Search

We set out a simulation to explore the follow-up of exoplanet candidates. We look at comparing photometric (transit method) and spectroscopic (Doppler shift method) techniques using three instruments: Next-Generation Transit Survey, High-Accuracy Radial-velocity Planetary Search, and CORALIE. We take into account the precision of follow-up and required observing time in attempt to rank each method for a given set of planetary system parameters. The methods are assessed on two criteria: signal-to-noise ratio (S/N) of the detection and follow-up time before characterization. We find that different follow-up techniques are preferred for different regions of parameter space. For S/N, we find that the ratio of spectroscopic to photometric S/N for a given system goes like |$R_{\rm p}/P^{{1}/{3}}$|⁠. For follow-up time, we find that photometry is favoured for the shortest period systems (<10 d) as well as systems with small planet radii. Spectroscopy is then preferred for systems with larger radius, and thus more massive planets (given our assumed mass–radius relationship). Finally, we attempt to account for the availability of telescopes and weight the two methods accordingly. [ABSTRACT FROM AUTHOR]

Pairs of planets in a system may end up close to their host star on eccentric orbits as a consequence of planet–planet scattering, Kozai, or secular migration. In this scenario, general relativity and secular perturbations have comparable time-scales and may interfere with each other with relevant effects on the eccentricity and pericenter evolution of the two planets. We explore, both analytically and via numerical integration, how the secular evolution is changed by general relativity for a wide range of different initial conditions. We find that when the faster secular frequency approaches the general relativity precession rate, which typically occurs when the outer planet moves away from the inner one, it relaxes to it and a significant damping of the proper eccentricity of the inner planet occurs. The proper eccentricity of the outer planet is reduced as well due to the changes in the secular interaction of the bodies. The lowering of the peak eccentricities of the two planets during their secular evolution has important implications on their stability. A significant number of two-planet systems, otherwise chaotic because of the mutual secular perturbations, are found stable when general relativity is included. [ABSTRACT FROM AUTHOR]

Periodograms are common tools used to search for periodic signals in unevenly spaced time series. The significance of periodogram peaks is often assessed using false alarm probability (FAP), which in most studies assumes uncorrelated noise and is computed using numerical methods such as bootstrapping or Monte Carlo. These methods have a high computational cost, especially for low FAP levels, which are of most interest. We present an analytical estimate of the FAP of the periodogram in the presence of correlated noise, which is fundamental to analyze astronomical time series correctly. The analytical estimate that we derive provides a very good approximation of the FAP at a much lower cost than numerical methods. We validate our analytical approach by comparing it with Monte Carlo simulations. Finally, we discuss the sensitivity of the method to different assumptions in the modeling of the noise. [ABSTRACT FROM AUTHOR]

The fastest pulsar and the slowest nova; the oldest galaxies and the youngest stars; the weirdest life forms and the commonest dwarfs; the highest energy particles and the lowest energy photons. These were some of the extremes of Astrophysics 2006. We attempt also to bring you updates on things of which there is currently only one (habitable planets, the Sun, and the Universe) and others of which there are always many, like meteors and molecules, black holes and binaries. © 2007 Springer Science+Business Media B.V.

Metals observed in the atmospheres of white dwarfs suggest that many have recently accreted planetary bodies. In some cases, the compositions observed suggest the accretion of material dominantly from the core (or the mantle) of a differentiated planetary body. Collisions between differentiated exoplanetesimalrrs produce such fragments. In this work, we take advantage of the large numbers of white dwarfs where at least one siderophile (core-loving) and one lithophile (rock-loving) species have been detected to assess how commonly exoplanetesimals differentiate. We utilize N -body simulations that track the fate of core and mantle material during the collisional evolution of planetary systems to show that most remnants of differentiated planetesimals retain core fractions similar to their parents, while some are extremely core rich or mantle rich. Comparison with the white dwarf data for calcium and iron indicates that the data are consistent with a model in which |$66^{+4}_{-6}{{\ \rm per\ cent}}$| have accreted the remnants of differentiated planetesimals, while |$31^{+5}_{-5}{{\ \rm per\ cent}}$| have Ca/Fe abundances altered by the effects of heating (although the former can be as high as |$100{{\ \rm per\ cent}}$|⁠ , if heating is ignored). These conclusions assume pollution by a single body and that collisional evolution retains similar features across diverse planetary systems. These results imply that both collisions and differentiation are key processes in exoplanetary systems. We highlight the need for a larger sample of polluted white dwarfs with precisely determined metal abundances to better understand the process of differentiation in exoplanetary systems. [ABSTRACT FROM AUTHOR]

We investigate the possibility of finding Earth-like planets in the habitable zone of 34 nearby FGK-dwarfs, each known to host one giant planet exterior to their habitable zone detected by RV. First we simulate the dynamics of the planetary systems in their present day configurations and determine the fraction of stable planetary orbits within their habitable zones. Then, we postulate that the eccentricity of the giant planet is a result of an instability in their past during which one or more other planets were ejected from the system. We simulate these scenarios and investigate whether planets orbiting in the habitable zone survive the instability. Explicitly we determine the fraction of test particles, originally found in the habitable zone, which remain in the habitable zone today. We label this fraction the resilient habitability of a system. We find that for most systems the probability of planets existing [or surviving] on stable orbits in the habitable zone becomes significantly smaller when we include a phase of instability in their history. We present a list of candidate systems with high resilient habitability for future observations. These are: HD 95872, HD 154345, HD 102843, HD 25015, GJ 328, HD 6718, and HD 150706. The known planets in the last two systems have large observational uncertainties on their eccentricities, which propagate into large uncertainties on their resilient habitability. Further observational constraints of these two eccentricities will allow us to better constrain the survivability of Earth-like planets in these systems. [ABSTRACT FROM AUTHOR]

Direct imaging is a tried and tested method of detecting exoplanets in the near-infrared (IR), but has so far not been extended to longer wavelengths. New data at mid-IR wavelengths (8–20  μ m) can provide additional constraints on planetary atmospheric models. We use the VLT Imager and Spectrometer for the mid-IR (VISIR) instrument on the VLT to detect or set stringent limits on the 8.7  μ m flux of the four planets surrounding HR 8799, and to search for additional companions. We use a novel circularized point spread function subtraction technique to reduce the stellar signal and obtain instrument limited background levels and obtain optimal flux limits. The BT SETTL isochrones are then used to determine the resulting mass limits. We find flux limits between 0.7 and 3.3 mJy for the J8.9 flux of the different planets at better than 5σ level and derive a new mass limit of 30 MJup for any objects beyond 40 au. While this work has not detected planets in the HR 8799 system at 8.7  μ m, it has found that an instrument with the sensitivity of VISIR is sufficient to detect at least four known hot planets around close stars, including β Pictoris b (1700 K, 19 pc), with more than 5σ certainty in 10 h of observing time in the mid-IR. [ABSTRACT FROM AUTHOR]

The detection of Earth-sized exoplanets around low-mass stars – in stars such as Proxima Centauri and TRAPPIST-1 – provide an exceptional chance to improve our understanding of the formation of planets around M stars and brown dwarfs. We explore the formation of such planets with a population synthesis code based on a planetesimal-driven model previously used to study the formation of the Jovian satellites. Because the discs have low mass and the stars are cool, the formation is an inefficient process that happens at short periods, generating compact planetary systems. Planets can be trapped in resonances and we follow the evolution of the planets after the gas has dissipated and they undergo orbit crossings and possible mergers. We find that formation of planets above Mars mass and in the planetesimal accretion scenario, is only possible around stars with masses M ⋆ ≥ 0.07 M sun and discs of M disc ≥ 10−2  M sun. We find that planets above Earth-mass form around stars with masses larger than 0.15  M sun, while planets larger than 5  M ⊕ do not form in our model, even not under the most optimal conditions (massive disc), showing that planets such as GJ 3512b form with another, more efficient mechanism. Our results show that the majority of planets form with a significant water fraction; that most of our synthetic planetary systems have 1, 2, or 3 planets, but those with 4, 5, 6, and 7 planets are also common, confirming that compact planetary systems with many planets should be a relatively common outcome of planet formation around small stars. [ABSTRACT FROM AUTHOR]

The latest estimation of Jupiter's gravitational field was obtained by processing the Doppler data from two gravity orbits of NASA's Juno mission, using the Jet Propulsion Laboratory software monte. In this work, we present the results of the analysis of the same measurements employing the orbit determination software orbit14 , developed at the University of Pisa, used here for the first time with real data. We found that the estimated values of Jupiter's spherical harmonic coefficients from the two solutions are consistent within the formal uncertainty. The analysis is complemented with a discussion on the results obtained with alternative set-ups. [ABSTRACT FROM AUTHOR]

Gravitational perturbations on an exoplanet from a massive outer body, such as the Kozai–Lidov mechanism, can pump the exoplanet's eccentricity up to values that will destroy it via a collision or strong interaction with its parent star. During the final stages of this process, any exomoons orbiting the exoplanet will be detached by the star's tidal force and placed into orbit around the star. Using ensembles of three- and four-body simulations, we demonstrate that while most of these detached bodies either collide with their star or are ejected from the system, a substantial fraction, |$\sim 10{{\ \rm per\ cent}}$|⁠ , of such 'orphaned' exomoons (with initial properties similar to those of the Galilean satellites in our own Solar system) will outlive their parent exoplanet. The detached exomoons generally orbit inside the ice line, so that strong radiative heating will evaporate any volatile-rich layers, producing a strong outgassing of gas and dust, analogous to a comet's perihelion passage. Small dust grains ejected from the exomoon may help generate an opaque cloud surrounding the orbiting body but are quickly removed by radiation blow-out. By contrast, larger solid particles inherit the orbital properties of the parent exomoon, feeding an eccentric disc of solids that drains more gradually on to the star via Poynting–Robertson drag, and which could result in longer time-scale dimming of the star. For characteristic exomoon evaporation times of ∼105–106 yr, attenuation of the stellar light arising from one or more out-gassing exomoons provides a promising explanation for both the dipping and secular dimming behaviour observed from KIC 8462852  (Boyajian's Star). [ABSTRACT FROM AUTHOR]

Atmospheric scintillation caused by optical turbulence in the Earth's atmosphere can be the dominant source of noise in ground-based photometric observations of bright targets, which is a particular concern for ground-based exoplanet transit photometry. We demonstrate the implications of atmospheric scintillation for exoplanet transit photometry through contemporaneous turbulence profiling and transit observations. We find a strong correlation between measured intensity variations and scintillation determined through optical turbulence profiling. This correlation indicates that turbulence profiling can be used to accurately model the amount of scintillation noise present in photometric observations on another telescope at the same site. We examine the conditions under which scintillation correction would be beneficial for transit photometry through turbulence profiling, and find that for the atmosphere of La Palma, scintillation dominates for bright targets of magnitude above V  ∼ 10.1 mag for a 0.5 m telescope, and at V  ∼ 11.7 mag for a 4.2 m telescope under median atmospheric conditions. Through Markov-chain Monte Carlo methods we examine the effect of scintillation noise on the uncertainty of the measured exoplanet parameters, and determine the regimes where scintillation correction is especially beneficial. The ability to model the amount of noise in observations due to scintillation, given an understanding of the atmosphere, is a crucial test for our understanding of scintillation and the overall noise budget of our observations. [ABSTRACT FROM AUTHOR]

Context. Hitherto, searches for exoplanetary dust have focused on the tails of decaying rocky or approaching icy bodies only at short circumstellar distances. At the same time, dust has been detected in the upper atmospheric layers of hot jupiters, which are subject to intensive mass loss. The erosion and/or tidal decay of hypothetic moonlets might be another possible source of dust around giant gaseous exoplanets. Moreover, volcanic activity and exozodiacal dust background may additionally contribute to exoplanetary dusty environments. Aims. In the present study, we look for photometric manifestations of dust around different kinds of exoplanets (mainly giants). Methods. We used linear approximation of pre- and post-transit parts of the long-cadence transit light curves (TLCs) of 118 Kepler objects of interest after their preliminary whitening and phase-folding. We then determined the corresponding flux gradients G1 and G2, respectively. These gradients were defined before and after the transit border for two different time intervals: (a) from 0.03 to 0.16 days and (b) from 0.01 to 0.05 days, which correspond to the distant and adjoining regions near the transiting object, respectively. Statistical analysis of gradients G1 and G2 was used for detection of possible dust manifestation. Results. It was found that gradients G1 and G2 in the distant region are clustered around zero, demonstrating the absence of artifacts generated during the light curve processing. However, in the adjoining region, 17 cases of hot jupiters show significantly negative gradients, G1, whereas the corresponding values of G2 remain around zero. The analysis of individual TLCs reveals the localized pre-transit decrease of flux, which systematically decreases G1. This effect was reproduced with the models using a stochastic obscuring precursor ahead of the planet. Conclusions. Since only a few TLCs show the presence of such pre-transit anomalies with no analogous systematic effect in the post-transit phase, we conclude that the detected pre-transit obscuration is a real planet-related phenomenon. Such phenomena may be caused by dusty atmospheric outflows or background circumstellar dust compressed in front of the mass-losing exoplanet, the study of which requires dedicated physical modeling and numeric simulations. Of certain importance may be the retarding of exozodiacal dust relative to the planet by the Poynting-Robertson effect leading to dust accumulation in electrostatic or magnetic traps in front of the planet. [ABSTRACT FROM AUTHOR]

We have identified a star, EPIC 249706694 (HD 139139), that was observed during K2 Campaign 15 with the Kepler extended mission that appears to exhibit 28 transit-like events over the course of the 87-d observation. The unusual aspect of these dips, all but two of which have depths of 200 ± 80 ppm, is that they exhibit no periodicity, and their arrival times could just as well have been produced by a random number generator. We show that no more than four of the events can be part of a periodic sequence. We have done a number of data quality tests to ascertain that these dips are of astrophysical origin, and while we cannot be absolutely certain that this is so, they have all the hallmarks of astrophysical variability on one of two possible host stars (a likely bound pair) in the photometric aperture. We explore a number of ideas for the origin of these dips, including actual planet transits due to multiple or dust emitting planets, anomalously large TTVs, S- and P-type transits in binary systems, a collection of dust-emitting asteroids, 'dipper-star' activity, and short-lived starspots. All transit scenarios that we have been able to conjure up appear to fail, while the intrinsic stellar variability hypothesis would be novel and untested. [ABSTRACT FROM AUTHOR]

Context. Doppler spectroscopy has been used in astronomy for more than 150 yr. In particular, it has permitted us to detect hundreds of exoplanets over the past 20 yr, and the goal today of detecting Earth-like planets requires a precision around 0.1 m s−1 or better. Doppler spectroscopy has also been and will be of major importance for other studies such as the variability of fundamental constants and cosmological studies. For all these applications, it is crucial to have the best possible wavelength calibration. Despite the fact that the HARPS spectrograph has been operational at the 3.6-m ESO telescope for more than 15 yr, and that it provides among the most precise Doppler measurements, improvements are still possible. One known problem, for instance, is the non-fully regular block-stitching of the charge-coupled devices (CCDs), which in some cases introduces one-year period parasitic signals in the measured radial velocity. Aims. The aim of the presented work is to improve the wavelength calibration of the HARPS spectrograph to push further its planet-detection capabilities. Methods. The properties of the CCD stitching-induced pixel-size anomalies were determined with light-emitting-diode (LED) flat-field frames, and then a physical, gap-corrected map of the CCDs is used for the fitting model of the spectral orders. We also used a new thorium line list, based on much higher-accuracy measurements than the one used up to now. We derive new wavelength solutions for the 15 yr of HARPS data, both before and after the fibre upgrade that took place in 2015. Results. We demonstrate that we do indeed correct the gap anomalies by computing the wavelength solutions of laser frequency comb exposures, known to have a very low dispersion, both with and without taking the gap correction into account. By comparing the rms of the most stable stars of the HARPS sample, we show that we globally decrease the radial velocity (RV) dispersion of the data, especially for the data acquired after the change of fibres of 2015. Finally, the comparative analysis of several individual systems shows that we manage to attenuate the periodogram power at one year in most cases. The analysis of the RVs derived from individual stellar lines also shows that we indeed correct the stitching-induced RV variation. Conclusions. This improved calibration of the HARPS spectrograph allows to go deeper in the search for low-amplitude radial-velocity signals. This new calibration process will be further improved by combining the thorium calibration spectra with laser frequency comb and Fabry–Perot calibration spectra, and this will not only be used for HARPS but notably also for HARPS-N and the new ESPRESSO spectrograph. [ABSTRACT FROM AUTHOR]

We present follow-up observations of the K2-133 multiplanet system. Previously, we announced that K2-133 contained three super-Earths orbiting an M1.5V host star – with tentative evidence of a fourth outer-planet orbiting at the edge of the temperate zone. Here, we report on the validation of the presence of the fourth planet, determining a radius of |$1.73_{-0.13}^{+0.14}$| R⊕. The four planets span the radius gap of the exoplanet population, meaning further follow-up would be worthwhile to obtain masses and test theories of the origin of the gap. In particular, the trend of increasing planetary radius with decreasing incident flux in the K2-133 system supports the claim that the gap is caused by photo-evaporation of exoplanet atmospheres. Finally, we note that K2-133 e orbits on the edge of the star's temperate zone, and that our radius measurement allows for the possibility that this is a rocky world. Additional mass measurements are required to confirm or refute this scenario. [ABSTRACT FROM AUTHOR]

Protoplanetary discs are thought to be truncated at orbital periods of around 10 d. Therefore, the origin of rocky short-period planets with P < 10 d is a puzzle. We propose that many of these planets may form through the Type-I migration of planets locked into a chain of mutual mean motion resonances. We ran N -body simulations of planetary embryos embedded in a protoplanetary disc. The embryos experienced gravitational scatterings, collisions, disc torques, and dampening of orbital eccentricity and inclination. We then modelled Kepler observations of these planets using a forward model of both the transit probability and the detection efficiency of the Kepler pipeline. We found that planets become locked into long chains of mean motion resonances that migrate in unison. When the chain reaches the edge of the disc, the inner planets are pushed past the edge due to the disc torques acting on the planets farther out in the chain. Our simulated systems successfully reproduce the observed period distribution of short-period Kepler planets between 1 and 2 R ⊕. However, we obtain fewer closely packed short-period planets than in the Kepler sample. Our results provide valuable insight into the planet formation process, and suggests that resonance locks, migration, and dynamical instabilities play important roles in the formation and evolution of close-in small exoplanets. [ABSTRACT FROM AUTHOR]

With the use of numerical models, we investigate whether Mean Motion Resonances (MMRs) with nearby moons to the J1407b ring system were the cause of the observed |$0.0267\,\mathrm{ au}$| wide gap located at |$0.4\,\mathrm{ au}$|⁠. Only one location of a moon at |$0.63\,\mathrm{ au}$| (corresponding to a 2:1 MMR) was found to form a gap at |$0.4\,\mathrm{ au} $| over short time periods of |$<\!\! 100\,\mathrm{ yr}$|⁠. However, the proximity of a low mass moon (⁠|$0.08\,{\mathrm{ M}_ \oplus })$| caused significant scattering of the outer ring edge at |$0.6\,\mathrm{ au}$| along with the formation of an additional gap at the 3:2 MMR (⁠|$0.485\,\mathrm{ au}$|⁠), which is not consistent with observations. Further models with moons located at MMRs 3:1, 4:1, 7:3, and 5:3 failed to form gaps at |$0.4\,\mathrm{ au}$| for time periods |$<\!\! 100\,\mathrm{ yr}$|⁠. Instead, gaps were formed in the ring at 3:2 and 2:1 MMRs which resulted in gaps at radial locations between |$0.44\!-\! 0.56\,\mathrm{ au}$|⁠. Additionally, gaps also take longer than one orbital period of J1407b about the primary to form. Given that J1407b is on a highly eccentric orbit and is thought to strongly perturb the ring at apocentre it appears unlikely that gaps form due to MMRs with nearby moons as opposed to embedded moons. Including an appropriate total mass of the ring equal to Earth a dampening effect was witnessed on the gap formation process, causing an increase in the time required to open a gap due to MMRs. Therefore, we conclude the observed gap at |$0.4\,\mathrm{ au}$| is unlikely to be caused by MMRs with nearby moons. [ABSTRACT FROM AUTHOR]

We present an approach that is able to both rapidly assess the dynamical stability of multiple planet systems, and determine whether an exoplanet system would be capable of hosting a dynamically stable Earth-mass companion in its habitable zone (HZ). We conduct a suite of numerical simulations using a swarm of massless test particles (TPs) in the vicinity of the orbit of a massive planet, in order to develop a predictive tool which can be used to achieve these desired outcomes. In this work, we outline both the numerical methods we used to develop the tool, and demonstrate its use. We find that the TPs survive in systems either because they are unperturbed due to being so far removed from the massive planet, or due to being trapped in stable mean-motion resonant orbits with the massive planet. The resulting unexcited TP swarm produces a unique signature in (a, e) space that represents the stable regions within the system. We are able to scale and translate this stability signature, and combine several together in order to conservatively assess the dynamical stability of newly discovered multiple planet systems. We also assess the stability of a system's HZ and determine whether an Earth-mass companion could remain on a stable orbit, without the need for exhaustive numerical simulations. [ABSTRACT FROM AUTHOR]

A search for extrasolar planetary transits using extended Kepler mission (K2) campaigns 9 and 11 revealed five new candidates towards the Galactic bulge. The stars EPIC 224439122, 224560837, 227560005, 230778501 and 231635524 are found to have low-amplitude transits consistent with extrasolar planets, with periods P  = 35.1695, 3.6390, 12.4224, 17.9856 and 5.8824 days, respectively. The K2 data and existing optical photometry are combined with multi-band near-IR photometry of the Vista Variables in the Via Lactea (VVV) survey and Two-Micron All-Sky Survey (2MASS) in order to measure accurate physical parameters for the host stars. We then measure the radii of the new planet candidates from the K2 transit light curves and also estimate their masses using mass–radius relations, concluding that two of these candidates could be low-mass planets and three could be giant gaseous planets. [ABSTRACT FROM AUTHOR]

Evidence from the Solar system suggests that, unlike Venus and Mars, the presence of a strong magnetic dipole moment on Earth has helped maintain liquid water on its surface. Therefore, planetary magnetism could have a significant effect on the long-term maintenance of atmosphere and liquid water on rocky exoplanets. We use Olson & Christensen's (2006) model to estimate magnetic dipole moments of rocky exoplanets with radii Rp ≤ 1.23 R⊕. Even when modelling maximum magnetic dipole moments, only Kepler-186 f has a magnetic dipole moment larger than the Earth's, while approximately half of rocky exoplanets detected in the circumstellar habitable zone have a negligible magnetic dipole moment. This suggests that planetary magnetism is an important factor when prioritizing observations of potentially habitable planets. [ABSTRACT FROM AUTHOR]

Context. Planet–planet (P–P) scattering is an efficient and robust dynamical mechanism for producing eccentric exoplanets. Coupled to tidal interactions with the central star, this phenomenon can also explain close-in giant planets on circularized and potentially misaligned orbits. Aims. We explore scattering events occurring close to the star and test if they can reproduce the main features of the observed orbital distribution of giant exoplanets on tight orbits. Methods. In our modeling we exploited a numerical integration code based on the Hermite algorithm and including the effects of general relativity, dynamical tides, and two-body collisions. Results. We find that P–P scattering events occurring in systems with three giant planets initially moving on circular orbits close to their star produce a population of planets similar to that presently observed, including eccentric and misaligned close-in planets. The contribution of tides and general relativity is relevant in determining the final outcome of the chaotic phase. Conclusions. Even if two-body collisions dominate the chaotic evolution of three planets in crossing orbits close to their star, the final distribution shows a significant number of planets on eccentric orbits. The highly misaligned close-in giant planets are instead produced by systems where the initial semimajor axis of the inner planet was around 0.2 au or beyond. [ABSTRACT FROM AUTHOR]

The period–mass and period–radius distributions of exoplanets are known to exhibit a desert. Unlike the existence of very hot (P orb < 3 d) super-Earths and hot Jupiters, no planets are known between super-Earths and sub-Jupiters with orbital periods as short as a day or two. In this letter, we show that the period boundary of this desert is dependent on stellar parameters (T eff, [ M/H ], log  g in order of significance), there is conclusive dependence on the incident stellar irradiation, and dependence on the stellar mass acting only on planets around T eff < 5600 K host stars. We found a significant lack of very inflated planets on the closest orbits to the host star. There is no significant dependence on tidal forces currently acting on the planet, the planet's surface gravity, or current filling factor of the Roche lobe. These distributions are most compatible with the dominant role of photoevaporation in forming the desert. [ABSTRACT FROM AUTHOR]

Super-Earths belong to a class of planet not found in the Solar system, but which appear common in the Galaxy. Given that some super-Earths are rocky, while others retain substantial atmospheres, their study can provide clues as to the formation of both rocky and gaseous planets, and – in particular – they can help to constrain the role of photoevaporation in sculpting the exoplanet population. GJ 9827 is a system already known to host three super-Earths with orbital periods of 1.2, 3.6, and 6.2 d. Here, we use new HARPS-N radial velocity measurements, together with previously published radial velocities, to better constrain the properties of the GJ 9827 planets. Our analysis cannot place a strong constraint on the mass of GJ 9827 c, but does indicate that GJ 9827 b is rocky with a composition that is probably similar to that of the Earth, while GJ 9827 d almost certainly retains a volatile envelope. Therefore, GJ 9827 hosts planets on either side of the radius gap that appears to divide super-Earths into pre-dominantly rocky ones that have radii below ∼1.5 R ⊕, and ones that still retain a substantial atmosphere and/or volatile components, and have radii above ∼2 R ⊕. That the less heavily irradiated of the three planets still retains an atmosphere, may indicate that photoevaporation has played a key role in the evolution of the planets in this system. [ABSTRACT FROM AUTHOR]

Transit timing variations (TTVs) are a valuable tool to determine the masses and orbits of transiting planets in multiplanet systems. TTVs can be readily modelled given knowledge of the interacting planets' orbital configurations and planet–star mass ratios, but such models are highly non-linear and difficult to invert. Markov Chain Monte Carlo (MCMC) methods are often used to explore the posterior distribution for model parameters, but, due to the high correlations between parameters, non-linearity, and potential multimodality in the posterior, many samplers perform very inefficiently. Therefore, we assess the performance of several MCMC samplers that use varying degrees of geometric information about the target distribution. We generate synthetic data sets from multiple models, including the TTVFaster model and a simple sinusoidal model, and test the efficiencies of various MCMC samplers. We find that sampling efficiency can be greatly improved for all models by sampling from a parameter space transformed using an estimate of the covariance and means of the target distribution. No one sampler performs the best for all data sets. For data sets with near Gaussian posteriors, the Hamiltonian Monte Carlo sampler obtains the highest efficiencies when the step size and number of steps are properly tuned. Two samplers – Differential Evolution Monte Carlo and Geometric adaptive Monte Carlo, have consistently efficient performance for each data set. Based on differences in effective sample sizes per time, we show that the right choice of sampler can improve sampling efficiencies by several orders of magnitude. [ABSTRACT FROM AUTHOR]

Current technology is not able to map the topography of rocky exoplanets, simply because the objects are too faint and far away to resolve them. Nevertheless, indirect effect of topography should be soon observable thanks to photometry techniques, and the possibility of detecting specular reflections. In addition, topography may have a strong effect on Earth-like exoplanet climates because oceans and mountains affect the distribution of clouds. Also topography is critical for evaluating surface habitability. We propose here a general statistical theory to describe and generate realistic synthetic topographies of rocky exoplanetary bodies. In the Solar system, we have examined the best-known bodies: the Earth, Moon, Mars, and Mercury. It turns out that despite their differences, they all can be described by multifractral statistics, although with different parameters. Assuming that this property is universal, we propose here a model to simulate 2D spherical random field that mimics a rocky planetary body in a stellar system. We also propose to apply this model to estimate the statistics of oceans and continents to help to better assess the habitability of distant worlds. [ABSTRACT FROM AUTHOR]

Transmission spectroscopy provides us with information on the atmospheric properties at the limb, which is often intuitively assumed to be a narrow annulus around the planet. Consequently, studies have focused on the effect of atmospheric horizontal heterogeneities along the limb. Here we demonstrate that the region probed in transmission – the limb – actually extends significantly towards the day and night sides of the planet. We show that the strong day–night thermal and compositional gradients expected on synchronous exoplanets create sufficient heterogeneities across the limb that result in important systematic effects on the spectrum and bias its interpretation. To quantify these effects, we developed a 3D radiative-transfer model able to generate transmission spectra of atmospheres based on 3D atmospheric structures. We first apply this tool to a simulation of the atmosphere of GJ 1214 b to produce synthetic JWST observations and show that producing a spectrum using only atmospheric columns at the terminator results in errors greater than expected noise. This demonstrates the necessity for a real 3D approach to model data for such precise observatories. Secondly, we investigate how day–night temperature gradients cause a systematic bias in retrieval analysis performed with 1D forward models. For that purpose we synthesise a large set of forward spectra for prototypical HD 209458 b- and GJ 1214 b-type planets varying the temperatures of the day and night sides as well as the width of the transition region. We then perform typical retrieval analyses and compare the retrieved parameters to the ground truth of the input model. This study reveals systematic biases on the retrieved temperature (found to be higher than the terminator temperature) and abundances. This is due to the fact that the hotter dayside is more extended vertically and screens the nightside – a result of the non-linear properties of atmospheric transmission. These biases will be difficult to detect as the 1D profiles used in the retrieval procedure are found to provide an excellent match to the observed spectra based on standard fitting criteria. This must be kept in mind when interpreting current and future data. [ABSTRACT FROM AUTHOR]

Context. Seasonal variations and climate stability of a planet are very sensitive to the planet obliquity and its evolution. This is of particular interest for the emergence and sustainability of land-based life, but orbital and rotational parameters of exoplanets are still poorly constrained. Numerical explorations usually realised in this situation are therefore in heavy contrast with the uncertain nature of the available data. Aims. We aim to provide an analytical formulation of the long-term spin-axis dynamics of exoplanets, linking it directly to physical and dynamical parameters, but still giving precise quantitative results if the parameters are well known. Together with bounds for the poorly constrained parameters of exoplanets, this analysis is designed to enable a quick and straightforward exploration of the spin-axis dynamics. Methods. The long-term orbital solution is decomposed into quasi-periodic series and the spin-axis Hamiltonian is expanded in powers of eccentricity and inclination. Chaotic zones are measured by the resonance overlap criterion. Bounds for the poorly known parameters of exoplanets are obtained from physical grounds (rotational breakup) and dynamical considerations (equipartition of the angular momentum deficit). Results. This method gives accurate results when the orbital evolution is well known. The detailed structure of the chaotic zones for the solar system planets can be retrieved from simple analytical formulas. For less-constrained planetary systems, the maximal extent of the chaotic regions can be computed, requiring only the mass, the semi-major axis, and the eccentricity of the planets present in the system. Additionally, some estimated bounds of the precession constant allow to classify which observed exoplanets are necessarily out of major spin-orbit secular resonances (unless the precession rate is affected by the presence of massive satellites). [ABSTRACT FROM AUTHOR]

Solar system, exoplanet, and stellar science rely on transits, eclipses, and occultations for dynamical and physical insight. Often, the geometry of these configurations are modelled by assuming a particular viewpoint. Here, instead, I derive user-friendly formulae from first principles independent of viewpoint and in three dimensions. I generalize the results of Veras & Breedt by (i) characterizing three-body systems that are in transit but are not necessarily perfectly aligned and by (ii) incorporating motion. For a given snapshot in time, I derive explicit criteria to determine whether a system is in or out of transit, if an eclipse is total or annular, and expressions for the size of the shadow, including their extreme values and a condition for engulfment. These results are exact. For orbital motion, I instead obtain approximate results. By assuming fixed orbits, I derive a single implicit algebraic relation that can be solved to obtain the frequency and duration of transit events – including ingresses and egresses – for combinations of moons, planets, and stars on arbitrarily inclined circular orbits; the eccentric case requires the solution of Kepler's equation but remains algebraic. I prove that a transit shadow – whether umbral, antumbral, or penumbral – takes the shape of a parabolic cylinder, and finally present geometric constraints on Earth-based observers hoping to detect a three-body syzygy (or perfect alignment) – either in extrasolar systems or within the Solar system – potentially as a double annular eclipse. [ABSTRACT FROM AUTHOR]

Understanding the origin of planets that have formed in binary stars is fundamental to constrain theories of binary and planet formation. The planet occurrence rate in binaries with a separation ≲50 au is only ∼one-third that of wider binaries or single stars. This may indicate that a close companion has a ruinous influence on planet formation, because it can truncate the protoplanetary disc and pump up planetesimals eccentricity and collision probability. Nevertheless, observations have revealed a few of these systems, which challenge current planet formation theories. Dynamical interactions can deliver planets into S-type orbits. In this paper, we consider as a possible scenario for forming S-type planets in close binaries the single star–binary star interactions that commonly take place in star clusters. We find that the final fraction and orbital properties of S-type planets in close binaries are mainly determined by the mass ratio of the stars involved in the close encounter, and the initial binary and planet semimajor axes. Present and upcoming missions, such as Transiting Exoplanet Survey Satellite (TESS), Planetary Transits and Oscillations of stars (PLATO), and CHaracterising ExOPlanets Satellite (CHEOPS), may shed new light on the origin of S-type planets in close binaries. [ABSTRACT FROM AUTHOR]

PRAIA – Package for the Reduction of Astronomical Images Automatically – is a suite of photometric and astrometric tasks designed to cope with huge amounts of heterogeneous observations with fast processing, no human intervention, minimum parametrization and yet maximum possible accuracy and precision. It is the main tool used to analyse astronomical observations by an international collaboration involving Brazilian, French and Spanish researchers under the Lucky Star umbrella for Solar System studies. Here, we focus on the concepts of differential aperture photometry and digital coronagraphy underneath PRAIA, used in the reduction of stellar occultations, rotational light curves, mutual phenomena and natural satellite observations. We highlight novelties developed by us and never before reported in the literature, which significantly enhance the precision and automation of photometry and digital coronagraphy, such as: (a) PRAIA's pixelized aperture photometry (PCAP), which avoids pixel sub-sampling or fractioning; (b) fully automatic object detection and aperture determination (BOIA), which abolishes the use of arbitrary sky background sigma factors, and finds better apertures than by using subjective FWHM factors; (c) better astrometry improving the aperture and coronagraphy centres, including the new Photogravity Center Method besides circular and elliptical Gaussian and Lorentzian generalized profiles; (d) coronagraphy of faint objects close to bright ones and vice-versa; e) use of elliptical rings for the coronagraphy of elongated profiles; (f) refined quartile ring statistics; (g) multiprocessing image capabilities for faster computation speed. We give examples showing the photometry performance, discuss the advantages of PRAIA over other popular packages for Solar System differential photometric observations, point out the uniqueness of its digital coronagraphy in comparison with other coronagraphy tools and methods, and comment about future planed implementations. Besides Solar System works, PRAIA can also be used in the differential photometry of variable and cataclysmic stars and transient phenomena like exoplanet transits and microlensing, and in the digital coronagraphy of astrophysical observations. PRAIA codes and input files are publicly available for the first time at: https://ov.ufrj.br/en/PRAIA/. • Automatic, fast, precise differential aperture photometry of astronomical images. • Pixelized Circular Aperture Photometry (no pixel count roundings). • Automatic digital coronagraphy. • Fixed/variable best apertures automatically found; flat/normalization of light curves. • Rich SAOimage ds9 output visualization; free software, complete User Guide w/ example. [ABSTRACT FROM AUTHOR]

Transiting exoplanet parameter estimation from time-series photometry and Doppler spectroscopy is fundamental to study planets' internal structures and compositions. Here we present the code pyaneti, a powerful and user-friendly software suite to perform multiplanet radial velocity and transit data fitting. The code uses a Bayesian approach combined with a Markov chain Monte Carlo sampling to estimate the parameters of planetary systems. We combine the numerical efficiency of fortran, the versatility of python, and the parallelization of OpenMP to make pyaneti a fast and easy to use code. The package is freely available at https://github.com/oscaribv/pyaneti. [ABSTRACT FROM AUTHOR]

This paper focuses on two-planet systems in a first-order (q + 1) |$\colon$| q mean motion resonance and undergoing type-I migration in a disc. We present a detailed analysis of the resonance valid for any value of q. Expressions for the equilibrium eccentricities, mean motions, and departure from exact resonance are derived in the case of smooth convergent migration. We show that this departure, not assumed to be small, is such that the period ratio normally exceeds but can also be less than (q + 1)/ q. Departure from exact resonance as a function of time for systems starting in resonance and undergoing divergent migration is also calculated. We discuss observed systems in which two low-mass planets are close to a first-order resonance. We argue that the data are consistent with only a small fraction of the systems having been captured in resonance. Furthermore, when capture does happen, it is not in general during smooth convergent migration through the disc but after the planets reach the disc inner parts. We show that although resonances may be disrupted when the inner planet enters a central cavity, this alone cannot explain the spread of observed separations. Disruption is found to result in the system either moving interior to the resonance by a few per cent or attaining another resonance. We postulate two populations of low-mass planets: a small one for which extensive smooth migration has occurred and a larger one that formed approximately in situ with very limited migration. [ABSTRACT FROM AUTHOR]

Context. The modeling of planetary interiors requires accurate equations of state (EOSs) for the basic constituents with proven validity in the difficult pressure–temperature regime extending up to 50 000 K and hundreds of megabars. While EOSs based on first-principles simulations are now available for the two most abundant elements, hydrogen and helium, the situation is less satisfactory for water where no wide-range EOS is available despite its requirement for interior modeling of planets ranging from super-Earths to planets several times the size of Jupiter. Aims. As a first step toward a multi-phase EOS for dense water, we develop a temperature-dependent EOS for dense water covering the liquid and plasma regimes and extending to the super-ionic and gas regimes. This equation of state covers the complete range of conditions encountered in planetary modeling. Methods. We use first-principles quantum molecular dynamics simulations and the Thomas-Fermi extension to reach the highest pressures encountered in giant planets several times the size of Jupiter. Using these results, as well as the data available at lower pressures, we obtain a parametrization of the Helmholtz free energy adjusted over this extended temperature and pressure domain. The parametrization ignores the entropy and density jumps at phase boundaries but we show that it is sufficiently accurate to model interior properties of most planets and exoplanets. Results. We produce an EOS given in analytical form that is readily usable in planetary modeling codes and dynamical simulations (a fortran implementation is provided). The EOS produced is valid for the entire density range relevant to planetary modeling, for densities where quantum effects for the ions can be neglected, and for temperatures below 50 000K. We use this EOS to calculate the mass-radius relationship of exoplanets up to 5000 MEarth, explore temperature effects in the wet Earth-like, ocean planets and pure water planets, and quantify the influence of the water EOS for the core on the gravitational moments of Jupiter. [ABSTRACT FROM AUTHOR]

Abstract Based on the newly released Gaia DR2 star catalogue, the CCD images of Neptunian satellites taken by the telescopes at Xinglong Observatory of National Astronomical Observatory in 2006–2007 were re-reduced. A total of 174 satellite positions were derived, including 34 new observed positions of Triton, 28 new and 112 updated observed positions of Nereid. Thanks to the high-quality reference catalogue Gaia DR2 and more suitable plate models, the precision of the re-reduction for Nereid is more than doubled and the dispersions of these observations are better than 80 mas. Moreover, the comparisons show that for the Neptune system in the period 2006–2007, there are some systematic discrepancies between different planetary ephemerides such as INPOP17a with DE431 and EPM2017, and the discrepancy can reach as much as 50 mas, which is reflected in the calculation of (O C) residuals of Neptunian satellites. Highlights • It is necessary to improve the precisions of old observations for natural satellites. • The old observations of Neptunian satellites in 2006-2007 were reduced based on Gaia DR2 catalogue. • 34 new observed positions of Triton, 28 new and 112 updated observed positions of Nereid were presented. • The precision of the re-reduction for Nereid is better than 80 mas. [ABSTRACT FROM AUTHOR]

We have performed high resolution three-dimensional compressible hydrodynamics simulations to investigate the effects of shocks and turbulence on energy transport into hot Jupiter atmospheres, under a variety of shear gradients. We focus on a local atmospheric region to accurately follow the small-scale structures of turbulence and shocks. We find that the effects of turbulence above and below a shear layer are different in scale and magnitude: below the shear layer, the effects of turbulence on the vertical energy transfer are local, generally ≲2 × (scale height). However, turbulence can have a spatially and thermally large influence on almost the entire region above the shear layer. We also find that shock formation is local and transient. Once the atmosphere becomes steady, the time-averaged heat flux at P ∼ 1 bar is insignificant, on the order of 0.001 per cent of the incoming stellar flux with a shear motion at P ≃ 1 mbar, and 0.1 per cent with a deeper shear layer at P ≃ 100 mbar. Accordingly, the diffusion coefficient is higher for the deeper shear layer. Therefore, our results suggest that turbulence near less dense (P ≃ 1 mbar) regions does not cause a sufficiently deep and large penetration of thermal energy to account for radius inflation in hot Jupiters, regardless of how violent the turbulence is. However, as the shear layer gets deeper, heat transfer becomes more effective throughout the atmosphere (upwards and downwards) due to a larger kinetic energy budget. Therefore, it is more important how deep turbulence occurs in the atmosphere, than how unstable the atmosphere is for effective energy transfer. [ABSTRACT FROM AUTHOR]

In this work, we hunt for the best places to find exo-Earths in the currently known exoplanet population. While it is still unclear whether Jupiter had a beneficial or detrimental effect on the creation of the right environment for a habitable Earth to develop, we focus on the 51 multiple planet systems that have at least one Jupiter-like planet and aim to identify which would be good candidates to host an exo-Earth. We conduct a series of numerical simulations to identify dynamically stable regions of the habitable zone of the multiple exoplanet systems capable of hosting an Earth-mass planet. We produce a candidate list of 16 systems that could host such a stable exo-Earth in their habitable zone, and for which the induced radial velocity signal of a hypothetical one, two or four Earth-mass planet on the host star would be detectable with the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations spectrograph. We find that whilst the gravitational interactions with the massive planet nearest the habitable zone are critical in determining stability, the secular resonant interactions between multiple planets can also have a dramatic influence on the overall stability of the habitable zone. [ABSTRACT FROM AUTHOR]

Time series observations are ubiquitous in astronomy and are generated, for example, to distinguish between different types of supernovae to detect and characterize extrasolar planets and to classify variable stars. These time series are usually modelled using a parametric and/or physical model that assumes independent and homoscedastic errors, but in many cases, these assumptions are not accurate and there remains a temporal dependence structure on the errors. This can occur, for example, when the proposed model cannot explain all the variability of the data or when the parameters of the model are not properly estimated. In this work, we define an autoregressive model for irregular discrete-time series based on the discrete time representation of the continuous autoregressive model of order 1. We show that the model is ergodic and stationary. We further propose a maximum likelihood estimation procedure and assess the finite sample performance by Monte Carlo simulations. We implement the model on real and simulated data from Gaussian as well as other distributions, showing that the model can flexibly adapt to different data distributions. We apply the irregular autoregressive model to the residuals of a transit of an extrasolar planet to illustrate errors that remain with temporal structure. We also apply this model to residuals of an harmonic fit of light curves from variable stars to illustrate how the model can be used to detect incorrect parameter estimation. [ABSTRACT FROM AUTHOR]

The satellites of Jupiter are thought to form in a circumplanetary disc. Here we address their formation and orbital evolution with a population synthesis approach, by varying the dust-to-gas ratio, the disc dispersal time-scale and the dust refilling time-scale. The circumplanetary disc initial conditions (density and temperature) are directly drawn from the results of 3D radiative hydrodynamical simulations. The disc evolution is taken into account within the population synthesis. The satellitesimals were assumed to grow via streaming instability. We find that the moons form fast, often within 104 yr, due to the short orbital time-scales in the circumplanetary disc. They form in sequence, and many are lost into the planet due to fast type I migration, polluting Jupiter's envelope with typically 15 Earth-masses of metals. The last generation of moons can form very late in the evolution of the giant planet, when the disc has already lost more than the 99 per cent of its mass. The late circumplanetary disc is cold enough to sustain water ice, hence not surprisingly 85 per cent of the moon population has icy composition. The distribution of the satellite masses is peaking slightly above Galilean masses, up until a few Earth-masses, in a regime which is observable with the current instrumentation around Jupiter-analogue exoplanets orbiting sufficiently close to their host stars. We also find that systems with Galilean-like masses occur in |$20{{\ \rm per\ cent}}$| of the cases and they are more likely when discs have long dispersion time-scales and high dust-to-gas ratios. [ABSTRACT FROM AUTHOR]

Cold outer debris belts orbit a significant fraction of stars, many of which are planet hosts. Radiative forces from the star lead to dust particles leaving the outer belts and spiralling inwards under Poynting–Robertson drag. We present an empirical model fitted to N -body simulations that allows the fate of these dust particles when they encounter a planet to be rapidly calculated. High-mass planets eject most particles, whilst dust passes low-mass planets relatively unperturbed. Close-in, high-mass planets (hot Jupiters) are best at accreting dust. The model predicts the accretion rate of dust on to planets interior to debris belts, with mass accretion rates of up to hundreds of kilograms per second predicted for hot Jupiters interior to outer debris belts, when collisional evolution is also taken into account. The model can be used to infer the presence and likely masses of as yet undetected planets in systems with outer belts. The non-detection of warm dust with the Large Binocular Telescope Interferometer (LBTI) around Vega could be explained by the presence of a single Saturn mass planet, or a chain of lower mass planets. Similarly, the detection of warm dust in such systems implies the absence of planets above a quantifiable level, which can be lower than similar limits from direct imaging. The level of dust detected with LBTI around β Leo can be used to rule out the presence of planets more massive than a few Saturn masses outside of ∼5 au. [ABSTRACT FROM AUTHOR]

Abstract The low-energy lunar trajectories with lunar flybys are investigated based on the Sun-Earth-Moon bicircular problem (BCP). The characteristics of the distribution of trajectories in the phase space are summarized. Using the invariant manifolds in the BCP system, the low-energy lunar trajectories with lunar flybys are sought. Then, take time as an augmented dimension in the phase space of a nonautonomous system, we present the state space map and reveal the distribution of these lunar trajectories in the phase space. Consequently, we find that the low-energy lunar trajectories exist as families, and that the every moment in the Sun-Earth-Moon synodic period can be the departure date. Finally, we analyse the velocity increment, transfer duration, and system energy for the different trajectory families, and obtain the velocity-impulse optimal family and the transfer-duration optimal family, respectively. [ABSTRACT FROM AUTHOR]

Applying the survival function analysis to the planet radius distribution of the Kepler confirmed/candidate planets, we have identified two natural divisions of planet radius at 4 Earth radii (R⊕) and 10 R⊕. These divisions place constraints on planet formation and interior structure model. The division at 4 R⊕ separates small exoplanets from large exoplanets above. When combined with the recently discovered radius gap at 2 R⊕, it supports the treatment of planets in between 2 and 4 R⊕ as a separate group, likely water worlds. For planets around solar-type FGK main-sequence stars, we argue that 2 R⊕ is the separation between water-poor and water-rich planets, and 4 R⊕ is the separation between gas-poor and gas-rich planets. We confirm the slope of the survival function in between 4 and 10 R⊕ to be shallower compared to either ends, indicating a relative paucity of planets in between 4 and 10 R⊕, namely the sub-Saturnian desert there. We name them transitional planets, as they form a bridge between the gas-poor small planets and gas giants. Accordingly, we propose the following classification scheme: (<2 R⊕) rocky planets, (2–4 R⊕) water worlds, (4–10 R⊕) transitional planets, and (>10 R⊕) gas giants. [ABSTRACT FROM AUTHOR]

Lyman α observations during an exoplanet transit have proved to be very useful to study the interaction between the stellar wind and the planetary atmosphere. They have been extensively used to constrain planetary system parameters that are not directly observed, such as the planetary mass-loss rate. In this way, Ly α observations can be a powerful tool to infer the existence of a planetary magnetic field, since it is expected that the latter will affect the escaping planetary material. To explore the effect that magnetic fields have on the Ly α absorption of HD 209458b, we run a set of 3D MHD simulations including dipolar magnetic fields for the planet and the star. We assume values for the surface magnetic field at the poles of the planet in the range of [0–5] G, and from 1 to 5 G at the poles of the star. Our models also include collisional and photo-ionization, radiative recombination, and an approximation for the radiation pressure. Our results show that the magnetic field of the planet and the star change the shape of the Ly α absorption profile, since it controls the extent of the planetary magnetosphere and the amount of neutral material inside it. The model that best reproduces the absorption observed in HD 209458b (with canonical values for the stellar wind parameters) corresponds to a dipole planetary field of ≲ 1 G at the poles. [ABSTRACT FROM AUTHOR]