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Astronomical colloquia.

The following colloquia were presented since March 2011.

SAAO and Combined Colloquia

Title: Recent advances in cosmological model building

Speaker: Dr Roberto Trotta (Imperial College)

Date: Wednesday 30 March, 2011

Venue: Main lecture theatre at AIMS

Abstract: As we enter the second decade of the 21st century, precision cosmology has become a mature science. The focus is now shifting from the determination of the parameters characterizing our Universe (which are now measured to sub-percent accuracy) to testing fundamental models and competing theories to explain the large variety of data at our disposal. In this talk I will review recent advances in cosmological model building, presenting the current observational situation and the statistical tools used to compare different theoretical models. As illustrative examples, I will focus on the questions of whether the Universe is infinite, whether dark energy is a cosmological constant, and how to decide which is the "best" model of inflation.

Title: The Factory & The Beehive: Stellar Rotations at 600 Myr

Speaker: Marcel Agueros (Columbia University)

Date: Tuesday 19 April 2011

Venue: SAAO Auditorium

Abstract: In a classic 1972 paper, Andrew Skumanich showed that stellar rotation decreases over time--as does chromospheric activity, a proxy for magnetic field strength. This relationship between age, rotation, and activity has been a cornerstone of stellar evolution work for over 40 years. However, rotation periods are scarce for stars with ages greater than 500 Myr, complicating the calibration of an age-rotation-activity relation that can be applied to field stars. The Columbia/Cornell/Caltech Palomar Transient Factory (CCCP) survey of open clusters is an effort to systematically map stellar rotation in open clusters. I will present the first CCCP results for Praesepe, a rich, nearby, 600 Myr open cluster. With light curves containing >150 measurements over more than three months, we have measured rotation periods for ~40 K & M-type cluster members. These rotation periods span the gap between the periods measured for the solar-type and lowest-mass Praesepe members, and indicate that the orderly mass-rotation relation seen for higher mass Praesepe members begins to break down at ~0.6 Msun. In addition, I will discuss our on-going effort to complete the portrait of the 600 Myr age-activity-rotation by measuring H-alpha emission for cluster stars.

Title: The IAC and Space Activities in South Africa

Speaker: Mr Pierre van Heerden

Date: Wednesday, 16 March 2011

Venue: MCB 2 (Molecular Biology building)

Abstract: This year, the International Astronautical Congress (IAC) will be held in Africa for the first time ever, along with various other events to be held in Cape Town during September and October-a series of events sure to be the highlight of the year. Naturally, this is a unique opportunity for interested individuals and organisations to gain international exposure, but also means that increased attention is being paid to the emerging South African space sector. During the presentation, I will take a step back to give a brief summary of space activities in South Africa -the people, organisations and projects aimed at making South Africa a key player in space-and why increased involvement in space is important. I will also highlight several ways by which students can become more active in the space arena and in events to be held during the time of the IAC.

Title: Double White Dwarf Mergers and the surface abundances of extreme helium and R Corona Borealis stars

Speaker: Simon Jeffery (Armagh Observatory)

Date: Thursday 31 March

Venue: SAAO Auditorium

Abstract: The theory of binary star evolution suggests that double white dwarf binaries will form in short-period orbits, and that these orbits decay to the point where substantial numbers will merge within the lifetime of a galaxy. The majority of these mergers will have combined masses below the Chandrasekhar limit, and will not explode. It has been proposed that the products include AM CVn, sdB, RCrB and Extreme Helium Stars. Theoretically, the evolution may be divided into three stages: binary star evolution leading to a double-degenerate (DD) binary, a dynamical merger phase, and subsequent evolution of the product. The latter is of particular importance for the identification of stars which might have been produced by DD mergers. Merger products provide several observables which may be used to test the theory, to identify the DD progenitors and potentially to explore the physics of the merger itself. Using observations of current surface abundances, together with models for the chemical evolution of AGB stars, and linear approximations for other constitutuents of a DD merger, we provide constraints on the past history and, in particular, the progenitor masses of EHe and RCrB stars.

Title: Radio interferometry, selfcal, and other horrors

Speaker: Oleg Smirnov (ASTRON)

Date: Thursday 7 April

Venue: SAAO Auditorium

Abstract: I'll give a brief overview of the basics of radio interferometry, and discuss the evolution of calibration approaches, from early radio observatories that were massively overdesigned on the hardware side so as to make calibration easier (and thus exceeded design requirements by orders of magnitude once self-calibration and other techniques were invented), to the new approach of building the telescopes as cheaply as possible and routinely expecting miracles from the software side. With the new generation of instruments such as MeerKAT, LOFAR, APERTIF and ASKAP, and with the SKA on the horizon, these problems are becoming especially interesting and important.

Title: Detecting lensing of the cosmic microwave background with the Atacama

Cosmology Telescope

Speaker: Prof Kavilan Moodley (UKZN)

Date: Tuesday 10 May 2011.

Venue: UWC-School of Public Health, Lecture Hall 1

Abstract: In this talk I describe the phenomenon of gravitational lensing of cosmic microwave background (CMB) photons by the large-scale mass distribution in the universe. Techniques for reconstructing the lensing field using high resolution maps of the cosmic microwave background are discussed. The recent detection of the CMB gravitational lensing signal by the Atacama Cosmology Telescope is highlighted.

At NASSP

Title: The Current State of the Earth's Magnetic Field

Speaker: Dr Pieter Kotze

Date: Wednesday, 8 March 2011

Venue: MCB 2 (Molecular Biology building

Title: The IAC and Space Activities in South Africa

Speaker: Mr Pierre van Heerden

Date: Wednesday, 16 March 2011

Venue: MCB 2 (Molecular Biology building)

Abstract: This year, the International Astronautical Congress (IAC) will be held in Africa for the first time ever, along with various other events to be held in Cape Town during September and October-a series of events sure to be the highlight of the year. Naturally, this is a unique opportunity for interested individuals and organisations to gain international exposure, but also means that increased attention is being paid to the emerging South African space sector. During the presentation,

I will take a step back to give a brief summary of space activities in South Africa -the people, organisations and projects aimed at making South Africa a key player in space-and why increased involvement in space is important. I will also highlight several ways by which students can become more active in the space arena and in events to be held during the time of the IAC.

Title: Dusty Plasmas in Space and in the Laboratory

Speaker: Dr Shimul Maharaj

Date: Wednesday, 23 March 2011

Venue: MCB 2 (Molecular Biology building)

Abstract: I will give an informative overview lecture on dusty plasmas, defining a "dusty" plasma, and mentioning where these plasmas occur in space environments. I will talk about two fundamental wave modes that propagate in a dusty plasma such as the dust-acoustic wave and the dust-ion-acoustic wave. I will then go on to discuss the experimental observation of the dust-acoustic wave and how the observed frequency matches with the theoretical dispersion relation for the mode. I will also discuss interesting observations of plasma crystal formation in strongly coupled dusty plasmas. I will then discuss some results from a current research topic of mine where I will discuss existence domains of large amplitude solitons in a dusty plasma based on a model composed of both positive and negative dust, non-thermal ions and Boltzmann electrons.

Title: The Dark Universe

Speaker: Prof Roy Maartens

Date: Wednesday, 20 April 2011

Venue: MCB 2 (Molecular Biology building)

Abstract: The current model of the Universe, based on Einstein's General Relativity and the Standard Model of Particle Physics, is very successful in many ways-but there are deep puzzles at its foundations. The galaxies that we observe cannot grow fast enough and cannot be held together-unless there is a new form of matter, which so far has not been detected on Earth, called "Dark Matter". The accelerating expansion of the Universe cannot be explained by Dark Matter-and so we need another form of matter, called "Dark Energy". For Dark Matter, the particle theorists at least have some possible particles. But for Dark Energy, there is still no satisfactory model. We live in a Dark Universe that we do not understand properly. Or perhaps there is something else wrong with our model of the Universe. Maybe the Universe is not as smooth as we think. And maybe Einstein's theory breaks down when we go beyond the solar system and the Milky Way.

Title: Testing the equivalence principle

Speaker: Jean-Philippe Uzan

Date: Wednesday, 4 May 2011

Venue: MCB 2 (Molecular Biology building)

Abstract: The equivalence principle is at the heart of the geometrisation of gravity and one of the building block of general relativity. It is tested to a high accuracy in the Solar system but poorly on astrophysical and cosmological scales. This seminar will summarized the role of the equivalence principle and its tests in the Solar system. It will then discuss the possibility to test it with the constant of nature and describe the various constraints that have been obtained from the comparison of atomic clocks in the lab to big-bang nucleosynthesis.

Speaker bio: Jean-Philippe Uzan has obtained its PhD from Paris XI university in 1998 and was a student of Nathalie Deruelle. After a postdoc at Geneva university he was hired by the CNRS, where he is now directeur de recherche and works at the Institut d'Astrophysique de Paris. His main works concern the tests of the underlying hypothesis of the standard cosmological model. It includes study of the topology of the universe, tests of general relativity and tests of the Copernican principle. He has also worked on scalar-tensor theories, as well as on inflation and CMB theory, focusing mostly on non-Gaussianity. He has been teaching physics at the Ecole des Mines de Paris and Cosmology at the Ecole Normale Superieure de Paris. He has co-authored the monography "Primordial cosmology" (OUP) and written several popular science books, among which books for children.
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Title Annotation:colloquia
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Date:Jun 1, 2011
Words:1751
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