2017 Seminar Archive

Brent Miszalski

Title: The role of binarity in Wolf-Rayet central stars of planetary nebulae
Abstract: Around 10% of central stars of planetary nebulae show spectra that mimic the appearance of massive Wolf-Rayet stars. While much progress has been made in identifying close binary central stars of planetary nebulae, with around 50 systems now known, only two are known to have Wolf-Rayet components. I'll give an overview of recent results in this area and report on some preliminary results from SALT spectroscopic    monitoring of Wolf-Rayet central stars.

Antonino P. Milone & Anna F. Marino

Title: Multiple stellar populations in Globular Clusters
Abstract: For half a century, globular clusters (GCs) have been considered as prototype of simple stellar populations and their color-magnitude diagrams (CMDs) were believed to be the proxy of an isochrone. Recent work has resulted in one of the most exciting and unexpected developments in stellar-population studies in recent years: the discovery that the CMDs of many GCs are made of two or more intertwined sequences that can be followed continuously from the hydrogen-burning limit to the last stages of the stellar evolution. These findings, together with the discovery that multiple sequences correspond to distinct stellar populations with different helium and light-element abundance, have dramatically changed the traditional picture of these seemingly simple stellar systems.

Among the open issues are the still-eluding second-parameter problem of the horizontal-branch morphology and the formation mechanisms that build the Galactic halo. Multiple populations may correspond to different generations of stars and prove that GCs, similarly to dwarf galaxies, have experienced a very complex star-formation history. As an alternative, they can be the product of exotic phenomena that have taken place in the proto-GC environment only.

Shi Dai

Title: Searching for pulsars in radio continuum surveys
Abstract: While pulsars are primarily detected and observed with high time resolution in order to resolve their narrow pulses, the phase averaged emissions of pulsars can be detected in radio continuum surveys. More importantly, continuum surveys are equally sensitive to all pulsars, not affected by the dispersion measure smearing, scattering or orbital modulation of spin periods, and therefore allow us to search for extreme pulsars, such as sub-millisecond pulsars, pulsar-black hole systems and pulsars in the Galactic Centre.

Next-generation radio continuum surveys, such as the ASKAP Evolutionary Map of the Universe (EMU), will map a large sky area at different radio frequencies with high sensitivities. Such surveys allow a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches.

In this talk, I will show you how to detect pulsars in radio continuum surveys and how to distinguish them from other compact radio sources. I will demonstrate a technique called variance imaging, which allows us to detect pulsars with interstellar scintillation, and show you how many new pulsars we can find with EMU.

Sachiko Kuroyanagi

Title: Anisotropies in the gravitational wave background as a probe of the cosmic string network
Abstract: Cosmic strings are one-dimensional topological defects, which arise naturally in scenarios of the early Universe, such as inflation based on string theory as well as phase transitions in field theories.  Pulsar timing array is the powerful tool to search for the existence of cosmic strings through detection of gravitational waves, and could provide us with insights on those high energy theories. 

In this talk, I will present how pulsar timing arrays can be used to search for cosmic strings and what types of information we can obtain if we detect gravitational wave background from them.  Furthermore I will show that we can extract more information on the cosmic string network by analyzing anisotropies in the gravitational wave background.

Andrew Lehmann

Title: Multi-fluid Shock Waves in Molecular Clouds, A Submitted Thesis
Abstract: The formation of stars occurs in the dense molecular cloud phase of the interstellar medium. Strong magnetic field gradients decouple the ionized component of molecular clouds from the neutral fluid. Similar decoupling occurs between gas and aerodynamic dust grains. Multi-fluid treatments are therefore required to accurately model the ubiquitous shock waves found in dynamic, violent molecular clouds. In this talk, I summarise my recently submitted thesis which focused on low-velocity turbulence driven magnetohydrodynamic shocks and dusty gas shocks in protoplanetary discs.

Luke Barnes

Title: How cosmological simulations can inform observational surveys and fundamental cosmology
Abstract: I will show two important ways in which cosmological simulations of galaxy formation can be used to inform astronomy and cosmology. Firstly, as part of the SAMI project, I have used a synthetic pipeline to produce mock SAMI datacubes of galaxies in simulations. In particular, I will show how synthetic galaxies have been "observed" with proposed designs for the Hector instrument.

Secondly, cosmological simulations can be used to investigate early-universe cosmological theories. Theories of cosmological inflation often predict that cosmic conditions will vary from place to place in the universe as a whole. In particular, the value of the cosmological constant can plausibly explained by a combination of environmental variation and its effect on galaxy formation.

In such models, it is crucial that we understand how quickly and efficiently the onset of accelerating expansion shuts down accretion of matter into dark matter haloes and galaxies. I will show simulations, based on the cosmological galaxy formation code of the Eagles collaboration that investigates this effect.

Leo Vanzi

Title: Zen and the art of building astronomical instruments... (in Chile!)
Abstract: In this seminar I will report on the work done at the Center of Astro Engineering of Pontificia Universidad Catolica de Chile in the area of astronomical instrumentation. In particular I will present our results in spectroscopy from the early steps to the recent installation of the high resolution spectrograph FIDEOS at the ESO 1m telescope of La Silla and the participation of our team in the project MOONS for the ESO VLT. Building astronomical instruments in a developing country is an interesting and challenging task, the purpose of the seminar is to share this experience in the broadest possible context.

Johannes Buchner

Title: Astrostatistics toolkit of the 21st century astronomer
Abstract: I will cover some methods for tasks astronomers face daily: (1) measuring a quantity of an astrophysical object (e.g. luminosity) under uncertainty (2) Combining multiple such uncertain objects for understanding the distribution of the population, sometimes under censorship. (3) comparing complex models of physical effects. New algorithms and easy-to-use implementations, including (Py)MultiNest and Stan, today make powerful tools available for analysing real problems with sufficient complexity.

Briefly, I will also give an overview of my X-ray astronomy research, which includes AGN obscuration, SMBH growth over cosmic time, GRBs and the analysis of cosmological hydrodynamic simulations.

Jordan Collier

Title: The path to ASKAP: faint things and curvy things
Abstract: During my thesis, I studied two classes of AGN: Infrared-Faint Radio Sources (IFRSs) and Gigahertz-Peaked Spectrum (GPS) / Compact Steep Spectrum (CSS) sources. IFRSs are recently discovered objects, whose nature was unconfirmed. We found a population of >1300 brighter IFRSs and measured the first spectroscopic redshifts, which showed they were high-z radio galaxies at z > 2 that might extend out to z ~ 7 and significantly increase the number of known high-redshift galaxies. We observed the faintest population of GPS/CSS sources to date, consisting of ~140 sources, using high-resolution ATCA observations. We observed the most compact of these with the LBA, determined their linear sizes and used many radio observations spanning 70 MHz - 34 GHz to model their radio spectra and spectral ages. We find evidence that low-luminosity GPS/CSS sources are similar to brighter samples, which are young and evolving GPS and CSS sources that may experience frustration and intermittent activity.

This study of young and distant radio sources led to working on the scientific validation of ASKAP continuum data, an important step both for commissioning the instrument and assessing its performance, and for beginning to develop the framework for the automated quality control and scientific verification that will be necessary for EMU. I will discuss the automated pipeline I have developed to produce a science validation report of ASKAP continuum data, the current results and the next steps.

Geoffrey C. Clayton

Title: Studying dust in the Universe with JWST
Abstract: The James Webb Space Telescope (JWST) is about to become a reality. It is scheduled to launch next year and the first round of proposals are due in August. The suite of instruments will do imaging and spectroscopy in the near- and mid-IR at a spatial resolution similar to that seen with Hubble Space Telescope. These instruments are ideal for the study of circumstellar and interstellar dust in a wide range of environments. I plan to discuss the capabilities of JWST and some of the exciting studies of dust that are being planned.

Darko Donevski

Title: Characterisation of high-z dusty galaxies in Herschel cosmological surveys
Abstract: The abundance of dusty galaxies at high-redshifts tests our theories about early galaxy formation. However, due to limited samples the contribution of dusty galaxies to the cosmic star formation rate density (SFRD) at z > 4 is still incomplete. One of widely used methods to detect potentially z>4 dusty galaxies is to select Herschel sources with thermal SED peak shifts to wavelengths longer than 500 microns (so-called "FIR-risers"). The method was successful to identify the most distant dusty starburst galaxies known to date (Riechers et al. 2013).We aim to build statistically significant sample of "FIR-risers" and to fully inspect selection biases. We consider one of the largest Herschel surveys, the Herschel Virgo Cluster Survey (HeViCS) centred at the heart of famous Virgo cluster. Since detection of "FIR-risers" is very challenging process due to the high source confusion, we implemented a new selection technique to find these sources, combining de-blending and SED fitting of sources (Donevski et al. 2017, to be submitted). We made a final sample of 133 "FIR-risers" reaching a good agreement with evolutionary models (e.g. Bethermin et al. 2012, 2017, Schreiber et al. 2016). It challenges previous studies in other Herschel fields (e.g. Asboth et al. 2016) which concluded to a significant under-prediction of the number of "FIR-risers" by the models. We further analyse mechanisms that could drive a galaxy to such prodigious infrared luminosities at early cosmic times.

Maria Lugaro

Title: Radionuclides: from Cosmochronology to Habitability
Abstract: Radionuclides with half-lives between 0.1 and 100 million years were present at the time of the birth of the Sun, as inferred from high-precision meteoritic analysis. Their abundances allows us to measure time intervals related to the birth of the Sun. Among these nuclei, aluminium-26 generated enough heat to contribute to the melting of ice and loss of water in ice-rich planetesimals in the early Solar System, with crucial implications on the amount of water delivered to the terrestrial planets in the habitable zone. However, the origin of aluminium-26 is still an open question and we do not know how common its presence may be in other planetary systems in the Galaxy.

Anna Ferré-Mate

Title: The diverse origins of compact Elliptical galaxies
Abstract: Compact elliptical galaxies (cEs) are rare in the local Universe, with only about two hundred reported to date. With very compact sizes (100-1000kpc) and intermediate stellar masses (10^8-10^10Msun), they have very high densities that resemble those  seen in the cores of massive ellipticals or disks. This suggest that cEs could be, in fact, the remnant of a larger, more massive galaxy that lost its stars via a stripping process. Other evidences support this claim, like the fact that they are typically found near a massive galaxy in dense environments or the fact that some have been caught in the act of stripping. However, some other recently found isolated cEs and cosmological models challenge this view, showing properties that demand another mechanisms of formation. Therefore, as it usually happens in nature, things are not simply white or black, and many factors come into play. Determining the origin and evolutionary stage of these rare cEs is not an easy task, but in this talk I will present a set of tools that can help discriminate between the possible formation mechanisms for cEs.

Tayyaba Zafar

Title: Australian-ESO partnership: instruments and applying time
Abstract: Australian astronomers got access to the Paranal and La Silla facilities including the 8m class telescopes after signing the decadal Strategic partnership with the European Southern Observatory (ESO). I as being the ex-ESO fellow and a support astronomer at Paranal will provide more insights to successfully apply for the ESO time. My talk will cover instruments available at Paranal and La Silla facilities. This will particularly give a good start to the users applying first time for the ESO night time. Hands on stuff, practical procedures, and phases for observing with ESO telescopes will be shown.

Wei Siang Tan

Title: SURVEY FOR C-BAND HIGH SPECTRAL LINES WITH THE ARECIBO TELESCOPE
Abstract: High-mass stars have masses greater than 8 solar masses and are the main source of heavy elements such as iron in the interstellar medium. This type of stars form in giant molecular clouds. Studying the molecular environment in star-forming regions is crucial to understand the physical structure and conditions that lead to the formation of high-mass stars. We present observations with the 305m Arecibo Telescope in Puerto Rico toward twelve high-mass star forming regions. Every source was observed in multiple spectral lines including transitions of CH₃OH, H₂CS, and OH lines, and radio recombination lines. The observations were conducted with the C-Band High receiver of the Arecibo Telescope in the frequency range of 6.0 to 7.4 GHz. The goals of the observations were to investigate the detectability of different molecular species and obtain high sensitivity observations of the 6.7 GHz CH₃OH line to detect absorption and use it as a probe of the kinematics of the molecular material with respect to the ionized gas. Among of the results of the observations, we report detection of 6.7 GHz CH₃OH masers toward nine regions, OH masers toward five sources, 6.7 GHz CH₃OH absorption toward four sources, and detection of H₂CS toward the star forming region G34.26+0.15. The 6.7 GHz CH₃OH and 6278.65 MHz H₂CS absorption lines were modeled using the radiative transfer codes RADEX and Molpop to investigate the physical conditions of the molecular clouds responsible for the absorption lines. Our analysis of the absorption lines supports the interpretation that the spectral lines are tracing molecular envelopes of HII regions. In the case of 6.7 GHz CH₃OH absorption, our results and data from an extensive literature review indicate that absorption is rare, but that a population of 6.7 GHz CH₃OH absorbers may be present at levels below 100mJy. In the case of the 6278.65 MHz H₂CS absorption in G34.26+0.15, the data are consistent with infalling gas onto the HII region, which supports the key principle of gravitational collapse of molecular clouds during the process of star formation.

Scott Croom

Title: Uncovering galaxy individuality with SAMI
Abstract: The SAMI Galaxy Survey aims to unravel the complexities of galaxy formation using integral field observations of thousands of galaxies. The sample spans a wide range in mass and environment, allowing a vast array of measurements to be made. I will discuss key results from SAMI, including the role of environment in star formation and the insights that kinematics gives us into formation history.

Inger Jørgensen

Title: Passive Galaxies in Massive Clusters - a Journey from z=1.27 to the Present
Abstract: Mapping galaxy evolution through observations of similar galaxies as a function of redshift can be used to constrain models of their formation and evolution. Here we focus on passive galaxies in dense cluster environments. We investigate possible size evolution, test the usability and limitations of a simple passive evolution model and establish how ages, metallicities and abundance ratios depend on galaxy velocity dispersion and on redshift. The data come from the Gemini/HST Galaxy Cluster project, covering 14 clusters with deep ground-based optical spectroscopy and HST imaging.

Pierfrancesco Di Cintio

Title: Dynamical origin of non-thermal states in filamentary structures in galactic molecular clouds
Abstract: Observations strongly suggest that filaments in galactic molecular clouds are in a non-thermal state. As a simple model of a filament we study a two-dimensional system of self-gravitating point particles by means of numerical simulations of the dynamics, with various methods: direct $N$-body integration of the equations of motion, particle-in-cell simulations and a recently developed numerical scheme that includes multiparticle collisions in a particle-in-cell approach. Studying the collapse of Gaussian overdensities we find that after the damping of virial oscillations the system settles in a non-thermal steady state whose radial density profile is similar to the observed ones, thus suggesting a dynamical origin of the non-thermal states observed in real filaments. Moreover, for sufficiently cold collapses the density profiles are anticorrelated with the kinetic temperature, i.e., exhibit temperature inversion, again a feature that has been found in some observations of filaments. The same happens in the state reached after a strong perturbation of an initially isothermal cylinder. Finally, we discuss our results in the light of recent findings in other contexts (including non-astrophysical ones) and argue that the same kind of non-thermal states may be observed in any physical system with long-range interactions.

George Jacoby

Title: The Other Side of Authorship
Abstract: I will describe what it is like to be a science editor for the AAS journals (e.g., ApJ, AJ) - that is, what happens backstage after an author submits a paper. I will discuss some of the lesser-known features of the AAS journals that are available to you, and how these may enhance your authorship experience, as well as the challenges that the science editors must manage on your behalf.

Stefania Barsanti

Title: Impact of group environment on star formation in GAMA
Abstract: It is well established that cluster galaxies show a suppression of star formation with respect to the field, but the situation is less clear for galaxies in groups. We studied 1197 Galaxy And Mass Assembly (GAMA) galaxy groups to explore whether and how the group environment may affect the star formation properties of infalling star-forming galaxies. We analysed the projected phase space in the low-mass halo regime, observing that the fraction of star-forming members is higher in the regions dominated by recently accreted galaxies, whereas passive galaxies dominate the virialised regions. We also observe a small decline in specific SFR of star-forming galaxies towards the group centre by a factor ∼1.2 with respect to field galaxies. Similar to cluster studies, we conclude that star-forming group galaxies represent an infalling population from the field to the halo and show suppressed star formation.

Mita Brierley

Title: AAL Member Update: Macquarie University
Abstract: I will include updates around the changes in the structure of optical infrastructure in Australia as a result of the strategic partnership with ESO.

Onno Pols

Title: Mysteries in the evolution of chemically polluted binaries
Abstract: Binary systems in which one star has been polluted by mass transfer from a former asymptotic red giant companion star, are excellent probes both of AGB nucleosynthesis and of binary interaction processes. Examples include post-AGB binaries, barium stars and (at low metallicity) carbon-enhanced metal-poor stars. The orbital periods and eccentricities of these systems are at odds with the predictions of standard binary evolution theory: they lie in a region where a gap is expected in the orbital period distribution. In this talk I will explore some of the ill-understood interaction processes that may be at work in these binaries, and present results of hydrodynamical mass-transfer simulations and binary population nucleosynthesis models that are starting to shed light on their mysterious orbits and abundance patterns.

James Allison

Title: The history of cold gas in the Universe using the SKA
Abstract: The Square Kilometre Array (SKA) and its pathfinder telescopes will provide a unique perspective on the cold neutral gas that fuels star formation and black hole growth in galaxies throughout cosmic history. Through detection of the HI 21-cm line in absorption towards distant radio-loud AGN, the SKA will be used to construct a census of the cold neutral medium in intervening galaxies out to look back times of 10 billion years and beyond. I will discuss a recent paper in which I proposed a method for measuring the fraction of cold-phase atomic hydrogen using a statistical approach based on the number of expected detections with the SKA and its pathfinders. I will also present recent science results with the Australian SKA Pathfinder (ASKAP), which have successfully demonstrated the feasibility of carrying out such a survey.

Cassie Fallscheer

Title: Astronomy At Sea: Four months teaching astronomy on a ship
Abstract: In January 2015, I embarked the MV Explorer as faculty on Semester At Sea. For four months I taught astronomy and traveled the world. In this talk, I will discuss differences between teaching astronomy in a classroom on land versus a floating classroom at sea. At a port stop in South Africa, the idea to build a spectrograph for the Central Washington University Research Telescope came about. The spectrograph is now underway, and I will give a short overview of the current status.