News and events
Macquarie University’s Research Centre for Astronomy, Astrophysics, and Astrophotonics is actively engaged in raising public awareness through debate on issues such as the loss of darkness for planetary observations and interpreting the latest breakthroughs in our understanding of the galaxy.
Dates for 2017 "Stars in Sydney" workshop have been announced:
20-21st November 2017 at Macquarie University.
Plenary speakers: Martin Asplund (ANU),Tim Bedding (USyd), Jarrod Hurley (Swinburne), Rosemary Mardling (Monash), Sarah Martell (UNSW), Ashley Ruiter (UNSW- ADFA), Peter Tuthill (USyd), Peter Wood (ANU), Dan Zucker (MQ).
Click here to register for the 2017 "Stars in Sydney" workshop (Registrations deadline: 3rd November 2017)
To download the 2017 "Stars in Sydney" Workshop, please click here.
|Michael Ashley||University of New South Wales|
|Tim Bedding||The University of Sydney|
|Isabel Colman||The University of Sydney|
|Daniel Cotton||University of New South Wales|
|Orsola De Marco||Macquarie University|
|Thomas Gretzinger||Macquarie University|
|Marc Teng Yen Hon||University of Wollongong|
|Roberto Iaconi||Macquarie University|
|Devika Kamath||Macquarie University|
|Chengyuan Li||Macquarie University|
|Tanda Li||The University of Sydney|
|Sarah Martell||University of New South Wales|
|Simon Murphy||The University of Sydney|
|Barnaby Norris||The University of Sydney|
|Thomas Reichardt||Macquarie University|
|Ashley Ruiter||ANU - ADFA|
|Dennis Stello||University of New South Wales|
|James Tocknell||Macquarie University|
|Peter Tuthill||The University of Sydney|
|Mark Walker||Many Astrophysics|
|Mark Wardle||Macquarie University|
|Daniel Zucker||Macquarie University|
Michael Ashley (UNSW)
Title: The Antarctic
advantage for precision photometry, spectroscopy, and optical transient
The rapid follow-up of transient sources will become an increasingly important aspect of astronomy over the next decade. This is primarily driven by new facilities coming on-line, such as LSST, more sensitive gravitational wave detectors, and precursors to SKA. Positioning a telescope in Antarctica has the obvious advantage that, during mid-winter at least, the sun has no effect on whether a source can be observed. Cloud permitting, observations can commence rapidly and continue uninterrupted for weeks, producing a higher quality and more uniform dataset than a network of telescopes from a lower latitude. There are a host of other advantages such as low-scintillation noise, low-airmass variations, low aerosols, and low & stable water vapor. There are also some more subtle advantages such as lower variations in CO2 content. On the negative side, aurora need to be taken into account. On the whole, Antarctica offers significant improvements for precision photometry and spectroscopy of stars, and make it an excellent location for following up transient sources.
Martin Asplund (ANU)
Title: Heavy metal, rock & stars
I will explain why the Sun has a sub-solar metal content and why it is lower than it should have been. The solar chemical composition, a fundamental yardstick in astronomy, has been dramatically reduced in recent years due to improvements in our analysis techniques of the solar spectrum, especially in terms of 3D radiative-hydrodynamical modelling of stellar convection and atmospheres and accounting for departures from LTE in the spectrum formation. However, the solar abundances were also reduced at the time of the birth of the solar system 4.5Gyr ago due to the formation of the (terrestrial?) planets. This chemical fingerprint is also present in some stars, opening the exciting prospect of identifying stars likely to harbour terrestrial planets through a detailed determination of the stellar chemical compositions.
Tim Bedding (Sydney)
Title:The Golden Age of Asteroseismology
Stellar astrophysics has entered a new golden age, thanks to wonderfully precise measurements being returned by NASA's Kepler mission. Kepler is a 0.9-metre space telescope that has been monitoring the brightness of more than 100,000 stars with extraordinary accuracy for more than four years. Its main goal is to discover extra-solar planets by detecting the small dips in light as they transit their parent stars. The mission has been spectacularly successful, with thousands of candidates reported. Meanwhile, Kepler's observations of oscillations in thousands
of stars have led to a revolution in asteroseismology. Key results include detecting gravity modes in red giant stars and characterizing stars found to host exoplanets. Upcoming results from ESA's Gaia mission will add to the excitement, as will the launch of TESS, which is an all-sky follow-up
mission to Kepler.
Simon Campbell (Monash)
Title: Attempts at 3D Models of Stellar Interiors
Whilst 1D stellar models have been very successful in reproducing many observables, some of their success is based on parameterisation and calibration, as opposed to good physical models or understanding. This is especially true for phases in which the structure is dominated by convection. In particular, the extent of convection, as delineated by convection boundaries, is a key uncertainty in stellar models. Here we present some of our initial attempts at 3D modelling of stellar interior convection zones for a core helium burning model and an oxygen burning shell.
Jeffrey Cooke (Swinburne)
Title: Deeper, Wider, Faster: Chasing the fastest bursts in the Universe
I will discuss the Deeper, Wider, Faster program (DWF) that searches for Galactic and extragalactic fast transients on seconds-to-hours timescales at all wavelengths. This timescale has been essentially unexplored as a result of previous technological and instrumental limitations. DWF overcomes these limitations by coordinating over 30 observatories worldwide and in space to perform (1) fast-cadenced, deep, wide-field, multi-wavelength observations on the same field at the same time, (2) real-time supercomputer data reduction and analysis (in seconds) and software and sophisticated visual transient candidate identification (in minutes), (3) rapid-response, deep follow-up 8m-class spectroscopy and imaging (in minutes), and (4) longer-term imaging and spectroscopic follow up observations using our network of 1-10m telescopes. I will discuss results from the program, including thousands of transient and variable events, and the need for fast transient characterisation for future large all-sky surveys and gravitational wave counterpart searches. DWF is the only program that can resolve the nature of fast radio bursts and is the deepest, and only, simultaneous multi-wavelength program for gravitational wave counterpart searches. I will conclude by discussing upcoming and future directions for the program.
Daniel Cotton (UNSW)
Title: Polarisation across the H-R diagram
Making use of the HIgh Precision Polarimetric Instrument (HIPPI) and its small telescope counter-part mini-HIPPI we have been systematically investigating the polarimetric behaviour of stars across the H-R diagram. The unprecedented parts-per-million precision of our instrumentation has allowed us to observe linear polarisation due to processes long predicted but not previously observed. Examples include polarisation due to differential saturation in active FGK dwarfs, and polarisation due to rotational distortion in the atmosphere of a rapidly rotating B-type star. Here I will provide an overview of this work and an update consisting of the latest results.
Lisa Harvey-Smith (CSIRO)
Title: The Stingray planetary nebula; radio monitoring of a rapidly evolving star
SAO 244567 is a post-AGB star that has evolved into a young planetary nebula (the Stingray nebula) over the past three decades. We have analysed Australia Telescope Compact Array data of this object from 4 to 23 GHz between 1991 and 2016. We produced the first spatially resolved radio images of the Stingray nebula from data taken in 2005. A ring structure, which appears to be associated with the ring seen in HST images, is visible. We also found a narrow extension to the radio emission towards the eastern and western edges of the nebula. We also derived the emission measure - this decreased between 1992 and 2011, suggesting the nebula is undergoing recombination and moving back towards the AGB. The radio spectral index is broadly consistent with a free-free emission mechanism, however a single data point hints that a steeper spectral index has possibly emerged since 2013, which could indicate the presence of synchrotron emission. If a non-thermal component has emerged, such as one associated with a region that is launching a jet or outflow, we predict that it would intensify in the years to come.
Marc Hon (UNSW)
Title: Deep Learning in Astroseismology
The astronomical volume of asteroseismic data anticipated from current and future space missions such as K2 and TESS invokes a very pressing need for highly efficient data analysis methods. My work attempts at this using deep learning, which is an approach to artificial intelligence that automatically learns features from the data. In asteroseismology, deep learning displays a great potential to provide accurate and efficient analysis tasks such as stellar classification, surpassing 'conventional' automated methods.
Chengyuan Li (Macquarie)
Title: An unexpected detection of bifurcated blue straggler sequences in young globular clusters
Formed as a result of either stellar collisions or binary evolution, blue straggler stars behave as peculiar, high-mass stars. They are located along the bright extension of the ‘main sequence’ in a star cluster’s observational Hertzsprung–Russell diagram. In very rare cases, particularly in old globular clusters, their distribution is bifurcated, a feature commonly interpreted as evidence of (cluster) core-collapse-driven stellar collisions as an efficient formation mechanism. Here, we report the detection of bifurcated blue straggler distributions in two young Large Magellanic Cloud clusters, NGC 1644 and NGC 2173, which both have relatively low central stellar number densities and ages younger than 2 billion years. Dynamical analysis shows that only binary mass transfer and mergers could have produced these young blue straggler stars. The bifurcated distribution pattern may relate to a special time in the clusters’ evolution, when the binary hardening rate and therefore stellar merger events reached a peak.
Rosemary Mardling (Monash)
Title: Absolute stellar and planetary masses and radii in multiplanet systems
Transiting planets allow for the determination of the planet-to-star radius ratio, and when additional transiting planets are present and transit timing variations (TTVs) are measurable, planet-to-star mass ratios. Except when a star has been studied asteroseismologically, a stellar model (requiring a stellar spectrum) is normally relied upon to estimate its mass and radius, which in turn provide estimates for the planet mass and radius which inherit typical errors of 10-30%. The same is true for planet mass estimates from radial velocity observations. I will show that it is possible to estimate absolute stellar and planetary masses and radii without relying on stellar models when TTVs are available together with radial velocity measurements, with errors of as small as 1-2% for Kepler stars with HARPS spectroscopy.
Sarah Martell (UNSW)
Title: Viewing stellar interiors with large survey data
Galactic archaeology surveys collect spectra for huge numbers of stars in the Milky Way as a way to explore its history of star formation, chemical enrichment, dynamical evolution and minor mergers. In addition to important insights about the development of disk galaxies, these data sets also contain a tremendous amount of information about the structure and evolution of stars. I will present recent work on stellar interiors based on big survey data, and discuss some of the remaining questions in stellar physics that Galactic archaeology-scale data sets might answer.
Bernhard Mueller (Monash)
Title: Modelling Core-Collapse Supernovae and Their Progenitors in 3D
Core-collapse supernovae, the violent deaths of massive stars, are among the most spectacular phenomena in astrophysics: Supernovae can outshine their host galaxy for weeks; they are laboratories for the behavior of matter at extreme densities; and they also play a central role for the chemical evolution of galaxies. Yet the mechanism by which massive stars explode has eluded us for decades. This is now changing as recent first-principle 3D simulations of these events have finally been able to demonstrate that the most popular explosion scenario, the so-called neutrino-driven mechanism, is viable. An important ingredient to success lies in including the initial seed asymmetries in the progenitors from convective shell burning, which facilitate the development of asymmetric supernova explosions. First long-time simulations of core-collapse supernovae based on 3D progenitor models already give plausible predictions for explosion energies, nickel masses, and neutron star birth properties.
Simon Murphy (Sydney)
Title: An exciting haul of planetary, binary and triple systems from pulsation timing
The orbital parameters of binary stars at intermediate periods (100-1000 d) are difficult to measure with conventional methods and are very incomplete. For the past couple of years I’ve been developing a method that uses stellar pulsations to determine the orbital parameters of binary stars, which is particularly suited to intermediate periods and can detect objects down to planetary masses. It has tripled the number of intermediate-mass stars with fully solved binary orbits. The detected companions include planets, brown dwarfs, and main sequence stars with masses between 0.1 and 2.5 Msun; over 20% are white dwarfs in blue straggler systems, and a few companions could be neutron stars or black holes. Some systems are clear triples, and many will become Type Ia supernovae and related phenomena. Statistically robust mass-ratio and eccentricity distributions will be presented, and I will explain what they tell us about binary star formation.
Barnaby Norris (Sydney)
Title: Directly imaging the innermost regions of AGB mass-loss envelopes at milliarcseconds scales with VAMPIRES
Asymptotic giant branch (AGB) stars are the single biggest contributor to the composition of interstellar dust, accounting for 75% of the total mass loss in the galaxy. However the understanding of the mass loss mechanisms involved is incomplete, hampered by the difficulty in directly observing the stars and their circumstellar dust shells due to the small angular sizes and high contrasts involved. Using our purpose-built VAMPIRES instrument at the Subaru telescope, we directly observe the innermost circumstellar regions around mass-losing AGB (and RSG) stars, with super-diffraction-limited resolution. Using this combination of polarimetry and interferometry, we resolve dust shells of the order of 1 stellar-radii from the star, consisting of micron-scale dust grains. We also observe asymmetric structures at the very base of the mass-loss region. This has important implications for the understanding of AGB mass loss mechanisms and the role of scattering in wind-driving.
Ashley Ruiter (UNSW ADFA)
Title: The magic of accretion: making a neutron star from a white dwarf
It is well known that neutron stars are born during the death of massive stars in iron core-collapse supernovae. However, they can also form via more exotic formation scenarios like the accretion-induced collapse of a white dwarf star in a binary system. I will show some early results of formation scenarios of neutron stars formed via the collapse of a heavy white dwarf, and comment on their contribution to the pulsar population among globular clusters, and their potential detectability with gravitational radiation. While the implementation of a sophisticated method to deal with the common envelope phase in binary population synthesis is still in its infancy, preliminary results show that we may be able to constrain common envelope physics with accretion-induced collapse (and also Type Ia supernova) progenitors using future space-based gravitational wave detectors.
Jeffrey Simpson (AAO)
Title: What happened to the horizontal branch of ESO280-SC06?
Globular clusters are some of the oldest structures in the Milky Way and they present an intriguing, but not fully understood set of observed properties that seem to require multiple periods of star formation with chemical pollution. As part of an ongoing research project to investigate unexplored regions of the globular cluster parameter space, I have used the Anglo-Australian Telescope to undertake the first spectroscopic observations of the poorly studied globular cluster ESO280-SC06. From these data I have identified 12 members of the cluster and found it to have a very low metallicity – [Fe/H]=-2.5 – the lowest metallicity Milky Way globular ever found. Even stranger is that this cluster appears to lack any stars at the horizontal branch stage of their evolution and very few bright red giant stars. A missing horizontal branch has only been observed in a handful of the 150 Milky Way globular clusters, and those clusters are much younger and more metal-rich than ESO280-SC06. In this talk, I will discuss the implications of finding such a low metallicity cluster, whether ESO280-SC06 could be one of the first globular clusters accreted by the Milky Way during its formation, and what might have happened to ESO280-SC06’s horizontal branch.
Simon Stevenson (Swinburne)
Title: Constraining common envelope evolution with Luminous Red Novae
Recently, a class of optical transients in the classical luminosity gap between novae and supernovae dubbed Luminous Red Novae (LRNe) have been associated with common envelope evolution. Around 10 LRNe have been observed, both within our own galaxy (such as V838 Mon), and in other galaxies (such as M85-OT). We use binary population synthesis to predict the rates and observable properties (plateau luminosity and duration) of LRNe observable by the Large Synoptic Survey Telescope (LSST). We find that LSST will observe hundreds to thousands of LRNe per year. The rate and properties of LRNe detected by LSST will allow us to constrain uncertainties in our models of common envelope evolution such as the efficiency with which orbital energy can be used to eject the envelope.
James Tocknell (Macquarie)
Title: Winds from Protoplanetary Discs
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.
Peter Tuthill (Sydney)
Title: A twist in the tail: the enigmatic dragon at the heart of REX-1
This talk is the first to presentation of a fascinating new stellar system which exhibits a startling list of extreme properties. REX-1 presents as a massive colliding-wind binary (CWB) with characteristics at the upper limits for the class. In the radio, it would be the brightest CWB with the exception of the singular object eta Carinae, with similarly outlying X-ray and mid-infrared brightness. The system sports a spectacular and elegant plume witnessed in mid-infrared imagery that takes the shape of a spiral, suggestive of the celebrated "pinwheel nebulae'' found in rare dusty Wolf-Rayet colliding wind systems. However the neat picture of established physics being beautifully illustrated by a new Rosetta-stone colliding wind system is confronted with a dramatic conflict in the data. Proper motion studies reveal an outflow an order of magnitude too slow for any known WR wind. This conundrum confronts our knowledge of wind-driven mass loss at the terminal phase of the most massive stars, and may lead to new physics governing the winds and the evolution of such objects, believed to be imminent precursors for supernovae and GRBs.
Mark Walker (Many Astrophysics)
Title: Interactions between stars and snow clouds
Recent progress in understanding quasar scintillation suggests that main sequence stars may often carry vast populations of tiny, molecular gas clouds — much like the globules seen in the Helix Nebula. Such clouds are likely to be self-gravitating, with the H2 solid-gas phase transition playing a central role in determining their physical properties. In other words: stars may commonly be surrounded by large numbers of snow clouds. Given this new ingredient, some phenomena which have previously been interpreted as "stellar" might be more readily understood in terms of the physical interactions between stars and snow clouds. I'll describe some of the interactions that are expected, and suggest connections to the "Wolf Rayet", "Be" and "R Cor Bor" phenomena.
Peter Wood (ANU)
Title: The period-luminosity sequences of red giants
I will discuss recent advances in our understanding of luminous variable red giants and their period luminosity sequences. One of the sequences consists of ellipsoidal binary variables. Modelling of these objects allows the derivation of the full orbital parameters. Their mass distribution in the LMC is consistent with a stellar population of red giants formed during star formation that had a burst a few Gyr ago. The eccentricity distribution is inconsistent with widely-used formulae for tidal interactions. There are five pulsation
sequences occupied by the red giants, but there are only four radial orders involved as two of the sequences correspond to the same order of radial pulsation. The final sequence has an unknown origin although pulsation is suspected.
Daniel Zucker (Macquarie)
Title: Finding Strangers in a Crowd
Abundant evidence for the accretion of dwarf galaxies and globular clusters onto the Milky Way has been discovered in recent years, both spatially (e.g., stellar streams on the sky), and kinematically (e.g.,
overdensities in phase space). However, the advent of large-scale high-resolution stellar spectroscopic surveys has opened a new frontier for studying the Milky Way’s accretion history — chemical space. The elemental compositions of most stars remain virtually unchanged from birth, and can be used as a kind of stellar DNA to identify stars of a common origin, yielding critical clues as to whether they formed in an accreted dwarf galaxy, an accreted globular cluster, or in situ within the Milky Way itself. I will discuss the application of chemical tagging techniques to identifying accreted stars of different origins in the ongoing million-star GALAH survey, as well as the complementarity of data from other major surveys (e.g., Gaia-ESO and APOGEE) for studying the accretion history of the Milky Way.
We have an active seminar series for the benefit of MQAAAstro members. We welcome all astronomers visiting Sydney to give us a seminar.
Seminars typically take place at 3pm on Fridays in building E6B, level 2, room 2.300 (see map here)
Please contact Admin for further information and assistance.
Seminar schedule 2017
If you would like a complete list and details of our previous seminars, please contact our centre administrator.