Southern Sky Research Articles

Evolutionary Map of the Universe (EMU): A pilot search for diffuse, non-thermal radio emission in galaxy clusters with the Australian SKA Pathfinder

Abstract Clusters of galaxies have been found to host Mpc-scale diffuse, non-thermal radio emission in the form of central radio halos and peripheral relics. Turbulence and shock-related processes in the intra-cluster medium are generally considered responsible for the emission, though details of these processes are still not clear. The low surface brightness makes detection of the emission a challenge, but with recent surveys with high-sensitivity radio telescopes we are beginning to build large samples of these sources. The Evolutionary Map of the Universe (EMU) is a Southern Sky survey being performed by the Australian SKA Pathfinder (ASKAP) over the next few years and is well-suited to detect and characterise such emission. To assess prospects of the full survey, we have performed a pilot search of diffuse sources in 71 clusters from the Planck Sunyaev–Zeldovich (SZ) cluster catalogue (PSZ2) found in archival ASKAP observations. After re-imaging the archival data and performing both (u, v)-plane and image-plane angular scale filtering, we detect 21 radio halos (12 for the first time, excluding an additional six candidates), 11 relics (in seven clusters, and six for the first time, excluding a further five candidate relics), along with 12 other, unclassified diffuse radio sources. From these detections, we predict the full EMU survey will uncover up to $\approx 254$ radio halos and $\approx 85$ radio relics in the 858 PSZ2 clusters that will be covered by EMU. The percentage of clusters found to host diffuse emission in this work is similar to the number reported in recent cluster surveys with the LOw Frequency ARray (LOFAR) Two-metre Sky Survey [Botteon, et al. 2022a, A&A, 660, A78], suggesting EMU will complement similar searches being performed in the Northern Sky and provide us with statistically significant samples of halos and relics at the completion of the full survey. This work presents the first step towards large samples of the diffuse radio sources in Southern Sky clusters with ASKAP and eventually the SKA.

Experience deploying an analysis facility for the Rubin Observatory’s Legacy Survey of Space and Time (LSST) data

The Vera C. Rubin Observatory is preparing for the execution of the most ambitious astronomical survey ever attempted, the Legacy Survey of Space and Time (LSST). Currently in its final phase of construction in the Andes mountains in Chile and due to start operations in 2025 for 10 years, its 8.4-meter telescope will nightly scan the southern sky and collect images of the entire visible sky every 4 nights using a 3.2 Gigapixel camera, the largest imaging device ever built for astronomy. Automated detection and classification of celestial objects will be performed by sophisticated algorithms on high-resolution images to progressively produce an astronomical catalog eventually composed of 20 billion galaxies and 17 billion stars and their associated physical properties.In this paper, we briefly present the infrastructure deployed at the French Rubin data facility (operated by IN2P3 computing center, CC-IN2P3) to deploy the Rubin Science Platform, a set of web-based services to provide effective and convenient access to LSST data for scientific analysis. We describe the main services of the platform, the components that provide those services and our deployment model. We also present the Kubernetes-based infrastructure we are experimenting with for hosting the LSST astronomical catalog, a petabyte-scale relational database developed for the specific needs of the project.

The Rubin Observatory’s Legacy Survey of Space and Time DP0.2 processing campaign at CC-IN2P3

The Vera C. Rubin Observatory, currently in construction in Chile, will start performing the Legacy Survey of Space and Time (LSST) in 2025 for 10 years. Its 8.4-meter telescope will survey the southern sky in less than 4 nights in six optical bands, and repeatedly generate about 2 000 exposures per night, corresponding to a data volume of about 20 TiB every night. Three data facilities are preparing to contribute to the production of the annual data releases: the US Data Facility will process 35% of the raw data, the UK data facility will process 25% of the raw data and the French data facility, operated by CC-IN2P3, will locally process the remaining 40% of the raw data.In the context of the Data Preview 0.2 (DP0.2), the Data Release Production pipelines have been executed on the DC-2 simulated dataset (generated by the Dark Energy Science Collaboration, DESC). This dataset includes 20 000 simulated exposures, representing 300 square degrees of Rubin images with a typical depth of 5 years.DP0.2 ran at the Interim Data Facility (based on Google cloud), and the full exercise was independently replicated at CC-IN2P3. During this exercise, 3 PiB of data and more than 200 million files were produced. In this contribution we will present a detailed description of the system that we set up to perform this processing campaign using CC-IN2P3’s computing and storage infrastructure. Several topics will be addressed: workflow generation and execution, batch job submission, memory and I/O requirements, etc. We will focus on the issues that arose during this campaign and how we addressed them and will present some perspectives after this exercise.

RG-CAT: Detection pipeline and catalogue of radio galaxies in the EMU pilot survey

Abstract We present source detection and catalogue construction pipelines to build the first catalogue of radio galaxies from the 270 $\rm deg^2$ pilot survey of the Evolutionary Map of the Universe (EMU-PS) conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The detection pipeline uses Gal-DINO computer vision networks (Gupta et al. 2024, PASA, 41, e001) to predict the categories of radio morphology and bounding boxes for radio sources, as well as their potential infrared host positions. The Gal-DINO network is trained and evaluated on approximately 5 000 visually inspected radio galaxies and their infrared hosts, encompassing both compact and extended radio morphologies. We find that the Intersection over Union (IoU) for the predicted and ground-truth bounding boxes is larger than 0.5 for 99% of the radio sources, and 98% of predicted host positions are within $3^{\prime \prime}$ of the ground-truth infrared host in the evaluation set. The catalogue construction pipeline uses the predictions of the trained network on the radio and infrared image cutouts based on the catalogue of radio components identified using the Selavy source finder algorithm. Confidence scores of the predictions are then used to prioritise Selavy components with higher scores and incorporate them first into the catalogue. This results in identifications for a total of 211 625 radio sources, with 201 211 classified as compact and unresolved. The remaining 10 414 are categorised as extended radio morphologies, including 582 FR-I, 5 602 FR-II, 1 494 FR-x (uncertain whether FR-I or FR-II), 2 375 R (single-peak resolved) radio galaxies, and 361 with peculiar and other rare morphologies. Each source in the catalogue includes a confidence score. We cross-match the radio sources in the catalogue with the infrared and optical catalogues, finding infrared cross-matches for 73% and photometric redshifts for 36% of the radio galaxies. The EMU-PS catalogue and the detection pipelines presented here will be used towards constructing catalogues for the main EMU survey covering the full southern sky.

First intensity interferometry measurements with the H.E.S.S. telescopes

ABSTRACT Intensity interferometry for astrophysical observations has gained increasing interest in the last decade. The method of correlating photon fluxes at different telescopes for high resolution astronomy without access to the phase of the incoming light is insensitive to atmospheric turbulence and does not require high-precision optical path control. The necessary large collection areas can be provided by Imaging Atmospheric Cherenkov Telescopes. Implementation of intensity interferometers to existing telescope systems such as VERITAS and MAGIC has proven to be successful for high-resolution imaging of stars. In 2022 April we equipped two telescopes of the H.E.S.S. array in Namibia with an intensity interferometry setup to measure southern sky stars and star systems during the bright moon period. We mounted an external optical system to the lid of the telescope cameras, which splits the incoming light and feeds it into two photomultipliers in order to measure the zero-baseline correlation within one telescope in addition to the cross-correlation between the telescopes. The optical elements are motorized, which enables live correction of tracking inaccuracies of the telescopes. During the campaign we measured the spatial correlation curves and thereby the angular diameters of λ Sco (Shaula) and σ Sgr (Nunki), while we also performed systematic studies of our interferometer using the multiple star system of α Cru (Acrux).

Are There Terrestrial Planets Lurking in the Outer Solar System?

Motivated by recent measurements of the free-floating-planet mass function at terrestrial masses, we consider the possibility that the solar system may have captured a terrestrial planet early in its history. We show that ∼1.2 captured free-floating planets with mass strictly greater than that of Mars may exist in the outer solar system, with a median predicted distance of ∼1400 au. If we consider a logarithmic bin centered on the mass of Mars, rather than a cutoff, we find that ∼2.7 captured free-floating planets with mass comparable to Mars may exist in the outer solar system. We derive an expectation value of ∼0.9 for the number of captured free-floating planets with mass comparable to that of Mars (∼1.4 for mass comparable to that of Mercury) that are currently brighter than the 10 yr coadded point-source detection limits of the Vera C. Rubin Observatory's Legacy Survey of Space and Time. Blind shift-and-stack searches could potentially enable the detection of such a planet if it is currently in the Southern sky. The theoretical argument presented here does not rely on the existence of posited patterns in the orbital elements of small bodies in and beyond the Kuiper Belt, in contrast with other hypothetical outer-solar-system planets motivated in recent years.

PHYSICAL PROPERTIES AND KINEMATICS OF DENSE CORES ASSOCIATED WITH REGIONS OF MASSIVE STAR FORMATION FROM THE SOUTHERN SKY

The results of spectral observations in the \( \sim {\kern 1pt} 84{\kern 1pt} - {\kern 1pt} 92\) GHz frequency range of six objects from the southern sky having dense cores and associated with massive star and star cluster forming regions are presented. The observations are carried out with the MOPRA-22m radio telescope. Within the framework of the local thermodynamic equilibrium (LTE) approximation, column densities and abundances of the H13CN, H13CO+, HN13C, HC3N, c-C3H2, SiO, CH3C2H and CH3CN molecules are calculated. Kinetic temperatures (\( \sim 30{\kern 1pt} - {\kern 1pt} 50\) K), sizes of emission regions (\( \sim 0.2{\kern 1pt} - {\kern 1pt} 3.1\) pc) and virial mass esimates (\( \sim 70{\kern 1pt} - {\kern 1pt} 4600{\kern 1pt} {{M}_{ \odot }}\)) are obtained. The linewidths in the three cores decrease with increasing distance from the center. Four cores exhibit asymmetry in the profiles of the optically thick HCO+(1–0) and HCN(1–0) lines, indicating the presence of systematic motions in the line of sight. In two cases, the asymmetry can be caused by contraction of gas. The model HCO+(1–0) and H13CO+(1–0) spectral maps obtained within the non-LTE spherically symmetric model are fitted into observed ones. Radial density (\( \propto {\kern 1pt} {{r}^{{ - 1.6}}}\)), turbulent velocity (\( \propto {\kern 1pt} {{r}^{{ - 0.2}}}\)) and contraction velocity (\( \propto {\kern 1pt} {{r}^{{0.5}}}\)) profiles in the G268.42–0.85 core are obtained. The contraction velocity radial profile differs from expected both in the case of free fall of gas onto a protostar (\({{r}^{{ - 0.5}}}\)), and in the case of global core collapse (contraction velocity does not depend on distance). A discussion of the results obtained is provided.

Low-frequency Radio Recombination Lines Away from the Inner Galactic Plane

Diffuse radio recombination lines (RRLs) in the Galaxy are possible foregrounds for redshifted 21 cm experiments. We use EDGES drift scans centered at −26.°7 decl. to characterize diffuse RRLs across the southern sky. We find that RRLs averaged over the large antenna beam (72° × 110°) reach minimum amplitudes of R.A. = 2–6 hr. In this region, the Cα absorption amplitude is 33 ± 11 mK (1σ) averaged over 50–87 MHz (27 ≳ z ≳ 15 for the 21 cm line) and increases strongly as frequency decreases. Cβ and Hα lines are consistent with no detection with amplitudes of 13 ± 14 and 12 ± 10 mK (1σ), respectively. At 108–124.5 MHz (z ≈ 11) in the same region, we find no evidence for carbon or hydrogen lines at the noise level of 3.4 mK (1σ). Conservatively assuming that observed lines come broadly from the diffuse interstellar medium, as opposed to a few compact regions, these amplitudes provide upper limits on the intrinsic diffuse lines. The observations support expectations that Galactic RRLs can be neglected as significant foregrounds for a large region of sky until redshifted 21 cm experiments, particularly those targeting cosmic dawn, move beyond the detection phase. We fit models of the spectral dependence of the lines averaged over the large beam of EDGES, which may contain multiple line sources with possible line blending, and find that including degrees of freedom for expected smooth, frequency-dependent deviations from local thermodynamic equilibrium (LTE) is preferred over simple LTE assumptions for Cα and Hα lines. For Cα we estimate departure coefficients 0.79 < b n β n < 4.5 along the inner Galactic plane and 0 < b n β n < 2.3 away from the inner Galactic plane.

Beyond Spectroscopy. II. Stellar Parameters for over 20 Million Stars in the Northern Sky from SAGES DR1 and Gaia DR3

We present precise photometric estimates of stellar parameters, including effective temperature, metallicity, luminosity classification, distance, and stellar age, for nearly 26 million stars using the methodology developed in the first paper of this series, based on the stellar colors from the Stellar Abundances and Galactic Evolution Survey (SAGES) Data Release 1 and Gaia Early Data Release 3. The optimal design of stellar-parameter sensitive uv filters by SAGES has enabled us to determine photometric-metallicity estimates down to −3.5, similar to our previous results with the SkyMapper Southern Survey (SMSS), yielding a large sample of over five million metal-poor ([Fe/H] ≤ −1.0) stars and nearly one million very metal-poor ([Fe/H] ≤ −2.0) stars. The typical precision is around 0.1 dex for both dwarf and giant stars with [Fe/H] > −1.0, and 0.15–0.25/0.3–0.4 dex for dwarf/giant stars with [Fe/H] < −1.0. Using the precise parallax measurements and stellar colors from Gaia, effective temperature, luminosity classification, distance, and stellar age are further derived for our sample stars. This huge data set in the Northern sky from SAGES, together with similar data in the Southern sky from SMSS, will greatly advance our understanding of the Milky Way, in particular its formation and evolution.

Postcards from a Cosmic Traveller: Thomas Ruff’s Images of Space

Thomas Ruff’s lifelong fascination with astronomy has resulted in a series of works that examine the process of image making in both his chosen medium of photography and astronomy. Drawing on a variety of sources ranging from the European Southern Observatory’s Southern Sky Atlas to the Cassini and Mars orbiters, Ruff has generated a body of altered and/or refashioned images that ruminate on issues of authorship, image manipulation, time, and objectivity, that have been amplified in our digital age. Astronomical imagery provides a unique focus on these issues and is revealed by Ruff as being an integral part of the questions he raises about our use and interpretation of images.

Discovery of the Magellanic Stellar Stream Out to 100 kpc

The Magellanic Stream (MS)—an enormous ribbon of gas spanning 140° of the southern sky trailing the Magellanic Clouds—has been exquisitely mapped in the five decades since its discovery. However, despite concerted efforts, no stellar counterpart to the MS has been conclusively identified. This stellar stream would reveal the distance and 6D kinematics of the MS, constraining its formation and the past orbital history of the Clouds. We have been conducting a spectroscopic survey of the most distant and luminous red giant stars in the Galactic outskirts. From this data set, we have discovered a prominent population of 13 stars matching the extreme angular momentum of the Clouds, spanning up to 100° along the MS at distances of 60–120 kpc. Furthermore, these kinematically selected stars lie along an [α/Fe]-deficient track in chemical space from −2.5 < [Fe/H] <− 0.5, consistent with their formation in the Clouds themselves. We identify these stars as high-confidence members of the Magellanic Stellar Stream. Half of these stars are metal-rich and closely follow the gaseous MS, whereas the other half are more scattered and metal-poor. We argue that the metal-rich stream is the recently formed tidal counterpart to the MS, and we speculate that the metal-poor population was thrown out of the SMC outskirts during an earlier interaction between the Clouds. The Magellanic Stellar Stream provides a strong set of constraints—distances, 6D kinematics, and birth locations—that will guide future simulations toward unveiling the detailed history of the Clouds.

The ALPACA experiment: The project of the first sub-PeV gamma-ray observation in the southern sky

The ALPACA experiment is a project aiming to observe sub-PeV gamma rays for the first time in the southern hemisphere. The main goal of ALPACA is to identify PeVatrons, the accelerators of Galactic PeV cosmic rays, by observing sub-PeV pion-decay gamma rays generated in interactions between PeV cosmic rays and the interstellar medium. This new air shower experiment is located at an altitude of 4,740 m above sea level in the middle of Mt. Chacaltaya in Bolivia. The air shower array consists of 401 scintillation counters covering an 83,000 m^22 surface area. In addition, a water-Cherenkov-type muon detector array with an area of 3,700 m^22 is installed to discriminate gamma rays from background cosmic rays. The prototype array ALPAQUITA will start data taking in 2022 and will extend to ALPACA in 2024. We report on a general introduction to ALPACA, the progress of the project, and the sensitivity to sub-PeV gamma rays.

Correlating High-energy IceCube Neutrinos with 5BZCAT Blazars and RFC Sources

We investigate the possibility that blazars in the Roma-BZCAT Multifrequency Catalogue of Blazars (5BZCAT) are sources of the high-energy astrophysical neutrinos detected by the IceCube Neutrino Observatory, as recently suggested by Buson et al. Although we can reproduce their ∼4.5σ result, which applies to 7 yr of neutrino data in the southern sky, we find no significant correlation with 5BZCAT sources when extending the search to the northern sky, where IceCube is most sensitive to astrophysical signals. To further test this scenario, we use a larger sample consisting of 10 yr of neutrino data recently released by the IceCube Collaboration, this time finding no significant correlation in neither the southern nor the northern sky. These results suggest that the strong correlation reported by Buson et al. using 5BZCAT could be due to a statistical fluctuation and possibly the spatial and flux nonuniformities in the blazar sample. We perform some additional correlation tests using the more uniform, flux-limited, and blazar-dominated Radio Fundamental Catalogue and find a ∼3.2σ equivalent p-value when correlating it with the 7 yr southern neutrino sky. However, this correlation disappears completely when extending the analysis to the northern sky and when analyzing 10 yr of all-sky neutrino data. Our findings support a scenario where the contribution of the whole blazar class to the IceCube signal is relevant but not dominant, in agreement with most previous studies.

SiO outflows in the most luminous and massive protostellar sources of the southern sky

Context. High-mass star formation is far less understood than low-mass star formation. It entails the ejection of matter through molecular outflows, which disturbs the protostellar clump. Studying these outflows and the shocked gas caused by them is the key to a better understanding of this process. Aims. The present study aims to characterise the behaviour of molecular outflows in the most massive protostellar sources in the southern Galaxy by looking for evolutionary trends and associating the presence of shocked gas with outflow activity. Methods. We present APEX SEPIA180 (Band 5) observations (beamwidth ~36″) of SiO(4-3) molecular outflow candidates towards a well-selected sample of 32 luminous and dense clumps, which are candidates for harbouring hot molecular cores. We study the emission of the SiO(4-3) line, which is an unambiguous tracer of shocked gas, and recent and active outflow activity, as well as the HCO+(2-1) and H13CO+(2-1) lines. Results. Results show that 78% of our sample (25 sources) present SiO emission, revealing the presence of shocked gas. Nine of these sources are also found to have wings in the HCO+(2-1) line, indicating outflow activity. The SiO emission of these nine sources is generally more intense (Ta &gt; 1 K) and wider (~61 km s−1 FWZP) than the rest of the clumps with SiO detection (~42 km s−1 FWZP), suggesting that the outflows in this group are faster and more energetic. This indicates that the shocked material gets dispersed as the core evolves and outflow activity decreases. Three positive linear correlations are found: a weak one (between the bolometric luminosity and outflow power) and two strong ones (one between the outflow power and the rate of matter expulsion and the other between the kinetic energy and outflow mass). These correlations suggest that more energetic outflows are able to mobilise more material. No correlation was found between the evolutionary stage indicator L/M and SiO outflow properties, supporting that molecular outflows happen throughout the whole high-mass star formation process. Conclusions. We conclude that sources with both SiO emission and HCO+ wings and sources with only SiO emission are in an advanced stage of evolution in the high-mass star formation process, and there is no clear evolutionary difference between them. The former present more massive and more powerful SiO outflows than the latter. Therefore, looking for more outflow signatures such as HCO+ wings could help identify more massive and active massive star-forming regions in samples of similarly evolved sources, and could also help identify sources with older outflow activity.

The GMRT High Resolution Southern Sky Survey for Pulsars and Transients. VI. Discovery of Nulling, Localization, and Timing of PSR J1244–4708

Many pulsars in the known population exhibit nulling, which is characterized by a sudden cessation and subsequent restoration of radio emission. In this work, we present the localization, timing, and emission properties of a pulsar discovered by the GMRT High Resolution Southern Sky survey: J1244–4708. Moreover, we find that this pulsar shows nulling, with a nulling fraction close to 60%. A quasiperiodicity is also seen in the nulling from this pulsar with two timescales. We demonstrate the broadband nature of nulling in this pulsar using simultaneous observations in band-3 (300–500 MHz) and band-4 (550–750 MHz) with the upgraded GMRT. We also present a comparison of the efficiency of various search approaches such as single pulse search, fast folding algorithm (FFA)–based search, and fast Fourier transform–based search to search for nulling pulsars. We demonstrated that the FFA search is advantageous for detecting extreme nulling pulsars, which is also confirmed with multiple epochs of observations for the nulling pulsars using the GMRT.

Identification of Galaxy–Galaxy Strong Lens Candidates in the DECam Local Volume Exploration Survey Using Machine Learning

Abstract We perform a search for galaxy–galaxy strong lens systems using a convolutional neural network (CNN) applied to imaging data from the first public data release of the DECam Local Volume Exploration Survey, which contains ∼520 million astronomical sources covering ∼4000 deg2 of the southern sky to a 5σ point–source depth of g = 24.3, r = 23.9, i = 23.3, and z = 22.8 mag. Following the methodology of similar searches using Dark Energy Camera data, we apply color and magnitude cuts to select a catalog of ∼11 million extended astronomical sources. After scoring with our CNN, the highest-scoring 50,000 images were visually inspected and assigned a score on a scale from 0 (not a lens) to 3 (very probable lens). We present a list of 581 strong lens candidates, 562 of which are previously unreported. We categorize our candidates using their human-assigned scores, resulting in 55 Grade A candidates, 149 Grade B candidates, and 377 Grade C candidates. We additionally highlight eight potential quadruply lensed quasars from this sample. Due to the location of our search footprint in the northern Galactic cap (b &gt; 10 deg) and southern celestial hemisphere (decl. &lt; 0 deg), our candidate list has little overlap with other existing ground-based searches. Where our search footprint does overlap with other searches, we find a significant number of high-quality candidates that were previously unidentified, indicating a degree of orthogonality in our methodology. We report properties of our candidates including apparent magnitude and Einstein radius estimated from the image separation.

Rubin Observatory LSST Stars Milky Way and Local Volume Star Clusters Roadmap

The Vera C. Rubin Observatory will undertake the Legacy Survey of Space and Time, providing an unprecedented, volume-limited catalog of star clusters in the Southern Sky, including Galactic and extragalactic star clusters. The Star Clusters subgroup of the Stars, Milky Way and Local Volume Working Group has identified key areas where Rubin Observatory will enable significant progress in star cluster research. This roadmap represents our science cases and preparation for studies of all kinds of star clusters from the Milky Way out to distances of tens of megaparsecs.

The ELM Survey South. II. Two Dozen New Low-mass White Dwarf Binaries

We present the results from our ongoing spectroscopic survey targeting low-mass white dwarf binaries, focusing on the southern sky. We used a Gaia DR2- and eDR3-based selection and identified 28 new binaries, including 19 new extremely low-mass (ELM) white dwarfs, one short period, likely eclipsing, DABZ, and two potential LISA binaries. We present the orbital and atmospheric parameters for each new binary based on our spectroscopic follow up. Four of our new binaries show periodic photometric variability in TESS 2 minutes cadence data, including one new eclipsing double-lined spectroscopic binary. Three others show periodic photometric variability in ZTF, including one new eclipsing binary. We provide estimates for the inclinations and scaled component radii for these ZTF variables, based on light-curve modeling of our high-speed photometric follow-up observations. Our observations have increased the sample of ELM Survey binaries identified in the southern sky to 41, an increase of 64%. Future time domain surveys, such as BlackGEM and the Vera C. Rubin Observatory Legacy Survey of Space and Time, will efficiently identify photometric variables in the southern sky and significantly increase the population of southern sky low-mass white dwarf binaries, leading to a more complete all-sky population of these systems.

Deep space debris—Detection of potentially hazardous asteroids and objects from the southern hemisphere

Space debris are composed of both natural and human made objects, some in near Earth orbits while others are passing through deep space. Asteroids may represent one form of near Earth and deep space debris. In this article we report on a set of asteroid observations from the southern hemisphere. We indicate that Apollo and Aten class asteroids represent another form of deep space debris of a potentially hazardous nature to orbiting spacecraft and/or Earth based locations. We also show some of the operational challenges, types of facilities and the importance of geographic diversity, that is, necessary for detecting, observing and characterising asteroids, especially PHA’s. For many years, space agencies and institutions have observed and monitored near Earth asteroids and objects (NEO’s) using high gain radio frequency antennas and optical telescopes in the northern hemisphere (GSSR, Arecibo, Catalina, Pan-STARRS, Atlas and Linear) 1) However a regular operational system to monitor the southern skies does not have the same level of maturity and is where a percentage of asteroids and various human made objects are not detected until they pass into northern skies. To fill that gap the Southern Hemisphere Asteroid Radar Program (SHARP) 2) located in Australia uses available antenna time on either a 70 or 34 m beam waveguide antenna located at the Canberra Deep Space Communication Complex (CDSCC) to transmit a Doppler compensated continuous radio wave at 2.114 GHz (14.2 cm) and 7.15945 GHz (4.2 cm) toward the NEO and receive its echoes at the 64 m Parkes or 6 m × 22 m Australia Telescope Compact Array (ATCA) antennas at Narrabri in Australia. This mode of NEO observation is termed a deep space bistatic radar. The southern hemisphere program has also recently been joined by the 12 m University of Tasmania antennas at Hobart (Tasmania) and Katherine (Northern Territory). Combining SHARPS bistatic radar with small optical apertures located at the University of New South Wales (UNSW) and University of Western Australia (UWA) allows combined optical/RF NEO detections. Whilst sub-metre class optical instruments have contributed independently to asteroid detection over decades, the use of coordinated small 0.3–0.5 m instruments synchronized to large asteroid radars offers an observational flexibility and adaptability when larger optical systems 3) are dedicated to other forms of professional optical astronomy. Since 2015, SHARP has illuminated and tracked over 30 NEO’s ranging in diameter from 7 to 5000 m at ranges of 0.1–18 lunar distances (LD) from Australia.

Plastic Laminate Antireflective Coatings for Millimeter-Wave Optics in BICEP Array

The BICEP/Keck series of experiments target the cosmic microwave background at degree-scale resolution from the South Pole. Over the next few years, the “Stage-3” BICEP Array (BA) telescope will improve the program’s frequency coverage and sensitivity to primordial B-mode polarization by an order of magnitude. The first receiver in the array, BA1, began observing at 30/40 GHz in early 2020. The next two receivers, BA2 and BA3, are currently being assembled and will map the southern sky at frequencies ranging from 95 to 150 GHz. Common to all BA receivers is a refractive, on-axis, cryogenic optical design that focuses microwave radiation onto a focal plane populated with antenna-coupled bolometers. High-performance antireflective coatings up to 760 mm in aperture are needed for each element in the optical chain, and must withstand repeated thermal cycles down to 4 K. Here, we present the design and fabrication of the 30/40 GHz anti-reflection coatings for the recently deployed BA1 receiver, with indices matched to its various polyethylene, nylon and alumina optical components. We describe an epoxy coating technique designed for alumina optics, which achieves better than 80% transmission at room temperature. For polyethylene optical elements, we present a new heat-compression approach that allows low-density polytetrafluoroethylene AR layers to reach sub-percent reflected power. We describe the planned use of these methods for the next BA cryostats, which may inform technological choices for future small-aperture telescopes of the CMB-S4 experiment.