Strong Dynamical Interactions Research Articles

Black hole binary mergers in dense star clusters: the importance of primordial binaries

ABSTRACT Dense stellar clusters are expected to house the ideal conditions for binary black hole (BBH) formation, both through binary stellar evolution and through dynamical encounters. We use theoretical arguments as well as N-body simulations to make predictions for the evolution of BBHs formed through stellar evolution inside clusters from the cluster birth (which we term primordial binaries), and for the sub-population of merging BBHs. We identify three key populations: (i) BBHs that form in the cluster, and merge before experiencing any strong dynamical interaction; (ii) binaries that are ejected from the cluster after only one dynamical interaction; and (iii) BBHs that experience more than one strong interaction inside the cluster. We find that populations (i) and (ii) are the dominant source of all BBH mergers formed in clusters with escape velocity vesc ≤ 30 $\mathrm{km\, s^{-1}}$. At higher escape velocities, dynamics are predicted to play a major role both for the formation and subsequent evolution of BBHs. Finally, we argue that for sub-Solar metallicity clusters with vesc ≲ 100 $\mathrm{km\, s^{-1}}$, the dominant form of interaction experienced by primordial BBHs (BBHs formed from primordial binaries) within the cluster is with other BBHs. The complexity of these binary–binary interactions will complicate the future evolution of the BBH and influence the total number of mergers produced.

TIC 219006972: a compact, coplanar quadruple star system consisting of two eclipsing binaries with an outer period of 168 d

ABSTRACT We present the discovery of a new highly compact quadruple star system, TIC 219006972, consisting of two eclipsing binary stars with orbital periods of 8.3 and 13.7 d, and an outer orbital period of only 168 d. This period is a full factor of 2 shorter than the quadruple with the shortest outer period reported previously, VW LMi, where the two binary components orbit each other every 355 d. The target was observed by Transiting Exoplanet Survey Satellite in full-frame images in sectors 14–16, 21–23, 41, 48, and 49, and produced two sets of primary and secondary eclipses. These show strongly non-linear eclipse timing variations (ETVs) with an amplitude of ∼0.1 d, where the ETVs of the primary and secondary eclipses and of the two binaries are all largely positively correlated. This highlights the strong dynamical interactions between the two binaries and confirms the compact quadruple configuration of TIC 219006972. The two eclipsing binaries are nearly circular, whereas the quadruple system has an outer eccentricity of about 0.25. The entire system is nearly edge-on, with a mutual orbital inclination between the two eclipsing binary star systems of about 1 deg.

A Census of Outflow to Magnetic Field Orientations in Nearby Molecular Clouds

We define a sample of 200 protostellar outflows showing blue- and redshifted CO emission in the nearby molecular clouds Ophiuchus, Taurus, Perseus, and Orion, to investigate the correlation between outflow orientations and local, but relatively large-scale, magnetic field directions traced by Planck 353 GHz dust polarization. At high significance (p ∼ 10−4), we exclude a random distribution of relative orientations and find that there is a preference for alignment of projected plane of sky outflow axes with magnetic field directions. The distribution of relative position angles peaks at ∼30° and exhibits a broad dispersion of ∼50°. These results indicate that magnetic fields have dynamical influence in regulating the launching and/or propagation directions of outflows. However, the significant dispersion around perfect alignment orientation implies that there are large measurement uncertainties and/or a high degree of intrinsic variation caused by other physical processes, such as turbulence or strong stellar dynamical interactions. Outflow to magnetic field alignment is expected to lead to a correlation in the directions of nearby outflow pairs, depending on the degree of order of the field. Analyzing this effect, we find limited correlation, except on relatively small scales ≲0.5 pc. Furthermore, we train a convolutional neural network to infer the inclination angle of outflows with respect to the line of sight and apply it to our outflow sample to estimate their full 3D orientations. We find that the angles between outflow pairs in 3D space also show evidence of small-scale alignment.

Massive central galaxies of galaxy groups in the Romulus simulations: an overview of galaxy properties at z = 0

ABSTRACT Contrary to many stereotypes about massive galaxies, observed brightest group galaxies (BGGs) are diverse in their star formation rates, kinematic properties, and morphologies. Studying how they evolve into and express such diverse characteristics is an important piece of the galaxy formation puzzle. We use a high-resolution cosmological suite of simulations Romulus and compare simulated central galaxies in group-scale haloes at z = 0 to observed BGGs. The comparison encompasses the stellar mass–halo mass relation, various kinematic properties and scaling relations, morphologies, and the star formation rates. Generally, we find that Romulus reproduces the full spectrum of diversity in the properties of the BGGs very well, albeit with a tendency toward lower than the observed fraction of quenched BGGs. We find both early-type S0 and elliptical galaxies as well as late-type disc galaxies; we find Romulus galaxies that are fast-rotators as well as slow-rotators; and we observe galaxies transforming from late-type to early-type following strong dynamical interactions with satellites. We also carry out case studies of selected Romulus galaxies to explore the link between their properties, and the recent evolution of the stellar system as well as the surrounding intragroup/circumgalactic medium. In general, mergers/strong interactions quench star-forming activity and disrupt the stellar disc structure. Sometimes, however, such interactions can also trigger star formation and galaxy rejuvenation. Black hole feedback can also lead to a decline of the star formation rate but by itself, it does not typically lead to complete quenching of the star formation activity in the BGGs.

Pairing instabilities of the Yukawa-SYK models with controlled fermion incoherence

The interplay of non-Fermi liquid and superconductivity born out of strong dynamical interactions is at the heart of the physics of unconventional superconductivity. As a solvable platform of the strongly correlated superconductors, we study the pairing instabilities of the Yukawa-Sachdev-Ye-Kitaev (Yukawa-SYK) model, which describes spin-1/2 fermions coupled to bosons by the random, all-to-all, spin-independent and dependent Yukawa interactions. In contrast to the previously studied models, the random Yukawa couplings are sampled from a collection of Gaussian ensembles whose variances follow a continuous distribution rather than being fixed to a constant. By tuning the analytic behaviour of the distribution, we could control the fermion incoherence to systematically examine various normal states ranging from the Fermi liquid to non-Fermi liquids that are different from the conformal solution of the SYK model with a constant variance. Using the linearised Eliashberg theory, we show that the onset of the unconventional spin-triplet pairing is preferred with the spin-dependent interactions while all pairing channels show instabilities with the spin-independent interactions. Although the interactions shorten the lifetime of the fermions in the non-Fermi liquid, the same interactions also dress the bosons to strengthen the tendency to pair the incoherent fermions. As a consequence, the onset temperature T_cTc of the pairing is enhanced in the non-Fermi liquid compared to the case of the Fermi liquid.

Structure and dynamics of the inner nebula around the symbiotic stellar system R Aquarii

Aims. We investigate the structure, dynamics, and chemistry of the molecule-rich nebula around the stellar symbiotic system R Aqr, which is significantly affected by the presence of a white dwarf (WD) companion. We study the effects of the strong dynamical interaction between the AGB wind and the WD and of photodissociation by the WD UV radiation on the circumstellar shells. Methods. We obtained high-quality ALMA maps of the 12CO J = 2−1, J = 3−2, and J = 6−5 lines and of 13CO J = 3−2. The maps were analyzed by means of a heuristic 3D model that is able to reproduce the observations. In order to interpret this description of the molecule-rich nebula, we performed sophisticated calculations of hydrodynamical interaction and photoinduced chemistry. Results. We find that the CO-emitting gas is distributed within a relatively small region ≲1.″5. Its structure consists of a central dense component plus strongly disrupted outer regions, which seem to be parts of spiral arms that are highly focused on the orbital plane. The structure and dynamics of these spiral arms are compatible with our hydrodynamical calculations. We argue that the observed nebula is the result of the dynamical interaction between the wind and the gravitational attraction of the WD. We also find that UV emission from the hot companion efficiently photodissociates molecules except in the densest and best-shielded regions, that is, in the close surroundings of the AGB star and some shreds of the spiral arms from which the detected lines come. We can offer a faithful description of the distribution of nebular gas in this prototypical source, which will be a useful template for studying material around other tight binary systems.

Formation of Orion fingers

ABSTRACT ‘Orion fingers’ are a system of dozens of bow shocks, with the wings of shocks pointing to a common system of origin, which is centred on a dynamically disintegrating system of several massive stars. The shock heads propagate with velocities of up to 300–400 km s−1, but the formation and physical properties of the ‘bullets’ leading the shocks are not known. Here, we summarize two possible scenarios for the formation of the ‘bullets’ and the resulting bow shocks (‘fingers’). In the first scenario, bullets are self-gravitating, Jupiter-mass objects that were formed rapidly and then ejected during the strong dynamical interactions of massive stars and their discs. This scenario naturally explains the similar time-scales for the outflow of bullets and for the dynamical interaction of the massive stars, but has some difficulty explaining the observed high velocities of the bullets. In the second scenario, bullets are formed via hydrodynamic instabilities in a massive, infrared-driven wind, naturally explaining the high velocities and the morphology of outflow, but the bullets are not required to be self-gravitating. The processes that created the Orion fingers are likely not unique to this particular star-forming region and may result in free-floating, high-velocity, core-less planets.

Cosmological evolution of orientations of cluster-sized dark matter haloes and their central galaxies in the Horizon-AGN simulation

Abstract It is known observationally that the major axes of galaxy clusters and their brightest cluster galaxies are roughly aligned with each other. To understand the origin of the alignment, we identify 40 cluster-sized dark matter (DM) haloes with masses higher than 5 × 1013 M⊙ and their central galaxies (CGs) at z ≈ 0 in the Horizon-AGN cosmological hydrodynamical simulation. We trace the progenitors at 50 different epochs between 0 < z < 5. We then fit their shapes and orientations with a triaxial ellipsoid model. While the orientations of both DM haloes and CGs change significantly due to repeated mergers and mass accretions, their relative orientations are well aligned at each epoch even at high redshifts, z > 1. The alignment becomes tighter with cosmic time; the major axes of the CGs and their host DM haloes at present are aligned on average within ∼30○ in the three dimensional space and ∼20○ in the projected plane. The orientations of the major axes of DM haloes on average follow one of the eigen-vectors of the surrounding tidal field that corresponds to the slowest collapsing (or even stretching) mode, and the alignment with the tidal field also becomes tighter. This implies that the orientations of CGs and DM haloes at the present epoch are largely imprinted in the primordial density field of the Universe, whereas strong dynamical interactions such as mergers are important to explain their mutual alignment at each epoch.

Are most Cataclysmic Variables in Globular Clusters dynamically formed?

AbstractWe have been investigating populations of cataclysmic variables (CVs) in a set of more than 300 globular cluster (GC) models evolved with themoccacode.[-120pt] One of the main questions we have intended to answer is whether most CVs in GCs are dynamically formed or not. Contrary to what has been argued for a long time, we found that dynamical destruction of primordial CV progenitors is much stronger in GCs than dynamical formation of CVs. In particular, we found that, on average, the detectable CV population is predominantly composed of CVs formed via a typical common envelope phase (≳70 per cent). However, core-collapsed models tend to have higher fractions of bright CVs than non-core-collapsed ones, which suggests then that the formation of CVs is indeed slightly favoured through strong dynamical interactions in core-collapsed GCs, due to the high stellar densities in their cores.

Kepler-411: a four-planet system with an active host star

We present a detailed characterization of the Kepler-411 system (KOI 1781). This system was previously known to host two transiting planets: one with a period of 3 days (R = 2.4 R⊕; Kepler-411b) and one with a period of 7.8 days (R = 4.4 R⊕; Kepler-411c), as well as a transiting planetary candidate with a 58-day period (R = 3.3 R⊕; KOI 1781.03) from Kepler photometry. Here, we combine Kepler photometry data and new transit timing variation (TTV) measurements from all the Kepler quarters with previous adaptive-optics imaging results, and dynamical simulations, in order to constrain the properties of the Kepler-411 system. From our analysis, we obtain masses of 25.6 ± 2.6 M⊕ for Kepler-411b and 26.4 ± 5.9 M⊕ for Kepler-411c, and we confirm the planetary nature of KOI 1781.03 with a mass of 15.2 ± 5.1 M⊕, hence the name Kepler-411d. Furthermore, by assuming near-coplanarity of the system (mutual inclination below 30°), we discover a nontransiting planet, Kepler-411e, with a mass of 10.8 ± 1.1 M⊕ on a 31.5-day orbit, which has a strong dynamical interaction with Kepler-411d. With densities of 1.71 ± 0.39 g cm−3 and 2.32 ± 0.83 g cm−3, both Kepler-411c and Kepler-411d belong to the group of planets with a massive core and a significant fraction of volatiles. Although Kepler-411b has a sub-Neptune size, it belongs to the group of rocky planets.

Kepler Object of Interest Network

Context. The Kepler Object of Interest Network (KOINet) is a multi-site network of telescopes around the globe organised to follow up transiting planet-candidate Kepler objects of interest (KOIs) with large transit timing variations (TTVs). Its main goal is to complete their TTV curves, as the Kepler telescope no longer observes the original Kepler field. Aims. Combining Kepler and new ground-based transit data we improve the modelling of these systems. To this end, we have developed a photodynamical model, and we demonstrate its performance using the Kepler-9 system as an example. Methods. Our comprehensive analysis combines the numerical integration of the system’s dynamics over the time span of the observations along with the transit light curve model. This provides a coherent description of all observations simultaneously. This model is coupled with a Markov chain Monte Carlo algorithm, allowing for the exploration of the model parameter space. Results. Applied to the Kepler-9 long cadence data, short cadence data, and 13 new transit observations collected by KOINet between the years 2014 and 2017, our modelling provides well constrained predictions for the next transits and the system’s parameters. We have determined the densities of the planets Kepler-9b and 9c to the very precise values of ρb = 0.439 ± 0.023 g cm−3 and ρc = 0.322 ± 0.017 g cm−3. Our analysis reveals that Kepler-9c will stop transiting in about 30 yr due to strong dynamical interactions between Kepler-9b and 9c, near 2:1 resonance, leading to a periodic change in inclination. Conclusions. Over the next 30 years, the inclination of Kepler-9c (-9b) will decrease (increase) slowly. This should be measurable by a substantial decrease (increase) in the transit duration, in as soon as a few years’ time. Observations that contradict this prediction might indicate the presence of additional objects in this system. If this prediction turns out to be accurate, this behaviour opens up a unique chance to scan the different latitudes of a star: high latitudes with planet c and low latitudes with planet b.

Analysis of the exoplanet containing system Kepler-13

We have applied the close binary system analysis program WinFitter, with its physically detailed fitting function, to an intensive study of the complex multiple system Kepler-13 using photometry data from all 13 short cadence quarters downloaded from the NASA Exoplanet Archive (NEA) ( http://exoplanetarchive.ipac.caltech.edu ). The data-point error of our normalized, phase-sequenced and binned (380 points per bin: 0.00025 phase interval) flux values, at 14 ppm, allows the model’s specification for the mean reference flux level of the system to a precision better than 1 ppm. Our photometrically derived values for the mass and radius of KOI13.01 are $6.8\pm0.6~\mbox{M}_{\mathrm{J}}$ and $1.44\pm0.04~\mbox{R}_{\mathrm{J}}$ . The star has a radius of $1.67\pm0.05~\mbox{R}_{\odot}$ . Our modelling sets the mean of the orbital inclination $i$ at $94.35\pm0.14^{\circ}$ , with the star’s mean precession angle $\phi_{p}$ — $49.1\pm5.0^{\circ}$ and obliquity $\theta_{o}$ $67.9 \pm 3.0^{\circ}$ , though there are known ambiguities about the sense in which such angles are measured. Our findings did not confirm secular variation in the transit modelling parameters greater than their full correlated errors, as argued by previous authors, when each quarter’s data was best-fitted with a determinable parameter set without prejudice. However, if we accept that most of the parameters remain the same for each transit, then we could confirm a small but steady diminution in the cosine of the orbital inclination over the 17 quarter timespan. This is accompanied by a slight increase of the star’s precession angle (less negative), but with no significant change in the obliquity of its spin axis. There are suggestions of a history of strong dynamical interaction with a highly distorted planet rotating in a 3:2 resonance with its revolution, together with a tidal lag of $\sim30~\mbox{deg}$ . The mean precessional period is derived to be about 1000 y, but at the present time the motion of the star’s rotation axis appears to be supporting the gravitational torque, rather than providing the balance against it that would be expected over long periods of time. The planet has a small but detectable backwarming effect on the star, which helps to explain the difference in brightness just after transit and just before occultation eclipses. In assessing these findings it is recognized that sources of uncertainty remain, notably with possible inherent micropulsational effects, variations from other components of the multiple star, stellar activity, differential rotation and the neglect of higher order terms (than $r_{1}^{5}$ ) in the fitting function, where $r_{1}$ is the ratio of the radius of the star to the mean orbital separation of planet and host star.

Mocca code for star cluster simulations – V. Initial globular cluster conditions influence on blue stragglers

The paper presents an analysis of properties of populations of blue stragglers (BSs) in evolving globular clusters, based on numerical simulations done with the MOCCA code for various initial globular clusters conditions. We find that various populations of BSs strongly depend on the initial semi-major axes distributions. With a significant number of compact binaries, the number of evolutionary BSs can be also significant. In turn, for semi-major axes distributions preferring binaries with wider orbits, dynamical BSs are the dominant ones. Their formation scenario is very distinct: for wide binaries the number of dynamical interactions is significantly larger. Most interactions are weak and increase only slightly the eccentricities. However, due to a large number of such interactions, the eccentricities of a number of binaries finally get so large that the stars collide. We study how larger initial clusters' concentrations influence the BSs. Besides the expected increase of the number of dynamically created BSs (for denser GCs the probabilities of strong dynamical interactions and collisions are higher), we find that the number of the evolutionary BSs is not affected even by very high initial concentrations. This has a very important implication on observations - it supports the theory that the evolutionary BSs are the result of the unperturbed evolution of the primordial binaries. In addition, the paper presents the evolution of the ratio between the number of BSs in binaries and as single stars R_B/S. For a vast diversity of models, the ratio R_B/S approaches the value ~0.4. Additionally, we identified two subgroups which differ in the initial semi-major axes distributions. The first group starts with a high ratio R_B/S, it decreases with time and settles around 0.4. The second group starts with lower values of the ratio R_B/S ... . (etc., abstract continues)

“Long-distance” H/D isotopic self-organization phenomena in scope of the infrared spectra of hydrogen-bonded terephthalic and phthalic acid crystals

This paper deals with the experimental and theoretical studies of abnormal properties of terephthalic acid (TAC) and phthalic acid (PAC) crystals manifested in the H/D isotopic exchange. The widely utilized deuteration routine appeared to be insufficiently effective in the case of the h6-TAC isotopomer. In the case of the d4-TAC derivative the isotopic exchange process occurred noticeably more effectively. In contrast, both isotopomers of PAC, h6 and d4, appeared much more susceptible for deuteration. A theoretical model was elaborated describing “long-distance” dynamical co-operative interactions involving hydrogen bonds in TAC and PAC crystals. The model assumes extremely strong dynamical co-operative interactions of hydrogen bonds from the adjacent (COOH)2 cycles. This leads to an additional stabilization of h6–TAC molecular chains. The interaction energies affect the chemical equilibrium of the H/D isotopic exchange. The model predicts a differentiated influence of the H and D atoms linked to the aromatic rings on to the process. In this approach the totally-symmetric CH bond stretching vibrations and the proton stretching totally symmetric vibrations couple with the π-electronic motions. It was also shown that identical hydrogen isotope atoms, H or D, in whole TAC molecules, noticeably enlarge the energy of the dynamical co-operative interactions in the crystals, in contrast to the case of different hydrogen isotopes present in the carboxyl groups and linked to the aromatic rings. The “long-distance” dynamical co-operative interactions in PAC crystals were found of a minor importance due to the electronic properties of PAC molecules.

MOCCA-SURVEY database I. Accreting white dwarf binary systems in globular clusters – I. Cataclysmic variables – present-day population

In this paper, which is the first in a series of papers associated with cataclysmic variables and related objects, we introduce the CATUABA code, a numerical machinery written for analysis of the MOCCA simulations, and show some first results by investigating the present-day population of cataclysmic variables in globular clusters. Emphasis was given on their properties and the observational selection effects when observing and detecting them. In this work we analysed in this work six models, including three with Kroupa distributions of the initial binaries. We found that for models with Kroupa initial distributions, considering the standard value of the efficiency of the common envelope phase adopted in BSE, no single cataclysmic variable was formed only via binary stellar evolution, i. e., in order to form them, strong dynamical interactions have to take place. We show and explain why this is inconsistent with observational and theoretical results. Our results indicate that the population of cataclysmic variables in globular clusters is, mainly, in the last stage of their evolution and observational selection effects can drastically change the expected number of observed cataclysmic variables. We show that the probability of observing them during the outbursts is extremely small and conclude that the best way of looking for cataclysmic variables in globular clusters is by searching for variabilities during quiescence, instead of during outbursts. For that, one would need a very deep observation which could reach magnitudes $\gtrsim$ 27 mag. Finally, we argue that cataclysmic variables in globular clusters are not necessarily magnetic.

MOCCA code for star cluster simulations – IV. A new scenario for intermediate mass black hole formation in globular clusters

We discuss a new scenario for the formation of intermediate mass black holes in dense star clusters. In this scenario, intermediate mass black holes are formed as a result of dynamical interactions of hard binaries containing a stellar mass black hole, with other stars and binaries. We discuss the necessary conditions to initiate the process of intermediate mass black hole formation and the influence of an intermediate mass black hole on the host global globular cluster properties. We discuss two scenarios for intermediate mass black hole formation. The SLOW and FAST scenarios. They occur later or earlier in the cluster evolution and require smaller or extremely large central densities, respectively. In our simulations, the formation of intermediate mass black holes is highly stochastic. In general, higher formation probabilities follow from larger cluster concentrations (i.e. central densities). We further discuss possible observational signatures of the presence of intermediate mass black holes in globular clusters that follow from our simulations. These include the spatial and kinematic structure of the host cluster, possible radio, X-ray and gravitational wave emissions due to dynamical collisions or mass-transfer and the creation of hypervelocity main sequence escapers during strong dynamical interactions between binaries and an intermediate mass black hole. All simulations discussed in this paper were performed with the MOCCA Monte Carlo code. MOCCA accurately follows most of the important physical processes that occur during the dynamical evolution of star clusters but, as with other dynamical codes, it approximates the dissipative processes connected with stellar collisions and binary mergers.

BLUE STRAGGLER STAR POPULATIONS IN GLOBULAR CLUSTERS. I. DYNAMICAL PROPERTIES OF BLUE STRAGGLER STARS IN NGC 3201, NGC 6218, AND ω CENTAURI

We present the first dynamical study of Blue Straggler Stars (BSSs) in three Galactic globular clusters, NGC\,3201, NGC\,5139 ($\omega$Cen), and NGC\,6218, based on medium-resolution spectroscopy (R 10000) obtained with IMACS. Our BSS candidate selection technique uses HST/ACS and ESO/WFI photometric data out to $>\!4.5\,r_c$. We use radial velocity measurements to discard non-members and achieve a success rate of $\sim93\%$, which yields a sample of 116 confirmed BSSs. Using the penalized pixel fitting method (pPXF) we measure the $v\sin(i)$ values of the sample BSSs and find their distribution functions peaked at slow velocities with a long tail towards fast velocities in each globular cluster. We find that the BSSs in NGC\,3201 and NGC\,6218 which show $v\sin(i)\!>\!50$ km s$^{-1}$ are all found in the central cluster regions, inside a projected $2\,r_c$, of their parent clusters. We find a similar result in $\omega$Cen for BSSs with $v\sin(i)\!>\!70$ km s$^{-1}$ which are all, except for two, concentrated inside $2\,r_c$. In all globular clusters we find rapidly rotating BSSs that have relatively high differential radial velocities which likely put them on hyperbolic orbits, suggestive of strong dynamical interactions in the past. We estimate that all the observed rapidly rotating BSSs are likely to form in their central cluster regions no longer than $\sim\!300$ Myr ago. Using dereddened $V\!-\!I$ colors of our photometric selection we show that blue BSSs in $\omega$Cen with $(V-I)_0$<0.25 mag show a significantly increased $v\sin(i)$ dispersion compared with their red counterparts and all other BSSs in our sample, therefore strongly implying that fast rotating BSSs in $\omega$Cen are preferentially bluer, i.e. more massive. This may indicate that this particular blue BSS population was formed in an unique formation event and/or through an unique mechanism.

THE PLANETARY SYSTEM TO KIC 11442793: A COMPACT ANALOGUE TO THE SOLAR SYSTEM

We announce the discovery of a planetary system with 7 transiting planets around a Kepler target, a current record for transiting systems. Planets b, c, e and f are reported for the first time in this work. Planets d, g and h were previously reported in the literature (Batalha et al. 2013), although here we revise their orbital parameters and validate their planetary nature. Planets h and g are gas giants and show strong dynamical interactions. The orbit of planet g is perturbed in such way that its orbital period changes by 25.7h between two consecutive transits during the length of the observations, which is the largest such perturbation found so far. The rest of the planets also show mutual interactions: planets d, e and f are super-Earths close to a mean motion resonance chain (2:3:4), and planets b and c, with sizes below 2 Earth radii, are within 0.5% of the 4:5 mean motion resonance. This complex system presents some similarities to our Solar System, with small planets in inner orbits and gas giants in outer orbits. It is, however, more compact. The outer planet has an orbital distance around 1 AU, and the relative position of the gas giants is opposite to that of Jupiter and Saturn, which is closer to the expected result of planet formation theories. The dynamical interactions between planets are also much richer.

STABILITY OF SATELLITES IN CLOSELY PACKED PLANETARY SYSTEMS

We perform numerical integrations of four-body (star, planet, planet, satellite) systems to investigate the stability of satellites in planetary Systems with Tightly-packed Inner Planets (STIPs). We find that the majority of closely-spaced stable two-planet systems can stably support satellites across a range of parameter-space which is only slightly decreased compared to that seen for the single-planet case. In particular, circular prograde satellites remain stable out to $\sim 0.4 R_H$ (where $R_H$ is the Hill Radius) as opposed to $\sim 0.5 R_H$ in the single-planet case. A similarly small restriction in the stable parameter-space for retrograde satellites is observed, where planetary close approaches in the range 2.5 to 4.5 mutual Hill radii destabilize most satellites orbits only if $a\sim 0.65 R_H$. In very close planetary pairs (e.g. the 12:11 resonance) the addition of a satellite frequently destabilizes the entire system, causing extreme close-approaches and the loss of satellites over a range of circumplanetary semi-major axes. The majority of systems investigated stably harbored satellites over a wide parameter-space, suggesting that STIPs can generally offer a dynamically stable home for satellites, albeit with a slightly smaller stable parameter-space than the single-planet case. As we demonstrate that multi-planet systems are not a priori poor candidates for hosting satellites, future measurements of satellite occurrence rates in multi-planet systems versus single-planet systems could be used to constrain either satellite formation or past periods of strong dynamical interaction between planets.

Kepler's missing planets

We investigate the distributions of the orbital period ratios of adjacent planets in high multiplicity \kepler\ systems (four or more planets) and low multiplicity systems (two planets). Modeling the low multiplicity sample as essentially equivalent to the high multiplicity sample, but with unobserved intermediate planets, we find some evidence for an excess of planet pairs between the 2:1 and 3:1 Mean Motion Resonances in the low multiplicity sample. This possible excess may be the result of strong dynamical interactions near these or other resonances or it may be a byproduct of other evolutionary events or processes such as planetary collisions. Three planet systems show a significant excess of planets near the 2:1 Mean Motion Resonance that is not as prominent in either of the other samples. This observation may imply a correlation between strong dynamical interactions and observed planet number---perhaps a relationship between resonance pairs and the inclinations or orbital periods of additional planets. The period ratio distributions can also be used to identify targets to search for missing planets in the each of the samples, the presence or absence of which would have strong implications for planet formation and dynamical evolution models.