Eric Sembrat's Test Bonanza

Abstract

The Kepler mission's census of transiting exoplanets has shown that sub-Neptune size planets with short orbital periods are extremely common. Given their small sizes, the properties of these planets can be difficult or impossible to constrain via radial velocity observations. Mutual gravitational interactions in multi-planet systems cause variations in the arrival times of planets' transits. These variations are a valuable probe for measuring planets' masses and eccentricities, thereby constraining their compositions and formation histories. I will discuss the results of our analysis of the transit timing variations (TTVs) of 145 Kepler planets from 55 multi-planet systems. Some of these multi-planet systems, like Kepler-11, are surprisingly compact and naturally raise the question: just how tightly can a planetary system be packed?

In the second part of my talk I will describe new analytic results for predicting the onset of chaos and instability in systems of two massive, eccentric planets. These analytic results elucidate the role of mean motion resonances in determining orbital stability and serve as a starting point for understanding chaos and instability in higher-multiplicity systems. 

Abstract:

Over the course of the past two decades, observational surveys have un- veiled the intricate orbital structure of the Kuiper Belt, a field of icy bodies orbiting the Sun beyond Neptune. In addition to a host of readily-predictable orbital behavior, the emerging census of trans-Neptunian objects displays dynamical phenomena that cannot be explained by interactions with the known eight-planet Solar System alone. Specifically, the observed physical clustering of orbits with semi-major axes in excess of ∼ 250 AU, the detachment of perihelia of select Kuiper belt objects from Neptune, as well as the dynamical origin of highly inclined/retrograde long-period orbits remain elusive within the context of the classical view of the Solar System.

This newly outlined dynamical architecture of the distant solar system points to the existence of planet with mass M9 ∼ 10M⊕ on a moderately inclined orbit with semi-major axis a9 ∼ 400−800 AU and eccentricity e9 ∼ 0.4−0.6. In this talk, I will review the observational motivation, dynamical constraints, and prospects for detection of this proposed object known as Planet Nine. 

Abstract: 

The Kepler space telescope observed a multitude of stars during its primary mission, where a fraction of those stars were discovered to be eclipsing binary stars.  Additionally, some of these binary stars were confirmed to host planets orbiting with a semimajor axis that was a few times larger than the host binary designating them as circumbinary planets (CBPs).  Dr. Quarles has recently investigated the minimum semimajor axis for a wide range of binary stars including the Kepler CBPs.  He will summarize the results for general systems and provide the theoretical context that makes observing CBPs so exciting. 

Additionally, he measured the proximity of a planet to the stability limit for the Kepler CBPs and concluded that most of the CBPs are far enough away from this limit so that additional planets on shorter period orbits could remain stable.  The Transiting Exoplanet Survey Satellite is expected to uncover 100s of CBPs using a novel detection method (e.g., Kepler-1647b) that uses the unique geometry of CBP systems, where multiple transits can occur during a single conjunction, and increasing the statistics of CBPs will provide key clues to processes of planet formation.

Abstract:

Eccentric nuclear disks, like the one in the Andromeda galaxy, are made up of stars on apsidally-aligned eccentric orbits. In this talk I will show how secular gravitational torques between the orbits not only maintains the stability of the nucleus but dramatically enhances the rates of tidal disruption events. As eccentric nuclear disks can form during gas-rich major mergers, this can explain the preference for tidal disruption events in recent- and post-merger galaxies.

Abstract

Optical phenomena visible to everyone abundantly illustrate important ideas in science and mathematics. The phenomena considered include rainbows, sparkling reflections on water, green flashes, earthlight on the moon, glories, daylight, crystals, and the squint moon. The concepts include refraction, wave interference, numerical experiments, asymptotics, Regge poles, polarization singularities, conical intersections, and visual illusions.

Biography

Michael Berry is a theoretical physicist known for his research in the ‘borderlands’ between classical and quantum theories and ray and wave optics. His emphasis is on geometrical singularities such as ray caustics and wave vortices. Michael discovered the geometric phase, a phase difference arising from cyclically changing conditions with applications in many areas of wave physics, including polarisation optics, condensed matter and XX and self-propulsion of animals and robots.

He delights in finding the arcane in the mundane: mathematical singularities in rainbows and the dancing lines at the bottom of swimming pools; the twists and turns of a belt that underlie the quantum behaviour of identical particles; a laser pointer shone through bathroom window glass to demonstrate abstract aspects of wave interference; and oriental magic mirrors, illustrating the mathematical Laplace operator.

Michael has received numerous awards, including the Maxwell Medal and the Dirac Medal of the Institute of Physics, the Royal Society’s Royal Medal, the London Mathematical Society’s Pólya Prize, the Wolf Prize and the Lorentz Medal. He serves on scientific committees of various institutes and was knighted in 1996.

About the Joseph Ford Commemorative Lecture

Joseph Ford was one of the pioneers in the field of chaotic dynamics in the 1960s. He spent most of his 34-year career furthering the discipline at the Georgia Tech School of Physics. He dedicated his time between research, supported largely by the National Science Foundation, and education, through conferences or in the classroom. This commemorative lecture is named to honor Ford's memory and influence as a scientist, teacher, and colleague in Georgia Tech and the scientific global community.

Abstract:

Well-isolated trapped atomic ions are attractive candidate qubits because of their spectroscopic features. Ions with nuclear spin ½  allow fast, high-fidelity initialization of hyperfine clock qubits with coherence times exceeding 10 minutes. Long-lived D-states allow for electron shelving of a qubit state to achieve ultra-low qubit readout errors. Visible wavelength transitions for laser cooling and qubit manipulation allow the leveraging of existing photonics technology. ¹³³Ba⁺ is the only atomic ion to simultaneously possess all of these features.

The successful trapping and laser cooling of ¹³³Ba⁺ along with the characterization of its excited state spectroscopy has allowed for the first hyperfine qubit manipulations of this goldilocks atomic ion. We implement electron shelving to dramatically increase the qubit readout fidelity without the need for efficient light collection. Our measurements suggest ¹³³Ba⁺ could have broad applications in quantum information processing, quantum networking, and the construction of compact quantum sensors and clocks.

Abstract 

Amphiphilic molecules have been harnessed by biology and engineering alike for their propensity to self-assemble into complex structures. In this, steric molecular-scale interactions dominate small aggregates, whilst emergent elasticity governs as objects grow to larger length-scales. 

Here, we use molecular dynamics simulation of a series of coarse-grained mesogenic systems to examine the self-assembly of such supramolecular structures. The simulated systems, which are bipartite mixtures of disc-shaped and spherical particles, combine the thread-like aggregation of chromonics with the frustrations and incommensurabilities of amphiphilicity.

A veritable zoo of structures, many of which possess emergent supramolecular chirality, are reproducibly obtained. These including double helices, twisted bilayers, multi-strand ropes and tubules. By assessing the sensitivity of these final structures to the underpinning particle-scale interactions, insight is gained into how emergent length-scales can develop in grown structures. Further, from time-lines of the associated hierarchical self-assembly processes, the importance of mesogenic intermediates and size-dependent morphological changes in the development of complex aggregates is evidence

Abstract

Dramatic progress in understanding fluid turbulence, especially at moderate Reynolds numbers, has been made in the past decade usi! ng a deterministic framework based on the state space geometry of unstable solutions of the Navier-Stokes equation. Initial results obtained by restricting attention to minimal flow units capable of sustaining turbulence and imposing unphysical (e.g., spatially periodic) boundary conditions seemed to suggest that fluid turbulence is in many ways similar to low-dimensional chaos, with unstable periodic solutions forming the geometric skeleton for dynamics.

However, extending these results to larger flow domains with physical boundary conditions both proved very challenging and produced a number of surprises. In particular, our experimental and numerical studies have shown that unstable equilibria, quasiperiodic states, and heteroclinic connections can play an equally important role. We have also demonstrated that unstable solutions can be used for forecasting the evolution of experimental turbulent flows.

Abstract:

A number of ongoing surveys, such as Pan-STARRS, the Catalina Sky Survey, OSSOS, and NEOWISE, as well as planned surveys such as ZTF, LSST, and NEOCam, are designed to pursue goals ranging from constraining models of planet formation, through finding evidence of additional planets in our solar system, to fulfilling the US Congressional mandate to discover 90% of the potential hazardous asteroids with diameters exceeding 140m.

The typical asteroid search strategy is based on identifying `tracklets’, a sequence of two or more observations that are taken over a time span that is short enough that it is likely that the detections correspond to the same moving object, and a long enough to distinguish solar system objects from stationary background sources. A primary goal is to obtain enough tracklets for each object that the corresponding orbit is accurately determined. By design, most objects are naturally re-observed in the course of these surveys. However, which observations correspond to which object must still be identified before the orbits of those objects can be determined. This is known as the `linking problem.’

The best current solution to the linking problem, the Pan-STARRS Moving Object Processing System (MOPS), employs a sophisticated variation of the brute force approach, bringing groups of three tracklets together to be tested with orbit fitting. The computational load of MOPS scales as $\mathcal{O}(N_t^3)$, where $N_t$ is the number of tracklets.

We present a novel approach, heliocentric linking and clustering, that scales as $\mathcal{O}(N_t \log N_t)$. We use this approach to identify thousands of new objects within the Minor Planet Center’s “Isolated Tracklet File”. Finally, we discuss the implications of our results for ongoing and future surveys.