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Astronomical colloquia.

These form an important part of a research facility, often as a sort of prepublication discussion or a discussion of an individual's current research, and as such it is virtually impossible to "publish" this material. However by recording the topics discussed in the form below does indicate to those, who are unable to attend, what current trends are and who has visited to do research: it keeps everyone 'in the loop' so to speak.

Also included in this section are the colloquia/seminars at the SAAO, NASSP, UWC and the Astrophysics, Cosmology and Gravity Centre at UCT, ACGC. Also included are the SAAO Astro-coffees which are 15-20min informal discussions on just about any topic including but not limited to: recent astro-ph papers, seminal/classic publications, education/outreach ideas and initiatives, preliminary results, student progress reports, conference/workshop feedback and skills-transfer.



Title: Activities of the IRSF

Speaker: Takahiro Nagayama

Venue: SAAO Auditorium

Date: 28 February

Time: 16h00

Abstract: IRSF is a Japanese 1.4m telescope with a near infrared JHK simultaneous camera, SIRIUS, which has been working from November 2000 at Sutherland. It is a joint project between Nagoya Univ. and SAAO. I review the activities of IRSF, the latest topics and the future plan for IRSF. The original purpose of IRSF was the simultaneous JHKs band survey of the southern sky, particularly of the Magellanic Clouds. The main survey was completed in 2005 and the photometric catalogue, containing 15 million sources for the LMC and 2.7 million sources for the SMC, was published in 2007. After completion of the Magellanic Clouds survey, we have added some unique capabilities to SIRIUS, as well as the continuation of long term monitoring of the Magellanic Clouds. The most unique capabilities of IRSF is a wide field NIR linear/circular imaging polarimeter. We also have ND (1% and 10%) filters and narrow band filters for Pa_Beta (1.28um), Br_ Gamma(2.16um), [Fell] (1.26um), and H_2 (2.12um). I present the recent data obtained from the above capabilities. As a future plan, we have two further developments for IRSF. One is a new low resolution spectrometer covering 0.45um-2.5um. Another is an addiional unit which enables simultaneous images of the current JHKs as well as an additional 2 or 3 optical bands. Finally, I also introduce our instrumentation for the SAAO 75cm telescope. Test observations of the simultaneous optical g'r'i' camera TRIPOL was successfully completed in October 2011, and it is commissioned as one of the SAAO instrument for the 75cm telescope now. In addition, we would like to propose a wide field i-band imaging polarisation camera for the 75cm telescpe, covering 15'x15' (goal 30'x30').

Title: Discovery of 23 min pulsations in an Ae star using the KELT telescope

Speaker: Thebe Medupe (University of

North West)

Venue: SAAO Auditorium

Date: 7 March

Time: 16h00

Abstract: Herbig Ae stars are intermediate mass premain-sequence stars identified by significant infrared excess and emission lines in their Balmer lines due to circumstellar dust. They show irregular photometric variability due to variable dust obscuration. Observations by KELT of one such Ae star, HD 68695 revealed delta Scuti-like pulsations with a period of 23 minutes. This makes this star one of the few dozen known pulsating Ae stars and allows us to apply asteroseismic techniques to it, to determine its physical properties. In this talk I will present a review of these stars, and the data collected by KELT on HD 68695 and a low resolution spectrum of it.

Title: Galaxy Evolution and Cosmology Studies Using Radio Data and HPC

Speaker: Catherine Cress (Centre for High Performance Computing)

Venue: SAAO Auditorium

Date: 14th March

Time: 16h00

Abstract: I will outline questions in galaxy evolution and cosmology that can be addressed using surveys carried out with radio telescopes. Galaxies detected via their neutral hydrogen content and those which are detected via their radio continuum emission will both be considered. I will focus on measurements of the clustering of sources, presenting results from the ALFALFA and FIRST surveys, and discuss related science that will be possible with future surveys carried out by the SKA and its pathfinders. I will also mention Astronomy initiatives underway at the Centre for High Performance Computing.

Title: AGN Prospects for the Cherenkov Telescope Array

Speaker: Markus Bottcher (NRF SARChI Chair of Astrophysics and Space Physics, UNW)

Venue: SAAO Auditorium

Date: 11 April

Time: 16h00

Abstract: In this talk, I will present an overview of the science prospects for very-high-energy gamma-ray observations of AGN by the planned Cherenkov Telescope Array. Progress is expected in a variety of science questions, including the physics of particle acceleration in relativistic jets, the unification between blazars and radio galaxies and the blazar sequence, population studies and questions of cosmological evolution of AGN, and explorations of signatures of gamma-gamma absorption both by the Extragalacic Background Light and by IR -UV radiation fields intrinsic to the AGN.


Title: Three-form Cosmology

Speaker: Tomi Koivisto

Venue: M111, Maths Building, UCT

Date: Tuesady 12 March

Time: 13h00:

Abstract: The possible role of three-form fields in cosmology as alternatives to scalar field inflations or quintessence fields is considered. It is shown that three-form models can predict viable background dynamics and new signatures in cosmological perturbations. Three-form inflation nonminimally coupled to electromagnetism provides the only known model that generates the observed amount of magnetic fields while avoiding the backreaction/strong coupling problem.

Title: D-branes and the Disformal Dark


Speaker: Danielle Wills (Durham)

Venue: M111 (UCT, Maths)

Date: Tuesday 19 March

Time: 13h00

Abstract: I will discuss a unified model of the cosmological dark sector in the context of Type IIB string theory, where the motion of a D-brane in the compact dimensions gives rise to dark energy from the four dimensional point of view, and the particles living on the world-volume appear as dark mater. This picture is a very natural embedding within a fundamental theory of so-called "disformal" gravity, an extension of Einstein's general relativity which entails a novel screening mechanism and provides a very promising framework for understanding the dark sector, and which can be efficiently constrained by its predictions for large scale structure.

Title: Dr Sidelobes-How I learned to stop worrying and love simulations

Speaker: Prof Oleg Smirnov, SKA Research Chair, Rhodes University

Venue: Room 304 Maths building, UCT.

Date: 9 April

Time: 13h00

Abstract: Radio interferometers are complex--and above all counter-intuitive --instruments, and we are constantly pushing the envelope of their performance with increasingly sophisticated science experiments. The combination of these two circumstances can produce some real surprises--most of them of the unpleasant variety. I will present some examples of surprising observational limitations, both in real-world and simulated data (DDEs, calibration ghosts, sidelobe confusion, calibration noise) and discuss their possible impact on future radio surveys.

Title: Axiverse cosmology and the energy scale of inflation.

Speaker: David Marsh, Perimeter


Venue: M111 Maths, UCT

Date: Tuesday 2 April

Time: 13h00

Abstract: Ultra-light axions (m_a<10^{-18} eV), motivated by the so-called "String Axiverse", can be a powerful probe of the energy scale of inflation. In contrast to heavier axions the isocurvature modes in the ultra-light axions can coexist with observable gravitational waves. Here it is shown that large scale structure constraints severely limit the parameter space for axion mass, density fraction and isocurvature amplitude. It is also shown that radically different CMB observables for the ultra-light axion isocurvature mode additionally reduce this space. The results of a new, accurate and efficient method to calculate this isocurvature power spectrum are presented, and can be used to constrain ultra-light axions and inflation.

Title: Leptonic and Hadronic Modeling of Fermi-Detected Blazars

Speaker: Prof Boettcher, NWU,


Venue: RW James Lecture Theater C

Date: Friday, 12 April

Time: 13h00

Abstract: We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in AGN in a temporary steady state. The new model implementations are used to fit snap-shot spectral energy distributions of a representative set of Fermi-LAT detected blazars from the first LAT AGN catalogue. We find that the leptonic model is capable of producing acceptable fits to the SEDs of almost all blazars with reasonable parameters close to equipartition between the magnetic field and the relativistic electron population. If charge neutrality in leptonic models is provided by cold protons, our fits indicate that the kineic energy carried by the jet should be dominated by protons. We find satisfactory representations of the snapshot SEDs of most blazars in our sample with the hadronic model presented here. However, in the case of two quasars the characteristic break at a few GeV energies can not be well modelled. All of our hadronic model fits require powers in relativistic protons in the range 10^{47}-10^{49} erg/s.


Title: Aspects of Linear and Nonlinear Waves in Space Plasmas

Speaker: Dr Jeandrew Brink.

Venue: RW James Lecture Hall C

Date: 20 Feb 2013

Time: 13h00

Abstract: Space plasmas are often not in thermodynamic equilibrium, and examples such as two-temperature plasmas and non-Maxwellian velocity distributions (with a superthermal "tail") are commonly encountered. The later are well modelled by a so-called kappa distribution. Plasmas can support a rich variety of waves. Many satellite-based experiments show evidence of waves in space. These may appear, for instance, as small amplitude (linear) waves or as large amplitude solitary waves. We first outline some of the high frequency waves that can play an important role in typical multi-component space plasmas. Next we consider some effects of high-energy tails on wave behaviour, with applications to both Saturn's magnetosphere and a dusty plasma environment. We shall then discuss nonlinear solitary waves in multi-species space plasmas, and in particular illustrate existence domains and report on kappa distribution effects as well as some recent fundamental developments.

Title: Red Supergiants in Open Clusters

Speaker: Ignacio Negueruela from the

University of Alicante

Venue: RW James Lecture Hall C

Date: 27 Feb 2013

Time: 13h00

Abstract: Red supergiants (RSGs) represent a crucial phase in the evolution of high-mass stars. Mass loss in this phase determines the ultimate fate of the star and its contribution to chemical enrichment. But the properties of RSGs are very difficult to study in isolaion. Accurate stellar parameters depend on a good estimation of their distances, while comparison of these parameters to evolutionary models requires knowledge of their ages. Such information is only available for RSGs in open clusters. Unfortunately, given the rarity of RSGs, few clusters contain more than one RSG (if any). I will review the properties of open clusters rich in RSGs, such as chi Persei and NGC 7419, and introduce the RSG population of Stephenson 2, the second most massive young cluster known in the Milky Way, which contains the largest collection of RSGs. An analysis of their properties strongly suggests that the spectral types of RSGs represent an evolutionary sequence. These and other recent results suggest that we have to seriously reconsider what we thought we knew about RSGs.

Title: Strategies and Tools for a Literature Survey

Speaker: Andrew Collier from UKZN

Venue: RW James Lecture Hall C

Date: 13 March

Time: 13h00

Abstract: Most research projects start with a literature survey. What is already known in the field? Who is already working in the field? Where is the data coming from? What methods are being used? What are the open questions? How can I contribute? Solid strategies are required to make sense of the extensive body of literature and good tools are necessary to compile all of this information in a useful format. This talk will provide some suggestions for undertaking a literature survey and presenting the results.

Title: Cosmology and galaxy evolution from cluster surveys

Speaker: Mat Hilton from UKZN

Venue: RW James Lecture Hall C

Date: 20 March 2013

Time: 13h00

Abstract: Galaxy clusters are the most massive gravitationally bound structures in the Universe and are ideal places to study the effects of dense environments on galaxies. Focusing on recent results obtained by the Atacama Cosmology Telescope, in this talk I will describe how cluster surveys can be used to measure cosmological parameters, such as the amounts of dark mater and dark energy in the Universe, and how they can even be used to constrain the masses of neutrinos. I will also briefly describe studies of galaxy evolution in clusters selected at X-ray wavelengths.

Title: The Hartebeesthoek Radio

Astronomy Observatory

Speaker: Alet de Wit, HartRAO

Venue: RW James Lecture Hall C

Date: 10 April 2013

Time: 13h00

Abstract: I will give an overview of HartRAO as well as some introduction to radio astronomy and interferometry.

Title: Probing structure formation using CMB lensing

Speaker: Kavilan Moodley UKZN

Venue: RW James Lecture Hall C

Date: 24 April

Time: 13h00

Abstract: The cosmic microwave background (CMB) acts as a backlight that illuminates the distribution of dark mater and baryons in the low-red-shit universe. In this talk I will focus on the effect of gravitational lensing on the CMB by the distribution of mater in the universe, which has recently been detected by the ACT, SPT and Planck experiments. I will first discuss how CMB lensing can be used to reconstruct the projected mass distribution on large and small scales. I will then illustrate a number of applications of the CMB lensing measurement that arise through its sensitivity to cosmological parameters and its correlation with tracers of the mass distribution.


Title: The Circumgalacic Medium: New Froniers in Understanding Galaxy Evolution

Speaker: Professor, Romeel Dave

Venue: Room 1.35 of the Physics

Department, UWC

Date: Wednesday 27 March

Time: 13h00

Abstract: The emerging "baryon cycle" paradigm of galaxy evolution suggests that galaxy growth is regulated by inflows and outflows from the galaxy's ISM, yet such inflows and outflows are difficult to detect and are poorly understood. The circumgalactic medium is where such processes must be occurring, and hence characterizing the CGM is a forefront challenge for current galaxy evolution studies. I will describe observational and theoretical progress towards this, highlighting work from the COS-Halos project, a major effort using the Cosmic Origins Spectrograph on HST along with state-of-the-art hydrodynamical simulations to probe the CGM using targeted absorption lines through a carefully selected sample of low-red-shift galaxy halos. Early results reveal the rich structure in density, temperature, and ionization that can be probed via multiple metal transitions, as well as some unexpected surprises for the ubiquity of cool gas in hot halos.
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Title Annotation:colloquia
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Geographic Code:6SOUT
Date:Apr 1, 2013
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