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Colloquia Series

For more information on colloquia at the Centre for Astrophysics and Supercomputing please contact Dr. Nikole Nielsen ()

Swinburne Virtual Reality Theatre
Applied Science Building, Room 406
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2003 Colloquia


Dec. 4 @ 16:00
George Hau (ESO)
Title: Stellar Kinematics of the Halos of Giant Elliptical Galaxies
Nov. 13 @ 16:00
Brent Tully (Hawaii)
Title: The Large Scale Structure of the Universe
Oct. 31 @ 11:00
Andrew Lange (Caltech)
Title: Exploring the Embryonic Universe via the Cosmic Microwave Background
After years of promises, precise measurements of the Cosmic Microwave Background are now being routinely made by a variety of instruments. The first resolved images of the CMB captured by BOOMERANG in 1999 provided convincing evidence that we live in a flat universe composed of 5% baryonic matter, 30% dark matter, and 65% "dark energy", thus bolstering the case for an Inflationary epoch in the very early universe. A new generation of experiments is now being designed to search for the extremely faint signature the the gravity-wave background associated with Inflation would have imprinted on the polarization of the CMB.
Oct. 30 @ 16:00
Jarrod Hurley (Monash)
Title: Virtual Globular Clusters: A Reality?
Often called the "gravitational million-body problem", the holy grail for stellar dynamicists is a complete and realistic model of a globular cluster performed on a star-by-star basis. Recent software and hardware developments have brought such a model within reach. I will give a short review of the history of star cluster modelling and the current state-of-the-art. Models performed using the GRAPE-6 special-purpose hardware will be presented with results focussing on the role of white dwarfs as cluster dark matter and chronometers.
Oct. 24 @ 16:00
Roberto Ricci (Trieste)
Title: First Results from the ATCA 18 GHz Pilot Survey
Oct. 9 @ 16:00
Alon Retter (Sydney)
Title: A Model of an Expanding Giant that Swallowed Planets for the Eruption of V838 Monocerotis
In early 2002 V838 Monocerotis had an extraordinary outburst whose nature is still unclear. The optical light curve showed at least three peaks and imaging revealed a light echo around the object - evidence for a dust shell which was emitted several thousand years ago and now reflecting light from the eruption. Spectral analysis suggests that the object was relatively cold throughout the event, which was characterized by an expansion to extremely large radii. We show that the three peaks in the light curve have a similar shape and thus it seems likely that a certain phenomenon was three times repeated. Our suggestion that the outburst was caused by the expansion of a red giant, followed by the successive swallowing of three relatively massive planets in close orbits, supplies a simple explanation to all observed peculiarities of this intriguing object.
Sep. 24 @ 16:00
Chris Power (Durham)
Title: The Structure of Dwarf Galaxy Halos in the LambdaCDM Model
The Cold Dark Matter (CDM) model and its variants predict that dark matter halos have divergent central densities or dark matter cusps. The seminal study of Navarro, Frenk & White (hereafter NFW; 1996, 1997) revealed that dark matter halos in dynamical equilibrium forming in a variety of hierarchical cosmologies, of which CDM is a prime example, can be well described by a universal density profile with a central density that runs as rho(r) = r^-1. On the other hand, higher resolution studies, such as those of Moore et al. (1998, 1999), have indicated that the behaviour of the central slope differed from the prediction of NFW, with a density run \rho(r) = r^{-1.5}. However, the generality of the results of these higher resolution studies was restricted by the small number of halos and by the range in mass (i.e. M > 1e12 Msun) considered.

In this talk, I will describe the results of high resolution simulations designed to investigate the internal properties of dark matter halos with virial masses spanning several orders of magnitude in mass at z=0, from M200 = 1e10 Msun, typical of dwarf galaxy halos, to M200 = 1e15 Msun, typical of clusters, forming in the LambdaCDM cosmology. The parameters of these simulations have been set according to the convergence criteria presented in Power et al. (2003); we find that >1 million particles within r200 are required if we are to reliably resolve the spherically averaged mass distribution within the central 1% of the virial radius, r200.

I shall highlight the main results of this work; in particular, I will consider the constraints on the slope of the density profile at the innermost resolved radius (of order 1% of r200), and discuss its mass dependence; comment on the shape of the density profiles of halos spanning several orders of magnitude in mass; and compare our results with theoretical expectations. I will also address possible mass dependence in the spherically averaged velocity and fields (velocity anisotropy, radial velocity); the shapes of isodensity surfaces within the halos; and the substructure content of the halos. Finally I shall comment on the significance of these results and discuss the implications for the CDM model.

Sep. 18 @ 16:00
Chris Blake (UNSW)
Title: Cosmology with Wiggles
A precise measurement of galaxy clustering on scales larger than 30 Mpc would reveal the "acoustic oscillations" imprinted at recombination. The positions of these wiggles in Fourier space, defined accurately by CMB physics in the early Universe, can be used as a "standard cosmological ruler" to accurately measure the dark energy that dominates in the late Universe. In this talk I will describe this method of measuring dark energy and argue that it powerfully complements other probes such as Type Ia supernovae. I will describe the results obtainable from future large-scale galaxy redshift surveys at z=1 and z=3.
Sep. 15 @ 16:00
Maxim Voronkov (ATNF)
Title: Studying the Dynamic Range of SKA Images
We present a study of dynamic ranges which can be reached for the images produced with the SKA. Preliminary results of simulation carried out for one spiral layout (SKA concept description, June 2002) has shown that AIPS++ Clark CLEAN can provide a dynamic range of about 1e5 for a single point source in the phase-tracking centre. However, the dynamic range decreases rapidly with the distance from the phase-tracking centre. Presumably, the most severe effect on the dynamic range is due to gridding and aliasing at the imaging stage. The Cotton-Schwab CLEAN where the model subtraction is preformed in the visibility domain gives a dynamic range of about 1e8 for a single point source in the phase-tracking centre, but the value still decreases for the off-axis cases. The dynamic range can be made constant throughout the field of view if one takes into consideration w-term in the relation between the sky brightness and visibilities while forming the model. Future plans include a study of the time-average and bandwidths smearing effects on the dynamic range. These effects are usually taken into consideration for wide field imaging but it can affect dynamic range even for a small field of view. Such a study involves a series of visibility data simulations for a set of distances of the model point source from the phase-tracking centre followed by the imaging procedure. Usage of the supercomputer can speed up the analysis considerably.
Aug. 26 @ 16:00
Bryan Gaensler (Harvard-Smithsonian CfA)
Title: In A Spin: Probing Neutron Stars Through Their Environments
One of the defining characteristics of neutron stars is that they are rapid rotators, and indeed this is one of the main reasons why these sources have proven to be such important astrophysical tools. The energetics associated with this rotation are considerable: the rotational kinetic energy of a newborn neutron star can be more than that released in the associated supernova explosion, while as the neutron star subsequently slows down, its rate of energy loss can exceed the bolometric luminosity of even the brightest stars. Two fundamental questions thus arise: from where do neutron stars get their spin, and how is this vast reservoir of energy then dissipated? I will present new radio and X-ray observations on neutron star environments, and will explain how these data can be used to answer these questions.
Aug. 18 @ 11:00
Brian Warner (Cape Town)
Title: Rapid Oscillations in Compact Binary Stars
Optical observations in the past few years have revealed a wide range of brightness oscillations in Cataclysmic Variable Stars (which contain white dwarfs). There are now various kinds of Dwarf Nova Oscillation and Quasi- periodic oscillation known. Only recently has it been realised that parallel behaviours exist in the X-Ray binaries - which contain neutron stars and black holes. The rich phenomenology will be described, and how magnetically-controlled accretion provides an explaition of at least the main aspects of the oscillations observed in the white dwarf systems.
Jul. 28 @ 16:00
Adrian Jenkins (Durham)
Title: Dark Mater Halos and Dark Energy
I will talk mainly about recent work within the Virgo consortium on modelling dark matter haloes in LCDM universes. Also I will talk about a recent paper with Eric Linder simulating a patch of universe with a dark energy component with a time varying equation of state.
Jul. 11 @ 16:00
Hans Zinnecker (AIP)
Title: HST/NICMOS Search for Giant Planets around White Dwarfs
We describe a programme of HST observations recently awarded to search for 5-10 M_jupiter mass self-luminous planets around the seven single white dwarfs in the Hyades cluster (45 pc, 625 Myr). Such planets would survive the mass loss of the progenitor star, and, because of the favourable contrast (1:1000 in the near-IR) and orbital separation after mass loss (of order 0.5 arcsec), this may be our best chance for a while to spatially resolve a giant planet in the glare of its parent star. As a second topic, we will also discuss the (slim) chances of earth-like planet formation under metal-poor conditions, such as those in the Large/Small Magellanic Clouds.
May. 23 @ 11:00
Richard Schilizzi (Director, International SKA Project)
Title: The Square Kilometre Array - the International Perspective
From the start, the SKA has been conceived as a global endeavour with Australia playing a leading role. A meeting in Sydney in 1997 signalled the start of a concentrated effort to develop SKA technology. On the organisational side, astronomical institutes in 11 countries signed a Memorandum of Understanding in 2000 to establish an International SKA Steering Committee (ISSC) and carry out cooperative technology development for the SKA. The ISSC coordinates the technical studies and site testing activities around the world, and has initiated preparation of a detailed science case and end-to-end simulations of the performance of the array.

The ISSC is working to a timeline that includes informing governments of the project and presenting a management plan late this year, an initial selection of promising technological concepts as well as the location of the array in 2005, the final selection of concept in 2007, world-wide coordinated proposals to governments for construction money in 2009, start of construction in 2012, and operational status late in the next decade.

There are many technological, political, financial and organisational challenges inherent in this international mega-science project. For example, account has to be taken of different funding cycles, different prior investment histories, different scientific interests, different stages of SKA-specific technology development, and different decision-making cultures in the various regions of the world. This presents a challenge to create an organisational and management structure for the SKA that is "light" but sufficient.

May. 2 @ 16:00
Brad Gibson (Swinburne)
Title: On Australian Participation in an Extremely Large Telescope Projec
In preparation for the 21 May 2003 "National Workshop on Extremely Large Telescopes" (http://www.mso.anu.edu.au/ELTWG/Workshop/), to which I would strongly encourage as many of you as possible attend, I will be holding an informal 'briefing session' this Friday 2 May at 4:00pm in the VR Theatre at Swinburne. I'll review the primary ELT projects currently under design, which ones offer the possibility for collaboration, their strengths/weaknesses, and the primary science drivers. Mostly though, this is an open forum at which to air your scientific and politcal interests/concerns, so please do come along. I will be presenting the "Galaxies and Stellar Systems Science Case" to the community at the National Workshop, so having any feedback from you beforehand would be most welcome.
Apr. 17 @ 16:00
John Dickey (Minnesota)
Title: A New and Clearer Look at the Southern Milky Way
The Southern Galactic Plane Survey (SGPS) is a 21-cm line study of the Milky Way disk using Parkes plus the Compact Array to obtain a combination of resolution and sensitivity that is unprecedented for studies of the inner Galaxy. Now that the first phase of this survey has been fully observed and reduced, we have a much clearer view than ever before of the structure and motions in the interstellar medium in the fourth quadrant of the Galaxy. In this talk I will start with the largest scales: the rotation curve, scale height, and corrugations of the midplane of the HI disk, and then move to progressively smaller scales to present the results of the survey. Dramatic shells and chimneys dominate the structure on scales of a few hundred parsecs, particularly in the outer Galaxy. Structure on even smaller scales, a few parsecs to tens of parsecs, appears to be stochastic. Statistical analysis suggests that it is caused by interstellar turbulence whose properties we can determine using the velocity information of the 21-cm line. Finally I will talk about the separation between warm and cool phases of the neutral atomic medium, how we measure the cool phase temperature using absorption spectra from the survey, and how the cool phase changes the appearence of the Galaxy at 21-cm. Comparison with 21-cm emission and absorption results for the LMC and SMC helps us make the connection between the mixture of thermal phases and the metallicity and radiation field in the Galactic environment.
Apr. 15 @ 11:00
Michelle Storey (ATNF)
Title: The Opportunity to Participate in the International LOFAR Project
Australia has a relatively 'radio-quiet' environment - an outstanding natural advantage for radio astronomy. Our strength in astronomy, together with our radio-quiet, has led to inland Australia being considered as a host site for three future projects: LOFAR (Low Frequency Array), the SKA (Square Kilometre Array), and a NASA Deep Space Network (DSN) facility. The first of these is LOFAR, which will be built within the next five years. LOFAR is a direct developmental step towards the Square Kilometre Array telescope. Hosting and participating in LOFAR would be an integral part of Australia's future radio astronomy development.

The international LOFAR Consortium plan to choose a site for LOFAR in 2003, and the telescope will become operational in 2006. A Western Australian site is on a short-list of three sites worldwide for the US$100M LOFAR project.

We are preparing a final proposal for hosting LOFAR in Australia and exploring ways in which Australia could join the LOFAR Consortium. In this talk I will outline the status of the LOFAR Project within Australia, and would like feedback on Australia's potential involvement in the international LOFAR Project.

Apr. 10 @ 16:00
Mike Dopita (ANU)
Title: Star Formation Rates in Galaxies: Halpha, What is it Good For?
Apr. 4 @ 11:00
Joeri van Leeuwen (Utrecht)
Title: Probing the Nulling and Subpulse-drifting Mechanisms in Radio Pulsars"
Both nulling (a sudden temporary stop of pulsar emission) and subpulse drifting (a striking second periodicity in the pulsar signal) are poorly understood phenomena. We probe their mechanisms by investigating how they interact in PSR B0809+74. We solve the subpulse alias order problem and find that one driftband represents one subbeam. From this we derive a subbeam-carousel rotation time of more than 200 seconds, much longer than predicted by theory.

We find that after nulls the drift-pattern is changed and that it can remain stably different for about 150 seconds. With the alias mode known, we can now tie these drift-pattern changes to changes in emission-region geometry. We show that post-null emission originates deeper in the pulsar magnetosphere. Both this emission-height change and the striking increase in carousel-rotation time can be explained by a post-null decrease in gap height. This offers a glance at the circumstances needed to make the pulsar turn off so dramatically.

Apr. 3 @ 16:00
Stuart Wyithe (Melbourne)
Title: Gravitational Radiation From Massive Black-Hole Binaries
I will discuss the expected gravitational radiation signal for the LISA satellite and for pulsar timing arrays arising from the coalescence of super-massive black-holes within a hierarchical Lambda CDM cosmology. I will begin by describing the simple scheme where black-hole growth is limited by feedback during luminous quasar phases (Silk & Rees 1998). This scheme leads directly to the observed relation between black-hole and dark matter halo circular velocity, and by associating quasar activity with galaxy mergers, to the details of the optical and X-ray quasar luminosity functions at redshifts from z=2 (below which clusters of galaxies become important) to z=6. Having demonstrated the applicability of the black-hole - circular velocity relation at high redshift I will show how it can be combined with the dark matter halo mass function and merger rate to find the expected rate of gravitational wave emission from merging black-holes. The event rate for the LISA satellite may be as high as several hundred per year unless most massive black-hole binaries have hardening timescales longer than a Hubble time. I will discuss the effect of reionization on the redshift distribution of gravitational wave sources and show that most sources for LISA may come from z>6. Finally I will show that the nHz frequency back-ground is dominated by black-hole binaries at z<2, and that pulsar timing experiments are already nearing the level where limits may be placed on the fraction of black-hole binaries that achieve coalescence.
Mar. 27 @ 16:00
Robert Proctor (Swinburne)
Title: Stellar Populations in Galactic Spheroids
Line-strengths and kinematics are presented from the central regions of 32 galaxies with Hubble types ranging from E to Sbc. Spectral indices, based on the Lick system, are measured in the optical and near infra-red (NIR). The 24 indices measured, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy and allow estimation of enhancements in specific light elements (particularly C and Mg). The large range of Hubble types observed allows direct comparison of line-strengths in the centres of early-type galaxies (E and S0) with those in spiral bulges, free from systematic differences that have plagued comparisons of results from different studies. The sample includes field and Virgo cluster galaxies. For early-type galaxies the data are consistent with previously reported trends of Mg2 and Mgb with velocity dispersion. In spiral bulges trends are found in all indices with velocity dispersion. Luminosity-weighted ages, metallicities and heavy element abundance ratios (enhancements) are estimated from optical indices. These show that bulges are less enhanced in light (alpha-capture) elements and have lower average age than early-type galaxies. Trends involving age and metallicity also differ sharply between early and late types. An anti-correlation exists between age and metallicity in early types, while, in bulges, metallicity is correlated with velocity dispersion. We consider the implications of these findings for models of the formation of these galaxies. We find that primordial collapse models of galaxy formation are ruled out by our observations, while several predictions of hierarchical clustering (merger) models are confirmed.
Mar. 20 @ 16:00
Kenji Bekki (UNSW)
Title: Origin of Ultra-compact Galactic Objects
Recent spectroscopic and morphological observational studies of galaxies around NGC1399 in the Fornax Cluster have discovered several `ultra-compact dwarf' (UCDs) galaxies with intrinsic sizes of 100 pc and absolute B band magnitudes ranging from -13 to -11 mag. We discuss how this enigmatic object (UCD) can be formed in the cluster environment, in particular, whether or not nucleated dwarf galaxies in the Fornax cluster can be morphologically transformed into UCDs by the strong cluster tidal field. We furthermore provide an unified model for the massive compact stellar objects such us OmegaCen, G1, and UCDs (and M32). The origin of OmegaCen is particularly discussed in terms of early dynamical interaction between the Galaxy and an ancient nucleated dwarf.
Mar. 13 @ 16:00
Martin Asplund (ANU)
Title: The Light Elements in the Early Universe
The light elements (here: lithium to oxygen) play a central role in astrophysics due to their vast diagnostic powers for stellar, galactic and cosmic evolution. I will describe an ongoing project aimed at determining accurate elemental and isotopic abundances of these elements in metal-poor halo stars and some early conclusions which have emerged from it. The observational data consists of a large amount of high-quality VLT/UVES spectra which are analysed using the state-of-the-art and unique 3D hydrodynamical model stellar atmospheres developed within our collaboration. The latter ingredient turns out to be crucial for much of the interpretations.
Mar. 3 @ 16:00
Duncan Lorimer (Jodrell Bank)
Title: Recent Discoveries of Radio Pulsars in New and Old Data Sets
Feb. 11 @ 16:00
Terry Bridges (AAO)
Title: Dwarf and Giant Elliptical Galaxies in the Coma Cluster
I'll present the results of a major photometric and spectroscopic study of dwarf and giant elliptical galaxies in the nearby, rich Coma cluster. I'll first discuss why galaxy clusters are good places to learn about when and how galaxies form, and how they are affected and transformed by various cluster processes. I'll then present our wide-field imaging and spectroscopic survey of Coma; we have spectra for nearly 300 confirmed Coma members. The photometry and spectroscopy are used to determine galaxy ages, chemical composition, morphology, kinematics, and luminosity functions, and the dependence of these on location in the cluster. Our results are used to compare the dwarf and giant galaxies in Coma, and with more distant clusters, and to learn more about the formation and evolution of elliptical galaxies in general.
Feb. 10 @ 16:00
Christophe Pichon (Strasbourg)
Title: Probing the Intergalactic Medium through QSO Absorption Lines
A review of the properties of the IGM which can be extracted from QSO absorption lines will be presented. An emphasis will be placed upon the 'inverse problem' approach. Specific applications of this approach will be covered, including the topology of the cosmic web, the evolution of large scale structure properties as a function of redshift (e.g. power spectrum, etc.), the ionisation history of the IGM, and the determination of fundamental cosmological parameters.
Feb. 3 @ 11:30
Joe Lazio (NRL)
Title: The 4-meter All-Sky Survey (4MASS)
The 4-meter All-Sky Survey (4MASS) is a program to survey the (northern) sky with the 74 MHz system on the VLA. High-sensitivity, low-frequency observations are an ideal way to detect steep-spectrum sources such as high-redshift radio galaxies, radio halos and relics in clusters of galaxies, pulsars, and possibly extrasolar planets. Indeed, low-frequency radio astronomy is responsible for much of modern astronomy, though until recently progress in low-frequency radio astronomy had languished relative to progress at higher frequencies. Problems faced by low-frequency observers have included the computational complexity of making wide-field images and dealing with the Earth's ionosphere. The 74 MHz system on the VLA has shown that these are solvable problems and has made it possible to produce a relatively sensitive survey at an angular resolution comparable to that for many high frequency surveys. However, conducting this survey has motivated new calibration and imaging methods. I describe the survey methodology and present results from the initial suite of observations.
Jan. 23 @ 16:00
Frazer Pearce (Nottingham)
Title: The Cosmic Cooling Catastrophe
A census of the Universe reveals that only a small fraction of the available baryonic material has cooled to form stars. Why didn't all the gas cool within dark matter haloes at high redshift? Numerical models of the Universe readily cool large fractions of their gas and the importance of getting the right cooling fraction is stressed. The self-regulation of the cooling process via the feedback of energy from star forming regions and some of the difficulties in arranging this balance are discussed.
Jan. 16 @ 16:00
Norbert Christlieb (Hamburg/ANU)
Title: Studying the Galactic Halo with the Hamburg/ESO Objective-prism Survey
The stellar content of the Hamburg/ESO objective-prism survey (HES) offers an unprecedented opportunity to study the galactic halo population. The HES covers the total southern extragalactic sky down to B=17.5, extending the survey volume for extremely metal-poor stars by almost one order of magnitude. Ongoing programs of moderate-resolution (5 A) follow-up spectroscopy have already led to an increase of the sample of stars with [Fe/H]<-3.0 by a factor of 3. Large samples are key for identifying extremely rare objects, such as the recently-discovered giant HE 0107-5240, a giant with [Fe/H]=-5.3, and studying the earliest phases of galactic chemical evolution.
Other efforts aim at identifying field horizontal-branch A-type stars in the digital HES data base of about 4,000,000 low-resolution (15 Angstroem at Hgamma) spectra. These stars are suitable for determining distances of high-velocity clouds, a crucial step towards understanding their nature.