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Colloquia Series

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

Swinburne Virtual Reality Theatre
AR Building, Room 104
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2010 Colloquia

Dec 21st 2010 @ 11:30am
Alan Duffy (ICRAR, UWA)
Title: TBD
Dec 16th 2010 @ 11:30am
Paul Lasky (University of Tubingen, Germany)
Title: Magnetic Fields in Strongly Magnetized Neutron Stars
Strongly magnetized neutron stars, known as magnetars, regularly produce flares with peak luminosities of order 10^42 erg/s, with the strongest of events reaching a staggering five orders of magnitude higher. Observed quasi-periodic oscillations (QPOs) in the tails of these giant flares represent global mass motions in the core and the crust of the star. Dynamics of the interior magnetic field are believed to play a vital role in both flare generation, possibly through intrinsic instabilities in the magnetic field, and the observed QPOs which are interpreted as Alfven oscillations. I will present ongoing work modeling these dynamic situations utilising a three-dimensional, general relativistic magnetohydrodynamics (GRMHD) code. I will discuss the onset and nature of various instabilities in full General Relativity, as well as ongoing efforts to determine possible magnetic field configurations for the interior region of the star.
Dec 9th 2010 @ 11:30am
Kevin Pimbblet (Monash University)
Title: Galaxies in Odd Places
Received wisdom and our recent results suggest that galaxy evolution is primarily driven by local galaxy density. In high density environments such as the cores of rich galaxy clusters, we observe primarily red, elliptical and none-star-forming galaxies whilst bluer, spiral and more actively star-forming galaxies are preferentially located in under-dense regimes. But this is not the full story of galaxy evolution: there are many galaxies that reside in 'odd' locations and environments given their physical parameters. I will detail our recent research developments about two categories of galaxies in odd locations: brightest cluster members that are far removed from the bottom of their cluster's gravitational well and lower mass galaxies in the outskirts of clusters that we believe once visited the high density core regions and have been slung out again.
Dec 2nd 2010 @ 11:30am
Katie Mack (Cambridge)
Title: The 21cm Forest
Future observations of the 21cm forest -- neutral hydrogen absorption against high-redshift radio sources -- will allow us to trace out the structure of the pre-reionization intergalactic medium (IGM), provided bright radio sources can be found at sufficiently high redshift. I will present a calculation of the expected 21cm forest as might be observed in coming years and show how statistical detection techniques could be used to overcome the low signal-to-noise. I will also discuss the trade-off between the availability of large populations of high-redshift background radio sources and the requirement that the IGM be sufficiently neutral for strong absorption.
Nov 25th 2010 @ 11:30am
Chris Brook (University of Central Lancashire)
Title: Forming Bulgeless Disc Galaxies Heirarchically
Using cosmological smoothed particle hydro-dynamical simulations of dwarf galaxies in a Lambda CDM Universe, we show how baryons attain a final angular momentum distribution which allows pure disc galaxies to form. Blowing out substantial amounts of gas through supernovae and stellar winds, which is well supported observationally, is a key ingredient in forming bulgeless discs. We outline why galactic outflows preferentially remove low angular momentum material, and show that this is a natural result when structure forms in a cold dark matter cosmology. The driving factors are a) the mean angular momentum of accreted material increases with time, b) lower potentials at early times, c) the existence of an extended reservoir of high angular momentum gas which is not within star forming regions, meaning that only gas from the inner region (low angular momentum gas) is expelled and d) the tendency for outflows to follow the path of least resistance which is perpendicular to the disc. We also show that outflows are enhanced during mergers, thus expelling much of the gas which has lost its angular momentum during these events, and preventing the formation of "classical", merger driven bulges in low mass systems. Stars formed prior to such mergers form a diffuse, extended stellar halo component.
Nov 18th 2010 @ 11:30am
Alis Deason (Cambridge)
Title: Mismatch and Misalignment: Dark Haloes and Satellites of Disc Galaxies
It has been known for some time that the eleven classical satellites of the Milky Way define a highly inclined plane relative to the disc of the Galaxy. However, it is not obvious if this peculiar spatial distribution can be explained within the context of our standard CDM theory of structure formation. I use state-of-the-art hydrodynamic cosmological simulations to study the phase-space distributions of satellites belonging to disc galaxies. The alignment (in both position and velocity space) of the satellite galaxies relative to the disc is yet to be studied as previous work has made use of cold dark matter simulations. I find that misalignments between the galaxy and dark matter halo can have important consequences for the alignment of the satellites with the disc. I discuss the implications of this result to the Milky Way galaxy and to studies of external galaxies.
Nov 11th 2010 @ 11:30am
Michael Murphy (Swinburne)
Title: Spatial variation in the fine-structure constant?
Any observed variation in the so-called "fundamental constants of nature", on any distance- or time-scale, would signal the need for a new fundamental theory of physics, perhaps one unifying the four known forces of nature. We previously reported observations of quasar spectra from the Keck telescope suggesting a smaller value of the fine-structure constant, alpha, at high redshift. I will present a new sample of 153 measurements from the ESO Very Large Telescope, probing a different direction in the universe, which also reveals a varying alpha, but in the opposite sense; that is, alpha appears on average to be larger in the past. The combined dataset is well represented by a spatial "alpha dipole" across the sky, significant at the 4.1 sigma level. I will present this new evidence together with tests for systematic errors using observations duplicated at both telescopes. It is currently difficult to explain our results without a varying alpha.
Nov 4th 2010 @ 11:30am
Scott Croom (University of Sydney)
Title: The evolution of quasars and super-massive black hole masses.
I'll talk about some recent results on the evolution of quasars and the measurement of downsizing in optical AGN. I will then discuss how we can get to the fundamental physical parameters, in particular black hole mass. In the course of this I will point out some serious concerns for the current virial approaches to black hole mass estimation.
Title: The next generation of multi-object spectroscopy: the case for MOS IFUs.a
Massively multiplexed single-fibre surveys have revolutionized our understanding of galaxies. I will make the case that the next major step for spectroscopic surveys should be the use of multi-object integral field spectrographs. I will discuss the technology which will enable this leap forward and outline an instrument called FIREBALL, we are proposing to build for the ESO VLT to achieve these goals.
Oct 27th 2010 @ 11:30am
Andrew Walsh (James Cook University)
Title: New flavours in Galactic Surveys: HOPS and MALT
HOPS is the H2O southern Galactic Plane Survey. Over the past three years, we have surveyed 100 square degrees of the Galactic plane with the Mopra radiotelescope in the 12mm band. The survey focusses on many spectral lines that are most relevant to high mass star formation within the Galaxy. I will report on early results from HOPS as well as how we hope to use the full data set. MALT is the Millimetre Astronomers Legacy Team - a collaboration of national and international astronomers who intend to utilise the fast mapping capabilities of Australian millimetre telescopes to study high mass star formation across the southern Galaxy. I will focus on MALT-45, which will use the ATCA to survey a large portion of the Galaxy in multiple spectral lines around 45GHz. This survey will push the recently upgraded ATCA to its limits with fast, wide-scale mapping in multiple spectral lines and continuum, as well as using both auto-correlation and cross-correlation for the first time.
Oct 21st 2010 @ 11:30am
Yuri Levin (Monash University)
Title: The stars near SgrA* black hole
Many young stars reside in the immediate vicinity of the SgrA* black hole. On the other hand, in the same region the population of the old stars is severely depleted. Both of these facts are in conflict with prior theoretical expectations. In this talk I will propose an explanation for both how the young stars are born and how the old stars are depleted near SgrA*, and discuss the implications for other galactic nuclei.
Oct 15th 2010 @ 11:30am
David Wake (Yale)
Title: Clustering in the NMBS: the stellar mass - halo mass relation at 1 < z < 2.
I will present clustering measurements for mass limited galaxy samples at 1 < z < 2 selected from the NEWFIRM Medium Band Survey. These measurements show for the first time that high redshift galaxies show mass dependent clustering much like galaxies in the local universe. Using the halo model I will show how these galaxies are related to the underlying dark matter distribution and how that relationship has changed over the past 10 Gyrs.
Oct 14th 2010 @ 11:30am
Jeremy Mould (University of Melbourne)
Title: Mapping the Dark Matter in the Local Universe
Conventional wisdom is that the distribution of dark matter in the Universe follows the distribution of galaxies. Indeed, the detailed models of the evolution of structure, such as the Millenium Simulation, embody that assumption. However, an observational test of the assumption is possible and is potentially very informative about the nature of dark matter. In this talk I'll describe how measurement of galaxy distances allows the non-Hubble-expansion velocities of galaxies to be determined, and how these data can be integrated to provide a map of the dark matter on 100 Mpc scales. Both current projects (using the 6dF galaxy redshift survey) and future projects using the Australian Square Kilometre Array Pathfinder (due to operate in 2012) will be described.
Oct 8th 2010 @ 11:30am
Rick Perley (NRAO)
Title: The Expanded Very Large Array
The EVLA project is a $90M upgrade of the Very Large Array which will multiply its scientific capabilities at least tenfold. Begun in 2000, the project will be completed by the end of 2012. Key goals for the project include: Complete frequency coverage from 1 to 50 GHz with maximum instantaneous bandwidth of up to 8 GHz; all-digital fiber-optic signal transmission from the antennas to optimize stability; a wide-bandwidth full-polarization correlator which will enable extraordinarily flexible observing modes. EVLA construction continues to progress well. All 28 antennas have been upgraded to modern standards, and about half of the 228 wideband cryogenically cooled receivers are now installed. The WIDAR correlator is now completed, and 2 GHz-wide data are now available for testing purposes. In this talk I will review the status of the project and the unique observational capabilities that the EVLA can now offer via the `OSRO' and `RSRO' programs. Examples of early science which demonstrate the potential of the completed project will be shown. The EVLA's capabilities will rapidly rise over time as the WIDAR correlator is brought to its full capability. However, the scientific productivity of the array will be set to a significant degreee by our ability to record, distribute, calibrate, and image the multi-TB datasets generated by the correlator -- these are the major challenges for the future, and I will spend some time on the observatory's plans to meet them.
Sep 30th 2010 @ 11:30am
John Blakeslee (NRC Herzberg Institute of Astrophysics, Victoria, Canada)
Title: What's New in Galaxy Surface Brightness Fluctuations
The surface brightness fluctuations (SBF) method measuresthe variance in a galaxy's light distribution arising from fluctuations in the numbers and luminosities of stars per resolution element. I'll briefly review how the method works, then present recent SBF measurements with the Hubble Space Telescope for 130 galaxies in the Virgo and Fornax clusters. These data yield a precise relative distance for these two important galaxy clusters and tell us about their internal structures. I'll discuss other related HST programs, including on an ongoing study with WFC3/IR of SBF and globular cluster optical-IR color distributions in Virgo and Fornax ellipticals.
Sep 23rd 2010 @ 11:30am
Elaine Sadler (University of Sydney)
Radio galaxies and galaxy evolution
It is now generally recognized that the evolution of massive galaxies over cosmic time can be profoundly influenced by feedback processes linked to radio jets powered by a central black hole. Paradoxically, these radio jets are invoked in the literature both to trigger star formation in galaxies and to inhibit late-time star formation. I will present some observational case studies, drawn from large radio and optical surveys, which may help to clarify the relationship between the optical and radio properties of massive galaxies over a wide range in redshift.
Sep 16th 2010 @ 11:30am
Richard Ellis (Caltech)
Title: Did Galaxies Reionize the Universe?
A few hundred million years after the Big Bang, the hydrogen in deep space was ionized into its component protons and electrons. Theorists speculate this landmark event was caused by the birth of the first galaxies. Can powerful telescopes, probing back in cosmic history, directly witness this event? Large telescopes have already traced the evolutionary history of galaxies back to when the Universe was 1 billion years old. The first results from the Wide Field Camera 3 onboard Hubble Space Telescope give a glimpse at primitive stellar systems at yet earlier times. The lecture will address the progress and challenges of this fundamental quest for our origins, and discuss the future prospects with the James Webb Space Telescope and the next generation of 30-40 meter aperture ground-based telescopes.
Sep 15th 2010 @ 11:30am
Alexandra Abate (LAL, Orsay)
There has recently been a resurgence of interest in peculiar velocity analysis because of its direct sensitivity to the derivative of the growth function. This renewed interest can be roughly catagorised into the following areas: bulk flow measurements; as a "useful" systematic to SN1a luminosity distance measurements; the kinematic Sunyaev-Zeldo'vich (kSZ) effect. The bulk flow results are of particular interest as they seem to show departures from LCDM on large scales. After analyzing the SFI++ galaxy peculiar velocity survey we find instead although a higher value of sigma_8 and a lower value of Omega_m are preferred, the values are still consistent when compared with WMAP5. However we note that although our analysis probes a variety of scales, the constraints will be dominated by the smaller scales, which have the smallest uncertainties. Additionally we also illustrate how the peculiar velocity effect in SN Ia data can be turned from a "systematic'' into a consistency test of the LCDM model; they are sensitive to both the expansion rate and growth of structure. For both data sets (separately) we assume a flat LCDM model and constrain gamma in the growth factor (Omega_m(z)^gamma). We find that with the size of these data samples we currently can not distinguish between standard Einstein gravity (gamma=0.55) and predictions from some modified gravity models. Lastly I describe some ongoing work, looking for signatures of a bulk flow in the magnitude fluctuations of distant luminous red galaxies.
Sep 7th 2010 @ 11:30am
Hilton Lewis (Keck Telescope Manager)
Title: Strategic thrusts at WMKO
Aug 26th 2010 @ 11:30am
Bart Pindor (University of Melbourne)
Title: The MWA EOR Experiment
One of the primary science goals of the Murchison Widefield Array (MWA) is to detect highly-reshifted 21cm radiation emitted by neutral hydrogen during the Epoch of Reinoization. I will introduce the physical significance of this radiation before focusing on the observational challenges faced by the MWA EOR experiment. In particular, I will discuss why bright point sources are a special class of astrophysical foreground and discuss a technique developed to treat them in the MWA data.
Aug 20th 2010 @ 10:30am
Peter McLeish
Title: Red Sprites
Aug 12th 2010 @ 11:30am
Aidan Hotan (Curtin University of Technology)
Title: Pulsars: Powerful Objects in the Nearby Universe
Since the discovery of radio pulsars in the late 1960s, ongoing research has revealed a wealth of information about the surprisingly wide and varied manifestations of neutron stars. We now have the ability to study these enigmatic objects across the entire electromagnetic spectrum and a unified picture of neutron star evolution is slowly beginning to emerge. This talk will review the observational properties of neutron stars, with a focus on results from the last 10 years.
Aug 10th 2010 @ 11:30am
David Koo (University of California, Santa Cruz)
Title: AEGIS: DEEP's Panchromatic Vista of Distant Galaxies and AGN's
I will give an overview of the Keck intermediate redshift DEEP programs and the AEGIS multiwavelength surveys and reasons why they are particularly well suited to study distant galaxies and AGN's. After a brief summary of our major science findings, more details will be given 1) about a new measure of kinematics to track disk evolution, 2) about a rare class of very low metallicity but very luminous galaxies, 3) about our discovery that galactic winds appear to be common at z ~1.4, and 4) about a hyper-LIRG whose energy comes from both star formation and AGN activity. I will close with a summary as well as a preview of several on-going, new, and planned surveys (Spitzer:SEDS and HST:CANDELS) that will dramatically enhance the information about very distant galaxies, AGN's, and supernovae.
Jul 29th 2010 @ 11:30am
Gerhardt Meurer (ICRAR, University of Western Australia)
Title: Star Formation Scaling Relations in HI Selected Galaxies
Star formation is complex, involving processes ranging from atomic reactions to the gravitational stability of entire galaxies. This makes it very hard to model even with the fastest computers. Instead, computer simulations of galaxy evolution usually resort to emprical based prescriptions to set the amount of ISM that is converted into stars (the Star Formation Law - SFL) and the mass distribution of stars formed (the Initial Mass Function - IMF). These "laws" have proved remarkably resilient, having been proposed over 50 years ago. I will show results and ongoing work from the Survey of Ionization in Neutral Gas Galaxies (SINGG) and the Survey of Ultraviolet emission in Neutral Gas Galaxies (SUNGG) which survey the star formation properties of galaxies as traced by H-alpha and Ultraviolet emission. Our simple neutral hydrogen (HI) only selection criteria results in a sample that captures all types of star forming galaxies, while the use of two star formation tracers and integrated HI fluxes provide new constraints on both the SFL and IMF. I will present results from this research and discuss plans to systematically dissect the prioperties of large samples of nearby galaxies.
Jul 22nd 2010 @ 11:30am
Kim-Vy Tran (Texas A&M University , University of Zurich)
Title: Star Formation in Galaxy Clusters Over the Past 10 Billion Years.
Understanding how galaxies form and evolve in clusters continues to be a fundamental question in astronomy. The ages and assembly histories of galaxies in rich clusters test both stellar population models and hierarchical formation scenarios. Is star formation in cluster galaxies simply accelerated relative to their field counterparts, or do cluster galaxies assemble their stars in a fundamentally different manner? To answer this question, I review results at 0 < z < 1 from our Spitzer/MIPS Infra-Red Cluster Survey (SMIRCS) and present first results from the highest redshift cluster yet detected at z=1.62.
Jul 15th 2010 @ 11:30am
Bram Venemans (ESO)
Title: Galaxies and quasars in the epoch of reionisation.
The reionisation of the neutral Hydrogen in the early Universe was a landmark event in cosmic history, rendering the Universe transparent to UV photons. Despite its importance, little is known about when reionisation occured. Measurements by WMAP point to a redshift above 8, while the size evolution of the HII regions around z > 6 quasars indicate that redshifts z~6-7 corresponds to the tail end of cosmic reionisation. In this talk I will present the results of various recent observational studies aimed at constraining the epoch of reionisation and discovering the sources responsible for it. I will end with highlighting the exciting progress a 42m E-ELT would bring to the field of observational cosmology.
Jul 1 - Jul 8
No Colloquium (ASA)
Jun 24th @ 11:30am
Sarah Maddison (Swinburne)
Title: Planet-disk interactions
Gravitational interactions between a young planet and its protoplanetary disk can alter the planetary orbit and result in the migration of the planet. The mass of the planet, along with disk conditions, determine the rate and direction of planetary migration, which can affect the configuration of the final planetary system. In this talk I will provide a brief overview of the planet formation process and discuss both type I migration (fast inward migration of low mass planets) and type II migration (slow migration of more massive planets), and how migration can explain the hot Jupiter population amongst the extrasolar planets, as well as those in mean motion resonances. I will also discuss how the gap induced by the planet affects the gas and dust in the disk and the observational consequences of the gap.
Jun 17th 2010
No Colloquium (GMT Workshop)
Jun 10th 2010 @ 11:30am
Joerg Fischera (Australian National University)
Title: Why you should care about dust!
Although only a small fraction of the total mass (less than 1%) of the interstellar medium is condensed in grains, dust will play a tremendous role in various modern astrophysical disciplines for the next decade. Several important effects arise from the ability of interstellar dust to attenuate light through dust absorption and scattering and to reprocess the absorbed emission to infrared radiation. In the talk I will highlight some essential problems for observational astrophysics and will discuss possible solutions based on our current understanding of the physical properties of interstellar grains.
Jun 3rd 2010 @ 11:30am
Chris Wright (UNSW@ADFA)
Title: Resolving structure in the disk around the young star HD100546 at millimetre and centimetre wavelengths
Several lines of evidence demonstrate the existence of a circumstellar disk around the Herbig Be star HD100546. Structure within the disk, such as an inner cavity and spiral pattern, as well as almost identical mineralogy of the dust grains to those seen in our own solar system, further suggest that the growth to planets may be well underway. To learn more about the processes occurring in this disk we have conducted a multi-frequency observing program with the Australia Telescope Compact Array (ATCA). At 3, 7 and 16 mm we have resolved the emission region, which probably consists of a compact disk of FWHM ~ 50 AU and an envelope of FWHM >= 100 AU. The mm-to-cm spectral index of the dust emission (integrated over the whole region) is ~ 2.3+/-0.2, and thus the dust opacity index is ~ 0.3. This suggests substantial growth of the solid particles, and when compared to dust models in the literature the maximum size is a few tens of centimetre. Structure in the mm dust emission is tentatively detected on a spatial scale broadly resembling the spiral pattern seen in scattered light images. At 3 and 7 mm we also resolve an inner disk clearing on the scale of a few tens of AU. We also present spectral line data from the HCO+ molecule in its lowest rotational transition, which demonstrates the presence of dense molecular gas in the disk. The line profile is double-peaked, with component velocities at ~ 3.5 and 7.0 km/s. Channel maps indicate a slight spatial offset between these velocity components, approximately along the disk major axis. If interpreted as Keplerian rotation the radius of the emission is ~ 350 AU, with the south-east side approaching and the north-west side receding from Earth. Overall our results suggest that HD100546 is probably younger than hitherto thought, perhaps less than 5 Myr instead of >= 10 Myr as generally assumed.
May 27th 2010 @ 11:30am
David Floyd (University of Melbourne)
Title: Quasars from kiloparsec to parsec scales
AGN feedback has become something of a panacea for theoretical models and numerical simulations of galaxy evolution, but observational evidence remains scarce. Quasars host galaxies are a key observable in understanding galaxy evolution, but they present us an enormous problem of dynamic range in both luminosity and scale. This is a problem in common with the search for exo-planets, and can be informed by such work. I shall review our current understanding of quasars and their host galaxies highlighting two innovative observational techniques, one for uncovering the host galaxy (using a planet finding camera on the ground) and the other for studying the nuclear emission region itself (through serendipitous microlensing). I argue that the major missing piece of the observational puzzle is an ability to detect and measure young stellar populations close to the centres of quasars, and briefly explore possible observational techniques for tackling this problem.
May 13th 2010 @ 11:30am
Ryan Cooke (Cambridge)
Title: UM 673: A unique system to study the properties of Damped Lyman-alpha Systems.
The sightline to the brighter member of the gravitationally lensed quasar pair UM 673A,B intersects a damped Lyman-alpha system (DLA) at z ~ 1.6. The neighbouring sightline, however, exhibits a drop in neutral Hydrogen column density by at least a factor of 400, over just 3 kpc. By reassessing this new case together with published data on other QSO pairs, we constrain the typical size of these neutral gas reservoirs at moderate redshifts. Furthermore, we detect a weak and narrow Lyman-alpha emission line which we attribute to star formation activity in the host galaxy of the DLA. We also find the DLA in UM 673A to be metal-poor, with an overall metallicity Z_DLA ~ 1/30 Z_solar. By studying the properties of these low-metallicity systems at high redshift, we may uncover some important clues into the nucleosynthesis from some of the first structures to form in the Universe.
May 11th 2010 @ 11:30am
Paola Merluzzi (INAF-Osservatorio Astronomico di Capodimonte, Naples)
Title: ACCESS: A Complete CEnsus of Star-formation and nuclear activity in the Shapley Supercluster
Abstract: ACCESS project aims to distinguish among the mechanisms which drive galaxy evolution across different ranges of mass examining how, when and where the properties of galaxies are transformed by the interaction with environment. This research is being pursued studying the properties of galaxies in the core of the Shapley supercluster. The multi-wavelength data-set, including panoramic imaging in the near and far UV, optical, near infrared and mid-infrared, plus high-S/N medium-resolution optical spectroscopy, is being complemented by new medium-resolution integral-field spectroscopy provided by the Wide Field Spectrograph (WiFeS) at the Australian National University 2.3m telescope. We will present the results obtained by studying the optical and NIR properties of galaxies in the supercluster environment, as well as the analysis of the mid-infrared survey with Spitzer.
May 6th 2010 @ 11:30am
Emily McNeil (Australian National University)
Title: Planetary nebula kinematics in the outer parts of early-type galaxies
Recent advancements in observational techniques are improving our understanding of the formation and evolution of early-type galaxies. As data extend into the faint outer halos of these objects, we are probing the area where the orbits have long dynamical timescales and the mass is dark-matter dominated. In the last 20 years, planetary nebulae (PNe) have emerged as successful kinematic tracers extending to several effective radii. I will describe a counter-dispersed slitless-spectroscopy technique used to generate catalogs of PN velocities in the outparts of early-type galaxies. Our sample includes the cD galaxy NGC 1399, the shell elliptical NGC 3923 and the BCG NGC 1316. The results from the PN kinematics underscore the importance of tracing the mass out to larger radii in the DM halos of these evolved systems.
Apr 29th 2010 @ 11:30am
Rosemary Mardling (Monash University)
Title: The determination of planetary structure in tidally relaxed systems
The recent discovery of a transiting short-period planet on a slightly non-circular orbit with a massive highly eccentric companion offers the possibility of probing the structure of the short-period planet. The ability to do this relies on the system being in a quasi-equilibrium state in the sense that the eccentricities are constant on the usual secular timescale and decay on a timescale which is much longer than the age of the system, all the time remaining apsidally aligned. Since the equilibrium eccentricity is effectively a function only of observable system parameters and the unknown Love number of the short-period planet, the latter can be determined with accurate measurements of the planet's eccentricity and radius. But this analysis relies on the assumption that the system is coplanar, a situation which seems unlikely given the high eccentricity of the outer planet. I will discuss how non-coplanarity transforms the fixed point into a limit cycle, generally reducing the ability to unambiguously determine the Love number of the short-period planet. For the HAT-P-13 system, however, current estimates of the eccentricity and radius of the transiting planet together with a reasonable lower bound on its Q-value suggest that the system is likely to be close to coplanar.
Apr 22nd 2010 @ 11:30am
Chris Conselice (University of Nottingham)
Apr 15th 2010 @ 11:30am
Geoff Clayton (Louisiana State University)
The Evolutionary History of the R Coronae Borealis Stars
The R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants, all apparently single stars which are consistent with being post-AGB stars. RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The mechanism of dust formation around RCB stars is not well understood but the dust is thought to form in or near the atmosphere of the stars. Their rarity may stem from the fact that they are in an extremely rapid phase of the evolution or in an evolutionary phase that most stars do not undergo. Several evolutionary scenarios have been suggested to account for the RCB stars including, a merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. The large overabundance of 18O found in most of the RCB stars favors the WD merger scenario while the presence of Li in the atmospheres of four of the RCB stars favors the FF scenario. In particular, the measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovae. I will present recent visible and IR observations of various RCB stars obtained with HST, Spitzer and ground-based telescopes.
Apr 1 - Apr 08
No Colloquium (Easter)
Mar 25th 2010 @ 11:30am
Ken Freeman (RSAA, Australian National University)
Title: Dark Matter in Galaxies
I will review the properties of dark matter in galaxies from an observational perspective. Topics include the mass and extent of the dark halos of large spirals like the Milky Way, modelling the dark halo, the maximum disk problem, the hydrostatics of the HI layer in disk galaxies as a probe of the galactic potential, dark matter in elliptical galaxies and dwarf spheroidal galaxies, scaling laws for dark halos, and the fractional contribution of galactic dark matter to the mass content of the universe.
Mar 19th 2010 @ 11:30am
James Taylor (University of Waterloo)
Title: The Suprime Survey: A Large Shear-selected Sample of Galaxy Clusters at z = 0.1-0.8
The Suprime survey consists of 22 square degrees of deep imaging with Suprime-Cam on the Subaru Telescope. Weak lensing analysis of these images and subsequent spectroscopic follow-up have produced the first large shear-selected sample of galaxy clusters. Clusters range in mass from 0.8-5e14 solar masses and cover the redshift range z = 0.1-0.8, although though the exact sensitivity of the survey depends strongly on the observing conditions and data quality in each field. I will discuss constraints on the equation of state and the amplitude of the power spectrum based on the highest quality data. These are not particularly strong for the current sample, but give a sense of the prospects for future lensing surveys. I will also discuss some other "value-added" analysis that could be applied to similar samples of clusters detected by lensing, X-ray, SZ or other means.
Mar 18th 2010 @ 11:30am
Caroline Foster (Swinburne)
Title: 30 Month PhD review.
Mar 12th 2010 @ 11:30am
A E L Davis (Imperial College)
Title: Celebrating Kepler's Astronomia Nova: a geometrical success story
I shall hope to show why Kepler was as important to astronomy as his contemporary Galileo, 400 years ago. In his ground-breaking work Kepler discovered the two laws of motion for a single planet, using only the methods of traditional geometry.
Mar 11th 2010 @ 11:30am
Max Pettini (IoA, Cambridge University and ICRA, University of Western Australia)
Title: Galactic Outflows at Redshifts z = 2 -3: Watching `Feedback' in Action.
`Feedback' -- the self-regulation of star formation activity -- is often claimed to be an essential ingredient of the galaxy formation process, and yet its physical characteristics have so far remained largely unconstrained. In this talk I shall describe some recent result of a major observational effort aimed at quantifying the properties of galaxy-wide outflows from star-forming galaxies at redshifts z = 2 - 3 and the interaction of this metal-enriched gas with the surrounding intergalactic medium.
Mar 4th 2010 @ 11:30am
Mike Gladders (University of Chicago)
Title: Strong Lensing by Optically-Selected Galaxy Clusters
Gravitational lensing by galaxy clusters was predicted in the 1930s, and finally discovered in 1980s. In the two decades following the initial discovery, several dozen significant cluster lenses were found, though only a handful of these have been studied extensively. Lensing clusters probe the distribution of massive halos in the universe; the expected arc production frequency can be predicted from simulations and compared to existing data. Massive lensing clusters act as 'natural telescopes', providing highly magnified images of background sources which cannot otherwise be studied using the current generation of telescopes. The details of the observed lensing in clusters also probes the internal properties of these massive halos. Most cluster strong lens studies to date have been limited by the small number and heterogeneous nature of the sample of known lenses (most of which are one-off discoveries). I will report on efforts to take the study of strong lensing clusters to a new statistical regime, by identifying and studying two new samples of strong lenses within large catalogs of optically selected galaxy clusters from the RCS-2 and SDSS surveys; in total we have found hundreds of new giant arcs. These efforts are now approximately three-quarters-complete; in this progress report I will describe some of the successes of these studies, and the remaining challenges.
Feb 25th 2010 @ 11:30am
Julia Scharwaechter (RSAA, Australian National University)
Title: Co-evolution of active galactic nuclei and their host galaxies
In current models, active galactic nuclei (AGN) are recognised as an integral part of galaxy evolution and as an important factor in the build-up of the M-sigma relation through fuelling and feedback processes. I will review aspects of AGN fuelling and feedback for a spectrum of AGN redshifts and luminosities using the well-known examples of 3C 48 (z=0.367), I Zw 1 (z=0.061) and NGC 1068 (z=0.0038). The discussion will include a summary of our previous case studies of 3C 48 and I Zw 1 as well as preliminary results from high resolution near-infrared spectroscopy of the circum-nuclear molecular hydrogen emission in NGC 1068, using CRIRES at the VLT (ESO). While major mergers are the likely triggering mechanism of luminous quasi-stellar objects (QSOs), the fuelling of nearby low-luminosity AGN seems to be dominated by minor mergers, bars, and/or stochastic accretion. We have recently started a multi-wavelenght survey targeting an intermediate population of "borderline" type-1 QSOs with luminosities around the classical demarcation between Seyfert galaxies and QSOs. A part of the survey is conducted with the new field spectrograph WiFeS at the ANU 2.3m telescope, for which I will present the first results.
Feb 24th 2010 @ 11:30am
Hannah Parkinson (IoA, University of Edinburgh)
Title: Paving the way with GAMA to better BAO measurements in SDSS.
The Galaxy And Mass Assembly (GAMA) survey is a large galaxy redshift survey, in the third year of observing in the Anglo-Australian Telescope. The main science aims of GAMA are: the Dark Matter Halo Mass Function and M/L ratio, from the group velocity dispersion; Galaxy Stellar Mass Functions; the evolution of galaxy merger rates. My application of GAMA is using the spectroscopic redshifts to calibrate photometric redshifts for the whole of SDSS, in order to make the best possible clustering measurements. I will talk about improvements to the GAMA spectroscopic pipeline in the form of PCA sky subtraction to improve the quality of the spectra. I will describe my method of producing photometric redshifts showing the improvement from existing photometric redshifts in SDSS. Finally I will show some preliminary results of measuring galaxy clustering as a function of redshift and intrinsic colour.
Feb 18th 2010
No Colloquium
Feb 11th 2010 @ 11:30am
Tiago Pereira (RSAA, Australian National University)
Title: 3D models as new paradigm in stellar atmospheres: trusting their results and working towards widespread adoption.
Models of stellar atmospheres are a fundamental tool in contemporary astronomy. Used to derive the chemical composition and many parameters of stars, their importance is far reaching but their systematic uncertainties are seldom discussed. I will tell the tale of the classical models and how the new 3D hydrodynamic models are changing the game. There have been a few bumps towards the adoption of 3D models, most notably the controversy surrounding the chemical composition of the Sun itself. I will discuss these problems and show some results from my PhD thesis, where I systematically tested the 3D solar models against several observations. Lastly, I will outline the state-of-the-art regarding 3D models for late-type cool stars and current efforts to allow a widespread adoption of this new tool in stellar spectroscopy.
Feb 4th 2010 @ 11:30am
Javier Gorosabel (Instituto de Astrofisica de Andalucia, Spain)
Title: The BOOTES network of robotic telescopes; hunting Gamma-Ray Bursts on the fly.
In this talk first I will shortly review the most important breakthroughs in the Gamma-Ray Burst (GRB) field occurred in the last year. Then I will talk on the important role in the field of the rapid responding robotic telescopes. Finally I will present the development status of the BOOTES network of robotic telescopes all over the world in order to catch their prompt optical-near IR emission.
Jan 28th 2010 @ 11:30am
James Bolton (University of Melbourne)
Title: Beyond the Gunn-Peterson trough: what else does the Lyman-alpha forest tell us about reionisation?
Quasar absorption spectra are a key observational probe of the hydrogen reionisation epoch. The appearance of the Lyman-alpha Gunn-Peterson trough approaching z=6 indicates the neutral hydrogen fraction in the intergalactic medium (IGM) is increasing with lookback time. However, the constraint this observation provides on the IGM neutral hydrogen fraction is very weak; Lyman-alpha absorption saturates at neutral hydrogen fractions which are still small - around 1 part in 10^4. Fortunately, the Lyman-alpha forest at z < 6 can still provide valuable constraints on the temperature of the IGM and the metagalactic ionising emissivity, and hence provide further, indirect insight into the reionisation and thermal history of the Universe at higher redshift. I will discuss the recent results of our work in this field, their implications for the reionisation history and conclude by discussing where future progress can be made.