Australia Telescope National Facility

S&A Colloquium: Meriem Beheri (SISSA)
2022-10-05 15:00 - 16:00 (Australia/Sydney)
Radio Selected NIR-dark sources shedding light on the dark side of high redshift SFR

Abstract

About 12 billion years ago, the Universe was first experiencing light again after the dark ages, and galaxies filled the environment with stars, metals, and dust. How efficient was this process, and how fast did these primordial galaxies form stars and dust? We can answer these questions by tracing galaxies star formation rate density (SFRD) back to its unexplored high redshift tail, traditionally observed in the Near-InfraRed (NIR), Optical, and UV-bands. This means that the dustiest objects were missing. Further, most studies on dust obscured galaxies at high redshift have been conducted in the sub-millimetre, possibly affected by dust temperature biases. In this talk, I will introduce you to the characterisation of Radio Selected NIR-dark (RS-NIRdark) sources in different fields with a panchromatic approach and new SED-fitting techniques developed by the GOThA (Galaxy Observational and Theoretical Astrophysics) group in SISSA.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Xiaojin Liu (Beijing Normal University, China)
2022-10-12 15:00 - 16:00
A Bayesian study of the spin-up process of millisecond pulsars

Abstract

Millisecond pulsars (MSPs) are one of the fastest-spinning objects in the Universe. They are usually believed to attain their fast spin via an accretion process that transfers angular momentum from their companions to the neutron stars, though the spin-up process remains mysterious and is usually not given with much detail in the literature. The accretion theories, however, do predict a simple relation constraining the spin period and its time derivative, i.e. the so-called spin-up line. Studying the spin-up line will reveal some secrets of the accretion process and probably shed light on finding the fastest spinning pulsars, including a sub-ms one. In this talk, I will present our study of the spin-up line using an MSP population. I will show the hierarchical Bayesian method we used and discuss the interesting results we found.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Bi-Qing For (UWA)
2022-10-19 15:00 - 16:00
ASKAP WALLABY: dwarf galaxies in the local universe

Abstract

Low-mass, or dwarf, galaxies are the primary source of ionising photons during the epoch of reionisation and they are the building blocks of galaxies in the early Universe. Thus, they play an important role as the strongest test for the standard Cold Dark Matter model on the smallest scale. In this talk, I will present the results and goals of two ongoing dwarf galaxies-related projects that utilise ASKAP WALLABY data in conjunction with other legacy multiwavelength data. The two main studies are (1) probing role of galaxy interactions in quenching at low-mass end and (2) probing the formation mechanisms of low-surface brightness ‘dwarf’ galaxies (ultra-diffuse galaxies) from the HI perspective.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Yik Ki Ma (ANU)
2022-10-26 15:00 - 16:00
ASKAP as the Magnetic Probe of the Small Magellanic Cloud?

Abstract

High spatial resolution observations of the diffuse atomic (HI) gas have led to the realisation that the HI filamentary structures in the solar neighbourhood are aligned with the ambient magnetic field. It remains unclear whether this is a general attribute of the ISM across a large Galactic volume, as well as in other galaxies with vastly different astrophysical characteristics. Using the high quality data from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope for the Galactic ASKAP HI (GASKAP-HI) survey, I investigated whether the ~10 pc-scale HI filaments in the Small Magellanic Cloud (SMC) can act as compass needles tracing the galactic magnetic field structure. Furthermore, I mapped the preferred orientation of these filamentary HI structures to reveal the astrophysical processes shaping the ISM in the SMC. In this talk, I will present the results from this work, as well as highlighting the potential synergies between the GASKAP-HI and the POSSUM surveys.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Shanika Galaudage (Monash)
2022-11-02 15:00 - 16:00
Investigating the lives of black holes and neutron stars with gravitational waves

Abstract

The field of gravitational-wave astronomy provides us with a wealth of information about the most extreme objects in the Universe. Since 2015, there have been over 90 detections of merging black holes and neutron stars. With the growing number of gravitational wave events, we can study the overall population of events, allowing us to probe stellar evolution and formation mechanisms of these compact binaries. In this talk, I describe the emerging picture of the formation of binary black hole systems using observations from LIGO-Virgo-KAGRA. I will also present some insights into the population of binary neutron stars, and the implications for radio and gravitational-wave astronomy.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Rick Perley (NRAO)
2022-11-18 15:00 - 16:00
MeerKAT and VLA Polarimetric Calibration – Establishing the true EVPAs of 3C286 and 3C138

Abstract

The radio quasars 3C286 and 3C138 have long been used to determine the EVPAs of polarimetric imaging with the VLA. Since at least the 1960s, it has been ‘accepted wisdom’ that the correct EVPA of 3C286 is 33 degrees at all frequencies. However, recent VLA observations of the moon, Venus, and Mars have shown there are small, but significant deviations from the presumed 33 degrees, resulting in about a 10 degree spread between 1 and 50 GHz. Recent MeerKAT observations have confirmed this spread at their frequencies of overlap, and strongly suggest much larger deviations to lower values are seen below 1 GHz. However, accurate estimation of the EVPAs below ~1 GHz will require accurate corrections for ionospheric Faraday rotation, which are currently lacking.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Quirino D'Amato (SISSA)
2022-11-23 15:00 - 16:00
High-redshift Supermassive Black Holes grow in dusty, gas-rich environment

Abstract

A large fraction of supermassive black holes (SMBHs) located in Active Galactic Nuclei (AGN) at galaxy centres grow hidden by dust and gas. In the local Universe, the obscuration is often associated with the (sub-)pc-scale circumnuclear medium surrounding the SMBH (i.e. the so-called torus), as postulated by the Unified Schemes. However, deep X-ray observations have shown that the fraction of obscured AGN dramatically increases with redshift. In addition, thanks to the revolution introduced by new (sub-)mm observatories, in the last decade increasingly detections of the dusty, gas-rich interstellar medium (ISM) have been collected in the host galaxies of distant (z≳1.5) AGN. The physical properties of the ISM in galaxies change rapidly with redshift and, on average, distant AGN host galaxies are found more compact and denser than their local counterpart. These results suggest that the increased obscuration with redshift might occur on the host galaxy kpc-scale. Observational evidence shows that distant large-scale structures are often composed of gas-rich members, including the progenitor of the future brightest cluster galaxies. Moreover, diffuse large reservoirs of cold gas have been detected in the central regions of the intra-cluster medium (ICM) in many proto-clusters. Galaxy clusters are the largest virialized structures in the Universe, and most of their assembly takes place at the cosmic epoch where both star formation and black hole accretion peak (1< z <3). Exploring the interplay between nuclear activity, star formation and gas supply in such objects addresses the processes responsible for the build-up of present-day most massive galaxies. The presence of such an extremely dense environment strongly affects the galaxy-SMBH co-evolution through mechanical/radiative feedback processes; in addition, AGN are known to produce powerful relativistic-particle jets onto scales of several hundreds of kpc, and increasingly evidence have shown that AGN-feedback can extend on distances far beyond the host galaxy scale.

In this talk I will review the main recent observational results about the ISM content in distant AGN and proto-cluster, highlight the importance of a multi-wavelength approach and high-resolution observations in determining the ISM/ICM gas reservoir properties such as size, morphology, distribution and kinematics. I will discuss the implications of such findings in modelling the evolution of massive galaxies and large-scale structures across cosmic time, and the role of AGN feedback in regulating such an evolution. In addition, I will discuss the role of the ISM in obscuring high-z AGN and the incidence of the obscured AGN fraction as a function of the redshift, presenting multi-wavelength observations and numerical simulations.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Grazia Umana (INAF)
2022-11-30 15:00 - 16:00
The impact of SKA on Galactic Science: a glimpse at the Galactic plane with SKA precursors

Abstract

About 50-70% of the first five years of SKA operations will be devoted to KSPs, and probably also to Generic Surveys that maximize commensality to a wide range of scientific objectives. There are already several proposed KSPs focused on Galactic Science and we foresee many other KSP concepts being submitted under the breadth of Our Galaxy SWG. SKA, providing better sensitivity and angular resolution than any of the ongoing/planned surveys of the Galactic plane, will give the opportunity to create a sensitive wide-field atlas of Galactic radio emission and to address several topics in the field of Galactic radioastronomy. In this talk, I will summarize the ongoing work aimed at achieving skills and expertise in the run-up to the development of the full SKA to be ready and competitive for leading and participating in a SKA KSP dedicated to Galactic studies, with particular regard to recent results from the use of SKA precursors.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Venkatesh Ramakrishnan (Aalto University)
2022-12-13 15:00 - 16:00
Roadmap to a compendium of black hole images

Abstract

The transformational science on the study of supermassive black holes and other non-horizon objects as enabled by the Event Horizon Telescope opens a window to directly test the effects of General relativity (GR) on various classes of accreting objects. The knowledge garnered from studies of M87* and Sgr A* has to be expanded to several other black holes to enhance our understanding of GR on a cosmological scale. I will present the plans and progress underway of a project with a sample of nearby galaxies. The work entails a multifrequency approach with data obtained from radio to gamma-rays for a more thorough modelling of the broadband SEDs and the variability of accretion flows that are within the gravitational potential of the black hole. Finally, the interest or the requirement in having both the theory and observations in a close interface for this study will also be discussed.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Mark Cheung (CSIRO)
2023-01-25 15:00 - 16:00
An introduction to Heliophysics

Abstract

Heliophysics is the study of the Sun and how it influences the space environments around the planets, other solar system bodies and the interstellar medium. The dynamical nature of the Sun’s activity drives space weather and space climate, which in turn impact the viability of life and technological infrastructure in the solar system. The Sun is also a natural laboratory for studying fundamental physical processes common to many astrophysical systems. In this talk, we present multi-wavelength observations for studying solar activity, give a primer on prominent physical processes (e.g. magnetic reconnection), and explore how CSIRO Space & Astronomy can make unique contributions to Heliophysics and space weather.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Yuanming Wang (University of Sydney)
2023-02-08 15:00 - 16:00
Image-plane radio transients on short-timescales with ASKAP

Abstract

Short bursts, flares, scintillation and other radio time-domain phenomena usually imply extreme astrophysical environments (e.g. strong magnetic fields) that are difficult to achieve on Earth. This time-domain parameter space, however, is relatively unexplored historically, mainly limited by instrumental sensitivity and field-of-view (FoV). In this talk I will present unusual time-domain transient events I have discovered with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, including extreme scintillation, flaring stars, and pulsars.

We have used ASKAP to probe timescales of seconds to hours, searching for rapidly varying radio sources. With the advantage of the large FoV, we discovered a group of fast-scintillating galaxies arranged linearly on the sky, spanning approximately 2 degrees. Using this unlikely sky distribution we inferred the presence of a nearby, straight, and high-pressured plasma filament between the Earth and those galaxies, which produces extreme scintillation. Circular polarisation is another poorly explored parameter-space. With ASKAP dual-polarisation beams, we identified a new pulsar (rapidly rotating neutron star) PSR J0523-7125 through its strong circularly polarised emission and variable behaviour. PSR J0523-7125 shows many unusual properties (e.g., upturn spectrum shape), which may shed light on the as-yet-unknown pulsar coherent emission mechanism.

Our discovery has filled gaps in this unexplored time-domain parameter space, and highlighted a new way of finding unusual pulsars – useful for future space-time experiments. The existence of a nearby, high-pressured plasma filament also changes our understanding of the origins of extreme scintillation, and requires new models to explain the underlying phenomenon, as existing theoretical models are incompatible with the structure we measured. The image above is an artist’s illustration of the new pulsar found in the LMC.

Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Nipanjana Patra (Curtin)
2023-02-15 15:00 - 16:00
“That is not only not right; it is not even wrong.” – Wolfgang Pauli

Abstract

Corroboration of the detection of a redshifted 21cm signal from the Cosmic Dawn is more challenging than the first detection. For, there exists no independent science-verification framework against which an individual telescope’s output can be tested to claim any successful detection. Consequently, experimental findings cannot be unambiguously verified, especially when unsupported by existing observational evidence. HYdrogen Probe of the Epoch of REIONization (HYPEREION) is an experiment designed to corroborate the first detection of the Cosmic Dawn signal. For the first time, the instrument design approach has delivered a set of global standards to be met by any second-generation 21cm experiments to claim a successful detection and corroborate each other’s findings. In this talk, I will discuss the instrument design, measurement methodology, initial results, and future plans.

Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Robert Main (MPIfR)
2023-03-01 15:00 - 16:00
Scintillation Arcs: Scattering Screens and Surprises

Abstract

Radio emission from pulsars scintillates in time and frequency – an interference pattern arising from small-scale inhomogeneities in electron density in the interstellar medium. The discovery of “scintillation arcs” showed that scintillation is often remarkably ordered, well described by scattering in highly anisotropic thin screens. Scintillation arcs are a powerful probe of small-scale structures in the ionized interstellar medium, and can be used to determine the location of screens, measure the variable time delays from scattering, and measure pulsar orbits on the plane of the sky. In this talk, I will show the first scintillation results from the Thousand Pulsar Array at MeerKAT, with scintillation arcs seen in upwards of 100 pulsars. I will then describe a long-term multi-frequency study of the high-velocity pulsar B1508+55 with LOFAR and Effelsberg, solving the observed scintillation from two interacting screens, and where low frequency `echoes’ preceded a change in scintillation by ~3 years. Motivated by this study, I will describe ongoing efforts to connect scintillation across many scales in frequency, and the most promising future avenues.

The image above shows scintillation arcs towards >100 pulsars observed as part of the MeerKAT Thousand Pulsar Array.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Trey Wenger (University of Wisconsin-Madison)
2023-03-08 15:00 - 16:00
Galactic HII regions, diffuse ionised gas, and structure in the Milky Way

Abstract

Radio recombination lines (RRLs) are an unobscured tracer of ionized gas in both the diffuse interstellar medium (ISM) as well as high-mass star-forming regions. The HII Region Discovery Surveys (HRDS) have nearly tripled the number of known high-mass star-forming regions in the Milky Way by detecting RRL emission toward infrared-identified HII region candidates. HII regions are the classic tracer of structure in galaxies, and their physical conditions (e.g., metallicity, internal kinematics) inform models of high-mass star formation and Galactic chemodynamical evolution. I will give a brief overview of our latest Australia Telescope Compact Array project, the Southern HII Region Discovery Survey, and some preliminary results with the first Galaxy-wide flux-limited HII region sample, including a novel technique to constrain the Milky Way morphological structure. We serendipitously discovered (1) a population of HII regions with ionized gas velocity gradients and (2) RRL emission from diffuse ionized gas. I will discuss these discoveries, their implications, and our follow-up work, which will inform both models of high-mass star formation as well as our understanding of the ISM and Galactic structure.

As part of a large Australia Telescope Compact Array (ATCA) project, the Southern HII Region Discovery Survey (SHRDS) serendipitously discovered ionized gas velocity gradients in a population of massive star forming regions. The figure above shows one such nebula, the HII region known as G297.651–00.973. The background color is a WISE three-color infrared image (22 micron in red, 12 micron in green, and 3.4 micron in blue), the black contours represent the SHRDS radio continuum brightness, and the colored contours represent the ionized gas velocity field. What is the origin and nature of these ionized gas velocity gradients? Follow-up work with the ATCA and the Very Large Array will hopefully answer these questions.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Douglas Scott (University of British Columbia)
2023-03-15 15:00 - 16:00
The Standard Cosmological Model

Abstract

All empirical data relating to our Universe are currently well fit by a basic model that contains only a few key ingredients: the background is described by homogeneous and isotropic solutions within General Relativity, in which there is domination by vacuum energy and cold dark matter in a roughly flat expanding geometry; the density fluctuations appear to be nearly scale-invariant, adiabatic and Gaussian (close to the simplest thing we could imagine); and all of today’s structure grew through gravitational instability. Within this picture the Universe is described by just a handful of numbers, which are now known to quite high precision. So what is left to do in cosmology? How many digits of precision do we need? Where did these values come from? Are there more numbers that we haven’t thought of yet? Is this model anything like the Standard Model of Particle Physics? Are there signs that we need “physics beyond the standard model”? Did someone say “anomalies” and “tensions”?
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Natasha Hurley Walker (ICRAR/Curtin)
2023-03-22 15:00 - 16:00
Long-period radio transients

Abstract

SKA pathfinder instruments are probing the radio sky in new ways, probing the sky on timescales hitherto poorly-explored. Sensitive image-plane surveys are discovering new kinds of radio transients, with unusual temporal, spectral, and polarisation properties. Two intriguing periodic transients were published last year: a pulsar-like object repeating every 76s that is growing fainter with time (Caleb et al. 2022), and a short-lived radio transient repeating every 18 minutes (Hurley-Walker et al. 2022a). Both are potential examples of “ultra-long period” (ULP) magnetars, and their radio emission might be explained by a temporary twisting and/or reorganisation of their intense magnetic fields.

These discoveries are spurring new searches for similar long-period sources. Last year we conducted a transient imaging survey of the Galactic plane with the MWA at 200 MHz. We were successful in detecting a further long-period transient, which compared to previous examples shows different pulse morphology, polarisation behaviour, and a staggeringly different activity window. Timing estimates place the source below the conventional “death lines” of emission mechanisms that explain radio emission in neutron stars. These sources are just the tip of the iceberg of a new population, the exploration of which will illuminate the behaviour of neutron stars and therefore physics in extreme environments. I will conclude the talk with future survey plans across a range of telescopes.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Michael Kramer (MPIfR, Bonn)
2023-03-31 15:00 - 16:00
Probing relativistic gravity with radio astronomy

Abstract

We experience a golden era in testing and exploring relativistic gravity. Whether it is results from gravitational wave detectors, satellite or lab experiments, radio astronomy plays an important complementary role. Here one can mention the cosmic microwave background, black hole imaging and, obviously, binary pulsars. This talk will provide an overview how these methods relate to each other, and will in particular focus on new results from the study of binary pulsars, where we can test the behaviour of strongly self-gravitating bodies with unrivalled precision. The talk will also give an outlook of what we can expect from new experiments, such as with MeerKAT or the SKA.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Chandra Murugesan (CSIRO)
2023-04-12 15:00 - 16:00
Resolved neutral atomic hydrogen (HI) gas studies to reveal the impact of intrinsic and environmental processes on Chandra Murugesan

Abstract

Neutral atomic Hydrogen (HI) gas is the fundamental reservoir from which stars in galaxies are eventually formed. As such, studying the HI gas properties in galaxies give us important insights into how star formation proceeds. In addition, the HI gas is affected by internal mechanisms/processes such as angular momentum (AM), star formation/AGN feedback, disk instabilities, as well as non-axisymmetric potentials such as bars. On the other hand, the HI gas is also sensitive to (external) environmental processes such as tidal and ram-pressure stripping. Disentangling the degree of influence of these processes on the HI gas is paramount. In this talk I will show the importance of resolved HI studies in decoding the effects of both internal and external processes on galaxy evolution. By virtue of the extended nature of the HI disks in galaxies, one can derive rotation curves out to many times their optical radii, making high-resolution HI studies very important for tracing the total AM in galaxies. I will present the AM – Mass relation for local galaxies which is fundamental for constraining our cosmological models. In addition, I will talk about the connection between AM, disk stability and HI gas fraction in galaxies. Drawing from the results of a new HI survey of ring galaxies, I will also highlight the effects of bars in redistributing the HI gas and star formation in galaxies. Finally, I will present some new data is being delivered by the ASKAP WALLABY HI survey and the impact this is likely to have on HI and AM studies of galaxies in the local Universe as we venture into the SKA era.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Caroline Foster (UNSW)
2023-04-19 15:00 - 16:00
Challenges in understanding the dynamical evolution of galaxies

Abstract

In this talk, I will discuss the dynamical transformation of galaxies across cosmic time. I will explore common barriers to and possible solutions for the accurate measurement and determination of the dynamical evolution of galaxies. I will focus on the necessity of changing dynamical probes / baryonic phases (neutral gas, ionised gas and stars) depending on the cosmic epoch or redshift.

In the first instance, I will discuss our attempt at quantifying and correcting for the impact of the progenitor bias with redshift using cosmological simulations. I will next address the implications of recent results on the dynamical coupling (or otherwise) of ionised gas and stars in galaxies on our ability to accurately infer dynamical evolution from observations at different epochs. Finally, I will outline how the Middle-Ages Galaxy Properties with Integral field spectroscopy (MAGPI) Survey was designed to explicitly overcome some of these barriers and show a selection of initial results.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Jayender Kumar (CSIRO)
2023-04-26 15:00 - 16:00
The dynamics and 3D structure of the Galactic long bar

Abstract

Understanding the 3D structure and associated dynamics of the inner 4-kpc of the Milky Way is very challenging because of high obscuration at optical wavelengths and our ability to accurately measure the distance and 3D motions of sources at these distances.

In this work, we measured parallax and proper motions of three 22.2 GHz water masers, each associated with a High-Mass Star-Forming Region (HMSFR) in the first quadrant of the Milky Way. With these measurements combined with other BeSSel projects’ published and un-published parallax and proper motion measurements of maser sources associated with HMSFRs within the 4 kpc region of the Galactic centre, we present evidence that the young HMSFRs in the inner galaxy are located in the gases following ’quasi-elliptical’ orbits. These represent the first direct measurements of the dynamics of the Milky Way’s bar.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Travis Rector (University of Alaska)
2023-05-03 15:00 - 16:00
How astronomers can be part of the solution to climate change

Abstract

From a social, environmental, and political standpoint climate change is the most important scientific topic of our time. Fortunately we can still avoid the worst consequences, but we need to take swift action. The good news is that climate change can be solved, and astronomers are especially well suited to make a difference. Through the classes we teach and our public outreach we can, and should, take the opportunity to help people understand the causes and consequences of, and solutions to, climate change.

We also need to address that astronomy as a profession is a contributor to climate change. From supercomputing, air travel, and operations we are responsible for an outsized carbon footprint. Astronomy is also being affected by climate change, from the increased risk of forest fires to the stability of the atmospheric conditions at our observatories. How should astronomers change how we work in order to reduce our carbon footprint? How should we adapt to the impacts of climate change and proposed mitigation efforts? And how can we make changes that improve the equity and productivity of our profession? In my talk I will discuss the roles that astronomers can– and are– playing in addressing the climate crisis.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Dale E. Gary (NJIT)
2023-05-10 15:00 - 16:00
Recent Advances in Solar Radio Imaging Spectroscopy

Abstract

An impressive number of new radio instruments have appeared on the scene, or are in the planning stages, that perform high-resolution imaging at many closely spaced frequencies over a broad frequency range. In the case of imaging of the Sun, this has ushered in a revolution in our understanding by providing radio imaging spectroscopy, i.e., spatially resolved brightness temperature spectra. Such spectra can be connected directly to basic physical parameters of the radiating particles and their environment, leading to a breakthrough in our understanding of solar flares and bursts as well as the structure and processes of the non-flaring solar atmosphere. This talk will cover the instruments and advances fueling this revolution, and present some of the recent results for the Sun and also (briefly) stars.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Nick Lomb (University of South Queensland) & Toner Stevenson (University of Sydney)
2023-05-24 15:00 - 16:00
Eclipse Chasers: Solar eclipses in Australia

Abstract

In this presentation, we give a few extracts from our book Eclipse Chasers, recently published by CSIRO Publishing. Toner will focus on the 1922 eclipse experiment to confirm Einstein’s general theory of relativity, while Nick will discuss the 1974 and 1976 total solar eclipses, highlighting the involvement of CSIRO scientists. He will also mention the various mixed government and media messages that influenced public viewing of these events. Toner will conclude the presentation by showing her spectacular images of the recent eclipse in Exmouth and will leave you anticipating the next total solar eclipse to be visible in Australia. Eclipse Chasers by Nick Lomb and Toner Stevenson, together with expert collaborators, is a complete guide to past and future Australian eclipses. Past total solar eclipse campaigns described include the Far North Queensland eclipse of 1871 that is significant in the history of Australian science, the famous 1922 “Einstein” eclipse in which the previously hidden role of women and First Nations people is emphasised and the eclipses of 1974 and 1976 in which CSIRO scientists had a major role. The book also explores the great significance of solar eclipses for First Nations peoples, and their observations and cultural meanings.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Amit Seta (ANU)
2023-06-08 15:00 - 16:00
Rotation measure structure functions with higher-order stencils as a probe of small-scale magnetic fluctuations and its application to Magellanic Clouds

Abstract

Magnetic fields and turbulence are important components of the interstellar medium (ISM) of star-forming galaxies. It is challenging to measure the properties of the small-scale ISM magnetic fields (magnetic fields at scales smaller than the turbulence driving scale). Using numerical simulations, we demonstrate how the second-order rotation measure (RM, which depends on thermal electron density and magnetic field) structure function can probe the properties of small-scale random magnetic fields. Particularly, we show that computing the RM structure function with a higher-order stencil (more than the commonly-used two-point stencil) is necessary to accurately estimate the slope of the structure function. We then apply our results to radio polarisation observations of the Small and Large Magellanic Clouds and determine the strength and scale of their small-scale magnetic fields.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Jean Francois Nezan (IETR – INSA, France)
2023-06-21 15:00 - 16:00
Dataflow models for the design and programming of computing systems in astronomy

Abstract

Projects in astronomy like the Square Kilometer Array (SKA) or the European Extremely Large Telescope are among the world’s largest Big Data projects and the largest international computing collaborations, with unique computing challenges in Signal Processing and Machine Learning (SPML) still to be solved. The challenge in terms of computing, data transport and storage capacity is to design a processing chain ranging from the acquisition of raw data from the sensors to the production and the analysis of multidimensional images of the sky with Worldwide Distributed Calculations. In that context, a new generation of Low-Power High-Performance Computing Systems has to replace general-purpose High-Performance Computing (HPC) systems to meet the challenge of climate change, including the reuse and upgrades of computing systems already operational in a recycling approach. State of the art Programming Models and their Development Frameworks are lagging behind in offering support for efficient use of resources, high service availability and quality and cost competitiveness. This presentation will discuss how dataflow models associated with platform- and component-based designs can help to tame complexity during the design and the operating phases of big projects in astronomy, assessing the performance both in time and energy of a complex scientific workflow on a not-yet-existing computing infrastructure.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Ashley Ruiter (UNSW, Canberra)
2023-06-28 15:00 - 16:00
Mergers of white dwarfs and the transients they make

Abstract

For the last decade, mergers of double white dwarfs have been considered to be a likely, possibly even favoured, progenitor scenario for Type Ia supernovae. Though the Milky Way harbours ~100 million double white dwarf binaries, only a small fraction of these will actually merge in a Hubble time, let alone possess the “right” physical properties to lead to a Type Ia supernova if they do even merge. A different outcome of a white dwarf merger is the creation of another type of stellar transient: a hydrogen-deficient carbon (HdC) star. We know of ~130 of such ‘dusty’ HdC stars in the Galaxy – these are the R Coronae Borealis (RCB) stars, and they are thought to be the end result of a merger of a carbon-oxygen white dwarf and a helium-rich white dwarf, though their formation is not completely understood. In 2021, another type of hydrogen-deficient carbon star was found in great numbers: 27 ‘dustless’ HdC stars were spectroscopically confirmed in our own Milky Way, increasing the known number of this class from 4 (discovered >50 yrs ago) to 31. In 2022 we were granted time on the high-resolution (R~80,000) Veloce echelle spectrograph with the aim of disentangling the difference in evolutionary history between the long-known ‘dusty’ RCB stars and the newly-discovered plethora of ‘dustless’ HdC stars – both classes of objects presumed to be the result of double white dwarf mergers. Though we were mostly fully clouded out and we await new opportunities for obtaining and analysing observational data, I will discuss how different formation channels of white dwarf mergers may be plausibly linked to various transient phenomena such as Type Ia supernovae, dusty RCB stars, and dustless HdC stars.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Ophelie Renaud (IETR-INSA, France)
2023-07-12 15:00 - 16:00
Designing and Programming Astronomy Computing Systems for Optimal Power Efficiency and Performance

Abstract

In this presentation, we address the challenging problem of deploying complex astronomical applications on efficient target architectures. The allocation of resources in such scenarios significantly impacts performance outcomes. To automate and expedite this process, we propose a method that leverages the Synchronous Dataflow (SDF) model and the Scaling up of Cluster of Actor on the Processing Element (SCAPE) technique. Our approach, implemented in the PREESM rapid prototyping tool, facilitates automated deployment on CPU, GPU, and FPGA architectures. We showcase the advanced implementation of CPU-based resource allocation in our tool, which serves as a foundation for other target architectures. By providing a fast and easy resolution to this NP-hard problem, our method greatly enhances the efficiency of deploying astronomical applications.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Darren Croton (Swinburne)
2023-07-19 15:00 - 16:00
How to model the Universe in N easy steps

Abstract

Much progress has been made in recent years in our understanding of the co-evolution of galaxies and supermassive black holes, and their connection to the underlying large-scale dark matter structure. In this talk I will discuss simulation and modelling techniques that bridge theories of galaxy and black hole formation with the properties of observed galaxy populations. In addition, I will discuss a number of open questions important for extra-galactic astronomy and cosmology, and explain how future large-scale surveys and galaxy formation models may jointly address them.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Shriharsh Tendulkar (NCRA, India)
2023-08-02 15:00 - 16:00
Multi-scale and multi-wavelength searches for FRBs (and other wavelengths)

Abstract

Fulfilling the true promise of fast radio bursts (FRBs) as cosmological probes, understanding their origins, and their association with other transients necessitates our understanding of the FRB emission mechanism, their formation channel(s), and their local environments. Most emission mechanisms expect that the prompt radio emission represents a small fraction of the total energy released — a larger fraction of the energy should be released at higher frequency wavebands: optical, UV, X-ray and in some cases, gravitational waves (GW) and neutrinos, either as prompt emission or as a longer-lived afterglow. Given that the observed rates of FRBs are two to three orders of magnitude higher than the sky rates of any other extragalactic transient, it is clear that most FRBs will not have detectable multi-wavelength counterparts. The X-ray bursts aligned with the FRB-like radio emission from SGR 1935+2154 highlight the need to be alert to the brightest and nearest FRBs since those will be the most likely to have detectable multi-wavelength counterparts. Theoretical expectations also highlight the need to search for radio transients not just in the millisecond timescale, but also at second timescales, an area of phase space that is badly ignored. In this talk, I will discuss results from CHIME/FRB in trying to constrain counterparts of FRBs, FRB-GRB connections, and FRB-GW connections and our efforts to increase the phase space of radio transients by searching for not-so-fast radio bursts. For these science cases, I will also discuss two new projects: The proposed All Sky Transient Radio Array (ASTRA), an ultra-wide field of view telescope to detect the brightest and nearest radio transients and Daksha, a proposed all-sky X-ray mission with 2-satellites in antipodal orbits to increase the detection rate of GRBs and electromagnetic counterparts of GW events.
Watch recording
Event details
Download iCal
Category
Colearnia

S&A Colloquium: Barnali Das (CSIRO)
2023-08-09 15:00 - 16:00
Coherent radio emission from hot magnetic stars

Abstract

Hot magnetic stars are the perfect laboratories for understanding stellar magnetospheric phenomena due to the fact that their fields are extremely stable throughout their lifetimes, and also have very simple topologies (dipolar in most cases). Their strong stellar winds interact with the magnetic fields giving rise to co-rotating magnetospheres extending up to several tens of stellar radii. The magnetosphere manifests itself via emission over a wide range of the electromagnetic spectrum, starting from radio to X-ray. These emissions convey different kinds of information, and together, they act as probes for wind-magnetic field interplay. Among the different emissions that these magnetospheres produce, the latest discovered, and consequently, the least understood one is the coherent radio emission, also referred to as auroral radio emission. This is produced by electron cyclotron maser emission (ECME, the same mechanism that drives auroral radio emission from magnetic ultracool dwarfs and planets). In my talk, I will take you on our journey towards demystifying this phenomenon, starting with some serendipitous discoveries, followed by a systematic sub-GHz survey, which ironically led to the discoveries of many more unexplained characteristics, including discovery of radio flares, in addition to providing solutions to existing problems. I will present the results that we have obtained so far regarding ECME incidence, wideband properties and stability, and potential scenarios to explain the observations. I will end with my future plan to obtain more definitive insights about magnetospheric operation and the role that ATNF instruments can play in achieving that goal.
Watch recording
Event details
Download iCal
Category
Colearnia
