High Eccentricity Research Articles

Low-high latitude interaction forcing on the evolution of the 400 kyr cycle in East Asian winter monsoon records during the last 2.8 Myr

Variability of the East Asian winter monsoon (EAWM), stronger during glacials and weaker during interglacials, has been tightly linked to the wax and wane of the Northern Hemisphere ice sheets (NHIS) via the Siberian High over the last 2.8 million years (Myr). However, the long eccentricity cycle (ca. 400 kyr) in the EAWM record from the late Pliocene to early-Pleistocene (2.8–1.2 Ma) could not be linked to NHIS changes, which lacked the long eccentricity cycle in the Pleistocene. Here, we present the first low latitude EAWM record of the last 2.8 Myr using surface and subsurface temperature difference from the northern South China Sea to evaluate interactions between tropical ocean and EAWM changes. The results show that the EAWM variability displayed significant 400 kyr cycle between 2.8 Ma and 1.2 Ma, with weak (strong) EAWM during high (low) earth orbital eccentricity state. A super El Niño–Southern Oscillation (ENSO) proxy record, calculated using west-east equatorial Pacific sea surface temperature differences, revealed 400 kyr cycles throughout the last 2.8 Myr with warm phase during high eccentricity state. Thus, we propose that super ENSO mean state strongly modulated the EAWM strength through remote forcing to generate the 400 kyr cycle between 2.8 Ma and 1.2 Ma, while low NHIS volume was not sufficient to dominate the EAWM variation as it did over the last 0.9 Myr with 100 kyr cycles in dominance.

The gravitational wave background from massive black hole binaries in Illustris: spectral features and time to detection with pulsar timing arrays

Pulsar Timing Arrays (PTA) around the world are using the incredible consistency of millisecond pulsars to measure low frequency gravitational waves from (super)Massive Black Hole (MBH) binaries. We use comprehensive MBH merger models based on cosmological hydrodynamic simulations to predict the spectrum of the stochastic Gravitational-Wave Background (GWB). We use real Time-of-Arrival (TOA) specifications from the European, NANOGrav, Parkes, and International PTA (IPTA) to calculate realistic times to detection of the GWB across a wide range of model parameters. In addition to exploring the parameter space of environmental hardening processes (in particular: stellar scattering efficiencies), we have expanded our models to include eccentric binary evolution which can have a strong effect on the GWB spectrum. Our models show that strong stellar scattering and high characteristic eccentricities enhance the GWB strain amplitude near the PTA sensitive "sweet-spot" (near the frequency $f = 1 \, \mathrm{yr}^{-1}$), slightly improving detection prospects in these cases. While the GWB $amplitude$ is degenerate between cosmological and environmental parameters, the location of a spectral turnover at low frequencies ($f \lesssim 0.1 \, \mathrm{yr}^{-1}$) is strongly indicative of environmental coupling. At high frequencies ($f\gtrsim 1 \, \mathrm{yr}^{-1}$), the GWB spectral index can be used to infer the number density of sources and possibly their eccentricity distribution. Even with merger models that use pessimistic environmental and eccentricity parameters, if the current rate of PTA expansion continues, we find that the International PTA is highly likely to make a detection within about 10 years.

Mean Motion Resonances at High Eccentricities: The 2:1 and the 3:2 Interior Resonances

Abstract Mean motion resonances (MMRs) play an important role in the formation and evolution of planetary systems and have significantly influenced the orbital properties and distribution of planets and minor planets in the solar system and in exoplanetary systems. Most previous theoretical analyses have focused on the low- to moderate-eccentricity regime, but with new discoveries of high-eccentricity resonant minor planets and even exoplanets, there is increasing motivation to examine MMRs in the high-eccentricity regime. Here we report on a study of the high-eccentricity regime of MMRs in the circular planar restricted three-body problem. Numerical analyses of the 2:1 and the 3:2 interior resonances are carried out for a wide range of planet-to-star mass ratio μ, and for a wide range of eccentricity of the test particle. The surface-of-section technique is used to study the phase space structure near resonances. We find that new stable libration zones appear at higher eccentricity at libration centers that are shifted from those at low eccentricities. We provide physically intuitive explanations for these transitions in phase space, and we present novel results on the mass and eccentricity dependence of the resonance widths. Our results show that MMRs have sizable libration zones at high eccentricities, comparable to those at lower eccentricities.

Structural reliability of biaxial loaded Short/Slender-Square FRP-confined RC columns

This paper presents a structural reliability analysis of RC square columns confined with FRP laminates. The structural analyses were carried out using the Finite Difference Method FDM considering material and geometrical nonlinearity. Both FRP laminates and steel stirrups confinement effects were considered. Different values and types of eccentricities (single & biaxial) were taken into account. An experimental dataset containing 32 confined/unconfined RC columns were collected from literature and used to examine the accuracy of the FDM model. Reliability analyses were performed using First Order Reliability Method FORM. The reliability analyses were investigated including geometrical, material and loading variables. Loads and resistance factors were considered according to ACI provisions. Results of the reliability analysis have confirmed that confining the RC section with FRP material can improve the reliability by 0.1→0.5 depending on value and type (uniaxial and/or biaxial) of the eccentricity. The study includes parametric analysis reflecting the relation between the thickness of FRP materials and both reliability index & % increases in live load at different values of slenderness ratio and eccentricity. Results indicate that % increases in live load is linearly related to FRP thickness while the relation between reliability index and FRP thickness depends on eccentricity and slenderness values. An additional safety factor of a value equal to 0.65 proposed to be considered in design rules in of case of high eccentricity (Normal force outside core of the section). As results of FORM algorithm, the sensitivity factors were provided which demonstrate that live load and model error are variable of the greatest importance. Furthermore, within material and geometrical variables considered, concrete compressive strength is the variable of the first importance followed by column dimension and steel strength, while all other variables can be treated as deterministic variables.

Revealing the Formation of Stellar-mass Black Hole Binaries: The Need for Deci-Hertz Gravitational-wave Observatories

Abstract The formation of compact stellar-mass binaries is a difficult, but interesting problem in astrophysics. There are two main formation channels: in the field via binary star evolution, or in dense stellar systems via dynamical interactions. The Laser Interferometer Gravitational-wave Observatory (LIGO) has detected black hole binaries (BHBs) via their gravitational radiation. These detections provide us with information about the physical parameters of the system. It has been claimed that when the Laser Interferometer Space Antenna (LISA) is operating, the joint observation of these binaries with LIGO will allow us to derive the channels that lead to their formation. However, we show that for BHBs in dense stellar systems dynamical interactions could lead to high eccentricities such that a fraction of the relativistic mergers are not audible to LISA. A non-detection by LISA puts a lower limit of about 0.005 on the eccentricity of a BHB entering the LIGO band. On the other hand, a deci-Hertz observatory, like DECIGO or Tian Qin, would significantly enhance the chances of a joint detection and shed light on the formation channels of these binaries.

An eccentric companion at the edge of the brown dwarf desert orbiting the 2.4M⊙giant star HIP 67537

We report the discovery of a substellar companion around the giant star HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP67537$\,b$: m$_b$sin$i$ = 11.1$^{+0.4}_{-1.1}$ M$_{\rm {\tiny jup}}$, $a$ = 4.9$^{+0.14}_{-0.13}$ AU and $e$ = 0.59$^{+0.05}_{-0.02}$. Considering random inclination angles, this object has $\gtrsim$ 65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf transition region. In addition, we analyzed the Hipparcos astrometric data of this star, from which we derived a minimum inclination angle for the companion of $\sim$ 2 deg. This value corresponds to an upper mass limit of $\sim$ 0.3 M$_\odot$, therefore the probability that HIP67537$\,b$ is stellar in nature is $\lesssim$ 7%. The large mass of the host star and the high orbital eccentricity makes HIP67537$\,b$ a very interesting and rare substellar object. This is the second candidate companion in the brown dwarf desert detected in the sample of intermediate-mass stars targeted by the EXPRESS radial velocity program, which corresponds to a detection fraction of $f$ = 1.6$^{+2.0}_{-0.5}$%. This value is larger than the fraction observed in solar-type stars, providing new observational evidence of an enhanced formation efficiency of massive substellar companions in massive disks. Finally, we speculate about different formation channels for this object.

Secular chaotic dynamics in hierarchical quadruple systems, with applications to hot Jupiters in stellar binaries and triples

Hierarchical quadruple systems arise naturally in stellar binaries and triples that harbour planets. Examples are hot Jupiters (HJs) in stellar triple systems, and planetary companions to HJs in stellar binaries. The secular dynamical evolution of these systems is generally complex, with secular chaotic motion possible in certain parameter regimes. The latter can lead to extremely high eccentricities and, therefore, strong interactions such as efficient tidal evolution. These interactions are believed to play an important role in the formation of HJs through high-eccentricity migration. Nevertheless, a deeper understanding of the secular dynamics of these systems is still lacking. Here, we study in detail the secular dynamics of a special case of hierarchical quadruple systems in either the ‘2+2' or ‘3+1' configurations. We show how the equations of motion can be cast in a form representing a perturbed hierarchical three-body system, in which the outer orbital angular-momentum vector is precessing steadily around a fixed axis. In this case, we show that eccentricity excitation can be significantly enhanced when the precession period is comparable to the Lidov–Kozai oscillation time-scale of the inner orbit. This arises from an induced large mutual inclination between the inner and outer orbits driven by the precession of the outer orbit, even if the initial mutual inclination is small. We present a simplified semi-analytic model that describes the latter phenomenon.

Binary Black Hole Mergers from Field Triples: Properties, Rates, and the Impact of Stellar Evolution

Abstract We consider the formation of binary black hole (BH) mergers through the evolution of field massive triple stars. In this scenario, favorable conditions for the inspiral of a BH binary are initiated by its gravitational interaction with a distant companion, rather than by a common-envelope phase invoked in standard binary evolution models. We use a code that follows self-consistently the evolution of massive triple stars, combining the secular triple dynamics (Lidov–Kozai cycles) with stellar evolution. After a BH triple is formed, its dynamical evolution is computed using either the orbit-averaged equations of motion, or a high-precision direct integrator for triples with weaker hierarchies for which the secular perturbation theory breaks down. Most BH mergers in our models are produced in the latter non-secular dynamical regime. We derive the properties of the merging binaries and compute a BH merger rate in the range (0.3–1.3) Gpc−3 yr−1, or up to ≈2.5 Gpc−3 yr−1 if the BH orbital planes have initially random orientation. Finally, we show that BH mergers from the triple channel have significantly higher eccentricities than those formed through the evolution of massive binaries or in dense star clusters. Measured eccentricities could therefore be used to uniquely identify binary mergers formed through the evolution of triple stars. While our results suggest up to ≈10 detections per year with Advanced-LIGO, the high eccentricities could render the merging binaries harder to detect with planned space based interferometers such as LISA.

Efficient computation of the gravitational wave spectrum emitted by eccentric massive black hole binaries in stellar environments

We present a fast and versatile method to calculate the characteristic spectrum $h_c$ of the gravitational wave background (GWB) emitted by a population of eccentric massive black hole binaries (MBHBs). We fit the spectrum of a reference MBHB with a simple analytic function and show that the spectrum of any other MBHB can be derived from this reference spectrum via simple scalings of mass, redshift and frequency. We then apply our calculation to a realistic population of MBHBs evolving via 3-body scattering of stars in galactic nuclei. We demonstrate that our analytic prescription satisfactorily describes the signal in the frequency band relevant to pulsar timing array (PTA) observations. Finally we model the high frequency steepening of the GWB to provide a complete description of the features characterizing the spectrum. For typical stellar distributions observed in massive galaxies, our calculation shows that 3-body scattering alone is unlikely to affect the GWB in the PTA band and a low frequency turnover in the spectrum is caused primarily by high eccentricities.

Supernova kicks and dynamics of compact remnants in the Galactic Centre

The Galactic Centre (GC) is a unique place to study the extreme dynamical processes occurring near a super-massive black hole (SMBH). Here we investigate the role of supernova (SN) explosions occurring in massive binary systems lying in a disc-like structure within the innermost parsec. We use a regularized algorithm to simulate 30,000 isolated three-body systems composed of a stellar binary orbiting the SMBH. We start the integration when the primary member undergoes a SN explosion, and we analyze the impact of SN kicks on the orbits of stars and compact remnants. We find that SN explosions scatter the lighter stars in the pair on completely different orbits, with higher eccentricity and inclination. In contrast, stellar-mass black holes (BHs) and massive stars retain memory of the orbit of their progenitor star. Our results suggest that SN kicks are not sufficient to eject BHs from the GC. We thus predict that all BHs that form in situ in the central parsec of our Galaxy remain in the GC, building up a cluster of dark remnants. In addition, the change of NS orbits induced by SNe may partially account for the observed dearth of NSs in the GC. About 40 per cent of remnants stay bound to the stellar companion after the kick; we expect up to 70 per cent of them might become X-ray binaries through Roche-lobe filling. Finally, the eccentricity of some light stars becomes > 0.7 as an effect of the SN kick, producing orbits similar to those of the G1 and G2 dusty objects.

Planetary chaos and the (In)stability of Hungaria asteroids

The Hungaria asteroid group is located interior to the main asteroid belt, with semimajor axes between 1.8 and 2 AU, low eccentricities and inclinations of 16–35 degrees. Recently, it has been proposed that Hungaria asteroids are a secularly declining population that may be related to the Late Heavy Bombardment (LHB) impactors (Cuk, 2012; Bottke et al., 2012). While Cuk (2012) and Bottke et al. (2012) have reproduced a Hungaria-like population that declined exponentially, the real Hungarias were never confirmed to be unstable to the same degree. Here we find that the stability of Hungarias is strongly dependent on the evolution of the eccentricity of Mars, which is chaotic and unpredictable on Gyr timescales. We find that the high Martian eccentricity chiefly affects Hungarias through close approaches with Mars, rather than planetary secular modes. However, current minimum perihelia of Hungarias (over Myr timescales) are not diagnostic of their long-term stability due to a number of secular and mean motion resonances affecting the Hungaria region Milani et al., 2010. We conclude that planetary chaos makes it impossible to determine the effective lifetimes of observed Hungarias. Furthermore, long-term changes of Martian eccentricity could lead to variable Hungaria loss over time. We speculate that some of the most stable Hungarias may have been placed in their present orbit when the eccentricity of Mars was significantly higher than today.

Evolution of massive black hole binaries in rotating stellar nuclei: Implications for gravitational wave detection

We compute the isotropic gravitational wave (GW) background produced by binary supermassive black holes (SBHs) in galactic nuclei. In our model, massive binaries evolve at early times via gravitational-slingshot interaction with nearby stars, and at later times by the emission of GWs. Our expressions for the rate of binary hardening in the "stellar" regime are taken from the recent work of Vasiliev et al., who show that in the non-axisymmetric galaxies expected to form via mergers, stars are supplied to the center at high enough rates to ensure binary coalescence on Gyr timescales. We also include, for the first time, the extra degrees of freedom associated with evolution of the binary's orbital plane; in rotating nuclei, interaction with stars causes the orientation and the eccentricity of a massive binary to change in tandem, leading in some cases to very high eccentricities (e>0.9) before the binary enters the GW-dominated regime. We argue that previous studies have over-estimated the mean ratio of SBH mass to galaxy bulge mass by factors of 2 - 3. In the frequency regime currently accessible to pulsar timing arrays (PTAs), our assumptions imply a factor 2 - 3 reduction in the characteristic strain compared with the values computed in most recent studies, removing the tension that currently exists between model predictions and the non-detection of GWs.

Obliquity evolution of the minor satellites of Pluto and Charon

New Horizons mission observations show that the small satellites Styx, Nix, Kerberos and Hydra, of the Pluto–Charon system, have not tidally spun-down to near synchronous spin states and have high obliquities with respect to their orbit about the Pluto–Charon binary (Weaver, 2016). We use a damped mass-spring model within an N-body simulation to study spin and obliquity evolution for single spinning non-round bodies in circumbinary orbit. Simulations with tidal dissipation alone do not show strong obliquity variations from tidally induced spin-orbit resonance crossing and this we attribute to the high satellite spin rates and low orbital eccentricities. However, a tidally evolving Styx exhibits intermittent obliquity variations and episodes of tumbling. During a previous epoch where Charon migrated away from Pluto, the minor satellites could have been trapped in orbital mean motion inclination resonances. An outward migrating Charon induces large variations in Nix and Styx’s obliquities. The cause is a commensurability between the mean motion resonance frequency and the spin precession rate of the spinning body. As the minor satellites are near mean motion resonances, this mechanism could have lifted the obliquities of all four minor satellites. The high obliquities need not be primordial if the minor satellites were at one time captured into mean motion resonances.

Secular dimming of KIC 8462852 following its consumption of a planet

The Kepler-field star KIC 8462852, an otherwise apparently ordinary F3 main-sequence star, showed several highly unusual dimming events of variable depth and duration. Adding to the mystery was the discovery that KIC 8462852 faded by 14% from 1890 to 1989, as well as by another 3% over the 4 year Kepler mission. Following an initial suggestion by Wright & Sigurdsson, we propose that the secular dimming behavior is the result of the inspiral of a planetary body or bodies into KIC 8462852, which took place ~10 to 1e4 years ago (depending on the planet mass). Gravitational energy released as the body inspirals into the outer layers of the star caused a temporary and unobserved brightening, from which the stellar flux is now returning to the quiescent state. The transient dimming events could then be due to obscuration by planetary debris from an earlier partial disruption of the same inspiraling bodies, or due to evaporation and out-gassing from a tidally detached moon system. Alternatively, the dimming events could arise from a large number of bodies comet- or planetesimal-mass bodies placed onto high eccentricity orbits by the same mechanism (e.g. Lidov-Kozai oscillations due to the outer M-dwarf companion) responsible for driving the more massive planets into KIC 8462852. The required high occurrence rate of KIC 8462852-like systems which have undergone recent major planet inspiral event(s) is the greatest challenge to the model, placing large lower limits on the mass of planetary systems surrounding F stars and/or requiring an unlikely probability to catch KIC 8462852 in its current state.

Comparison of novel active semiconductor pixel detectorwith passive radiation detectors during the NASA Orion Exploration Flight Test 1 (EFT-1)

The first unmanned flight of the Orion Multipurpose Crew Vehicle (MPCV) was successfully completed on December 5, 2014. The total mission duration was 4.5 h, and the EFT-1 trajectory consisted of a high apogee (∼6000 km, 28.6° inclination), high eccentricity orbit through the Van Allen belts. Radiation measurements on Orion included a novel Battery-operated Independent Radiation Detector (BIRD) based on Timepix hybrid pixel technology, luminescence dosimeters (LiF:Mg,Ti, 6LiF:Mg,Ti, 7LiF:Mg,Ti, CaF2:Tm and Al2O3:C) and plastic nuclear track detectors (CR-39). This paper will discuss the advantages of the BIRD instrument with respect to analysis of the environment changes along the flight trajectory using the time stamp tracking capability of the pixel detector. In addition, a dosimetry comparison between the active BIRD instrument and the passive radiation area monitor (RAM) detectors in terms of mission absorbed dose.

Ferrofluid lubrication of finite journal bearings using Jenkins model

AbstractThe present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Jenkins model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analyzed using 2 control parameters: magnetic force coefficient and Jenkins viscosity. The obtained results are compared to those from Neurenger‐Rosensweig model. It is shown that pressure, load capacity, attitude angle, and side leakage increase and friction factor decreases when increasing the value of each control parameter at low and medium eccentricity ratios. However, the Jenkins viscosity parameter decreases the load capacity and increases the friction factor at high eccentricity ratios.

Periodic Orbits of the Planar Anisotropic Kepler Problem

In this paper, we prove that at every energy level the anisotropic Kepler problem with small anisotropy has two periodic orbits which bifurcate from elliptic orbits of the Kepler problem with high eccentricity. Moreover we provide approximate analytic expressions for these periodic orbits. The tool for proving this result is the averaging theory.

The most massive heartbeat: an in-depth analysis of ι Orionis

{\iota} Ori is a well studied massive binary consisting of an O9 III + B1 III/IV star. Due to its high eccentricity (e = 0.764) and short orbital period (P orb = 29.13376 d), it has been considered to be a good candidate to show evidence of tidal effects; however, none have previously been identified. Using photometry from the BRITE-Constellation space photometry mission we have confirmed the existence of tidal distortions through the presence of a heartbeat signal at periastron. We combine spectroscopic and light curve analyses to measure the masses and radii of the components, revealing {\iota} Ori to be the most massive heartbeat system known to date. In addition, using a thorough frequency analysis, we also report the unprecedented discovery of multiple tidally induced oscillations in an O star. The amplitudes of the pulsations allow us to empirically estimate the tidal circularization rate, yielding an effective tidal quality factor Q $\approx 4 \times 10^{4}$ .

Partial Confinement Utilization for Rectangular Concrete Columns Subjected to Biaxial Bending and Axial Compression

The prediction of the actual ultimate capacity of confined concrete columns requires partial confinement utilization under eccentric loading. This is attributed to the reduction in compression zone compared to columns under pure axial compression. Modern codes and standards are introducing the need to perform extreme event analysis under static loads. There has been a number of studies that focused on the analysis and testing of concentric columns. On the other hand, the augmentation of compressive strength due to partial confinement has not been treated before. The higher eccentricity causes smaller confined concrete region in compression yielding smaller increase in strength of concrete. Accordingly, the ultimate eccentric confined strength is gradually reduced from the fully confined value fcc (at zero eccentricity) to the unconfined value f_{c}^{{prime }} (at infinite eccentricity) as a function of the ratio of compression area to total area of each eccentricity. This approach is used to implement an adaptive Mander model for analyzing eccentrically loaded columns. Generalization of the 3D moment of area approach is implemented based on proportional loading, fiber model and the secant stiffness approach, in an incremental-iterative numerical procedure to achieve the equilibrium path of P–ε and M–φ response up to failure. This numerical analysis is adapted to assess the confining effect in rectangular columns confined with conventional lateral steel. This analysis is validated against experimental data found in the literature showing good correlation to the partial confinement model while rendering the full confinement treatment unsafe.

On the Existence of Regular and Irregular Outer Moons Orbiting the Pluto–Charon System

Abstract The dwarf planet Pluto is known to host an extended system of five co-planar satellites. Previous studies have explored the formation and evolution of the system in isolation, neglecting perturbative effects by the Sun. Here we show that secular evolution due to the Sun can strongly affect the evolution of outer satellites and rings in the system, if such exist. Although precession due to extended gravitational potential from the inner Pluto–Charon binary quench such secular evolution up to a crit ∼ 0.0035 au (∼0.09 R Hill the Hill radius; including all of the currently known satellites), outer orbits can be significantly altered. In particular, we find that co-planar rings and satellites should not exist beyond a crit; rather, satellites and dust particles in these regions secularly evolve on timescales ranging between 104 and 106 years, and quasi-periodically change their inclinations and eccentricities through secular evolution (Lidov–Kozai oscillations). Such oscillations can lead to high inclinations and eccentricities, constraining the range where such satellites (and dust particles) can exist without crossing the orbits of the inner satellites or crossing the outer Hill stability range. Outer satellites, if such exist are therefore likely to be irregular satellites, with orbits limited to be non-circular and/or highly inclined. Current observations, including the recent data from the New-Horizons mission explored only inner regions (<0.0012 au) and excluded the existence of additional satellites; however, the irregular satellites discussed here should reside farther, in the yet uncharted regions around Pluto.