Spectropolarimetry as a tool for understanding the diversity of planetary atmospheres

The polarization state of starlight reflected by a planetary atmosphere uniquely reveals coverage, particle size, and composition of aerosols as well as changing cloud patterns. It is not possible to obtain a comparable level of detail from flux-only observations. It is therefore a powerful tool to better understand the crucial role played by clouds and aerosols in the chemistry, dynamics, and radiative balance of a planet. Furthermore, polarization observations can probe the atmosphere of planets independently of the orbital geometry (hence it applies to both transiting and non-transiting exoplanets). A high-resolution spectropolarimeter with a broad wavelength coverage, particularly if attached to a large space telescope, would enable simultaneous study of the polarimetric planetary properties of the continuum and to look for and characterize the polarimetric signal due to scattering from single molecules, providing detailed information about the composition and vertical structure of the atmosphere.

Testing Hypotheses About Glacial Dynamics Using a Statistical Model of Paleo-Climate

We test hypotheses about glacial dynamics by evaluating the ability of a linear statistical model to simulate climate during the previous ~800,000 years. During this period, the linear model simulates the timing and magnitude of glacial cycles, including the saw-tooth pattern in which ice accumulates gradually and ablates rapidly, without falsely simulating an interglacial after each peak in obliquity. Conversely, the linear model fails to simulate experimental observations that are created by a nonlinear data generating process. Together, these (in)abilities suggest that nonlinearities, threshold effects, bifurcations, and/or phase-specific governing equations do not play a critical role in glacial cycles during the late Pleistocene. Furthermore, the model’s accuracy throughout the sample period suggests that changes in orbital geometry create the Mid-Brunhes event.

Sampling theorem of satellite gravimetry from the perspective of the Bender configuration

<p>Satellites in different orbital configurations acquire gravity signals differently. Thus, a difference in admissible spectral coefficients can be expected when the orbital geometry changes. A simple illustration of this phenomenon is seen in the Bender configuration of two GRACE-like satellite pairs - polar and inclined. In the Bender configuration, the polar pair covers the entire globe. In contrast, the inclined pair does not cover the higher latitudes leaving a local discontinuity around the poles in the acquired signal (better known as the <em>Polar Gap problem</em>). Similarly, due to its north-south orientation, the polar pair can capture the features that are predominantly oriented in the east-west direction. Trying to understand better the relationship between satellite geometry and signal acquisition led us to take our first steps in the direction of a unified sampling theory in satellite gravimetry. To this end, we employed the concepts behind the rotation of spherical harmonic coefficients built upon Inclination functions to express the geopotential functionals. Our work utilizes the Lomb-Scargle Periodogram based approach to ascertain limiting frequencies from the systemic quasi-regular sampling net formed on the satellite torus contrary to interpolation and FFT based techniques used in earlier such research endeavors. Through our work, we aim at improving our understanding of how the transformation of the geopotential occurs from the global to the spectral domain. We hope that this will help design future satellite missions with geometries best suited for their objective based on the precise determination of essential spectral coefficients.</p>

Spatially resolved star formation and fuelling in galaxy interactions

We investigate the spatial structure and evolution of star formation and the interstellar medium (ISM) in interacting galaxies. We use an extensive suite of parsec-scale galaxy merger simulations (stellar mass ratio = 2.5:1), which employs the ’Feedback In Realistic Environments-2’ model (fire-2). This framework resolves star formation, feedback processes, and the multi-phase structure of the ISM. We focus on the galaxy-pair stages of interaction. We find that close encounters substantially augment cool (HI) and cold-dense (H2) gas budgets, elevating the formation of new stars as a result. This enhancement is centrally-concentrated for the secondary galaxy, and more radially extended for the primary. This behaviour is weakly dependent on orbital geometry. We also find that galaxies with elevated global star formation rate (SFR) experience intense nuclear SFR enhancement, driven by high levels of either star formation efficiency (SFE) or available cold-dense gas fuel. Galaxies with suppressed global SFR also contain a nuclear cold-dense gas reservoir, but low SFE levels diminish SFR in the central region. Concretely, in the majority of cases, SFR-enhancement in the central kiloparsec is fuel-driven (55% for the secondary, 71% for the primary) - whilst central SFR-suppression is efficiency-driven (91% for the secondary, 97% for the primary). Our numerical predictions underscore the need of substantially larger, and/or merger-dedicated, spatially-resolved galaxy surveys - capable of examining vast and diverse samples of interacting systems - coupled with multi-wavelength campaigns aimed to capture their internal ISM structure.

Surveying the Trans-Neptunian Solar System with TESS

<p>In recent years, the observed orbital geometry of extreme trans-Neptunian objects (TNOs) has provided tantalizing evidence predicting the existence of an as-yet undiscovered “Planet Nine.” Combined with orbit stability models, these observations permit a detailed prediction of Planet Nine's properties, with a shrinking parameter space as more of these rare objects are discovered. I will present the first results from a new survey utilizing light curve data from the Transiting Exoplanet Survey Satellite (TESS) to search for TNOs at distances 70-800 au, with a magnitude limit V~22. This survey leverages an innovative new pipeline designed to extract the locations, magnitudes, and 27-day orbital arcs of undiscovered outer solar system objects, including both Planet Nine and the population of extreme trans-Neptunian objects pertinent to the Planet Nine theory, using a blind shift-stacking search along all plausible outer solar system orbits. Together with the extensive sky coverage of the TESS survey, this search will place stringent constraints upon the as-yet undiscovered TNO population, with great potential to either discover Planet Nine or almost entirely rule out its existence.</p>

A significant mutual inclination between the planets within the π Mensae system

Context. Measuring the geometry of multi-planet extrasolar systems can provide insight into their dynamical history and the processes of planetary formation. These types of measurements are challenging for systems that are detected through indirect techniques such as radial velocity and transit, having only been measured for a handful of systems to date. Aims. We aim to place constraints on the orbital geometry of the outer planet in the π Mensae system, a G0V star at a distance of 18.3 pc that is host to a wide-orbit super-Jovian (M sin i = 10.02 ± 0.15MJup) with a 5.7-yr period and an inner transiting super-Earth (M = 4.82 ± 0.85M⊕) with a 6.3-d period. Methods. The reflex motion induced by the outer planet on the π Mensae star causes a significant motion of the photocenter of the system on the sky plane over the course of the 5.7-year orbital period of the planet. We combined astrometric measurements from the HIPPARCOS and Gaia satellites with a precisely determined spectroscopic orbit in an attempt to measure this reflex motion, and in turn we constrained the inclination of the orbital plane of the outer planet. Results. We measure an inclination of ib = 49.9−4.5+5.3 deg for the orbital plane of π Mensae b, leading to a direct measurement of its mass of 13.01−0.95+1.03 MJup. We find a significant mutual inclination between the orbital planes of the two planets, with a 95% credible interval for imut of between 34.°5 and 140.°6 after accounting for the unknown position angle of the orbit of π Mensae c, strongly excluding a co-planar scenario for the two planets within this system. All orbits are stable in the present-day configuration, and secular oscillations of planet c’s eccentricity are quenched by general relativistic precession. Planet c may have undergone high eccentricity tidal migration triggered by Kozai-Lidov cycles, but dynamical histories involving disk migration or in situ formation are not ruled out. Nonetheless, this system provides the first piece of direct evidence that giant planets with large mutual inclinations have a role to play in the origins and evolution of some super-Earth systems.

Plasmaspheric electron density estimation based on COMISC/FORMOSAT-3 data

<p>The plasmasphere is a region of continuous study due to some open questions related to the plasmaspheric internal dynamics, boundaries, and coupling processes with the magnetosphere and ionosphere, in particular during space weather events. Given such interests, the results of a new tomographic method to estimate the plasmaspheric electron density will be presented. The tomographic reconstruction is applied using measurements of Total Electron Content (TEC) from the Global Positioning System (GPS) receivers aboard the Constellation Observing System for Meteorology, Ionosphere, and Climate / Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3). Despite relevant challenges imposed by the orbital geometry to obtain stable electron density reconstructions of a large area such as the plasmasphere, the developed approach was capable of representing the natural variability of the plasma ambient in terms of geographic/geomagnetic latitude, altitude, solar activity, season, and local time. The quality assessment was carried out using two years of in-situ electron density measurements from spacecraft deployed by the Defense Meteorological Satellite Program (DMSP). Our investigation revealed that improvements over 20% can be achieved for electron density specification by TEC data assimilation into background ionization.</p>

Long-term activity of Comet C/2007 N3 (Lulin) as monitored by the SLT at the Lulin Observatory

The green comet C/2007 N3 (Lulin) is a new Oort cloud comet that has a retrograde orbit (inclination of $178^{\circ }$). It reached its perihelion on 2009 January 10, and its closest distance to Earth was 0.411 astronomical units (au) on February 24. Soon after its discovery on 2007 July 11, the coma activity of Comet Lulin was monitored closely by an Super Light Telescope 41 cm telescope until 2009 April. After long-term monitoring of Comet Lulin, the dust production rate [A(θ)fρ] was estimated. An unexpected increase in the ${A(0)f\rho}$ near the perigee appears to indicate an opposition effect. By investigating the surface brightness profiles, dust-to-gas ratios, and magnitudes, we ruled out the influences of gas and ion contamination and the outburst phenomenon. We discovered the anti-tail in late December 2008 but were unsure of the composition. We found that this abnormal tail lasted for a considerable time because of the effect of the orbital geometry. We also found that the jet activity coincided with the peak ${A(\theta)f\rho}$ values, and this clue helped us realize what was happening in the dust coma of Comet Lulin.

Hydrodynamic Simulations of Circumstellar Envelopes under the Gravitational Influence of a Wide Binary Companion: Comparison Between Circular and Elliptical Orbits

Shapes of circumstellar envelopes around mass losing stars contain information of the very inner region of the envelope where mass loss process takes place. It’s well known that the presence of a binary companion leads to strong influence on the structure of the envelope through orbital motion of the mass losing star and the gravitational interaction of the companion with the stellar wind. To investigate this effect and structures of envelopes, we have performed high resolution hydrodynamic simulations of a wide binary system in a number of orbital configurations. Our simulations clearly show the importance of the equation of state of the gas because in isothermal case the width of the spiral arm is significantly broadened with respect to the ideal gas case, therefore resulting in unrealistic spiral patterns. As the orbital geometry changes from circular to elliptical, our simulation results show that the spiral becomes bifurcated and increasingly asymmetric as indicated in previously published results. In the polar direction, the prominent alternating arcs associated with circular orbital configuration morph into almost continuous circular rings. The physical condition of the gas in the envelope is shown to vary strongly between the spiral arm and inter-arm regions. Our hydrodynamic simulations will be useful to interpret high angular resolution observations of circumstellar envelopes.