DRAO Seminar Series 2023

Remote Talk: A decameter pulsar/transient «blind» survey of the northern sky. Results of transient searching

Vyacheslav Zakharenko (Institute of Radio Astronomy NAS Ukraine)

This report presents a detailed description of the Decameter pulsar/ transient survey of the northern sky, which was performed using the world’s largest low-frequency radio telescope at decameter wavelengths – UTR-2. This large-scale survey covers the northern sky with an inclination of -10 degrees to +80 degrees, a temporal resolution of 8 ms, and dispersion measure up to 30 pc/cm3.
The main advantage of the decameter range is a wide relative frequency band in which the dispersion delay reaches tens and hundreds of seconds, which allows us to distinguish cosmic pulse signals, and RFI and to determine the dispersion measure with very high accuracy.
380 transients were detected. The conducted tests show that the detected signals cannot be explained by the scintillation of the ionosphere.

Remote Talk: Search for magnetized high-velocity clouds using Faraday rotation

Lyla Jung (Australian National University)

High-velocity clouds (HVCs) around the Milky Way provide direct evidence of ongoing gas accretion that could fuel the future star formation activity of the Galaxy. Theories and numerical simulations predict that the magnetic field significantly affects the efficiency of the mixing at the cloud-halo interface, which could in the long run affect the survival of the clouds. There have been active searches for magnetized HVCs using polarization observations. In this presentation, I will discuss possible obstacles in detecting magnetized HVCs using Faraday rotation and how future polarization surveys will improve the situation. We test the conditions of the detection using the IllustrisTNG50 suite of cosmological simulation. This presentation will provide insight on how to find magnetized HVCs as the first step towards understanding the role of magnetic fields on the evolution of gas clouds around the Galaxy.

Spectral-line Polarization Commissioning and Observations of the FAST Telescope

Tao-Chung Ching (NRAO)

As the world’s largest filled-aperture single-dish radio telescope, the Five-hundred-meter Aperture Spherical Telescope (FAST) offers sensitive polarization capability. The full polarization commissioning of the FAST L-band 19-beam receiver is recently finished. Here I present the design, pipeline, and result of the polarization calibration of the 19-beam spectral-line data. We perform spider scans of quasars to characterize the polarization leakage and polarization angle of the system. The polarized beam patterns are measured by performing on-the-fly mappings across quasars. The resulting measurement errors are well controlled to below 0.5% in polarization degrees and below 0.8 degrees in polarization angles. In the talk, I will also present the results of FAST spectral-line polarization observations including HI, HINSA, and OH Zeeman effects of low-mass and high-mass star-forming regions and the preliminary discovery of linear polarization in HI 21-cm line.

The On-going Revolution in Exoplanets: Planet Characterization with JWST

Charles Beichman (JPL)

I will discuss the new capabilities of the James Webb Space Telescope which are revolutionizing our knowledge of exoplanets and systems. At high spectral resolution, JWST is measuring the atmospheres of planets, from Earth-sized planets orbiting cool star to ultra-Hot Jupiters orbiting hotter stars. With highly sensitive direct imaging, JWST is searching for planet candidates with masses as low of Uranus and Neptune. JWST’s long wavelength observations are revealing new structures of the debris disks including rings and gaps indicative of the presence of planets.

Australian Square Kilometre Array Pathfinder – A brief overview and challenges

Wasim Raja (CSIRO)

The Australian Square Kilometre Array Pathfinder (ASKAP) started full survey operations in November last year. In this talk I will introduce ASKAP – its novel features, the associated challenges, and highlight evolution of key strategies at overcoming those since its Commissioning and Early Science phases.

How do environmental processes quench cluster galaxies?

Toby Brown (HAA/DAO)

The Virgo Environment Traced in CO Survey (VERTICO) is an Atacama Large Millimeter/submillimeter Array Large Program that has mapped the distribution and kinematics of star-forming molecular gas across 51 Virgo Cluster satellite galaxies on sub-kpc scales. In this talk, I will showcase VERTICO results revealing how environmental mechanisms actively remove molecular gas, alter its distribution, and change the composition of the interstellar medium in cluster galaxies. I will also show that ram pressure stripping systematically increases molecular gas densities and triggers star formation activity on the leading half of the galaxy during the early stages of cluster infall, while lengthening gas depletion times and quenching galaxies in the latter stages.

The Missing Supernova Remnant Problem: Searching for Galactic Supernova Remnants with EMU & POSSUM

Brianna Ball (University of Alberta)

Supernova remnants (SNRs) are an important part of the stellar feedback cycle that regulates star formation and influences the evolution of galaxies. It is widely accepted that there is a significant discrepancy between the number of SNRs that have been discovered in our Galaxy and the number that models predict we should be able to detect at radio frequencies. This is often referred to as the “missing supernova remnant problem”. Based on our current catalogues, the missing SNR population is believed to mostly consist of low surface brightness sources and sources located in regions with complex backgrounds and high concentrations of other Galactic radio sources, like HII regions. I will demonstrate how we used pilot data from the EMU and POSSUM sky surveys, conducted with ASKAP, as a test case to assess the capabilities of these surveys to uncover new SNR candidates. Remarkably, we were able to detect 21 SNR candidates in a field that previously only contained 7 known SNRs. By comparing our candidates to the known Galactic SNR population, we demonstrate that ASKAP should be capable of detecting many more of these faint sources that likely comprise the majority of the missing SNR population.

The Mystery of the Auroral Generator

David Knudsen (U Calgary)

Auroral arcs are the familiar curtains of green or red light that often extend from horizon to horizon in the polar sky. Their lower border marks the inner boundary of the space environment, making them accessible to high-resolution measurements by both ground and space-based instruments. Popular descriptions attribute the aurora to solar wind particles striking the upper atmosphere. However, arcs are much more structured than can be explained by the solar wind alone. Moreover, the kinetic energy of auroral electrons is orders of magnitude larger than those in the solar wind. Spacecraft measurements dating back to the beginning of the space age have established that the source of energy and structure of auroral arcs – the so-called auroral generator – lies well within Earth’s magnetosphere. However, no spacecraft has yet been able to detect the magnetospheric “root” of an auroral arc, or to determine the fundamental conditions responsible for their formation and dynamics. This talk will address the gap between auroral observations and theories. Time permitting, I will also describe a new generation of charged particle detector used to probe the signatures and effects of auroral electron bombardment of the upper atmosphere.