Distribution Of Planets Research Articles

Connecting planets around horizontal branch stars with known exoplanets

We study the distribution of exoplanets around main sequence (MS) stars and apply our results to the binary model for the formation of extreme horizontal branch (EHB; sdO; sdB; hot subdwarfs) stars. By Binary model we refer both to stellar and substellar companions that enhance the mass loss rate, where substellar companions stand for both massive planets and brown dwarfs. We conclude that sdB (EHB) stars are prime targets for planet searches. We reach this conclusion by noticing that the bimodal distribution of planets around stars with respect to the parameter M_p*a^2, is most prominent for stars in the mass range 1Mo < M < 1.5Mo; 'a' is the orbital separation, 'M' is the stellar mass and 'M_p' the planet mass. This is also the mass range of the progenitors of EHB stars that are formed through the interaction of their progenitors with planets (assuming the EHB formation mechanism is the binary model). In the binary model for the formation of EHB stars interaction with a binary companion or a substellar object (a planet or a brown dwarf), causes the progenitor to lose most of its envelope mass during its red giant branch (RGB) phase. As a result of that the descendant HB star is hot, i.e., an EHB (sdB) star. The bimodal distribution suggests that even if the close-in planet that formed the EHB star did not survive its RGB common envelope evolution, one planet or more might survive at a>1AU. Also, if a planet or more are observed at a>1AU, it is possible that a closer massive planet did survive the common envelope phase, and it is orbiting the EHB with an orbital period of hours to days.

The SOPHIE search for northern extrasolar planets

We report the detection of a Jupiter-mass planet discovered with the SOPHIE spectrograph mounted on the 1.93-m telescope at the Haute-Provence Observatory. The new planet orbits HD109246, a G0V star slightly more metallic than the Sun. HD109246b has a minimum mass of 0.77 MJup, an orbital period of 68 days, and an eccentricity of 0.12. It is placed in a sparsely populated region of the period distribution of extrasolar planets. We also present a correction method for the so-called seeing effect that affects the SOPHIE radial velocities. We complement this discovery announcement with a description of some calibrations that are implemented in the SOPHIE automatic reduction pipeline. These calibrations allow the derivation of the photon-noise radial velocity uncertainty and some useful stellar properties (vsini, [Fe/H], logR'HK) directly from the SOPHIE data.

Orbital evolution of eccentric planets in radiative discs

With an average eccentricity of about 0.29, the eccentricity distribution of extrasolar planets is markedly different from the solar system. Among other scenarios considered, it has been proposed that eccentricity may grow through planet-disc interaction. Recently, it has been noticed that the thermodynamical state of the disc can significantly influence the migration properties of growing protoplanets. However, the evolution of planetary eccentricity in radiative discs has not been considered yet. In this paper we study the evolution of planets on eccentric orbits that are embedded in a three-dimensional viscous disc and analyse the disc's effect on the orbital evolution of the planet. We use the three-dimensional hydrodynamical code NIRVANA that includes full tensor viscosity and implicit radiation transport in the flux-limited diffusion approximation. The code uses the FARGO-algorithm to speed up the simulations. First we measure the torque and power exerted on the planet by the disc for fixed orbits, and then we let the planet start with initial eccentricity and evolve it in the disc. For locally isothermal we confirm previous results and find eccentricity damping and inward migration for planetary cores. In the case of radiative discs, the planets experience an inward migration as long as its eccentricity lies above a certain threshold. After the damping of eccentricity cores with masses below 33 Earthmasses begin to migrate outward in radiative discs, while higher mass cores always migrate inward. For all planetary masses studied (up to 200 Earthmasses) we find eccentricity damping. In viscous discs the orbital eccentricity of embedded planets is damped during the evolution independent of the mass. Hence, planet-disc interaction does not seem to be a viable mechanism to explain the observed high eccentricity of exoplanets.

The occurrence and the distribution of masses and radii of exoplanets

AbstractWe analyze the statistics of Doppler-detected planets and Keplere-detected planet candidates of high integrity. We determine the number of planets per star as a function of planet mass, radius, and orbital period, and the occurrence of planets as a function of stellar mass. We consider only orbital periods less than 50 days around Solar-type (GK) stars, for which both Doppler and Kepler offer good completeness. We account for observational detection effects to determine the actual number of planets per star. From Doppler-detected planets discovered in a survey of 166 nearby G and K main sequence stars we find a planet occurrence of 15+5−4% for planets with M sin i = 3–30 ME and P &lt; 50 d, as described in Howard et al. (2010). From Keplere, the planet occurrence is 0.130 ± 0.008, 0.023 ± 0.003, and 0.013 ± 0.002 planets per star for planets with radii 2–4, 4–8, and 8–32 RE, consistent with Doppler-detected planets. From Keplere, the number of planets per star as a function of planet radius is given by a power law, df/dlog R = kRRα with kR = 2.9+0.5−0.4, α = −1.92 ± 0.11, and R = RP/RE. Neither the Doppler-detected planets nor the Keplere-detected planets exhibit a “desert” at super-Earth and Neptune sizes for close-in orbits, as suggested by some planet population synthesis models. The distribution of planets with orbital period, P, shows a gentle increase in occurrence with orbital period in the range 2–50 d. The occurrence of small, 2–4 RE planets increases with decreasing stellar mass, with seven times more planets around low mass dwarfs (3600–4100 K) than around massive stars (6600–7100 K).

THE INVISIBLE MAJORITY? EVOLUTION AND DETECTION OF OUTER PLANETARY SYSTEMS WITHOUT GAS GIANTS

We present 230 realizations of a numerical model of planet formation in systems without gas giants. These represent a scenario in which protoplanets grow in a region of a circumstellar disk where water ice condenses (the "ice line''), but fail to accrete massive gas envelopes before the gaseous disk is dispersed. Each simulation consists of a small number of gravitationally interacting oligarchs and a much larger number of small bodies that represent the natal disk of planetesimals. We investigate systems with varying initial number of oligarchs, oligarch spacing, location of the ice line, total mass in the ice line, and oligarch mean density. Systems become chaotic in ~1 Myr but settle into stable configurations in 10-100 Myr. We find: (1) runs consistently produce a 5-9 Earth mass planet at a semimajor axis of 0.25-0.6 times the position of the ice line, (2) the distribution of planets' orbital eccentricities is distinct from, and skewed toward lower values than the observed distribution of (giant) exoplanet orbits, (3) inner systems of two dominant planets (e.g., Earth and Venus) are not stable or do not form because of the gravitational influence of the innermost icy planet. The planets predicted by our model are unlikely to be detected by current Doppler observations. Microlensing is currently sensitive to the most massive planets found in our simulations. A scenario where up to 60% of stars host systems such as those we simulate is consistent with all the available data. We predict that, if this scenario holds, the NASA Kepler spacecraft will detect about 120 planets by two or more transits over the course of its 3.5 yr mission. Future microlensing surveys will detect ~130 analogs over a 5 yr survey. Finally, the Space Interferometry Mission (SIM-Lite) should be capable of detecting 96% of the innermost icy planets over the course of a 5 yr mission.

CONSTRAINTS ON LONG-PERIOD PLANETS FROM ANL′- ANDM-BAND SURVEY OF NEARBY SUN-LIKE STARS: MODELING RESULTS

We have carried out an L' and M band Adaptive Optics (AO) extrasolar planet imaging survey of 54 nearby, sunlike stars using the Clio camera at the MMT. Our survey concentrates more strongly than all others to date on very nearby F, G, and K stars, in that we have prioritized proximity higher than youth. Our survey is also the first to include extensive observations in the M band, which supplemented the primary L' observations. These longer wavelength bands are most useful for very nearby systems in which low temperature planets with red IR colors (i.e. H - L', H - M) could be detected. The survey detected no planets, but set interesting limits on planets and brown dwarfs in the star systems we investigated. We have interpreted our null result by means of extensive Monte Carlo simulations, and constrained the distributions of extrasolar planets in mass $M$ and semimajor axis $a$. If planets are distributed according to a power law with $dN \propto M^{\alpha} a^{\beta} dM da$, normalized to be consistent with radial velocity statistics, we find that a distribution with $\alpha = -1.1$ and $\beta = -0.46$, truncated at 110 AU, is ruled out at the 90% confidence level. These particular values of $\alpha$ and $\beta$ are significant because they represent the most planet-rich case consistent with current statistics from radial velocity observations. With 90% confidence no more than 8.1% of stars like those in our survey have systems with three widely spaced, massive planets like the A-star HR 8799. Our observations show that giant planets in long-period orbits around sun-like stars are rare, confirming the results of shorter-wavelength surveys, and increasing the robustness of the conclusion.

PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS. II. PREDICTIONS FOR OUTER EXTRASOLAR PLANETARY SYSTEMS

We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii beyond 5 AU. Our hypothesis is that dynamical evolution in outer planetary systems is controlled by a combination of planet-planet scattering and planetary interactions with an exterior disk of small bodies ("planetesimals"). Using 5,000 long duration N-body simulations, we follow the evolution of three planets surrounded by a 50 Earth mass primordial planetesimal disk. For large planet masses (above that of Saturn) the influence of the disk is modest, and we recover the observed eccentricity distribution of extrasolar planets (observed primarily at smaller radii). We explain the observed mass dependence of the eccentricity by invoking strong correlations between planet masses in the same system. For lower mass planets we observe diverse dynamical behavior: strong scattering events, sudden jumps in eccentricity due to resonance crossings, and re-circularization of scattered low-mass planets in the disk. We present distributions of the final eccentricity and inclination, and discuss how they vary with planet mass and initial system architecture. We predict a transition to lower eccentricities for low mass planets at radii where disks influence the dynamics. Radial velocity measurements capable of detecting planets with K~5 m/s and periods in excess of 10 years will constrain this regime. We also study the population of resonant and non-resonant multiple planet systems. We show that, among systems with Jupiter-mass planets that avoid close encounters, the planetesimal disk acts as a damping mechanism that frequently populates mean motion resonances. Resonant chains ought to be common among massive planets in outer planetary systems.

Планетарное распределение среднемасштабных атмосферных гравитационных волн по данным спутниковых измерений

Планетарное распределение среднемасштабных атмосферных гравитационных волн по данным спутниковых измерений

Survival and Detectability of Long Period Planets Beyond 100 AU

Direct imaging searches have begun to detect planetary and brown dwarf companions and to place constraints on the presence of giant planets at large separations from their host star. This work helps to motivate such planet searches by predicting a population of young giant planets that could be detectable by direct imaging campaigns. Both the classical core accretion and the gravitational instability model for planet formation are hard-pressed to form such planets in situ . Therefore, direct imaging searches have traditionally appealed to the possibility of in situ planet formation via a large scale gravitational instability. Here, we show that dynamical instabilities among planetary systems that originally formed multiple giant planets much closer to the host star could produce a population of giant planets at large separations. The number and distribution of such planets is a strong function of time, complicating the statistical analysis of direct imaging surveys. The number and radial distribution of such planets is related to the number of giant planets formed per host star and the timescale for the disk evolution. Thus, direct imaging programs with sufficient sensitivity and survey size could place interesting constraints on planet formation models.

Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations

We examine the implications for the distribution of extrasolar planets based on the null results from two of the largest direct imaging surveys published to date. Combining the measured contrast curves from Masciadri et al. (2005) and Biller et al. (2007), we consider what distributions of planet masses and semi-major axes can be ruled out by these data, based on Monte Carlo simulations of planet populations. We can set the following upper limit with 95% confidence: the fraction of stars with planets with semi-major axis between 20 and 100 AU, and mass above 4 M Jup , is 20% or less. Also, with a distribution of planet mass of in the range of 0.5–13 M Jup , we can rule out a power-law distribution for semi-major axis () with index 0 and upper cut-off of 18 AU, and index –0.5 with an upper cut-off of 48 AU. For the distribution suggested by Cumming et al. (2008), a power-law of index –0.61, we can place an upper limit of 75 AU on the semi-major axis distribution.

A Survey of Multiple Planet Systems

As of August 2008, over 30 multiple exoplanet systems are known, and 28% of stars with planets show significant evidence of a second companion. I briefly review these 30 systems individually, broadly grouping them into five categories: 1) systems with 3 or more giant (Msini > 0.2 M_Jup) planets, 2) systems with two giant planets in mean motion resonance (MMR), 3) systems with two giant planets not in MMR but whose dynamical evolution is affected by planet-planet interactions, 4) highly hierarchical systems, having two giant planets with very large period ratios (> 30:1), and 5) systems of ``Super-Earths'', containing only planets with (Msini < 20 M_Earth). It now appears that eccentricities are not markedly higher among planets in known multiple planet systems, and that planets with Msini < 1 M_Jup have lower eccentricities than more massive planets. The distribution of semimajor axes for planets in multiplanet systems does not show the 3-day pile-up or the 1 AU "jump" of the apparently-single planet distribution.

THE ORBITAL EVOLUTION OF GAS GIANT PLANETS AROUND GIANT STARS

Recent surveys have revealed a lack of close-in planets around evolved stars more massive than 1.2 Msun. Such planets are common around solar-mass stars. We have calculated the orbital evolution of planets around stars with a range of initial masses, and have shown how planetary orbits are affected by the evolution of the stars all the way to the tip of the Red Giant Branch (RGB). We find that tidal interaction can lead to the engulfment of close-in planets by evolved stars. The engulfment is more efficient for more-massive planets and less-massive stars. These results may explain the observed semi-major axis distribution of planets around evolved stars with masses larger than 1.5 Msun. Our results also suggest that massive planets may form more efficiently around intermediate-mass stars.

GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS

We present models of giant planet migration in evolving protoplanetary disks. Our disks evolve subject to viscous transport of angular momentum and photoevaporation, while planets undergo Type II migration. We use a Monte Carlo approach, running large numbers of models with a range in initial conditions. We find that relatively simple models can reproduce both the observed radial distribution of extra-solar giant planets, and the lifetimes and accretion histories of protoplanetary disks. The use of state-of-the-art photoevaporation models results in a degree of coupling between planet formation and disk clearing, which has not been found previously. Some accretion across planetary orbits is necessary if planets are to survive at radii <~1.5AU, and if planets of Jupiter mass or greater are to survive in our models they must be able to form at late times, when the disk surface density in the formation region is low. Our model forms two different types of "transitional" disks, embedded planets and clearing disks, which show markedly different properties. We find that the observable properties of these systems are broadly consistent with current observations, and highlight useful observational diagnostics. We predict that young transition disks are more likely to contain embedded giant planets, while older transition disks are more likely to be undergoing disk clearing.

Probability distribution of terrestrial planets in habitable zones around host stars

With more and more exoplanets being detected, it is paid closer attention to whether there are lives outside solar system. We try to obtain habitable zones and the probability distribution of terrestrial planets in habitable zones around host stars. Using Eggleton's code, we calculate the evolution of stars with masses less than 4.00 \mo. We also use the fitting formulae of stellar luminosity and radius, the boundary flux of habitable zones, the distribution of semimajor axis and mass of planets and the initial mass function of stars. We obtain the luminosity and radius of stars with masses from 0.08 to 4.00 \mo, and calculate the habitable zones of host stars, affected by stellar effective temperature. We achieve the probability distribution of terrestrial planets in habitable zones around host stars. We also calculate that the number of terrestrial planets in habitable zones of host stars is 45.5 billion, and the number of terrestrial planets in habitable zones around K type stars is the most, in the Milky Way.

The SOPHIE search for northern extrasolar planets

We report on the discovery of a substellar companion or a massive Jupiter orbiting the G5V star HD 16760 using the spectrograph <i>SOPHIE<i/> installed on the OHP 1.93-m telescope. Characteristics and performances of the spectrograph are presented, as well as the <i>SOPHIE<i/> exoplanet consortium program. With a minimum mass of 14.3 , an orbital period of 465 days and an eccentricity of 0.067, HD 16760b seems to be located just at the end of the mass distribution of giant planets, close to the planet/brown-dwarf transition. Its quite circular orbit supports a formation in a gaseous protoplanetary disk.

ORBITAL EVOLUTION OF A PARTICLE INTERACTING WITH A SINGLE PLANET IN A PROTOPLANETARY DISK

We investigate the motion of a particle around a low mass planet embedded in a non-turbulent gaseous disk. We take into account the effect of the gas structure that is modified by the gravitational interaction between the planet. We derive an analytic formula that describes the change of the semi-major axis of the particle due to the encounter with the planet using local approximation in distant encounter regime. Our final formula includes the effects of steady, axisymmetric radial gas flow, the global gas pressure gradient in the disk, planet gravity, and the structure of the gas flow modified by the planet's gravity. We compare the analytic results with numerical calculations, and indicate that our formula well describes the secular evolution of the dust particles' semi-major axes well, especially for small particles with large drag coefficient. We discuss the conditions for dust gap opening around a low mass planet and radial distribution of dust particles. Our formula may provide a useful tool for calculating radial distribution of particles in a disk around the planet.

ON THE SEMIMAJOR AXIS DISTRIBUTION OF EXTRASOLAR GAS GIANT PLANETS: WHY HOT JUPITERS ARE RARE AROUND HIGH-MASS STARS

Based on a suite of Monte Carlo simulations, I show that a stellar-mass-dependent lifetime of the gas disks from which planets form can explain the lack of hot Jupiters/close-in giant planets around high-mass stars and other key features of the observed semimajor axis distribution of radial velocity-detected giant planets. Using reasonable parameters for the Type II migration rate, regions of planet formation, and timescales for gas giant core formation, I construct synthetic distributions of Jovian planets. A planet formation/migration model assuming a stellar-mass-dependent gas disk lifetime reproduces key features in the observed distribution by preferentially stranding planets around high-mass stars at large semimajor axes.

RAPID FORMATION OF ICY SUPER-EARTHS AND THE CORES OF GAS GIANT PLANETS

We describe a coagulation model that leads to the rapid formation of super-Earths and the cores of gas giant planets. Interaction of collision fragments with the gaseous disk is the crucial element of this model. The gas entrains small collision fragments, which rapidly settle to the disk midplane. Protoplanets accrete the fragments and grow to masses 1 M ⊕ in ~ 1 Myr. Our model explains the mass distribution of planets in the solar system and predicts that super-Earths form more frequently than gas giants in low-mass disks.

Extrasolar Planet Eccentricities from Scattering in the Presence of Residual Gas Disks

Gravitational scattering between massive planets has been invoked to explain the eccentricity distribution of extrasolar planets. For scattering to occur, the planets must either form in -- or migrate into -- an unstable configuration. In either case, it is likely that a residual gas disk, with a mass comparable to that of the planets, will be present when scattering occurs. Using explicit hydrodynamic simulations, we study the impact of gas disks on the outcome of two-planet scattering. We assume a specific model in which the planets are driven toward instability by gravitational torques from an outer low mass disk. We find that the accretion of mass and angular momentum that occurs when a scattered planet impacts the disk can strongly influence the subsequent dynamics by reducing the number of close encounters. The eccentricity of the innermost surviving planet at the epoch when the system becomes Hill stable is not substantially altered from the gas-free case, but the outer planet is circularized by its interaction with the disk. The signature of scattering initiated by gas disk migration is thus a high fraction of low eccentricity planets at larger radii accompanying known eccentric planets. Subsequent secular evolution of the two planets in the presence of damping can further damp both eccentricities, and tends to push systems away from apsidal alignment and toward anti-alignment. We note that the late burst of accretion when the outer planet impacts the disk is in principle observable, probably via detection of a strong near-IR excess in systems with otherwise weak disk and stellar accretion signatures.

Classification of celestial bodies within planetary systems

This paper suggests a set of general criteria for classifying celestial bodies that are elements of planetary systems. An additional criterion based on the phenomenological formula of the distribution of planets in the Solar system is suggested for the Solar system for ascertaining whether celestial bodies belong to the category of planets or dwarf planets.