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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.

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SAAO

Title: Monet, school kids and eclipsing binaries

Speaker: Tim-Oliver Husser (Universitat Gottingen)

Date: 27 June

Venue: 1896 Building

Time: 16:00

Abstract: Everybody knows the large black 'tool box' sitng on the plateau in Sutherland. Open rarely, few know that there actually is a 1.2m-telescope inside! Even less know that it has a twin at MacDonald Observatory in Texas. The history of the Monet telescopes is a long and fraught one and so firstly I would like to give a brief tour of the need-to-know of what was, is, and will be. Contrary to the Monet in Sutherland, the one in Texas is in fact working and has been used extensively by school kids. I will be reporting on one of their projects in which they looked for timing variations in the periods of eclipsing post-common binaries in a search for exoplanets--with great success! This motivated extension of the project with observations from SALT and the SAAO 1.9m.

Title: A trip in modified gravity theories: from cosmological background to perturbations evolution

Speaker: Alvaro de la Cruz-Dombriz (ACGC, University of Cape Town)

Date: 18 July

Venue: SAAO Auditorium

Time: 16:00

Abstract: Modified gravity theories have attracted a lot of attention in order to find a geometrical explanation for the late time acceleration of the Universe. Different techniques for a better understanding of the cosmological background evolution as well as the structure of black holes have been developed in the last years. Nevertheless, a comparison of the matter power spectrum predictions made by these theories with available data has not yet been subjected to a detailed analysis. In this talk, I will show the evolution of cosmological scalar perturbations and the implications of focusing theorem in the context of f(R) and f(R,T) theories of gravity. Finally, I will also describe the predicted power spectra features using a dynamical systems approach and comparing the theoretical results with the SDSS data.

Title: The echo of the Big Bang as seen by the Planck satellite

Speaker: Prof Marin Kunz (University of Geneva)

Date: 30 July

Venue: SAAO Auditorium

Time: 11:00

Abstract: Earlier this year ESA's Planck space telescope released the most detailed map ever created of the cosmic microwave background--the relic radiation from the Big Bang. The map shows the Universe at a time when it was just 380 000 years old, and the tiny fluctuations that it contains represent the seeds of all future structure: the stars and galaxies of today. The new data by the Planck satellite agree quite well with the cosmological standard model, and we will see what this implies for our understanding of the Universe. But we will also encounter some surprises in the Planck data that may eventually force us to reconsider some of our basic assumptions.

Title: La Caille's visit to the Cape

Speaker: Dr Ian Glass

Date: 8 August

Venue: SAAO Auditorium

Time: 16:00

Abstract: This year sees the 300th birthday of Nicolas-Louis de La Caille, the first important scientist to visit the Cape. One of the ablest astronomers of his time, he was a member of the Royal Academy of Sciences, a writer of influential textbooks and a propagandist for Newtonianism. His chief interest lay in refining the orbits of solar system objects through precision observations. At the age of 39, he came to the Cape and built an observatory from which he determined the distances of the planets. He surveyed the southern sky through a telescope--the first such systematic survey ever made. Feeling that the heavens were poorly described, he named fourteen new constellations, one of them being Table Mountain (Mons Mensa). While here, he decided to measure the earth's local radius. His astonishing conclusion, affected by the gravitational attraction of nearby mountains, was that the planet seemed to be pear-shaped! La Caille made other important contributions. For example, he devised a practical way to determine time at sea using observations of the Moon and he mapped the western part of the Cape. It was also he who gave Halley's Comet its name.

Title: The Equilibrium Model for Galaxy Evolution

Speaker: Prof Romeel Dave (SARChI in Cosmology with Multiwavelength Surveys, SAAO/UWC/AIMS)

Date: 15 August

Venue: SAAO Auditorium

Time: 16:00

Abstract: I will present a new analytic formalism for the evolution of the stellar, gaseous, and metal content of galaxies. It is based on the idea, inspired by state-of-the-art cosmological hydrodynamic stimulations, that galaxies live in a slowly-evolving equilibrium between inflows, outflows, and star formation. The critical parameters in this formalism describe ejective feedback (outflows), preventive feedback (retardation of inflows), and wind recycling (return of ejected material). I will illustrate some straightforward predictions of this model, such as the evolution of the specific star formation rates and the second-parameter dependence of the mass-metallicity relation on star formation, that are broadly in agreement with observations. I will highlight areas where the intuition provided by this scenario for the origin of global galaxy properties differs substantially from canonical views. At its core, the equilibrium model intimately connects galaxies and their surrounding gas in a cycle of baryons that is centrally responsible for governing galaxy growth, and hence suggests that improving observations of gas in and around galaxies is the key to understanding galaxy evolution. If time permits I will present early results from a large Hubble program to do so.

UCT

Title: Fragile Binary Stars: Observational Leverage on Difficult Astrophysical Problems

Speaker: Terry D. Oswalt, Florida Institute of Technology, Melbourne, FL

Date: 1 July

Venue: RW James lecture theatre C

Time: 12:00

Abstract: Loosely bound, "fragile" binary stars are like star clusters with two components of the same age and original composition. They provide a largely overlooked avenue for the investigation of many astrophysical questions. For example, their orbital characteristics provide limits on the cumulative effects of the Galactic environment. In older pairs, orbits have been amplified by post-main-sequence mass loss, potentially providing useful constraints on the initial-to-final mass relation for white dwarfs. The nearly featureless spectrum of a white dwarf usually provides little information about its radial velocity, space motion, population membership, or chemical abundance. However, a distant main sequence companion provides a benchmark against which those properties can be determined. Conversely, the cooling age of a white dwarf provides a useful limit on the age of a distant main sequence companion, independent of other stellar age determination methods. This talk will summarize how fragile binaries provide useful leverage on these and other problems of interest.

Title: Measuring Pulsar Masses in Black Widow and Redback Systems

Speaker: Rene Breton (University of Southampton)

Venue: M111, Maths Building, UCT

Date: 19 July

Time: 13:00

Abstract: Typical neutron star densities are beyond the reach of Earth laboratory experiments and the study of their equation of state can provide important knowledge about the behaviour of ultra-dense mater. While the neutron star equation of state remains elusive due to observational challenges (e.g. namely the lack of reliable simultaneous mass and radius measurements), the most massive neutron stars can constrain it to increasingly stiff models. The most promising candidates to search for massive neutron stars are the binary millisecond pulsars, which are old, once-slowly rotating pulsars that have been spun-up by accreting mass from a close companion star. Empirically, the so-called black-widow systems seem particularly promising: for the prototype system, PSR B1957+20, we recently inferred a mass of 2.4 solar masses. If confirmed by further study, this would make it the heaviest know neutron star. In this talk, I will describe how the light curve and spectrum of the strongly irradiated companion was used to determine the black-widow pulsar mass. I will also discuss perspectives of several new mass measurements in similar systems detected with the help of the Fermi gamma-ray observatory (also delivered at AIMS on 16 July).

Title: The polarized radio sky

Speaker: Dr Gianni Bernardi (SKA-SA)

Venue: Lecture Theatre D RW James Building UCT

Date: 29 July

Time: 13:00

Abstract: Radio polarization is one of the best probes of magnetic fields on a wide range of cosmic scales. I will present results from radio polarization observations at cm and meter wavelengths, discussing what they tell us about Galactic ISM, diffuse emission in galaxy clusters and the physical condition in extragalactic radio sources. I will conclude by describing the future perspectives in the light of the new radio telescopes (SKA pathfinders).

ACGC

Title: On viable modified gravities and the cosmological evolution

Speaker: Diego Saez Gomez (UCT)

Venue: M111, Maths Building, UCT

Date: 16 July

Time: 12:00

Abstract: In recent years, much attention has been paid on modified gravities, and specifically on the possibility to describe the dark energy epoch by tiny modifications of General Relativity (GR). Within these theories, a subclass called viable gravities can keep the main predictions of GR and also reproduce a realistic cosmological evolution. In this talk, I will review some aspects of these theories, and point to some of their problems, as the occurrence of cosmological singularities, and possible solutions. Moreover, the cosmological evolution for some simple models will be shown. In addition, another class of modified gravities with a non-standard coupling among the gravitational field and the mater sector, will be discussed.

Title: xPand: An algorithm for perturbing homogeneous cosmologies

Speaker: Obinna Umeh, UCT/UWC

Venue: M111, Maths Building, UCT

Date: 20 August

Time: 12:00

Abstract: I will describe in detail a package we developed recently that uses a fully geometrical method to derive perturbation equations about a spatially homogeneous background. The package uses the capabilities of the tensor algebra package xTensor in the xAct distribution along with its extension for perturbations xPert. The package is extremely user friendly especially for the UCT cosmology group since it relies on 1+3 decomposition technique. With xPan d, deriving perturbation equations up to any order in perturbation theory and for any metric theory of gravity becomes very simple

NASSP

Title: From voids to clusters: HI imaging surveys of galaxies in different environments.

Speaker: Prof Jacqueline van Gorkom of Columbia University

Venue: RW James Lecture Hall C

Date: 17 July

Time: 13:00

Abstract: Our understanding of the formation and evolution of galaxies and the large scale structure has advanced enormously over the last decade, thanks to an impressive synergy between theoretical and observational efforts. While the growth of the dark mater component seems well understood, the physics of the gas, during its accretion, removal and/or depletion is less well understood. Increasingly large scale optical surveys are tracing out the cosmic web of filaments and voids and mathematical tools have been developed to describe these structures and identify galaxies in specific environments. H~I imaging surveys begin to answer the question: how do galaxies get and lose their gas. The best evidence for ongoing gas accretion is found in the lowest density environments, while removal of gas in the highest density environments stops star formation and reddens the galaxies. Although current HI emission surveys are mostly limited to redshifts less than 0.2, several HI imaging telescopes are being commissioned or planned that will be able to observe out to larger reships. I will conclude with a brief discussion of what has been done recently and what will soon be possible.

Title: Exploring the Early Universe with the Cosmic Microwave Background

Speaker: Jean-Christophe Mauduit (IAU office at SAAO)

Venue: RW James Lecture Hall C

Date: 24 July

Time: 13:00

Abstract: The International Astronomical Union (IAU) is the largest body of professional astronomers in the world and has set up the Office of Astronomy for Development (OAD) in partnership with the South African National Research Foundation (NRF). The OAD is located at the South African Astronomical Observatory (SAAO) in Cape Town. Its mission is to realise the IAU's Strategic Plan, which aims to use astronomy as a tool for development. In 2012 the first open Call for Proposals was launched, focusing on three main areas: "Universities and Research", "Children and Schools" and "Public Outreach". Eighteen projects worldwide have been approved for 2013 and are currently under way. The OAD is also setting up regional nodes and language expertise centres around the world. This presentation will describe the ongoing activities of the OAD and plans for the future.

Title: LOFAR fringe-finding

Speaker: Ian Stewart (University of Bonn in Germany).

Venue: RW James Lecture Hall C

Date: 31 July

Time: 13:00

Abstract: The LOFAR interferometer array consists of a large number of antennas, has some international baselines, and observes at meter radio wavelengths over a substantial bandwidth. These factors introduce several complications into the task of calibrating the observations, some of which will also be faced by the SKA. In this talk I try to explain why phase is a centrally important quantity in interferometry; I outline the main issues that have to be addressed in (phase) calibration; and finally I discuss some of the calibration approaches I have been trying out. At the end of the talk you should at least know what fringes are and how you find them.

Title: Hubble's Diverse Universe

Speaker: Dr Jarita Holbrook (UWC)

Venue: RW James Lecture Hall C

Date: 31 July

Time: 13:00

Abstract: Hubble's Diverse Universe is a 40 minute documentary focused on nine African American and Hispanic American astronomers and astrophysicists. Ethnic diversity and a diverse set of scientific topics are explored within astronomy: The astrophysicists discuss their research and their experiences being minority astronomers. An inspirational film, the astrophysicists share their personal stories and give advice on how to succeed in the sciences. The film was conceived and produced by Jarita Holbrook and Romeel Dave' of the University of Arizona now both at University of the Western Cape.

Title: First HI Observations with KAT-7 and updates on MeerKAT & the SKA

Speaker: Dr Claude Carignan (UCT)

Venue: RW James Lecture Hall C

Date: 14 August

Time: 13:00

Abstract: I will present the first HI observations obtained with KAT-7, the pathfinder for the SKA precursor MeerKAT. I will show that because of its short baselines and low system temperature, KAT-7 is the ideal instrument to observe large scale low surface brightness HI emission. These new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32 arcmin, doubling the angular extent of previous measurements. KAT-7 detected 40% more flux than previous VLA observations. Finally, I will give a short update on the MeerKAT project and on SKA, phase 1.

UWC

Title: The luminosity function and clustering of mJy radio sources at 0.1<z<3.

Speaker: Stephen Fine

Venue: Room 1.35 of the Physics Department, UWC

Date: 12 July

Time: 13:00

Abstract: I will discuss a technique for constraining the source density and clustering strength of samples that have no redshift information through cross correlations with samples that do. We apply the technique to the NVSS catalogue using spectroscopic QSOs as the redshift markers. We reproduce the known evolution of mJy sources to z~1.5 and continue past that to z~3. Contrary to brighter samples we find no evidence for a turnover in the density of mJy (L<~10A27W) sources at z~2. In the range 2<z<3 the NVSS probes the roughly the peak of the luminosity density distribution and these results constrain the bulk of the radio emission in the Universe at these reships.

Title: The likelihood ratio as a tool for cross-matching the SKA and Euclid.

Speaker: Kim McAlpine

Venue: Room 1.35 (Physics UWC)

Date: 19 July

Time: 13:00

Abstract: The scientific return of continuum radio surveys can be greatly enhanced by the cross-matching with optical and infrared datasets. These provide photometric redshifts for studies of the evolution of radio sources with cosmic time as well as a more detailed characterisation of the properties of the radio source host galaxies. As surveys push to greater depths reliably identifying the true optical/infrared counterpart becomes an increasingly difficult task. The increasing source density at fainter fluxes results in a higher incidence of both multiple potential counterparts and random spatial alignments between two catalogues. The relatively poorer resolution of radio maps compared to optical observations provides a further complication. The likelihood ratio is a powerful tool to identify the correct counterparts when matching deep datasets with mismatched resolutions. I will present results on the completeness and contamination produced by this method when matching current radio and infrared datasets, and how this performance degrades with lower resolution and deeper datasets.

Title: Examples of mixtures of distributions

Speaker: Prof Chris Koen (UWC)

Venue: Room 1.35 (Physics UWC)

Date: 26 July

Time: 13:00

Abstract: Some examples of fitting mixtures of statistical distributions to astronomical data will be presented.

Title: An overview of Euclid and its science goals

Speaker: Prof Marin Kunz (U. of Geneva & AIMS)

Venue: Room 1.35 (Physics UWC)

Date: 16 August

Time: 13:00

Abstract: Euclid is an ESA medium class mission selected for launch in 2020 in the Cosmic Vision 2015-2025 programme. The main goal of Euclid is to understand the origin of the accelerating expansion of the Universe, but it will address a wide range of science questions. In my presentation I will give an overview of the mission and of the cosmological science goals of Euclid, with a special emphasis on constraints on the properties of the dark energy and tests of modified gravity

SKA

Title: CHILES, an HI deep field with the Very Large Array

Speaker: Prof Jacqueline van Gorkom (Columbia University)

Venue: 2nd floor auditorium, SKA-SA Office, Cape Town

Date: 25 July

Time: 13:00

Abstract: Although the growth of large scale structure in dark mater seems well understood, many questions remain on the formation and evolution of galaxies. HI images of galaxies over a range of redshifts can help constrain the gaseous physics at play. This is one of the key science drivers for the SKA path finders. The recent upgrade of the VLA has made it possible to probe in one observation a redshift range from 0 to 0.45.

I will present the results of a pilot for such a survey covering the range from z=0 to z=0.2. I will discuss problems and promises for such surveys, which may also be relevant for MeerKAT, ASKAP and SKA.

AIMS

Title: Cosmology with the redshifted 21cm line

Speaker: Dr Gianni Bernardi (SKA)

Venue: The Hall, AIMS research centre

Date: 14 August

Time: 12:00

Abstract: In the last two decades, theoretical models have shown the potential of the redshifted 21cm line to unveil the epoch of reionization and the dark ages. Several experiments are currently underway, attempting the first measurement of the 21cm signal form the epoch of reionizaion. I will review the experimental challenge, the current status of the observations and the future perspectives

Astro-coffee

Title: SALT's spectrographs, from the inside out

Speaker: Lisa Crause (SAAO)

Date: 4 July

Venue: 1896 Building

Time: 11:00

Abstract: Exciting instrumentation projects involving SALT's two spectrographs will be outlined in a photo-rich synopsis of a recent trip to the US and the UK. The US leg was associated with preparations for our collimator repair project that aims to restore the throughput of the Robert Stobie Spectrograph (RSS), while the UK visit was to participate in the pre-ship acceptance testing of the High Resolution Spectrograph (HRS) at Durham University's Centre for Advanced Instrumentation. With HRS due to be installed and commissioned during the coming months and RSS to undergo its optical tune-up in the first half of next year, SALT's spectroscopic prospects are set to ramp up substantially in the year ahead. While some of the RSS photos may prove upsetting for those with delicate optical sensibilities, photographs of the HRS optics ought to provide ample compensation for any discomfort experienced. All welcome!
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Title Annotation:colloquia
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Geographic Code:6SOUT
Date:Oct 1, 2013
Words:3438
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