2019 Abstracts

2019 Abstracts

Mr Dylan Bollen

Title: Modelling jets in post-AGB binary systems
Abstract: The post-asymptotic giant branch (post-AGB) is a short-lived phase in the life of dying low- to intermediate-mass stars. The past ten years, we have obtained a large set of high-resolution optical spectra of post-AGB stars in binary systems with the MERCATOR telescope (La Palma, Spain). This has revealed the presence of jets that are launched by these systems.
We aim to understand the accretion and jet creation processes in post-AGB binaries. In order to do so, we have created a spatio-kinematic model of the jet which we use in an MCMC-fitting routine to determine the spatio-kinematic structure of the jet. Additionally, we have made a radiative transfer model of the system to determine the mass-loss rate by the jet. By doing so, we can constrain theories of jet launching and the impact of jets on the evolution of the system as a whole.

Dr Smitha Subramanian

Title: Evolution of the Small Magellanic Cloud as traced by VMC and Gaia

Abstract: Formation and evolution of galaxies are mainly driven by mergers and interactions. The signatures of these interactions are expected to be imprinted on their structure and stellar populations of these galaxies and hence, are excellent probes to understand galaxy evolution. In the low redshift, minor mergers dominate. Magellanic System is one of the nearest examples of a minor merger event. In this talk, I will present the 3D structure and kinematics of the stellar populations of the Small Magellanic Cloud obtained using the data from the VISTA Survey of the Magellanic Clouds and Gaia and the implications of the results on our understanding of the evolution of the Magellanic System.

Dr Hannah Worters

Title: The South African Astronomical Observatory.

Abstract: The SAAO hosts 24 optical/infrared telescopes in the semi-arid desert region of the Karoo.  I will give an informal overview of what we have (including the 10-m SALT telescope), what we're working on (a bunch of new instruments, remote observing and AI), and what you can apply to use (without any membership requirements or fees).

Dr Vanessa Moss

Title: Survey of Weak Intensity Southern HI: Uncovering the hidden iceberg structure of the Galactic halo.

Abstract: How the Milky Way gets its gas and keeps its measured star formation rate going are both long-standing mysteries in Galactic studies, with important implications for the relationship of galaxies to their circumgalactic media throughout the Universe. I will present our discovery of two populations of neutral hydrogen (HI) in the halo of the Milky Way: 1) a narrow line-width dense population typical of the majority of bright high velocity cloud (HVC) components, and 2) a fainter, broad line-width diffuse population that aligns well with the population found in very sensitive pointings such as in Lockman et al. (2002). This discovery of diffuse HI, which appears to be prevalent throughout the halo, takes us closer to solving the Galactic mystery of accretion and reveals a gaseous neutral halo hidden from the view of most large-scale surveys. We have carried out deep Parkes observations as part of the Survey of Weak Intensity of Southern HI (SWISH) to investigate these results further, in order to truly uncover the nature of the diffuse HI and determine whether the 3:1 diffuse/dense ratio (based on the limited existing data) is consistent with what is seen when Parkes and the 140 ft Green Bank telescope are employed at comparable sensitivity. With these data, through a combination of both known and new sightline measurements, we aim to reveal the structure of the Galactic halo in more detail than ever before and connect our results to the recent studies of ionised UV absorption towards HVCs.

Ms Amy Whitney

Title: Unbiased size evolution in the GOODS fields.

Abstract: We present a new analysis of a sample of galaxies from the GOODS North and South fields of CANDELS using distance independent relative surface brightness metrics to determine an unbiased measure of the size evolution over the redshift range 1<z<7. We introduce a new method of removing background objects from images of galaxies, used in order to reduce the effect extraneous objects have on measuring the size of a galaxy. Using the Petrosian radius, we are able to determine whether the size of a galaxy increases most in the inner or outer regions. We find a slower evolution of the inner regions of galaxies compared to the outer regions which imply mass is added to the outer edges of a galaxy as it evolves and therefore suggests inside-out formation. Our results place new limits on the history of galaxy structural evolution through the past 12 Gyr of cosmic evolution.

Prof. Andy Bunker


"Exploring the high redshift Universe with JWST”



Prof. Shu-ichiro Inutsuka

Title: Filament Paradigm and Star Formation in the Galactic Disk.

Abstract: Recent observations of molecular clouds in the solar neighborhood have emphasized the importance of the formation and evolution of magnetized filamentary molecular clouds in the process of star formation. Theoretical and observational investigations have provided convincing evidence for the formation of protostars by the gravitational fragmentation of filamentary molecular clouds, which quantitatively explains both mass function and angular momentum distribution of molecular cloud cores. We summarize our current understanding of various processes that are required in describing star formation through the filamentary molecular clouds in the Galactic disk.

Ms Stefania Barsanti

Title: SAMI: bulge and disk stellar populations in cluster galaxies.

Abstract: The formation of S0 galaxies is stille a deep mystery in astrophysics. Our aim is to disentangling the properties of the stellar populations in the bulge and the disk, which can help us in understanding the origin of S0 galaxies. We study galaxies in dense environments, using the cluster sample of the SAMI galaxy survey which contains 8 low-redshift clusters. We perform 2D photometric bulge-disk decomposition in multiple bands and we use Bayesian techniques for galaxy characterization. For 192 double-component galaxies we estimate the colour, mass-weighted age and metallicity of the bulge and the disk. To measure age and metallicity we investigate a new method based on galaxy
stellar mass weights for the two components. We find that bulges are mainly redder than the surrounding disks. Bulges are observed to be both older and younger than the disk counterparts, but they are mainly more metal-rich. Redder bulges tend to be more metal-rich, suggesting that their redder colour is due to their metallicity. In this talk, I will present our new method of analysis and discuss our results which break the age-metallicity degeneracy.

Dr Lorenzo Spina

Title: The Milky Way disk that we have never observed.

Abstract: Galaxies are factories that convert gas into stars: in the process, they constantly produce new metals and evolve. Linking this chemical build-up to the history of galaxies is possible by studying the chemical makeup of stars in our own Galaxy. I will present the results of our latest studies on the chemical composition of the Milky Way disk. Then I will discuss the main factor that cripples our best efforts to unravel the Galaxy's history (e.g., Gaia, GALAH) and some new ideas to overcome it.

Prof. Toshifumi Futamase

Title: Subaru Weak lensing Survey of Dark Matter Subhalos in Coma and nearby clusters of galaxy.

Abstract: The hierarchical structure formation scenario based on the cold dark matter (CDM) paradigm has been very successful in explaining various cosmological observations such as the large scale distribution of galaxies, and thus became the standard scenario for structure formation. However there is almost no observational evidence to test it on the Mpc scale where mass assembly history becomes important. We have performed weak lensing observation of COMA cluster at z = 0.027. and other nearby

clusters with z<0.05 to test CDM predictions in Mpc scale. We detected convincingly more than 100 subhalos in a model-independent manner in our cluster sample, in particular 32 subhalos down to the order of 10−3 of the virial mass of the Coma Cluster. WL mass measurements of shear-selected subhalos allow us to investigate subhalo properties and the correlation between subhalo masses and galaxy luminosities for the first time. The constructed mass function is consistent with the prediction by N-body simulation based on CDM scenario. In this talk I will give a brief introduction of weak lensing and then show our results and ongoing weak lensing survey of very nearby cluster z<0.05 using Subaru/HSC.

Dylan Michelson Paré

Title: A VLA Polarimetric Study of the Galactic Center Radio Arc: Characterizing Polarization, Rotation Measure, and Magnetic Field Properties".

Abstract: "The Galactic Center (GC) is a unique observational target containing molecular cloud densities, magnetic field strengths, and gas temperatures more extreme than found elsewhere in the Galaxy. One way to study the properties of the strong magnetic field in this region is to analyze the unique non-thermal filaments (NTFs) -- extended, synchrotron-emitting structures. The most prominent set of NTFs is known as the Radio Arc. In this talk I present the results of my VLA study of the Radio Arc and compare my findings with those obtained for other NTFs in the GC. I detail the complex region the Arc NTFs are embedded within and also detail the polarized intensity structure of the Arc NTFs. We analyze the distribution of RM values for the source and determine the rotation is likely caused by external media along the line of sight. After correcting for Faraday rotation, the intrinsic magnetic field orientation is found to generally trace the extent of the NTFs. However, the intrinsic magnetic field in several regions of the Radio Arc shows an ordered pattern that is rotated by about 60 degrees to the extent of the NTFs. This changing pattern may be caused by an additional magnetized structure local to the Radio Arc, so that we observe two field systems superposed in our observations."

Dr Alessandro Maini

Title: Radio-Quiet AGN: What brews into the cauldron?

Abstract: The radio-quiet/radio-loud dichotomy of Active Galactic Nuclei is an outstanding and long-lasting open question in Astrophysics research, dating back to the '60s of the past century. Only some 30 years ago the Astrophysics community started to shed some light on the topic, but the more we dug into the dichotomy the more the questions that were raised. Today, we can say that it is quite clear what radio-loud AGN are, but the same answer for radio-quiet objects eludes us. In this talk, I will briefly recall the historical evolution of the dichotomy topic, to show how it started and where we are now. I will also show my personal contribution to the research on the topic, focusing on findings about the nature of some radio-quiet AGN I worked on during and after my PhD work.

Dr Meridith Joyce

Title: Better Stellar Modeling: Numerical Tools and Techniques for the Modern Observational Landscape.

Abstract: These data will help us calibrate stellar models!" is an oft-quoted refrain in justifications for scientific projects, yet we hear less frequently and in less detail about the ways large surveys of stars or precision measurements of individual systems actually do drive improvement in our stellar models.  In this talk, I will highlight a few recent cases in which the contemporaneous expansion of our modeling capabilities and the increased availability of observational constraints have aligned to provide us with exciting new insights on stars and stellar physics.

I will discuss the seismic and evolutionary modeling of T Ursae Minoris using the Modules for Experiments in Stellar Astrophysics (MESA) code and advertise the new 1D-MESA2HYDRO-3D software package just released this month. The latter is a Python tool for projecting 1D MESA profile models into 3D particle distributions that can be used as initial conditions for hydrodynamical modeling with Phantom smoothed-particle hydrodynamics program, designed with the help of collaborators here at Macquarie University and at Monash University.

Mr Chikaedu Ogbodo

Title: A-Masing Star is born!: When magnetic fields don't go Gaga!

Abstract: Observed at the Galactic scale, magnetism plays an essential role at the onset of star formation, going from weak diffuse interstellar fields to amplified compressed fields. Weak, large-scale Galactic magnetic fields in diffuse gas have been extensively studied. In contrast, high density regions of the Galactic spiral arms which host high-mass star forming (HMSF) regions have typical magnetic field strengths order(s) of magnitude stronger. I study the correlation between orientations observed in the diffuse large-scale magnetic field and the Galactic-scale magnetic field directions traced in high-density regions, using observations of four ground-state OH masers towards 554 sites of 6.7-GHz methanol masers (exclusive tracers of HMSF). I use the Zeeman effect to measure the in-situ magnetic field direction and strength in these high-density regions. An expected outcome is to determine if the information about field orientation is retained after contraction from weak large-scale magnetic fields to the high densities found in high-mass star forming regions. I'll present the complete polarimetric and detection results for the rarer 1720-MHz OH maser transition, and the Galactic magnetic field distribution revealed by the in-situ magnetic field orientation of the 1720-MHz maser transition.

Ms Rachel Rayner

Title: Science Communication

Abstract: The field of science communication is growing exponentially; but what does it look like and how can it help obtain research goals? By exploring methods of science communication used on land, air and sea, we can extract tools for the communication of astronomy to larger and broader audiences.

Prof Isabel Perez Martin

Title: Are galactic bars efficient at stirring and mixing their discs?

Abstract: Bars are believed to be major drivers of secular evolution and radial mixing in spiral galaxies through its dynamical interaction with the disc and the halo. Bars are present in around 70% of dic galaxies and they are thought to be key to the rearrangement of material and angular momentum as well as in the building up of the central bulge. I will review our current understanding of how bars affect their hosting galaxies throughout time, placing in this context the Milky Way bar. I will present recent observational results based on integral field spectroscopy of 2D and radial distribution of the stellar and the ionised gas properties of a large sample of galaxies. I will also show some recent observational results on the issues of bar formation and evolution to conclude on the importance of bars in the galaxy makeover.

Dr Robert Harris

Title: Astrophotonics at the Landessternwarte, Heidelberg.

Abstract: As astrophotonic instruments increase in maturity they are moving from small prototypes to capable scientific instruments. This development is leading to further challenges of long term stability and increased performance. In this talk, I will describe the on-going work at the Landessternwarte, Heidelberg, to model and develop some of these devices and instruments. I will detail our astrophotonic group’s work on modelling past experiments, the development of a 3D printed microlens ring for use as a tip-tilt sensor for the iLocater on the Large Binocular Telescope and the development of the MCIFU, a multi-core fibre fed integral field spectrograph. I will also discuss our future plans for the instruments.

Ms Anita Petzler

Title: Getting excited about excitation: Making sense of a scary molecule

Abstract: The molecular gas of the interstellar medium (ISM) provides the raw material for star formation, but it can be difficult to observe. Molecular hydrogen (H2) doesn't undergo any readily observable transitions in the temperature and density regimes prevalent in the ISM, so we must observe it via other tracer molecules. I study the ISM via observations of the four hyperfine transitions of the ground state of the hydroxyl radical. The relative population of this four-level system is very sensitive to environmental conditions such as temperature, density and radiation. I have developed an automated gaussian fitting algorithm that employs Bayesian model selection to determine the populations in the four levels of the hydroxyl ground state (amoeba: automated molecular excitation bayesian line-fitting algorithm). Quantifying the excitation of the hydroxyl radical allows us to then employ molecular excitation models to determine the local environmental conditions of the gas, thus informing stellar formation models.

Dr Daniel Cotton

Title: A New Age of Stellar Polarimetry.

Abstract: We have entered a new age of stellar polarimetry, and are poised to answer some of the outstanding questions in stellar evolution. These questions include the interior structure of stars, their rotation and the complications of binarity, which are currently the biggest sources of uncertainty in stellar evolution models (e.g. Heger 2000, Georgy et al. 2017). In this talk, I will give an overview of the technique of polarimetry, the progress we have made on these questions and the future direction of this research.

Since the discovery of interstellar polarisation in the 1940s, the applications of optical stellar linear polarimetry have been largely limited to examining dust and gas in interstellar and circumstellar processes. Yet, in his seminal paper, that spurred the development of the first modern instruments, Chandrasekhar (1946) envisioned studying the atmospheres of eclipsing binaries. Since then Harrington & Collins (1968) have shown polarimetry can be used to measure the true rotational speeds of stars, and Odell (1979) that polarimetry has the power to determine the modes of oscillation in heavy stars – revealing the structure of their interiors. For 70 years instrumental imprecision has prevented the pursuit of these endeavours.

Over the last 5 years, my colleagues and I have been at the forefront of the development and application of a new generation of high-precision stellar polarimeters. With these instruments, we have pushed the limits of their conventional uses, contributed to the study of exoplanet atmospheres with them, and with the aid of radiative transfer models, pioneered their application to stellar atmospheres. We have made the first measurement of intrinsic polarisation resulting from rapid rotation (Cotton et al. 2017), and most recently observed polarimetric variation due to non-radial pulsation in beta Cephei stars. We have also made the first determination of true reflection in binary star systems (Bailey et al. 2019) – an effect that was never predicted, and yet is readily observable with our instrument using even an amateur-sized telescope!

References: | Heger et al. (2000) ApJ 528, 1. | Georgy et al. (2017) ABSC Conf., 37. |Chandrasekhar (1946) ApJ 103, 351. | Harrington & Collins (1968) ApJ 151, 1051. | Odell (1979) PASPC 91, 326. | Cotton et al. (2017) Nature Ast. 1, 690. | Bailey et al. (2019) Nature Ast. in press.

Dr Joanne Drazkowska

Title: How do planets form?

Abstract: Recent years brought a paradigm shift for how planets form. It has become clear that planet formation is a rule rather than an exception. Nevertheless, this process remains poorly understood. I will present the most recent discoveries and concepts emerging in the planet formation community. I will particularly focus on the earliest stages of planet formation when small dust grains present in disks surrounding young stars grow towards the building blocks of planets, called planetesimals.

Dr Andy Sheinis

Title: Update on the Maunakea Spectroscopic Explorer.

Abstract:  Australia is a partner in the Maunakea Spectroscopic Explorer (MSE), a massively multiplexed pectroscopic survey facility that will be built in the coming decade on the Canada-France-Hawaii telescope site on Maunakea, Hawaii.   MSE will be a dedicated, 11.25 m, wide-field telescope that will observe more than 4000 targets distributed over 1.5 square degrees in every pointing.  MSE will use 8 fibre-fed spectrographs to capture ~3000 low resolution spectra (R~3000) and ~1000 high-resolution spectra (R~40,000) covering the full 1.5 sq. degree field contiguously with each resolution. MSE will have a survey speed that is ~6x faster than PFS and ~20X faster than MOONS based on perture size x field of view x multiplexing x observing time.  Furthermore, it will produce the same number of spectra as the full SDSS Legacy Survey every 7 weeks. Some of the initial science goals will be to identify the astrophysical location and details of stellar nucleosynthesis; unveil the composition and dynamics of the faint universe through chemical abundance studies of stars in the outer Galaxy; measure the masses of thousands of black holes at the cores of galaxies; weigh neutrinos; and test exotic models of cosmology where dark energy properties vary at high redshift. Australian scientists make up approximately 10 % of the MSE Science Team that now involves close to 400 astronomers from 30 countries. Furthermore, Australia has been picked to develop the fibre positioner system based on the systems AAO produced for Subaru and 4Most.  Here, I will review the technical aspects of the facility and discuss scientific potential of the only dedicated 10-meter class spectroscopic facility planned for the coming decade.

Mr Abdelbassit Senhadji

Title: A new channel for the formation and evolution of subdwarf stars.

Abstract: We present a detailed analysis of the conditions required to form subdwarf stars in wide binaries via stable Roche Lobe overflow. Starting with an evolutionary grid of almost 4000 primordial binaries with component masses between approximately 1 to 8 Msun and initial orbital periods of ~1 to 200 days, many of these binaries experience an Algol-like phase of evolution and a substantial fraction of those produce binaries containing subdwarfs with orbital periods of between ~20 to 500 days. We conclude that: (1) the final period is largely dependent on the assumed physics of non-conservative mass transfer; (2) the donor star (subdwarf progenitor) typically has a mass of between about 3 and 6 solar masses; (3) there is a very natural evolution of subdwarfs from a long-lived sdB stage (~100 Myr) to the sdO stage (~30 Myr); and, (4) the range of masses and effective temperatures of sdB and sdO stars can overlap substantially depending on the properties of the primordial binary. Specifically, we find that the masses can range from ~0.4 to 0.8 Msun, and that sdBs have temperatures in the range of 15000 < Teff (K) < 45000 while the range for sdOs is about 25000 < Teff (K) < 100000. One example of a post-Algol binary that is evolving towards the subdwarf stage is MWC882 (Zhou et al. 2018). The observational implications of this channel are also discussed.

Mr James Tocknell

Title: Winds from Protoplanetary Discs

Abstract: Magnetically-driven disc winds have significant effects on the evolution of protoplanetary discs, via the removal of angular momentum and mass from the disc. However, existing models typically ignore non-ideal magnetohydrodynamic effects, such as Hall drift, but these are known to operate inside these discs, and affect their structure and evolution, for example suppressing magnetically-driven turbulence and magneto-rotational instability. In my talk, I will present preliminary results of self-similar disc wind models which include non-ideal magnetohydrodynamic effects within the disc.

Mr Greg Goldstein

Title: The Distribution of Star Formation Across Galaxi Disks

Abstract: The distribution of the star formation across galaxy disks using integral field spectroscopy is studied to determine if the distribution varies according to the location of a galaxy on, above or below the main sequence of star formation. Radial profiles of the star formation rate surface density demonstrate that central suppression of star formation may occur in galaxies in all locations. It is considered there is an evolutionary sequence moving from MS, to quenching-in-progress, to quenched allowing tests of proposed mechanisms for quenching.  The findings favor quenching models such as the compaction model, and bar-driven quenching that involve a sequence of processes including: disk instabilities that trigger gas inflows, central starbursts, stellar feedback and gas outflows, and central quenching associated with gas depletion.

Mr Hiep Nguyen

Title: “Exploring the properties of warm and cold atomic hydrogen in the Taurus and Gemini regions".

Abstract: We report Arecibo 21 cm absorption-emission observations to characterise the physical properties of neutral hydrogen (HI) in the proximity of five giant molecular clouds (GMCs): Taurus, California, Rosette, Mon OB1, and NGC 2264. Strong HI absorption was detected toward all 79 background continuum sources in the ~60x20 square degree region. Gaussian decompositions were performed to estimate temperatures, optical depths and column densities of the cold and warm neutral medium (CNM, WNM). The properties of individual CNM components are similar to those previously observed along random Galactic sightlines and in the vicinity of GMCs, suggesting a universality of cold HI properties. The CNM spin temperature (Ts) histogram peaks at ~50K. The turbulent Mach numbers of CNM vary widely, with a typical value of ~4, indicating that their motions are supersonic. About 60% of the total HI gas is WNM, and nearly 40% of the WNM lies in thermally unstable regime 500-5000K. The observed CNM fraction is higher around GMCs than in diffuse regions, and increases with increasing column density (NHI) to a maximum of ~75%. On average, the optically thin approximation (N*(HI)) underestimates the total N(HI) by ~21%, but we find large regional differences in the relationship between N(HI) and the required correction factor, f=N(HI)/N*(HI). We examine two different methods (linear fit of f vs log10(N*(HI)) and uniform Ts) to correct for opacity effects using emission data from the GALFA-HI survey. We prefer the uniform Ts method, since the linear relationship does not produce convincing fits for all subregions.

Prof Rupert Croft

Title: Relativistic probes of galaxies and the large-scale structure of the Universe

Abstract: In the next 5 years, the number of galaxies with measured redshifts will increase into the tens of millions. This will enable us to map the large-scale structure of the Universe with great precision.  New tests of dark energy, dark matter and the nature of gravity will become possible. One avenue is to search for evidence of relativistic effects, which alter the relationship between the intrinsic and observed properties of galaxies. These include the gravitational redshift (first seen in Earth-bound laboratories in 1960), that depends on the depth of galaxy potential wells. Another is relativistic beaming, which is sensitive to the interplay between galaxy peculiar velocities and their spectra. The first large surveys of galaxies have begun to make measurements of these effects possible, and they offer us a new way look at the relationships between galaxies and their surrounding dark matter.  I will describe how to measure these effects, including results from hydrodynamic simulations as well as the first measurements from both large scale structure survey data and individual galaxies.

Prof Tiziana Di Matteo

Title: A Universe of Black Holes

Abstract: Massive black holes are fundamental constituents of our cosmos. Understanding their formation at cosmic dawn, their growth, and the emergence of the first, rare quasars in the early Universe remains one of our greatest theoretical and observational challenges. Hydrodynamic cosmological simulations self-consistently combine the processes of structure formation at cosmological scales with the physics of smaller, galaxy scales. They capture our most realistic understanding of massive black holes and their connection to galaxy formation. I will focus on the predictions for the first quasars and their host galaxies in the BlueTides simulation. Next generation facilities and the advent of multi-messenger astrophysics brings new exciting prospects for tracing the origin, growth and merger history of massive black holes across cosmic ages.

Mr Abner Zapata

Title: “FIDEOS spectrograph: radial velocity stability results at the ESO1m”

Abstract: The Fiber Dual Echelle Optical Spectrograph (FIDEOS) is a high-resolution spectrograph developed by the Center of Astro-engineering UC, Chile, and installed in the ESO1m telescope at La Silla Observatory. We present the results of the commissioning and early science. The radial velocity (RV) precision and stability were improved during the early operation reaching values as good as 5 m/s in a single night and long term stability better than 10 m/s. Also, we present a brief overview of our ongoing and future projects.

Dr. Esha Kundu

Title: SNe IIb in Radio

Abstract: Massive stars that loss most of their hydrogen envelope explode as Type IIb supernovae (SNe IIb). The progenitors of these SNe may be single massive stars that undergo huge mass loss due to strong winds. Alternatively, the mass stripping can happen due to an interaction with a companion star in a binary system. A useful way to investigate the pre-SN systems is to look for radio emission from the interaction of SN ejecta with the circumstellar medium (CSM). The flux of radio emission is roughly proportional to the density of the particle in the CSM, which, in general, is shaped by the mass ejection from the pre-SN star. Therefore, by studying this radiation one can map the mass-loss history of the progenitor star. In this talk, I will mainly focus on radio emission from two very well observed SNe IIb, SN 1993J and SN 2011dh, and discuss how the detailed modelling of their radio emission has enabled us to gain vital information about the evolution of their progenitors before explosion.

Dr Simon Ellis

Title: Making the near-infrared night sky dark.

Abstract: The near-infrared night sky is extremely bright due to emission from atmospheric OH molecules.  The high surface brightness makes sky-subtraction intrinsically noisy.   Furthermore, the OH emission is highly variable, spatially and temporally, leading to large systematic errors in sky-subtraction.   This long-standing problem has severely hindered near-infrared astronomy for decades, but we are now close to a ground-based solution for the first time. PRAXIS is a unique near-infrared spectrograph currently being commissioned on the AAT, which selectively filters the atmospheric OH lines from the incoming light using fibre Bragg gratings, rendering the sky dark.  I will describe the principles of OH suppression with fibre Bragg gratings, and the development of this novel technology up to the present day, culminating in PRAXIS.  I will present preliminary results from the first two commissioning runs, and describe possible future developments.

Dr Elaina Hyde

Title: Science vs. DataScience Astrophysics Face-Off: Who Will Win?

Abstract: This talk will cover my journey through Astrophysics and Data Science with some tips and tricks that I picked up along the way as well as some of the processes that I use in my work. I will compare Data Science and Science methodologies and discuss what it means for Astrophysics. I will additionally cover some of the tools that have helped me build my career in STEM so far. If we have time, we will even play a Machine Learning game.

Mr Georges Georgevits

Title: Searching for Kuiper Belt objects by stellar occultation.

Abstract: The Kuiper Belt is the region of the solar system extending from the orbit of Neptune to ~50AU. A large number of objects, known as Kuiper Belt Objects (KBOs), are thought to reside there. Only the largest of these can be seen by direct observation, since they are so distant and faint. Small KBOs, too faint to be seen by direct observation, can be detected by stellar occultation when they pass in front of a suitable background star.

Our work reports the results obtained from a ground-based stellar occultation survey using the 1.2m UK Schmidt telescope fitted with 100 optical fibres feeding a CCD camera with continuous readout and 10msec time resolution. We accumulated 6,500 star-hours of data on the ecliptic, including Neptune’s L4 Lagrangian region. Our setup is capable of detecting KBOs with radii greater than about ~0.25km. This is two orders of magnitude smaller than that achievable by direct observation.

We report one detection event---a KBO of radius ~0.43km at a distance of 46AU. This is the best resolved KBO occultation event reported to date, and arguably the first credible ground based detection. From our survey results we constrain the implied cumulative population density for KBOs with radii greater than 0.25km within ±2 degrees of the ecliptic to ~10^7 objects per square degree of sky.

Dr Lucyna Kedziora-Chudczer

Title: Light scattered from the atmosphere of a planet and its surface is polarised.

Abstract: In contrast, light from solar-type stars is largely unpolarised. Therefore polarimetry can be used for the detection and characterisation of extrasolar planets around such stars. The degree of polarisation due to reflected starlight depends strongly on the composition and physical properties of planetary atmospheres. Ultimately observations of polarisation could provide the clues about the water droplets in the planetary atmosphere and possible detection of liquid water on the planetary surface via glint reflection.

I will discuss processes that lead to polarisation of light. Next I will talk about techniques of polarisation measurements and describe polarimetric observations of hot Jupiters with the high precision polarimeter, HIPPI built for the AAT at the UNSW. I will also describe capabilities of the newly developed polarimeter, HIPPI-2, to be used on the 8-metre Gemini telescope and will briefly mention other projects carried out with the HIPPI polarimeter.

Professor Di Li

Title: "How to Catch the Cold Gas"

Abstract: Star formation is the key process in producing 'luminous' matter in galaxies. To allow gravity to drive matter toward nuclear fusion, interstellar medium (ISM) needs to evolve from atomic to molecular forms. H2 formation, mainly happening in cold gas, is hard to observe and thus not well constrained nor understood, as demonstrated by the current controversy regarding the so-called 'dark gas' (Grenier et al. 2005). I report here our measurements of cold gas and H2 formation, mostly through absorption techniques.  Based on the HI Narrow Self-Absorption (HINSA: Li et al. 2003) method, we published the first clear detection of the birth of a molecular dark cloud (Zuo et al. 2018). The formation time scale, and thus the lower limit of star formation time scale, is longer than 6 million years. In the region where a stable abundance of CO is not established, we found that OH is a good tracer of the total H2 content (Xu et al. 2016). We measure the OH excitation temperature through quasar absorption to be close to that of the Galactic background (Li et al. 2018), explaining why OH, the first radio-discovered and abundant molecule,  remains elusive. Upcoming sensitive radio facilities, namely ASKAP, FAST, MeerKAT, SKA1, etc., will provide a complete inventory of Galactic cold gas through absorption (McClure-Griffith et al. 2015).

Ms Rebecca Davies

Title: Resolved Properties and Demographics of Ionized Gas Outflows at z~1-3

Abstract: Outflows are ubiquitous at the peak epoch of star formation (z~1-3), and are likely to play an important role in shaping the growth and evolution of galaxies. Near-IR integral field spectroscopy is a powerful tool to investigate the physical properties of galactic winds at this epoch because it enables us to kinematically disentangle them from gravitational motions, and to map the launch sites, extent, and geometry of outflows. In this talk I will present the most recent results from our integral field studies of outflows at z~1-3. I will summarise the properties and scaling relations of outflows resolved on 1-2 kpc scales using SINFONI with adaptive optics, and place these results in the context of our study of global outflow properties and demographics from the KMOS^3D survey.

Dr Samyaday Choudhury

Title: Study of sparse star clusters and metallicity maps of the Magellanic Clouds.

Abstract: I will present our studies directed towards two frotiners: (1) understanding sparse star clusters and their importance in our neighbouring galaxies, the Magellanic Clouds (MCs, the LMC & SMC), and (2) understanding the metallicity variation in these two galaxies. The MCs apart from rich populous clusters also host poor/sparse star clusters. Our work on sparse star clusters in the LMC, is aimed to increase our understanding of such objects, using deep Washington photometric data of 45 star clusters. A systematic study was performed to estimate their parameters, and they were grouped the into two categories based on their genuineness. The sizes and masses of these inconspicuous clusters emphasizes that the LMC has a significant population of clusters, which are similar to the open clusters in our Galaxy.  Motivated by the above finding, a larger team is looking into the low mass open cluster like systems (identification, cataloging, estimating properties) in the LMC & SMC using existing large area surveys (e.g. OGLE III). To understand the metallicity variation within the LMC and the SMC, we created first of its kind high-spatial resolution metallcity map with field Red Giant Branch (RGB) stars as the tool, using two large scale photometric surveys: the MCPS and OGLE III data. These maps reveal the metallicity trend across the inner ~ 5 deg and 2.5 deg field region of the LMC and SMC respectively. We have used the maps to estimate the mean metallicity within different regions of the MCs, their metallcity gradient, as well as identified outliers, which are important in the context of understanding the chemical evolution of these galaxies. The metallicity gradient of the LMC is found to be almost constant within the bar region and falls off beyond that, indicating that the bar might have been active in the past. Whereas, a shallow but gradual metallicity gradient of the SMC presents a different story of evolution compared to the LMC.

Dr Andrew Cameron

Title: "The latest results from the HTRU-S Low Latitude Pulsar Survey: a zoo of new and exciting pulsars"

Abstract: "Pulsars, rapidly-rotating and highly-magnetised neutron stars, can be utilised as tools in the study of many aspects of fundamental physical, most notably in the application of binary pulsars to the study of gravitational theories such as General Relativity. The discovery of ever-more relativistic binary systems than those presently known will allow for such tests to probe even deeper into the nature of gravity. Here, I will present results from the processing of 44% of the the HTRU-South Low Latitude pulsar survey (HTRU-S LowLat), the most sensitive blind survey of the southern Galactic plane taken to date. This includes the discovery and long-term timing of 40 new radio pulsars identified through the continued application of a novel “partially-coherent segmented acceleration search” technique, which was specifically designed to discover highly-relativistic binary systems. These pulsars display a range of scientifically-interesting behaviours including glitching, pulse-nulling and binary motion, and appear to comprise a population of generally older, lower-luminosity pulsars as compared to the previously-known population. In addition, I will also present an in-depth report on PSR J1757-1854, the only relativistic binary pulsar to have been discovered in HTRU-S LowLat to date. This extreme binary system (which remains the most accelerated pulsar binary ever discovered) promises to provide new insights into gravitational theories within the coming years."

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