coll2011

Astronomy & Physics

Colloquia & Current Events 2011-12

Colloquia Abstracts

SUBJECT TO CHANGE! Be sure to check back often.

Friday September 2, 3:15pm, AT101

Mr Stefan Elief
Sander Geophysics
Science and Scenery from Polar Airborne Gravity

Airborne gravity measurements have been part of scientific research and resource exploration for several decades. In the 1990s, Sander Geophysics developed and began operating an airborne gravity meter designed specifically for the airborne environment with improved accuracy, resolution, and tolerance of motion. These characteristics sparked interest from Lamont-Doherty Earth Observatory (LDEO) of Columbia University in using one of these instruments as part of a large International Polar Year research project to explore the Gamburtsev Mountains, buried completely beneath the East Antarctic ice sheet. The successful Antarctic field campaign took place in 2008-2009, leading to ongoing work with LDEO providing gravity data for NASA's project IceBridge, a multi-year mission to monitor the ice at the Earth's poles using NASA's large DC8 and P3 airborne science platforms. The presentation will provide a general overview of these projects along with some context for the research surrounding them, and try to give a sense of what it is like collecting airborne gravity data in the harsh, remote, and spectacular polar environment.

Friday September 16, 3:00pm, AT101

Dr Augusto Macchiavelli

Lawrence Berkeley National Lab

Atomic nuclei constitute unique many body systems of strongly interacting fermions. Their properties and structure are of paramount importance in many areas of physics. Phenomena encountered in nuclei share basic ingredients with other mesoscopic systems, and nuclei continue to offer unique laboratories to study these phenomena.
The structure of nuclei far from the stability line is a central theme of research in nuclear physics. Key to this program has been the worldwide development of radioactive beam facilities and novel detector systems, which provide the tools needed to produce and study these exotic nuclei.

Some of the interesting aspects being addressed concern: -The evolution of shell structure with isospin, -The characterization of the elementary modes of excitation in neutron rich nuclei, -The role of isoscalar neutron-proton pairing along the N=Z line, and -The structure of the very heavy elements.

In this talk I will present recent results from our group that shed light on the above. They include: i) Experiments carried out at NSCL/MSU to measure the quadrupole collectivity in neutron rich carbon isotopes and in the region around 64Cr, and ii) A study of the 44Ti(3He,p) at the ATLAS facility at ANL to address the question of np pairing.

I will end the presentation with a short review of the gamma-ray tracking technique. LBNL has been leading the US effort in the development of GRETINA, a spectrometer based on this technique. The status of the project and the exciting physics opportunities that will be possible with this instrument will be discussed.

*Work supported by the US-DOE under contract number DE-AC02-05CH11231.

Friday October 7, 3:00pm, AT101

Dr Falk Herwig

University of Victoria

Origin of the Elements

All elements heavier than H, He and Li are produced in subsequent generations of stars and stellar explosions, starting from the Big Bang through the first generations of stars, recycling of stellar ejecta in the interstellar and intergalactic medium and finally leading up to the abundance distribution of our solar system. A wide range of nuclear production sites have been identified, mostly in the advanced final stages of stars when the most extreme conditions are encountered. Elements are produced by a range of nucleosynthesis processes in these nuclear production site. I will describe results from a range of computational nuclear and stellar astrophysics projects, that demonstrate the our present quantitative understanding of the origin of the elements.

Friday October 21, 3:15pm, AT101

Mr Vance Tiede
Astro-Archaeology Surveys, Inc.

Ziggurat, Khirigsuur & Ling: Ancient Astro-Architecture Across Asia

The histories of Mesopotamian and Chinese astronomy are among the oldest in antiquity. Both originated with court astronomers who oriented imperial monumental architecture, prepared luni-solar calendars and made eclipse predictions (O. Neugebauer 1957 and J. Needham 1959). In Mesopotamia, for example, the mud-brick inscriptions at the Great Ziggurat of Ur-Nammu (ca. 2100 BC) document dedication to Nanna the Moon God, the patron deity of Ur, and also at the adjacent temple to Ningal the Moon Goddess (P.R.S. Moorey 1982). In China, two ancient Chinese texts, the Chou-Pei-Suan- Ching/Zhou Bei Suan Jing (???æ≠) and Chou Li/Zhouli (÷‹?), record that the Imperial Astronomer (Feng Hsian Shin) made solar observations to orient structures to the four cardinal directions with a circle and gnomon, and to determine the solstices and equinoxes. Accordingly, two distinguished sinologists concluded that Mesopotamian ziggurat architectural grammar may have diffused eastward along Central Asia’s Silk Road influencing the design change from underground Shang Dynasty royal shaft-tombs at Hsi-Pei-Kang/Xibeigang, Henan Province, China to above ground Chin, Zhou and Han Dynasty royal mound-tombs (líng ¡Í) near the ancient imperial capital of Chang-an, Shensi/Shaanxi Province, China (J. Needham 1959 and S. Ling, 1967).

This study presents new evidence from astro-archaeology supporting the hypothesis that Mesopotamian, Central and East Asian monumental architecture was oriented to astronomical targets found in their respective mythologies. The research is based on combining the algorithms for astro-archaeology (G. S. Hawkins 1968) with DEM/ArcGIS terrain modeling and satellite imagery. To date, the sample includes the Great Ziggurat of Ur-Nammu (Nasiriyah, Iraq), Ziggurat of Aqar Quf (Baghdad, Iraq), Chogha Zanbil (Khuzestan, Iran), Sialk (Kashan, Iran), twin Khirigsuurs (Khanuy River Valley, Mongolia) (F. Allard 2007) and twenty-nine rectangular mound tombs (ling) (near Sian/Xian, Shensi/Shaanxi Province, China) (V. Tiede 1978, 2010).

Monday October 24, 4:00pm, SB260 SPECIAL DATE, TIME, AND LOCATION
Dr Aaron Sigut

University of Western Ontario

The Be Stars of the Small Magellanic Cloud

The Small Magellanic Cloud (SMC) is an excellent testbed for the evolution of massive stars at low metallicity. An intriguing result is that the fraction of main sequence B stars possessing circumstellar disks (i.e. Be stars) is much larger in SMC clusters than those in the Milky Way. In this talk, I will review what is known about the Be stars in general and then discuss how this difference in their frequency in the SMC might be understood. I will also discuss the challenge Be stars present to current models of rotationally-driven mixing among stars of the upper main sequence.

Friday October 28, 3:15pm, AT101

Dr Catherine Lovekin

Los Alamos National Laboratory

Luminous Blue Variables

Massive stars are known to pulsate at many stages of evolution. Among the most spectacular are the Luminous Blue Variables (LBVs), in which pulsation is one possible origin for the S-Dor type outbursts. This phase of evolution is poorly understood. The driving mechanisms for the variability are not known, and there are even questions as to how this phase connects with other evolutionary phases. Some recent evidence shows that these stars may undergo supernovae, producing Type IIn events.

In this work, I will discuss the radial pulsations of stars with initial masses of 20, 40, 60 and 85 solar masses using both linear and non-linear pulsation codes. The pulsations can then interact with time-dependent convection, which increases the luminosity until the Eddington limit is exceeded locally, potentially driving mass loss and S-Dor outbursts. We consider models at various stages of evolution and metallicity, covering the observed properties of the majority of the observed LBV and LBV candidates. Preliminary results characterizing the pulsations as functions of Y and Z are presented.

The mass loss driven by these pulsations forms a circumstellar shell, which will affect the light curve when the central star explodes. This interaction produces narrow lines in the spectra, but can also enhance the luminosity of the supernova remnant. I will discuss preliminary calculations of core-collapse supernovae interacting with a variety of circumstellar shells.

Friday November 4, 3:15pm, AT101

Dr Alan Dressler

Observatories of the Carnegie Institution of Washington

The IMACS Cluster Building Survey

A small collaboration is completing a spectrophometric study of 5 rich clusters 0.32 < z < 0.52 and the field population over 0 < z < 0.7 as part of an ongoing effort to understand galaxy evolution in the context of the rapidly declining rate of star formation that has occurred since z = 1. I will provide a basic description of the project, including the role played by the Inamori-Magellan Areal Camera and Spectrograph on Magellan-Baade, and focus on the history of star formation in the ~5000 galaxies and its relation to the process of cluster assembly.

Friday November 18, 3:15pm, AT101

Dr Ian Short

Saint Mary's University

Computational Modelling of Red Giant Spectra: Non-LTE vs LTE

The chemical composition of old, metal-poor red giant stars contains clues to the evolution of the Milky Way. I will present the results of some recent advances in the physical realism of the modelling of the atmospheres and spectra of red giant stars, and the impact on the derived parameters of these stars. In particular, the PHOENIX atmospheric modelling and spectrum synthesis code can calculate the thermodynamic state of dozens of chemical species, and the resulting opacity of thousands of spectral absorption lines, with a more realistic treatment of thermodynamic equilibrium ("Non-Local Thermodynamic Equilibrium, or Non-LTE). The most significant original result is that this leads to a downward revision in the effective temperature calibration of the MK spectral classes of G and K III stars of 30 to 60 K, but has negligible impact on the calibration for GK V (main sequence) stars.

Friday November 25, 3:15pm, AT101

Mr David Williamson

Saint Mary's University

Do collisions between molecular clouds make a significant difference on a galactic scale?/

With simple analytic methods, it has been estimated that collisions between clouds are not an efficient sink of kinetic energy. This time-scale of this "effective viscosity" has been evaluated to be 1000 Gyr or more. However, computational power has recently advanced such that galaxy-scale simulations of molecular cloud dynamics have been possible. Using the AP3M code Hydra, we have performed simulations and determined the viscous time-scale to be orders of magnitude shorter - on the order of 10 Gyr. Although this estimate still does not suggest that the viscosity due to cloud-cloud collisions is a dominant effect, the large disparity when contrasted with analytic models must be reconciled.

Friday December 2, 3:15pm, AT101

Dr Jane Rigby NASA

NASA Goddard Space Flight Center

Watching Galaxy Evolution in High Definition

As Einstein predicted, mass deflects light. In hundreds of known cases, "gravitational lenses" have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to "cheat" at studying how galaxies evolve, because lensing can magnify galaxies by factors of 10--100 times, transforming them from objects we can barely detect to bright objects we can study in detail. I'll summarize new results from a comprehensive program, using multi-wavelength, high-quality spectroscopy, to study how galaxies formed stars at redshifts of 1--3, the epoch when most of the Universe's stars were formed.

Friday January 6, 3:00pm, AT101

Dr Scott Chapman
IoA, Cambridge

The Z-PAndAS spectroscopic survey of M31: understanding the outer disk and satellite systems of our giant spiral neighbour in a cosmological context

I will provide an overview of our Z-PAndAS (Pan Andromeda Archaeological Survey) spectroscopic survey of M31, comprising some 30 plus nights of Keck-II/DEIMOS time surveying the outer disk,halo and satellites of M31 and M33. I will highlight the differences found from the Milky Way and describe the ongoing goals of the project to exploit the full galactic archaeological potential of our nearest large spiral neighbour.

Friday January 20, 3:00pm, AT101

Dr Peter Poole
St. Francis Xavier University

Supercooled Water

While water is by far the most common example of the liquid state that we encounter in everyday life, its properties are quite unusual when compared to other liquids. As a consequence, water continues to be the focus of considerable research, both as a proving ground for theories of the liquid state, as well as a challenging system for experimental study. We'll review some of the unusual physical properties of water, especially as they relate to the supercooled liquid and the amorphous solid states. We will also discuss how computer simulations have shaped our understanding of water in recent years, focussing in particular on the possibility of a liquid-liquid phase transition in the supercooled regime.

Friday February 10, 3:00pm, AT101

Dr Randall Brooks

Canada Science and Technology Museums Corp.

A Problem of Provenance, A Technical Analysis of the "Champlain" Astrolabe

A small mariner's astrolabe has been associated with the French explorer Samuel de Champlain, almost since its recovery in Canada in 1867. Queries sparked while in the Astronomy Dept, at SMU in the 1980s led to my interest and consultation by the then National Museum of Science and Technology in Ottawa on their possible acquisition of the instrument. The attribution to Champlain, however, is not well established and is largely based on circumstantial evidence. This paper reviews that evidence and provides new documentary evidence. Data acquired from a metallurgical analysis establishes that only some components of the astrolabe's composition are consistent with the date inscribed on the astrolabe, 1603, and with the smelting methods of the period. Further, an analysis of Champlain's observational data has been compared with measurements and analysis of the scale errors of the astrolabe in an attempt to establish a link to Champlain. If this association can be confirmed, it would make the astrolabe unique in that a set of early seventeenth-century data could be attached to a specific, existing observational instrument. The instrument was, in fact, subsequently acquired by the Canadian Museum of Civilization for the opening of their new facility in 1989 at a cost of $250,000 US and was for many years displayed in what can only be described as a "shrine".

Wednesday February 29, TBD pm, TBD

CAP LECTURE TOUR

Dr Tony Noble
Queens University

The Neutrino Enigma and other Dark Matters

The elusive neutrino has been responsible for many fascinating developments in our understanding of physics at the smallest of scales – the very structure and properties of the most basic building blocks of nature --- as well as being influential in defining the formation of structure and the evolution of the Universe. The nature of Dark Matter, a mysterious form of matter which appears to dominant the Universe, likewise has untold secrets which current experiments may begin to elucidate. In this talk I will discuss the physics motivation and prospects for the next generation of experiments studying neutrinos and searching for dark matter at the world’s foremost accelerators and deep underground facilities.

Friday March 2, 3:00pm, AT101

Dr Theodore Gull
NASA Goddard Space Flight Center

Eta Carinae: a Demanding Mistress

In the 1840's a southern star, Eta Argus, brightened to rival Sirius for nearly a decade, then faded. Today, we see the Homunculus, an hourglass figure with tutu, a dusty shell exceeding 12 solar masses expanding outward at 500 km/s. Many observers have systematically studied the massive binary total shrouded by interacting winds and its ejecta. More recently 3-D wind-wind collision models have begun to explain the extended structures resolved by Hubble Space Telescope. Now Herschel Space Observatory infrared scans are revealing wind interaction emissions and complex molecules left over from the dust that formed out of gas originally overabundant in nitrogen and greatly-depleted in oxygen and carbon. Many questions remain to be answered: What is the dust that formed in the 1840s event? What are the end states of the two massive companions... SN, GRB, Hypernova? and When? Friday March 30, 3:00pm, AT101

Friday March 9, 3:00pm, AT101

Dr Jonathan Braithwaite
Argelander Institute for Astronomy, Bonn University

Weak magnetic fields in early-type stars

Recently weak (~ gauss) magnetic fields have been detected in the main-sequence A stars Vega and Sirius, and it seems likely that all A stars contain fields of at least this strength. I present two theories for the origins of these fields: (a) a "failed fossil" theory where the field is continuously evolving from some field inherited from birth and (b) a dynamo mechanism residing in a subsurface convection layer. Both theories seem equally plausible at present, so I describe some observations which could distinguish between them. In contrast, in more massive stars (O and early B) magnetic fields from subsurface convection seems very likely but with current technology probably not directly measurable, so I briefly discuss some indirect observational signatures of such magnetic fields.