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We present a new model designed to simulate the process of energetic particle precipitation, a vital coupling mechanism from Earth's magnetosphere to its atmosphere. The atmospheric response, namely excess ionization in the upper and middle atmosphere, together with bremsstrahlung X-ray production, is calculated with kinetic particle simulations using the Geant4 Monte Carlo framework. Mono-energy and mono-pitch angle electron beams are simulated and combined using a Green's function approach to represent realistic electron spectra and pitch angle distributions. Results from this model include more accurate ionization profiles than previous analytical models, deeper photon penetration into the atmosphere than previous Monte Carlo model predictions, and predictions of backscatter fractions of loss cone electrons up to 40%. The model results are verified by comparison with previous precipitation modeling results, and validated using balloon X-ray measurements from the Balloon Array for RBSP Relativistic Electron Losses mission and backscattered electron energy and pitch angle measurements from the Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving CubeSat mission. The model results and solution techniques are developed into a Python package for public use. 

Abstract Calcium dicarbide, CaC₂, has been characterized at high resolution in the laboratory, and its main isotopologue,⁴⁰CaC₂, has been assigned to 14 rotational emission lines between 14 and 115 GHz, including 12 previously unassigned lines, in the expanding molecular envelope of the evolved carbon star IRC+10216. Aided by high-level quantum calculations and measurements of multiple isotopologues, CaC₂is determined to be a T-shaped molecule with a highly ionic bond linking the metal atom to the C₂unit, very similar in structure to isovalent magnesium dicarbide (MgC₂). The excitation of CaC₂is characterized by a very low rotational temperature of 5.8 ± 0.6 K and a kinetic temperature of 36 ± 16 K, similar to values derived for MgC₂. On the assumption that the emission originates from a 30″ shell in IRC+10216, the column density of CaC₂is (5.6 ± 1.7) × 10¹¹cm⁻². CaC₂is only the second Ca-bearing molecule besides CaNC and only the second metal dicarbide besides MgC₂identified in space. Owing to the similarity between the predicted ion–molecule chemistry of Ca and Mg, a comparison of the CaC₂abundance with that of MgC₂and related species permits empirical inferences about the radiative association–dissociative recombination processes postulated to yield metal-bearing molecules in IRC+10216 and similar objects. 

The M81 galaxy group is surrounded by an HI debris field scattered by the tidal interactions of its galaxies, a situation that has obvious similarities to the Magellanic stream and illuminates the formation of in-situ stars in stellar halos during galaxy collisions. Using observations of stars across the M81 group from the Subaru Hyper Suprime-Cam, and observations of the neutral HI from the Very Large Array, we find that within this HI debris the density of young stars broadly correlates with the density of gas, as expected given the Schmidt-Kennicutt star formation law and the results of previous work. Yet, there are regions that have systematically different behaviors in distributions of stars and gas. We focus on two stretches of HI coming off NGC 3077: the Southern tidal bridge (between M81 and NGC 3077) and the Northern tidal bridge (from NGC 3077 in the direction of M82). The Southern bridge has a narrow strip of young stars down its center, and the Northern bridge is mostly devoid of stars. While the driver(s) for this kind of behavior remain uncertain, our analysis of star formation in galaxy group-scale mergers from the TNG50 hydrodynamical galaxy simulations shows that the differences between projected line-of-sight distances of the gas may be an important consideration. 

Abstract We report the detection of magnesium dicarbide, MgC₂, in the laboratory at centimeter wavelengths and assign²⁴MgC₂,²⁵MgC₂, and²⁶MgC₂to 14 unidentified lines in the radio spectrum of the circumstellar envelope of the evolved carbon star IRC+10216. The structure of MgC₂is found to be T-shaped with a highly ionic bond between the metal atom and the C₂unit, analogous to other dicarbides containing electropositive elements. A two-temperature excitation model of the MgC₂emission lines observed in IRC+10216 yields a very low rotational temperature of 6 ± 1 K, a kinetic temperature of 22 ± 13 K, and a column density of (1.0 ± 0.3) × 10¹²cm⁻². The abundance of MgC₂relative to the magnesium–carbon chains MgCCH, MgC₄H, and MgC₆H is 1:2:22:20 and provides a new constraint on the sequential radiative association–dissociative recombination mechanisms implicated in the production of metal-bearing molecules in circumstellar environments. 

We report on the Sr isotopic composition of pore fluids recovered from Sites U1480 and U1481 drilled during International Ocean Discovery Program Expedition 362, which sampled the incoming sedimentary section of North Sumatra to investigate the causes of shallow seismogenesis in the Sumatra-Andaman margin. Sr isotope data are valuable in identifying diagenetic alteration of the incoming sequence, which can alter mechanical properties of the sedimentary wedge and subsequently affect its seismogenic behavior. Site U1480 recovered input sediment to ~1420 meters below seafloor (mbsf), and sediment was sampled from 1150 to 1500 mbsf at Site U1481. To determine the Sr isotopic composition, acidified pore fluid samples recovered at sea were loaded directly onto columns containing EICHROM Sr-Spec resin and followed by analyses using a NU multicollector inductively coupled plasma–mass spectrometer (MC-ICPMS). We observed a marked increase in 87Sr/86Sr ratios to 0.71376 in the Sr contribution from alteration of terrigenous material from the Bengal-Nicobar Fan. This trend is reversed in the deeper sequence, where 87Sr/86Sr ratios decrease to 0.70820 in the deepest sample analyzed (1300 mbsf). Only the deepest sediment was recovered at Site U1481, and the pore fluids also show a decrease in 87Sr/86Sr ratios from 0.71296 at 1172 mbsf to 0.70913 at 1495 mbsf. 

Abstract The XLZD collaboration is developing a two-phase xenon time projection chamber with an active mass of 60–80 t capable of probing the remaining weakly interacting massive particle-nucleon interaction parameter space down to the so-called neutrino fog. In this work we show that, based on the performance of currently operating detectors using the same technology and a realistic reduction of radioactivity in detector materials, such an experiment will also be able to competitively search for neutrinoless double beta decay in¹³⁶Xe using a natural-abundance xenon target. XLZD can reach a 3σdiscovery potential half-life of 5.7 × 10²⁷years (and a 90% CL exclusion of 1.3 × 10²⁸years) with 10 years of data taking, corresponding to a Majorana mass range of 7.3–31.3 meV (4.8–20.5 meV). XLZD will thus exclude the inverted neutrino mass ordering parameter space and will start to probe the normal ordering region for most of the nuclear matrix elements commonly considered by the community. 

Abstract The next core-collapse supernova in the Milky Way or its satellites will represent a once-in-a-generation opportunity to obtain detailed information about the explosion of a star and provide significant scientific insight for a variety of fields because of the extreme conditions found within. Supernovae in our galaxy are not only rare on a human timescale but also happen at unscheduled times, so it is crucial to be ready and use all available instruments to capture all possible information from the event. The first indication of a potential stellar explosion will be the arrival of a bright burst of neutrinos. Its observation by multiple detectors worldwide can provide an early warning for the subsequent electromagnetic fireworks, as well as signal to other detectors with significant backgrounds so they can store their recent data. The supernova early warning system (SNEWS) has been operating as a simple coincidence between neutrino experiments in automated mode since 2005. In the current era of multi-messenger astronomy there are new opportunities for SNEWS to optimize sensitivity to science from the next galactic supernova beyond the simple early alert. This document is the product of a workshop in June 2019 towards design of SNEWS 2.0, an upgraded SNEWS with enhanced capabilities exploiting the unique advantages of prompt neutrino detection to maximize the science gained from such a valuable event.