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Astronomical colloquia.

These form an important part of a research facility, often as a sort of pre-publication 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.

SAAO Colloquia

Title: The Nainital-Cape Survey

Date: Thursday 26 May

Time: 12.30 PM

Venue: SAAO Auditorium

Speaker: Santosh Joshi (Aryabhatta Research Institute of Observational Sciences (ARIES), India)

Abstract: The Nainital-Cape survey is an ongoing survey programme to search for the new rapidly oscillaing Ap (roAp) stars in the Northern hemisphere. In this talk I shall present an overview of the project and discuss the future prospective of the project in the light of up-coming observing facilities at ARIES.

Title: Long-term Modulations in Ultraluminous X-Ray Sources

Date: Thursday 23 June

Time: 12.30 PM

Venue: SAAO Auditorium

Speaker: Deatrick Foster (Vanderbilt/SAAO)

Abstract: The nature of ultraluminous X-ray sources (ULXs) found in nearby galaxies continues to be a subject of intense speculation and debate. ULXs had been considered possible hosts of intermediate-mass black holes (IMBHs); however more recent models invoke slightly heavier than stellar-mass black holes (20-50 solar masses) in extreme accretion states to account for their observed spectra and luminosities. I will summarise the latest results on ULXs and discuss the need for a systematic investigation of their long-term periodic and aperiodic modulations.

Title: The binary central stars of planetary nebulae

Date: Thursday 2 June

Time: 12.30 PM

Venue: SAAO Auditorium

Speaker: Brent Miszalski (SAAO)

Abstract: Planetary Nebulae represent a powerful window into the evolution of low-intermediate mass stars that have undergone extensive mass-loss on the asymptotic giant branch. The nebula manifests itself in an extremely wide variety of shapes, but exactly how nebulae are shaped into such a diverse range of morphologies is still highly uncertain despite over thirty years of vigorous debate. Binaries have long been thought to offer a solution to this vexing problem. Now, thanks to recent surveys and improved observing strategies, it appears clear that a binary channel, in particular common-envelope (CE) evolution, is responsible for a large fraction of planetary nebulae. Binary central stars provide invaluable contributions to the study of common-envelope evolution and to the formation of jets in binary systems. We have started to identify strong links between binarity and morphology, including a high proportion of bipolar nebulae and rings of low-ionisation filaments resembling SN 1987A. Equally important are the newly found binary CSPN with intermediate periods, which appear linked to chemically peculiar stars whose composition was modified by binary evolution. In this talk, I will give an overview of recent results and on-going work in this rapidly changing field. I'll also discuss potential projects with South African telescopes.

Title: The New Generation of Wide-Field Surveys

Date: Thursday 9 June

Time: 12.30 PM

Venue: SAAO Auditorium

Speaker: David Gilbank (SAAO)

Abstract: Large surveys will be responsible for a significant fraction of the major discoveries in astronomy in the coming decade, with considerable funds and resources devoted to projects such as LSST, DES and Pan-STARRS. In this talk, I will discuss the status and latest results of a recently completed 1000 square degree imaging survey, the second Red-sequence Cluster Survey (RCS-2), primarily aimed at discovering clusters of galaxies out to z~1. I will summarise the science goals relating to cosmology, strong gravitational lensing, and the physical properties of galaxy clusters, and describe the areas in which SALT might efficiently be used to maximise returns from on-going science. In the second half of the talk, I will focus on results from galaxy evolution using the survey data themselves, and discuss a new project, only recently begun, probing the structure of our own Galaxy using the Sagittarius Stream unveiled via maps of stellar overdensity.

Title: Lenticular Galaxy Formation - An Observer'S Perspective

Date: Thursday 7 July

Time: 12.30 PM

Venue: 1896 Building

Speaker: Sudhanshu Barway (SAAO)

Abstract: Lenicular (S0) galaxies form a morphological transition class between ellipticals and early-type spirals in the Hubble (1936) classification system. When comparing properties, it is found that the bulges of lenticular galaxies are very similar to elliptical galaxies, while their disks have similarities to the disks of spiral galaxies, except that they lack conspicuous spiral arms. Our understanding of the formation and evolution of lenticular galaxies, in terms of the individual physical processes involved, is still unclear, inspite of extensive attempts both by observational and theoretical means. In my talk, I will present an overview of our efforts to understand the formation and evolution of lenticular galaxies. We made detailed investigation of the morphology of representative sample of lenticular galaxies, using our own observations as well as data from SDSS and 2MASS. Our finding suggests that the formation of lenticular galaxies not only depends on the total luminosity of galaxy but also on the environment of the host galaxy. I will also describe the detailed analysis of correlations between various observed properties of lenticular galaxies as a function of luminosity and environment of host galaxy.

Joint Cape Town Cosmology & Astrophysics Colloquia

Title: Wide Field Spectroscopic Surveys in the Era of HETDEX and SKA

Date: Monday, 13 June

Time: 11:00

Venue: RW James C

Speaker: Gary Hill (McDonald Observatory)

Abstract: The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) aims to make a direct detection of dark energy at z~3, in the case that it is a cosmological constant. HETDEX uses baryonic acoustic oscillations and the shape of the Lyman-alpha emitting (LAE) galaxy power spectrum to constrain H(z) and Da(z) to percent levels. As a result, the experiment will place light constraints on possible dark energy evolution, complementing studies of the phenomenon at low redshit (e.g. BOSS and DES). HETDEX will also provide the most accurate constraint on the curvature of the Universe, needed by the lower redshift surveys to break the degeneracy with the effects of dark energy on the expansion rate.

In late 2011 and 2012 the US$34M HETDEX project will upgrade the 10 m HET and outfit it with a new wide field corrector and an array of 150 integral-field spectrographs to survey a 400 sq. degree area in the north galactic cap. Each fiber-coupled unit spectrograph will cover 350-550 nm, simultaneously at 5.7 A resolution, providing ~36,000 spectra per exposure. This instrument, called VIRUS, will open up surveys of the optical emission-line universe for the first time, and in particular will be used to detect ~0.8 million LAE galaxies with 1.9 < z < 3.5 and more than a million [OII] emitting galaxies with z < 0.5. The 3-D map of LAE galaxies in 9 cubic Gpc volume will be used to constrain the expansion history at this early epoch.

The prototype of the VIRUS unit spectrograph (VIRUS-P) is a powerful instrument in its own right. Used on the McDonald 2.7 m Smith reflector, it covers the largest area of any integral field spectrograph, and has coverage down to 340 nm. We have used VIRUS-P to complete a pilot survey to better measure the properties of LAE galaxies in support of HETDEX, among other investigations where it is uniquely powerful.

I will discuss the lessons learned in this major upgrade of the HET, and how they may apply to SALT. I will also discuss the synergy between HETDEX, SALT, and the Square Kilometer Array (SKA), which could lead to new avenues for South African astronomy.

Title: Observing the Darkness

Date: Wednesday 29 June

Time: 12 noon (followed by lunch)

Venue: Main lecture theatre at AIMS

Speaker: Prof. Martin Kunz (University of Geneva)

Abstract: The presence of a mysterious dark energy in the universe poses many challenges for cosmology. In my talk, I will discuss the current limits on the equation of state, and show why during another period of accelerated expansion--inflation-an omega close to -1 is not necessarily an indication for a cosmological constant. I will then review the different possibilities for the nature of the dark energy, focusing especially on the importance of the dark energy perturbations, their role in distinguishing between scalar field dark energy and modified gravity models, and on our current and expected future constraints on them.
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Title Annotation:colloquia
Publication:Monthly Notes of the Astronomical Society of Southern Africa
Article Type:Conference notes
Geographic Code:6SOUT
Date:Aug 1, 2011
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