2009 SIfA Seminars - Titles and Abstracts
This page contains the abstracts and titles supplied by the speakers as they become available. This is the main SIfA Seminars page
Jan 30 - Ivan Baldry (Liverpool John Moores University)
Accounting for stellar and baryonic mass in the galaxy population: Checks and balances.
First, I will briefly present a bit of history on galaxy and stellar classification. Then, I will describe recent measurements of the galaxy stellar and baryonic mass functions in the context of the current cosmological paradigm: where are all the baryons? I will conclude with prospects of definitive measurement of galaxy mass functions, with the recently started survey GAMA and future surveys, such as with ASKAP.
Feb 6 Stephen Fine (USyd)
Active super-massive black holes
I will review some of the techniques we use for weighing super-massive black holes, and will discuss some recent results derived from an analysis of current large spectroscopic databases.
Feb 20 - Sun Kwok (University of Hong Kong, Hong Kong, China)
Synthesis of Organic Compounds in the Late Stages of Stellar Evolution
The last phase of stellar evolution from the asymptotic giant branch (AGB) to proto-planetary nebulae, to planetary nebulae represents the most active period of synthesis of organic compounds in a star’s life. Both inorganic and organic molecules and solids are found to form in the circumstellar envelopes created by stellar winds. Over 60 gas-phase molecules, including rings, radicals, and molecular ions have been identified by millimeter-wave and infrared spectroscopic observations through their rotational and vibrational transitions.
Infrared spectroscopic observations of emissions from the stretching and bending modes of aliphatic and aromatic compounds have revealed a continuous synthesis of organic material from the end of the AGB to proto-planetary nebulae, to planetary nebulae. These results show that complex carbonaceous compounds can be produced in a circumstellar environment over a period of only a few thousand years. Most interestingly, there are a number of unidentified emission features which are almost certainly carbonaceous in nature but their exact chemical composition is unknown. These include the 21 and 30 micron emission features, and the extended red emission observed in proto-planetary nebulae and planetary nebulae.
Isotopic analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence of pre-solar grains similar to those formed in evolved stars. This provides a direct link between star dust and the solar system and raises the possibility that the early solar system was chemically enriched by stellar ejecta.
In this talk, we will summarize some of the recent spectroscopic observations of the circumstellar envelopes of evolved stars and present a scenario of chemical evolution including the possible role of photochemistry in the late stages of stellar evolution.
Reference
Kwok, S. The Synthesis of Organic and Inorganic Compounds in Evolved Stars, Nature, 430, 985
Feb 27 - Franz Bauer
SN1996cr: SN1987A's Wild Cousin?
SN1996cr is the one of the five closest SNe to explode in the past 30 yr, yet lay undiscovered for many years. Due to its fortuitous location in the Circinus Galaxy, we have a wealth of serendipitous archival data available to piece together its early evolution. Like SN1987A, it appears to have exploded into a wind-blown bubble structure, sparking a unique temporal evolution. SN1996cr, however, is several orders of magnitude more luminous and a factor of several more compact, making it a compelling object in its own right. I'll describe current multi-wavelength constraints on SN1996cr and the physical interpretations they lead to. I will also highlight how future observations and hydrodynamical modeling should refine our understanding, setting strong constraints on the structure of the nebula established by the progenitor winds and, by extension, the evolution of the progenitor itself.
March 6 - Joint CS/SIfA Seminar - Prof. Dr. Franz-Josef Luebken, Director of the Leibniz Institute of Atmospheric Physics.
Physics in the border zone between the atmosphere and space
The important physical processes in the atmosphere change fundamentally in the mesosphere (50 to 100 km), primarily due to the reduction of gas density being orders of magnitude smaller compared to the troposphere. For example, molecules are no longer in thermodynamic equilibrium with radiation and the mixing ratios of inert species change with height. Furthermore, gravity waves generated in the troposphere achieve large amplitudes in the mesosphere, get instable and produce turbulence. This in turn causes a modification of the general circulation which leads to a substantial cooling (heating) in the summer (winter) mesosphere. Consequently, the summer mesopause (90 km) at polar latitudes is much colder than in winter and cools down to approximately 150 Kelvin (the coldest place in the Earth's atmosphere) despite permanent sunshine. The extremely low temperatures lead to ice particles known as noctilucent clouds (NLC). The same ice particles produce very strong radar echoes (PMSE, or polar mesosphere summer echoes). During the last few years NLC and PMSE were studied in detail with lidars (light induced detecting and ranging) and radars, respectively. This has led to a better understanding of the physical processes involved in ice particle formation, their influence on the background plasma, and the importance of the background atmosphere. Large temperature trends are observed in the mesosphere at mid latitudes. Based on radio wave propagation experiments performed at the IAP since the 1950s a temperature decrease of up to 20 degrees in 40 years is observed, i. e., a factor of 40 larger compared to the troposphere. Since ice particles are very sensitive to atmospheric temperatures, NLC and PMSE are proposed to be sensitive indicators for trends in the upper atmosphere. The basic physical processes leading to the thermal structure of the upper atmosphere and to NLC and PMSE are explained in the presentation and potential long term and solar cycle variations are discussed.
March 13 - Joint Particle/SIfA Seminar - Dr Elizabeth Winstanley (Sheffield)
Black Holes at the LHC
Brane world models in string theory suggest that our universe is a slice, or "brane", of a higher-dimensional space-time. This would alter the geometry of astrophysical black holes. Another consequence of these models is that the energy scale of quantum gravity may be many orders of magnitude lower than previously thought, and may be as low as a few TeV. If this is the case, copious numbers of black holes will be formed by collisions at the LHC or by high-energy astrophysical phenomena such as cosmic rays. In this talk we will review aspects of the formation and subsequent evaporation of these mini-black holes. For simplicity, we will consider only the simplest brane world models, where the extra space-time dimensions are flat. We focus particularly on the emission of particles by a black hole formed at the LHC, both particles visible within the detectors and particles which contribute to the missing energy.
March 20 - Stephane Regnier (St Andrews)
Solar coronal magnetic field extrapolations and all that
As the 3D structure of the magnetic field in solar corona cannot be currently derived directly from observations, a method has been developed to extrapolate the coronal magnetic field from photospheric observations. The extrapolation method can rely on several assumptions of equilibrium: potential fields, force-free fields and magnetohydrostatic fields. I will review the progress that has been done in this field of research during the last 15 years. Especially I will describe the different requirements which lead to understanding the solar corona. I will thus summarize the physical processes that can be tackled with these extrapolation methods (e.g., flares, magnetic reconnection, instabilities, Alfven waves). To conclude, the next improvements required to better understand the solar atmosphere are discussed.
March 26 - Angel R Lopez-Sanchez (ATNF)
A multiwavelength analysis of Blue Compact Dwarf galaxies: HI results.
Blue compact dwarf galaxies (BCDGs) represent the subset of low-luminosity galaxies undergoing a strong and short-lived episode of star formation at the present time. We are obtaining deep multiwavelength data of some nearby BCDGs combining broad-band optical/NIR and H_alpha photometry, optical spectroscopy and 21-cm radio observations in order to understand their chemical and physical properties, star formation activity, kinematics, estimate the importance of the young/old stellar populations within them and the environment in which they reside. In this talk, we will present new exciting HI results for some of these objects, all showing evident interaction features in their neutral gas component. We remark on the apparent rotation of the HI component about the optical major axis of NGC 5253 (Lopez-Sanchez et al. 2008a; data from the "Local Volume HI Survey" -LVHIS- project), the complex neutral gas morphology and kinematics found in Tol 9 (Lopez-Sanchez et al. 2008b), the prominent HI tidal tails and detached HI cloud found in Tol 30, a long HI bridge between two galaxies in Tol 1924-416, and the huge and disturbed HI content of the NGC 1512 / NGC 1510 system (Koribalski & Lopez-Sanchez, 2009; data also from the LVHIS project).
April 24 - Timothy C. Beers (Michigan State University)
New results from SDSS/SEGUE
I report on recent (mostly unpublished) results from stellar studies of data obtained with the Sloan Digital Sky Survey, in particular the sub-survey SEGUE: Sloan Extension for Galactic Understanding and Exploration. These results include a discussion of the SEGUE-1 and SEGUE-2 observing stategies, as well as the techniques used for photometric metallicity mapping (and extensions thereof), the most metal-poor stars identified to date from SEGUE, the determination of alpha-to-iron ratios from R=2000 spectra, and an examination of the kinematics of local M-type dwarfs based on millions of individual photometric distance and proper motion measurements.
May 1 - Brian Schmidt (Mt Stromlo Observatory, the Australian National University)
Surveying the Southern Skies with SkyMapper
SkyMapper is a 1.3m widefield telescope that is currently being commissioned at Siding Spring Observatory. I will discuss the history of the telescope, its scientific capability, and key science projects for the telescope, which include a survey of 20000 sq degrees of the southern sky, as well as transient searches for supernovae, gamma ray bursts, and even gravitational wave sources. I will also discuss the potential for Sydney University Astronomers to access the SkyMapper data stream through collaborative programs.
May 7 - Siddharth Malu
A Novel Approach to finding B-modes in CMB Polarization:
CMB studies are now a data-rich field in astrophysics. The power spectrum of CMB is well measured and cosmological models have been characterized and polarization has been detected in the CMB. All results fit well within and are explained well by the inflationary paradigm. But current evidence for inflation is indirect. The next generation of CMB experiments will aim at providing the most direct evidence for inflation through the detection of B-modes in CMB polarization. Despite improvements in experimental techniques, it is as yet unclear what configuration and approach a CMB polarization experiment should adopt, in view of lack of information about polarization foregrounds and instrument systematic effects. I will describe a novel approach to these measurements, called bolometric interferometry, which avoids many of the systematic errors found in imaging systems. In particular, I will describe a prototype, the Millimeter-wave Bolometric Interferometer (MBI). I will present a few promising approaches from our collaboration, the Q-and-U Bolometric Interferometer for Cosmology (QUBIC) and discuss plans for feasibility studies for detecting CMB polarization foregrounds and signals with adding interferometers.
May 8 - Alberto Sesana
LISA and Pulsar timing: upcoming new windows in astrophysics & cosmology
In the next decade the detection of gravitational waves will (hopefully) be a reality, opening a completely new window on the Universe. The primary actors on this upcoming stage are expected to be massive black hole binaries. After a short introduction about hierarchical galaxy and MBH formation, and GW detection, I will discuss the possibility of constraining black hole formation and cosmic evolution scenarios using the planned laser interferometer space antenna (LISA) and pulsar timing arrays (PTAs), assessing their capability of providing unique high (and low)-redshift information difficult to obtain by other means.
May 15 - Esko Gardner (Turku University)
Bar-driven Hercules
The Hercules stream is a prominent feature in our local velocity space. What causes it is fairly clear - the bar in our galaxy. With all the new information about the galactic center confusing us, we have to ask ourselves, which feature is the one that actually causes it? I will present some simulations and some other interesting results on the effects of the inner galaxy on our lively corner of the Galaxy.
May 22 - Anna Frebel (Harvard-Smithsonian Center for Astrophysics)
What the most metal-poor stars tell us about the early Universe
The chemical evolution of the Galaxy and the early Universe is a key topic in modern astrophysics. The most metal-poor Galactic halo stars are now frequently used in an attempt to reconstruct the onset of the chemical and dynamical formation processes of the Galaxy. These stars are an easily-accessible local equivalent of the high-redshift Universe, and can thus be used to carry out near-field cosmology. The discovery of two astrophysically very important metal-poor objects has recently lead to a significant advance in the field. One object is the most iron-poor star yet found (with [Fe/H]=-5.4). The other star displays the strongest known overabundances of heavy neutron-capture elements, such as uranium, and nucleo-chronometry yields a stellar age of ~13 Gyr. Both stars already serve as benchmark objects for various theoretical studies with regard to nucleosynthesis processes in the early Galaxy. I will discuss how the abundance patterns of these and other metal-poor stars solidify and advance our understanding of the early Universe, and provide constraints on the nature of the first stars, as well as their explosion mechanisms and corresponding supernova nucleosynthesis yields. Large samples of these old objects are also employed to test theoretical predictions about the formation of the very first low-mass stars and the lowest observable metallicity. I will finish the talk with some new results of halo-like abundances of stars in dwarf galaxies which suggests that systems like these might have been the building blocks of the Milky Way's halo.
May 29 - Rainer Hollerbach (Monash University)
The Hall Effect in Neutron Stars.
Neutron stars have the strongest magnetic fields found in the universe, with field strengths of up to 1015 G in so-called magnetars. At these field strengths the familiar Hall effect, whereby a magnetic field B deflects an electric current J in the direction JxB, can become crucially important. Starting from Faraday's law, Ampere's law and Ohm's law, I will derive the relevant magnetic induction equation, and show how the Hall effect leads to a quadratic nonlinearity whereby the magnetic field influences its own evolution. I will then present two- and three-dimensional numerical solutions of this governing equation, in Cartesian and spherical shell geometries. I will also include depth-dependent density, and show that it interacts with the basic Hall effect in interesting and unexpected ways. In particular, depending on the orientation of the internal toroidal magnetic field, we predict that a neutron star's magnetic field should be concentrated at either the poles, or else spread out in a ring around the equator. We suggest that this may have observable consequences for real neutron stars.
June 5 - Lee Spitler (Swinburne University)
Galaxy Dark Matter Halos and Globular Cluster Systems
Massive globular star clusters are only produced during epochs of strong star formation. Observations of ancient globular cluster systems thus provide a unique way to understand the early star formation history of individual galaxies and help constrain galaxy formation models. This idea is further confirmed with the recent discovery of a strong connection between globular cluster systems and their host galaxy dark matter halos. I will discuss the implications of this finding and demonstrate how it might be used to measure the total dark matter masses of diffuse galaxy filaments. The talk will conclude with a brief summary of our work to constrain the internal kinematics of galaxies out to unprecedented effective radii using a novel observational technique.
Tuesday June 9 - Senior Physics Talks
Paul Stewart: Planet Hunting: Exploring Nearby Moving Groups with Aperture Masking
Very young co-moving associations of stars offer ideal conditions for the direct detection of extra-solar planets. This report prestents the results of a project which aimed to systematically analyse observations of such young stars, made with the Keck II telescope with aperture masking, to identify any potential faint companions. Aperture masking was used to allow observations to be made at the diffraction limit of the telescope, providing the best possible opportunity for making such detections. In this project seven confirmed detections were made, most of these were low mass stellar companions, but two emerged as high mass planetary detections with high confidences (99.9%).
Shivansh Kochhar: Jets, Streamers and Cones: Probing the environment of LMC X-1
This talk reports GMOS integral field spectroscopy of the nebula surrounding the X-ray binary LMC X-1. The high resolution He II/H\beta ratio line map reveals a wide, heterogenous system of emission-line filaments and globules. The emission-line filaments do not seem to be lining the boundary of a large conical cavity. Therefore, contrary to the assertions found in a previous study, there is little evidence found supporting the existence of an ionization cone emanating from LMC X-1. The talk details how the data reduction program IRAF was used to process the GMOS data. Significant outstanding problems associated with the calibration and data reduction are also outlined and possible solutions proposed.
July 10 - Moshe Elitzur (University of Kentucky)
The 10 micron dust silicate feature in AGNs and ULIRGs
The 10mic silicate absorption feature is never deep in AGN. In marked contrast, ULIRGS display some extremely deep features. In this talk I will cover the essential theory of dust absorption features, identify the fundamentals of the dust distributions giving rise to the stark differences between the two classes of sources and explain some novel properties displayed by the feature observations.
July 24 - Marcella Massardi (INAF-Osservatorio Astronomico di Padova, Italy)
The Sunyaev-Zel'dovich Effect: "old" stories and new possibilities
The Sunyaev-Zel'dovich effect is the spectral distortion of the Cosmic Microwave Background radiation due to inverse Compton scattering in the direction of ionized clouds. It is a powerful tool to investigate high redshift structures and to constrain some cosmological parameters. In this talk we will review the effect presenting the results of some past and present observations and some future applications of it which show how it can be used to investigate the internal structure of galaxy clusters and the early stages of galaxy formation.
August 21 - Jess Broderick
The environments of distant radio galaxies
High-redshift radio galaxies (HzRGs; z > 2) are unique laboratories for studying the formation and evolution of massive galaxies. In this talk, I will give an overview of the results from my thesis, which explored the radio, optical spectroscopic and near-infrared properties of a large southern sample of HzRG candidates. In particular, I will discuss how radio polarimetry can be used to investigate the magnetoionic environments of HzRGs. I will also speak about some recent work I have done on the polarimetric properties of the extraordinary nearby radio galaxy MRC B1221-423 (z = 0.17), an ideal system for testing the relationship between the active galactic nucleus and its environment in general.
August 28 - Kelton Temby
The Photonic Lantern: Towards an Integrated Photonic Spectrograph
The Photonic Lantern device designed by Bland-Hawthorn et al. is poised to revolutionise ground-based near infra-red astronomy by enabling systems for hydroxyl airglow suppression orders of magnitude better than previous attempts. This talk presents an overview of an integrated photonic lanteren-based system, and the motivations behind its development. It introduces the hydroxyl suppression problem and presents optic fibre properties related to the functioning of the photonic lantern itself. The talk will include visualisations of the device and concept overall system developed using computer aided design software packages.
September 4 - Shane O'Sullivan (University of Cork, Ireland)
Magnetic field properties of AGN jets from multi-frequency VLBA polarimetry
I will present results on multi-frequency (4.6, 5.1, 7.9, 8.9, 12.9, 15.4, 22 and 43 GHz) VLBA polarization observations of the parsec-scale region of several "blazar" jets. Observing across a wide range of frequencies, separated by short and long intervals, enabled reliable determination of the distribution of Faraday rotation on a range of jet scales and hence, the intrinsic jet magnetic field structure. Detection of transverse rotation measure (RM) gradients provided strong evidence for the presence of helical magnetic fields in the magneto-ionic material surrounding the jet. The results also show that the magnitude of the core RM increases systematically with frequency, simply implying that the electron density and/or magnetic field strength is increasing as we get closer to the central engine.
Accurate measurement of the frequency-dependent shift of the self-absorbed radio core ("core-shift") is required for multi-frequency analysis of VLBI data. The measured core-shifts were used to calculate equipartition magnetic field strengths of the order of 10's to 100's of mG in the radio jet cores from 4.6 to 43 GHz. Extrapolating the results back to the accretion disk and black hole jet-launching distances, the magnetic field strengths are found to be consistent with those expected from theoretical models of magnetically powered jets.
September 15 - Geoffrey Bower, UC Berkeley
RIPl: Radio Interferometric Planet Search
RIPL, the Radio Interferometric Planet Search, is a 3-year program (BB240) using the Very Long Baseline Array and the 100m Green Bank Telescope to search for the astrometic signatures of massive planets around nearby ($D < 10$ pc), low-mass (M dwarf) stars. We are observing a sample of 30 stars a total of 12 times over the 3-year period with the expectation of achieving 0.1 milliarcsecond astrometric accuracy per epoch, and ultimately having the sensitivity to detect Jupiter mass planets at 1 AU. This astrometric search is an important complement to radial velocity searches for planets: 1) greater sensitivity to low mass stars; 2) greater sensitivity to long-period planets; 3) greater sensitivity to active stars; and, 4) greater sensitivity to planets that may be imaged with extreme adaptive optics. RIPL explores parameter space that is relevant for the proposed SIM spacecraft. We report on recent results that permit us to set limits of a few Jupiter masses on companions at 1AU to four nearby stars.
September 18 - Daniel Bayliss (Research School of Astronomy and Astrophysics, Australia National University)
Searching for Southern Transiting Planets
While there have been over 370 extrasolar planets discovered, only 60 of these transit in front of their host star. These transiting planets are very important, as they alone allow us to study a wide range of planetary properties, ranging from bulk density to temperature to atmospheric composition. The majority of transiting planets have been detected in the northern hemisphere, primarily by groups using dedicated, small aperture telescopes. I will discuss two projects aimed at finding transiting planets in the southern hemisphere. The first of these is the SuperLupus project, a long-duration transit search close to the Galactic Plane. This project is now complete, and we found that the rate of Hot Jupiter planets around Galactic field stars is lower than previously estimated (0.3% rather than 1%). The second project is the HAT-South project, which is a global network of small aperture, wide-field telescopes. One of the three network sites for this project is Siding Spring Observatory.
September 25 - Oleg Titov (Geoscience Australia)
Geodetic VLBI for astrometry and cosmology
Some models of the expanding Universe predict that the astrometric proper motion of distant radio sources do not vanish as radial distance from observer to the source grows. Systematic effects due to the proper motion can even increase with the distance making possible to measure them with high- precision astrometric techniques like VLBI. The dipole systematic component due to the Galactocentric acceleration was also predicted. We analyzed a large set of geodetic VLBI data spanning from 1979 till 2008 to estimate the dipole, the rotational, and the quadrupole harmonics in the expansion of the vector field of the proper motions of quasars in the sky. We estimated the vector spherical harmonics (three - for the dipole, three - for the rotational, and ten - for the quadrupole systematic) from the individual apparent motion of 687 VLBI radio sources. The individual motion are supposed to be caused by the effect of intrinsic structure variations of the active galactic nuclei (AGN). In addition, the estimates have been obtained separately for different red shift zones. It was shown that the dipole harmonic does not vary significantly, whereas the amplitude of the quadrupole gradually increases with the red shift. This quadrupole pattern can be interpreted either as an anisotropic Hubble expansion, or as an indication of the primordial gravitational waves in the early Universe. However, a more prosaic explanation can be also given. In the next decade the geodetic VLBI technique might approach the level of accuracy needed to test cosmological models of the Universe.
September 28 - Sylvain Veilleux (Maryland)
Galaxy Mergers, Ultraluminous Infrared Galaxies, and Quasar Activity
Galaxy merging is a key driving force of galaxy evolution. In hierarchical CDM models of galaxy formation and evolution, merging leads to the formation of some elliptical galaxies, triggers major starbursts, and may account for the growth of supermassive black holes and the formation of quasars. In order to assess quantitatively the physics of the merger process and its link to elliptical galaxy formation and QSO activity, we must first understand the details of galaxy merging and its relationship to starbursts and AGNs in the local universe. Here I present the recent results from a comprehensive multiwavelength investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. The issues of the occurrence, importance, and duty cycle of black hole driven nuclear activity in these objects will be covered along with their host galaxy properties and the evidence for massive gas flows in and out (past and present) of their central cores. The implications of these results on our understanding of ULIRGs and quasars in a cosmological context will also be addressed.
October 9 - Stan Owocki (University of Delaware)
Magnetospheres of Magnetic Massive Stars
Hot, massive stars lack the convection zones thought to drive the magnetic activity cycles in the sun and other cool stars. Nonetheless, recent advances in spectropolarimetry have revealed a growing list of such massive stars to have global magnetic fields, with strengths ranging up to 10,000 G. This talk will describe how such fields channel the radiatively driven stellar wind outflow of such stars into a circumstellar magnetosphere. These magnetospheres can be diagnosed through their rotationally modulated Balmer line emission, by X-ray emission from shocks formed as the wind flow feeds into the circumstellar medium, and by hard X-ray flares associated with magnetic reconnection driven by centrifugal mass ejections. Overall, magnetic massive stars are proving to be unexpectedly rich and diverse astrophysical laboratories for studying the complex interactions between magnetic fields, rotation, and radiatively driven outflow.
October 16 - Chris Lidman (new Future Fellow)
Galaxy clusters as probes of dark energy
Galaxy clusters are the most massive virialised structures in the Universe. Their number density depends on both the geometry of the Universe and the rate at which structure grows.
Galaxy clusters are also rich in relatively dust-free, early-type galaxies, which are known to host only Type Ia supernovae. Evidence from several surveys now suggest that Type Ia supernovae hosted by early-type galaxies are better standard candles than Type Ia supernovae hosted by galaxies of other types.
In this talk I will describe how clusters can be used as a dark energy probe, both through the number density of clusters and the through the Type Ia supernovae that can be found in them.
October 23 - Duncan Forbes (Swinburne)
Revealing Elliptical Galaxy Halos
Halos contain most of a galaxy's mass but they are poorly probed. Individual elliptical galaxy masses are difficult to measure. Here I discuss a new technique to probe galaxy halos and measure elliptical galaxy masses. The technique is illustrated with data from the Deimos spectrograph on Keck. Initial results and some galaxy formation model predictions are described. Finally a new survey called GHOST is presented.
November 13 - S. George Djorgovski (Caltech)
Exploring The Time Domain With Synoptic Sky Surveys
Time-domain astronomy is rapidly becoming an exciting new research frontier, touching on fields ranging from studies of the Solar system, to cosmology and extreme relativistic astrophysics. A new generation of digital synoptic sky surveys is now creating Terascale data streams, and moving rapidly into the Petascale regime. We will describe briefly some of the ongoing studies based on the Palomar-Quest survey and Catalina Real-Time Transient Survey, and some of the computational challenges, focusing on the automated classification of transient events and their follow-up.
November 20 - Andrew Hopkins (AAO)
Is the stellar initial mass function universal?
Many independent lines of evidence in the past few years have tantalisingly suggested that the stellar initial mass function (IMF) is not universal, but in fact varies between galaxies, and possibly evolves with time, being more top-heavy at high redshift. The IMF is fundamental to almost all aspects of galaxy evolution, governing (for example) the star formation rates inferred from total luminosity measurements of galaxies. I will review some of the recent evidence suggesting variations in the IMF. Then, after a brief introduction to the GAMA (Galaxy And Mass Assembly) survey, I will present measurements using GAMA spectra that show for the first time that the high-mass slope of the IMF appears to have a very strong underlying dependency on galaxy star formation rate. This result provides a natural explanation for the recent suggestions that the IMF must have been more top-heavy at high-redshift.
November 27 - Brian Reville (Max Planck)
Magnetic Field Amplification and particle acceleration in
supernova remnant shocks
There is a growing wealth of evidence that electrons, and possibly protons, are accelerated to high energies at supernova remnant shocks. The most popular model for accelerating these energetic particles is the diffusive shock acceleration process. Recent models suggest that the efficient acceleration of cosmic-rays can also lead to significant amplification of the magnetic field. I will review some of the observational results that have motivated these suggestions and the theories that have been put forward to explain these observations.
December 3 - Katherine Mack (IoA, Cambridge)
Primordial black holes in the Dark Ages
I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen.
December 4 - Pat Scott (Stockholm University)
The search for particle dark matter
With the launch of the Fermi satellite and the impending startup of the LHC, interest in particle dark matter has exploded in recent years. I will describe some complementary approaches to the problem of identifying dark matter, and show how they can be integrated into a global, multi-messenger, multiwavelength fit to available astronomical and terrestrial data. The impact of dark matter particles on stars can constrain their interations with nuclei, whilst their mass and annihilation cross-section can be probed with searches for gamma rays produced by annihilation in astronomical targets. Ultracompact, primordially-produced dark matter minihalos might prove especially promising in this respect. Global fits turn out to be quite technically challenging, even with the simplest predictive models and the addition of complementary data from a bevy of terrestrial experiments; I will show how genetic algorithms can help in this respect.
December 11: Nathan Smith (UC Berkeley)
Eta Carinae and Pre-Supernova Temper Tantrums of Massive Stars
The evolved massive stars known as luminous blue variables (LBVs) have enjoyed renewed interest in recent years for three reasons: 1) we have learned that eruptions of LBVs probably dominate the total mass lost during a star's lifetime, strongly influencing the star's death, 2) their eruptions make up many of the transient sources fainter than supernovae that will be discovered in increasing numbers in coming years, and 3) LBVs are the likely progenitors of the most luminous supernovae known, giving us a potential window to the deaths of massive stars in the early universe. Despite astonishing mass-loss rates of as much as 1 Msun/yr and total energies of more than 1e50 ergs, the physical mechanism driving these recurring eruptions remains unexplained after decades of research. There is hope that the new wave of transients will help improve the situation. I will begin by summarizing what we have learned from detailed study of Eta Carinae and how it fits in with the range of observed LBV properties, what some outstanding mysteries are, and how this can help guide our intuition for studying luminous supernovae and eruptive transients that result from similar stars in other galaxies.