last evolutionary stage for the majority of main-sequence stars. With nuclear burning having ceased, these stars are slowly cooling. There is observational evidence indicating that planetary remnants, and possibly even planets, orbit a considerable fraction of the known white dwarf population. These objects are interesting targets for transit observations due to their large planet-to-star radius ratio. Especially interesting is the possible outgassing from such objects and their eventual observational prospects. Aims. Here, we investigate whether electromagnetic induction heating can drive additional volcanic outgassing from small planetary remnants orbiting white dwarfs. This mechanism can be important for such bodies in addition to tidal heating due to the extremely strong magnetic fields of some white dwarfs and close orbital distances of planets to their host stars. Methods. We calculated the heating and related magmatic effects for a Moon-sized body around a magnetized white dwarf using an analytical model for induction heating and a numerical model for interior processes. We also calculated induction heating inside asteroid-sized bodies. Results. We show that induction heating can melt the mantle of a Moon-sized object within a geologically short time and contribute to desiccation of small asteroids on extremely tight orbits. These findings can have important implications for the evolution of rocky bodies orbiting white dwarfs and the potential detection of their outgassing. [ABSTRACT FROM AUTHOR]

Exoplanets on close-in orbit are subject to intense interactions with their host star. They receive a strong irradiation from the star, trigger tides within their host, and stars and close-in planets can be magnetically connected. In this review, I introduce the physical concepts behind these three types of interaction. I provide simple scaling-laws for their relative strengths, and highlight the aspects of the interactions that still elude our understanding. For each interaction, I also review their detectable effects on both specific star-planet systems and on the population of exoplanets as we know it today.

We investigate the orbital dynamics of an exosystem consisting of a solar-mass host star, a transiting body, and an Earth-size exoplanet within the framework of the generalized three-body problem. Depending on its mass, the transiting body can either be a super-Jupiter or a brown dwarf. To determine the final states of the Earth-size exoplanet, we conduct a systematic and detailed classification of the available phase space trajectories. Our classification scheme distinguishes between the bounded, escape, and collisional motions of the Earth-size exoplanet. Additionally, for cases of ordered (regular) motion, we further categorize the associated initial conditions based on the geometry of their respective trajectories. These bounded regular trajectories hold significant importance as they provide insights into the regions of phase space where the motion of the Earth-size exoplanet can be dynamically stable. Of particular interest is the identification of initial conditions that result in a bounded exomoon-like orbit of the Earth-size exoplanet around the transiting body.

Tidal disruption events are common in the Universe, which may occur in various compact star systems and could account for many astrophysical phenomena. Depending on the separation between the central compact star and its companion, either a full disruption or a partial disruption may occur. The partial disruption of a rocky planet around a neutron star (NS) can produce kilometer-sized clumps, but the main portion of the planet can survive. The dynamical evolution of these clumps is still poorly understood. In this study, the characteristics of partial disruption of a rocky planet in a highly elliptical orbit around a NS is investigated. The periastron of the planet is assumed to be very close to the NS so that it would be partially disrupted by tidal force every time it passes through the periastron. It is found that the fragments generated in the process will change their orbits on a time scale of a few orbital periods due to the combined influence of the NS and the remnant planet, and will finally collide with the central NS. Possible outcomes of the collisions are discussed. [ABSTRACT FROM AUTHOR]

We model the evaporation histories of the three planets around K2-136, a K-dwarf in the Hyades open cluster with an age of 700 Myr. The star hosts three transiting planets, with radii of 1.0, 3.0, and 1.5 Earth radii, where the middle planet lies above the radius–period valley and the inner and outer planets are below. We use an XMM–Newton observation to measure the XUV radiation environment of the planets, finding that the X-ray activity of K2-136 is lower than predicted by models but typical of similar Hyades members. We estimate the internal structure of each planet, and model their evaporation histories using a range of structure and atmospheric escape formulations. While the precise X-ray irradiation history of the system may be uncertain, we exploit the fact that the three planets must have shared the same history. We find that the Earth-sized K2-136b is most likely rocky, with any primordial gaseous envelope being lost within a few Myr. The sub-Neptune, K2-136c, has an envelope contributing 1–1.7 per cent of its mass that is stable against evaporation thanks to the high mass of its rocky core, whilst the super-Earth, K2-136d, must have a mass at the upper end of the allowed range in order to retain any of its envelope. Our results are consistent with all three planets beginning as sub-Neptunes that have since been sculpted by atmospheric evaporation to their current states, stripping the envelope from planet b and removing most from planet d whilst preserving planet c above the radius-period valley. [ABSTRACT FROM AUTHOR]

The Sun and other solar-type stars have magnetic fields that permeate their interior and surface, extend through the interplanetary medium, and are the main drivers of stellar activity. Stellar magnetic activity affects the physical processes and conditions of the interplanetary medium and orbiting planets. Coronal mass ejections (CMEs) are the most impactful of these phenomena in near-Earth space weather and consist of plasma clouds with a magnetic field, ejected from the solar corona. Precisely predicting the trajectory of CMEs is crucial in determining whether a CME will hit a planet and impact its magnetosphere and atmosphere. Despite the rapid developments in the search for stellar CMEs, their detection is still very incipient. In this work, we aim to better understand the propagation of CMEs by analysing the influence of initial parameters on CME trajectories, such as position, velocities, and the stellar magnetic field's configuration. We reconstruct magnetograms for Kepler-63 (KIC 11554435) and Kepler-411 (KIC 11551692) from spot transit mapping, and use a CME deflection model, ForeCAT, to simulate trajectories of hypothetical CMEs launched into the interplanetary medium from Kepler-63 and Kepler-411. We apply the same methodology to the Sun, for comparison. Our results show that in general deflections and rotations of CMEs decrease with their radial velocity and increase with ejection latitude. Moreover, magnetic fields stronger than the Sun's, such as Kepler-63's, tend to cause greater CME deflections. [ABSTRACT FROM AUTHOR]