Effects of Strong Magnetic Fields in Strange Baryonic Matter

We investigate the effects of very strong magnetic fields upon the equation of state of dense bayonic matter in which hyperons are present. In the presence of a magnetic field, the equation of state above nuclear density is significantly affected both by Landau quantization and magnetic moment interactions, but only for field strengths $B>5\times10^{18}$ G. The former tends to soften the EOS and increase proton and lepton abundances, while the latter produces an overall stiffening of the EOS. Each results in a supression of hyperons relative to the field-free case. The structure of a neutron star is, however, primarily determined by the magnetic field stress. We utilize existing general relativistic magneto-hydrostatic calculations to demonstrate that maximum average fields within a stable neutron are limited to values $B\le 1-3 \times10^{18}$ G. This is not large enough to significantly influence particle compositions or the matter pressure, unless fluctuations dominate the average field strengths in the interior or configurations with significantly larger field gradients are considered.Comment: 12 pages, 3 figures. To be submitted to Phys. Lett.

Potential for an underwater glider component as part of the Global Ocean Observing System

The contributions of autonomous underwater gliders as an observing platform in the in-situ global ocean observing system (GOOS) are investigated. The assessment is done in two ways: First, the existing in-situ observing platforms contributing to GOOS (floats, surface drifters, moorings, research/commercial ships) are characterized in terms of their current capabilities in sampling key physical and bio-geochemical oceanic processes. Next the gliders’ capabilities are evaluated in the context of key applications. This includes an evaluation of 140 references presented in the peer-reviewed literature. It is found that GOOS has adequate coverage of sampling in the open ocean for several physical processes. There is a lack of data in the present GOOS in the transition regions between the open ocean and shelf seas. However, most of the documented scientific glider applications operate in this region, suggesting that a sustained glider component in the GOOS could fill that gap. Glider data are included for routine product generation (e.g. alerts, maps). Other noteworthy process-oriented applications where gliders are important survey tools include local sampling of the (sub)mesoscale, sampling in shallow coastal areas, measurements in hazardous environments, and operational monitoring. In most cases, the glider studies address investigations and monitoring of processes across multiple disciplines, making use of the ease to implement a wide range of sensors to gliders. The maturity of glider operations, the wide range of applications that map onto growing GOOS regional needs, and the maturity of glider data flow all justify the formal implementation of gliders into the GOOS. Remaining challenges include the execution of coordinated multinational missions in a sustained mode as well as considering capacity-building aspects in glider operations as well as glider data use

LADUMA: looking at the distant universe with the MeerKAT array

The cosmic evolution of galaxies’ neutral atomic gas content is a major science driver for the Square Kilometre Array (SKA), as well as for its South African (MeerKAT) and Australian (ASKAP) precursors. Among the H I large survey programs (LSPs) planned for ASKAP and MeerKAT, the deepest and narrowest tier of the “wedding cake” will be defined by the combined L-band+UHF-band Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey, which will probe H I in emission within a single “cosmic vuvuzela” that extends to z = 1.4, when the universe was only a third of its present age. Through a combination of individual and stacked detections (the latter relying on extensive multi-wavelength studies of the survey’s target field), LADUMA will study the redshift evolution of the baryonic Tully–Fisher relation and the cosmic H I density, the variation of the H I mass function with redshift and environment, and the connection between H I content and galaxies’ stellar properties (mass, age, etc.). The survey will also build a sample of OH megamaser detections that can be used to trace the cosmic merger history. This proceedings contribution provides a brief introduction to the survey, its scientific aims, and its technical implementation, deferring a more complete discussion for a future article after the implications of a recent review of MeerKAT LSP project plans are fully worked out

The SARAO MeerKAT 1.3 GHz Galactic Plane Survey

We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251○ ≤l ≤ 358○ and 2○ ≤l ≤ 61○ at |b| ≤ 1 5). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8″ and a broadband RMS sensitivity of ∼10–20 μJy beam−1. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908–1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE H II region candidates are not true H II regions; and a large sample of previously undiscovered background H I galaxies in the Zone of Avoidance

The MeerKAT Galaxy Cluster Legacy Survey: I. Survey overview and highlights

Please abstract in the article.The South African Radio Astronomy Observatory (SARAO), the National Research Foundation (NRF), the National Radio Astronomy Observatory, US National Science Foundation, the South African Research Chairs Initiative of the DSI/NRF, the SARAO HCD programme, the South African Research Chairs Initiative of the Department of Science and Innovation.http://www.aanda.orghj2022Physic

Water masses and baroclinic transports in the South Atlantic and southern oceans

We describe the World Ocean Circulation Experiment (WOCE) A23 hydrographic section from Antarctica to Brazil, nominally along 35W. The section crossed the center of the Weddell Gyre, the Antarctic Circumpolar Current (ACC) and the Subtropical Gyre in the Argentine Basin. We precisely define the locations of fronts, the changes in water mass properties across them, and their transports. The Antarctic Slope Front was crossed above the continental slope of Antarctica, with a baroclinic transport of 4 Sv, part of the cyclonic Weddell Gyre circulation of 19 Sv. We repeated a section in the Weddell Sea occupied in 1973, and saw a marked warming of the inflowing Warm Deep Water layer by some 0.2°C, but no discernible change in the outflowing northern limb of the gyre. An inflow of recently ventilated water with the same characteristics as Weddell Sea Deep Water (WSDW) was observed flowing into the Weddell Sea from the east. The Weddell Front was crossed at 61°7'S and the Southern Boundary (SB) of the ACC (often referred to as the Scotia Front) at 58°38'S. Between these lay the Weddell-Scotia Confluence, contributing 16 Sv of eastward transport. The first crossing of the Southern ACC Front (SACCF) lay south of South Georgia at ~55°30'S. It then wrapped anticyclonically around South Georgia and was encountered at 53°40'S before retroflecting and returning eastward at ~53°30'S. The baroclinic transport was ~15 Sv at each crossing. In this region the SACCF is most clearly identified by a decrease in the salinity of the temperature minimum layer. The core of the Polar Front (PF) lay at ~49S where the isotherms plunged down sharply to the north, and transported 67 Sv. The PF and Subantarctic Front (SAF) were barely distinguishable with only one station clearly in the Polar Frontal Zone. The SAF, transporting 57 Sv, was encountered at ~48°45'S where the subsurface salinity minimum of Antarctic Intermediate Water (AAIW) began to descend. The Subtropical Front (STF) marks the boundary between the waters of the subtropical gyre and the colder, fresher subantarctic waters to the south; its southernmost crossing was at 44-45S transporting ~25 Sv. This is several hundred kilometers farther south than historical locations of the STF at this longitude. The Brazil Current Front (BCF) was encountered at ~38S transporting 43 Sv. Whereas previous observations found the STF to be the primary means for eastward flow of the waters of the Brazil Current after it has separated from the coast, during A23 we find that the BCF carries the majority of this transport. A further Deep Front, possibly marking the center of the subtropical gyre, was crossed at 34°22'S associated with a transport of 2.5 Sv. In the western Vema Channel we encountered a recirculation of the Brazil Current, flowing to the northeast with a transport of 23 Sv. The section ended prematurely without crossing the Brazil Current. To close the subtropical gyre transport would require a Brazil Current significantly in excess of the historical estimates based on shallow reference levels. Both the SACCF and STF exhibited meanders probably caused by bathymetry. The STF meander may be caused by the eastern end of the circulation around the Zapiola Rise. Both the SB and PF had associated eddies. The SB had shed a cyclonic eddy to the north, which had subsequently been capped by local water. It transported 8 Sv azimuthally. The PF had shed an anticyclonic eddy to the south, which was also capped and circulated at least 3 Sv. A small anticyclonic subsurface lens of AAIW was observed in the Vema Channel with a transport of the order of I Sv. In the Vema Channel, a level of no motion between the North Atlantic Deep Water and the Lower Circumpolar Deep Water (LCDW) gives a net northward flow of 1.2 Sv WSDW and 4 Sv LCDW from the Argentine to the Brazil Basin

Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements

Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue, Trolltunga, that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200m thick Ice Shelf Water (ISW) layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in delta-18O) to the upper 100–150m of the water column in the southeast Weddell Sea

On the circulation of bottom water in the region of the Vema Channel

The circulation and transport of Antarctic Bottom Water (4<45.87) in the region of the Vema Channel are studied along three WOCE hydrographic lines, the geostrophic velocities referenced to previously published direct current measurements. The primary supply of water to the deep Vema Channel is from the Argentine Basin's deep western boundary current, with no indication of an inflow from the southeast. In the northern Argentine Basin, detachment of lower North Atlantic Deep Water from the continental slope is associated with a deep thermohaline front near 34°S. To the north of this front, the upper part of the AABW bound for the Vema Channel (4<46.01) exhibits a significant NADW influence. Further modification of the throughflow water occurs near 30°30?S, where the channel orientation changes by ~50°. Southward flow of bottom water on the eastern flank of the Vema Channel, amounting to ~1.5 Sv, represents a significant countercurrent to the deep channel transport. Inclusion of this countercurrent reduces the net flow of AABW through the Vema Channel from 3.2±0.7 to 1.7±1.1 Sv. Water properties imply that the near-zero net flow over the Santos Plateau results from a near-closed cyclonic circulation fed by the deep Vema Channel throughflow. A disruption of the northward boundary current in the upper AABW (lower circumpolar water) is required by this flow pattern. The extension of the cyclonic circulation on the Santos Plateau enters the Brazil Basin as a ~1 Sv flow distinct from the outflow in the Vema Channel Extension (6.2 Sv). The high magnitude of the latter suggests a southward recirculation of bottom water near the western boundary to the north of the region of study

Collection of water samples from an autonomous underwater vehicle for tracer analysis

A compact water sampler rated to full ocean depth has been deployed from an autonomous underwater vehicle (AUV) to enable oceanographic tracer measurements. Techniques developed to allow the instrument to collect up to 49 samples of sufficient purity for tracer measurement without the need for extensive flushing have increased its sampling frequency, allowing a 200-mL seawater sample to be collected in 10 min. This is achieved by flushing the instrument and sample containers before deployment with a fluid of known properties that can be detected after recovery using salinity analysis. A deployment in which water samples were collected for oxygen isotope ratio analysis is presented as an example. Factors limiting the reliability of the instrument when deployed from an AUV are identified and procedures are developed to address critical problems.<br/