University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Prowse Room


Fall 2012 & Spring 2013 Schedule


August 31 To Be or Not to Be: The Origin of Be Star Disks
M. Virginia McSwain (Lehigh University)

Be stars are a fascinating class of hot, massive stars that form disks around the equator of the star. I will present results from an extensive survey to detect Be stars and discuss the phenomenon in the context of stellar evolution. I will also show recent results that indicate the circumstellar disks are not permanent - they frequently grow or shrink in size, sometimes disappearing completely. Measurements of the changing disk masses can constrain the physical processes responsible for the disk, and I will show that nonradial pulsations over the stellar surface are a likely explanation for their formation.

September 14 Observations of Terrestrial Planet Formation
Carl Mellis, NSF AAPF Fellow/CASS Postdoctoral Fellow (University of California, San Diego)

We are conducting a survey to identify stars that are orbited by copious amounts of warm dust at terrestrial planet-like separations. We argue that these dusty systems are the result of recent giant impacts between rocky planetary embryos or planets orbiting in the stars' terrestrial planet-zone and hence are a tell-tale sign of the final stages of terrestrial planet formation. Some systems identified in our search challenge our understanding of the rocky planet formation process, including a star that could potentially host a carbon dominated rocky planet, a star whose intense terrestrial planet-zone disk emission disappeared on a few year timescale, and a star that hosts sufficient terrestrial planet zone dust to intercept 17% of the incoming stellar light. Synthesis of all stars with evidence for terrestrial planet-zone dust allows us to identify the age range during which terrestrial planets undergo final mass accretion through giant impacts. For stars of roughly Solar mass, we find this age range to be between 30 and 100 Myr while for stars a few times the mass of the Sun we find this age range to be between 10 and 20 Myr. For both groups we find that terrestrial planets are likely common (roughly one terrestrial planet for every star).

September 18 Magnetodynamics and magnetostatics in nano-scale structures and spintronic materials
Michael Pechan (Miami University)

Following a brief introduction, I will discuss our recent and ongoing investigations in nanoscale physics and spintronics. The main probe utilized in this talk is ferromagnetic resonance. First I will discuss magnetostatic and magnetodynamic effects in exchange coupled permalloy nano-dots in collaboration with Hitachi Global Storage. Next I will present anisotropy and damping results in single crystal films of Fe3O4 on MgO with and without a silver overlayer (to probe spin-pumping effects) from room temperature through the Verwey transition. This project is done in collaboration with Casey Miller at U of South Florida. Finally, I will describe some new and exciting spectra arising from hard/soft, core/shell nanoparticles done in collaboration with Josep Nogues from Unviversitat Aut˛nama de Barcelona, Spain.
(This talk is supported by the IEEE distinguished lecture series)

September 28 Nearby Galaxies as Seen with HST
Daniel Weisz (University of Washington)

The Hubble Space Telescope (HST) allows us to resolve nearby galaxies into individual stars. From a galaxy's resolved stellar population we can make detailed measurements of its past patterns of star formation and chemical evolution, as well as probe its star cluster population, construct high resolution dust maps, and constrain fundamental parameters such as the stellar initial mass function. In this talk, I will synthesize new insights into the formation and evolution of nearby galaxies as we have learned by resolving their stellar content with HST. I will include recent findings from the ACS Nearby Galaxy Survey Treasury (ANGST), a systematic survey of 70 nearby low mass galaxies and the Panchromatic Hubble Andromeda Treasury (PHAT), an ongoing HST multi-cycle program that will provide near-UV through near-IR imaging of ~ 150 million resolved stellar stars from ~ 1/4 of M31's star-forming disk.

October 5 An orientation bias in quasar black hole mass measurements
Jessie Runnoe (University of Wyoming)

In quasars, the mass of the central black hole is a fundamental property that must be reliably measured in order to investigate how quasars relate to their host galaxies and fit into the bigger picture of galaxy evolution. The black hole mass can be directly measured via reverberation mapping, but the observations are time intensive and have only been made for about 50 nearby active galactic nuclei. More commonly, black hole masses are estimated from measurements of continuum luminosity and broad emission-line width made from a single-epoch spectrum using reverberation mapping-based scaling relationships. Self-consistent scaling relationships are calibrated for the C IV, Mg II, and Hβ emission lines, but there is significant scatter between them. We show that this scatter is in part due to orientation effects that plague the Mg II and Hβ emission lines and we make a correction to the black hole mass scaling relationships for orientation.

October 12 WIRO OPEN HOUSE, NO COLLOQUIUM
October 26 The Study of Exoplanet Atmospheres with Ground-based Telescopes
Mercedes Lopez-Morales (Department of Terrestrial Magnetism, Carnegie Institution of Washington)

A new era in exoplanet studies is currently underway, as we move from a 'just finding another planet' field to a richer field where we can unveil more detailed physical properties of those worlds, in particular the properties of their atmospheres. Space observatories, such as Spitzer and Hubble, have been key during the initial stages of exoplanet atmospheric studies, but the increasing number of targets and the need for larger photon collectors to detect the minuscule signals of exoplanet atmospheres have us looking into both the next generation of space facilities, such as JWST, and into current and future large ground-based telescopes. In this talk I will summarize the main exoplanet atmospheric detections thus far, with a special focus on the results obtained using ground-based facilities. I will summarize the advantages and disadvantages of observing exoplanet atmospheres from the ground and will also highlight some of the new observational ideas currently underway. Finally, I will discuss ideas about the instrumentation needed to improve exoplanet atmospheric studies in the near future.

November 9 Stratospheric Observatory for Infrared Astronomy (SOFIA)
Robert Gehrz (University of Minnesota)

The joint U.S. and German Stratospheric Observatory for Infrared Astronomy (SOFIA), a program to develop and operate a 2.5-meter infrared airborne telescope in a Boeing 747SP, has obtained first science results with the FORCAST camera in the 5 to 40 micron spectral region and the GREAT heterodyne spectrometer in the 130 to 240 micron spectral region. We briefly review the characteristics and status of the observatory and present the early science results. Spectacular images of regions of star formation will be discussed. The FORCAST images show several discoveries that exploit SOFIA's potential for determining how massive stars form in our Galaxy. The GREAT heterodyne spectrometer has made mapping observations of the [C II] line at 158 microns, high J CO lines, and other molecular lines including SH. The HIPO high speed photometer and the high speed camera FDC were used to observe the 2011 June 23 UT stellar occultation by Pluto. Gehrz's biographical information and CV may be downloaded at http://homepages.spa.umn.edu/~gehrz/ .

November 19 Photosynthetic Energy Transfer in Cryptophyte Algae
Daniel Turner (Toronto)

Electronic energy transfer in molecular systems occurs over a range of timescales and under a variety of coupling conditions. Although energy transfer in photosynthetic proteins has been treated successfully using the F÷rster and Redfield models, recent experiments using two-dimensional electronic spectroscopy challenged these models and opened the door for improved treatments. An important subtopic in the study of electronic energy transfer is how intermolecular electronic coupling and intramolecular vibrations influence the response of the protein to optical excitation. In this contribution, I will present transient-absorption and two-dimensional electronic spectra measured using femtosecond laser pulses that reveal coherent contributions to the measured dynamics in light-harvesting antenna proteins from cryptophyte algae. Analysis of the oscillations reveals the relative contributions from electronic and vibrational coherences. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pulses with physiological illumination conditions. As a final topic, I will describe a new experiment, incoherent two-dimensional electronic spectroscopy, that can address the temporal incoherence component of this question.

November 23 THANKSGIVING, NO COLLOQUIUM
November 27 Low Dimensional Electronic Properties at Interfaces of Materials Studied by Scanning Tunneling Microscopy - from Fundamental Physics Toward Energy Materials
TeYu Chien

This colloquium will be in CR 214

Properties of condensed materials could be affected by the dimensionality of the materials due to spatially confinement environment and/or translational broken symmetry. Examples could be found when creating surfaces or interfaces of materials. One of the most famous examples is the 7x7 surface structural reconstruction on the Si (111) surface [1].
      When depositing another material on clean surfaces, the interfaces are created. In addition to the spatially confinement environment and/or translational broken symmetry, chemical modification at interfaces offers an extra degree of freedom for controlling/engineering the interface properties. In fact, the interfaces are the foundation of the semiconductor industry for decades. On the other hand, interface properties also play very important roles in energy materials, for example, the interfaces of organic photovoltaic cell (OPVC) provide the charge separation centers for charge excitons. Recently, due to the novel functionalities, complex oxides are considered not only as the playgrounds for discovering emerging physics, but also as the possible materials for next generation electronic devices. Intriguing properties, as such two-dimensional highly mobile electron gas at interfaces of two band insulators - LaAlO3/SrTiO3 [2]; and orbital reconstruction at interfaces of superconductor-ferromagnetic materials - YBa2Cu3O7/La1-xCaxMnO3 [3], were all recently reported.
      Length scale of the region of interest is within a few nm from interfaces. To fully understand the electronic properties in the low dimensional environments, the scanning tunneling microscope (STM), which could acquire the electronic properties with sub-nanometer scale, is an ideal tool. The key information of the electronic properties at the vicinity of the buried interfaces is very challenging, but could be measured by STM in cross-sectional geometry.
      In this talk, I will briefly discuss the recent development of our pioneer work on the cross-sectional STM (XSTM) for studying perovskite complex oxide interfaces. After understanding the fracturing control, the electronic properties at complex oxide interfaces could be routinely measured. Three types of all-oxide interfaces will be discussed: p-n junction; Schottky barrier at metal and n-type junction; and interfaces between superconducting and ferromagnetic materials. One of the key impact of this study is that the developed XSTM, in general, is suitable for non-cleavable materials. It is expected that the XSTM has wider application on many other non-cleavable materials, such as organic molecule interfaces used in organic photovoltaic cell.

References:

1. G. Binnig et al., Phys. Rev. Lett. 50, 120-123 (1983)
2. A. Ohtomo and H. Y. Hwang, Nature 427, 423 (2004)
3. J. Chakhalian et al., Science 318, 1114-1117 (2007)

December 3 Materials-driven physics: a versatile toolbox for solving old problems and finding new ones
Ryan Baumbach (Los Alamos National Lab)

Rapid advances in condensed matter physics that shift or define new paradigms often result from "materials driven physics"; e.g., high temperature superconductivity in the cuprates and iron pnictides, skyrmion behavior in noncentrosymmetric B20 compounds, unconventional superconductivity in CeTIn5 (T = Co, Rh, In), etc. Recently, the newly discovered CeRu2M2X (M = Al and Ga, X = B and C) layered tetragonal compounds have proven to be a deep reservoir for unexpected behavior, as they exhibit local moment ferromagnetism: a ground state that is especially unusual in Ce-based systems [1-3]. In these '1221' materials, the occurrence of local moment magnetism arises from the dominance of the RKKY interaction over the Kondo interaction, whereas for most Ce-based materials these effects are finely balanced, sometimes leading to "emergent phenomena" such as quantum criticality, unconventional superconductivity and non-Fermi-liquid behavior. While many such systems can be generically categorized within the Doniach phase diagram, a large number continue to defy a complete description, even after extensive research: e.g., CeTIn5 (T = Co, Rh, Ir), URu2Si2, UCoGe, and some correlated electron antiferromagnets. In this seminar, I will present results for these and related materials, where a diverse toolbox of synthesis techniques has proven to be essential for uncovering their fundamental behavior. In particular, I will address (1) approaches to uncover new materials (such as the 1221's) which may exhibit new physics, (2) exploration of phase diagrams in correlated electron materials to search for emergent phenomena and develop physical insight, and (3) synthesis of ultra high purity samples for use in measurements which distinguish between existing theories and help to develop new ones. Based on this work, I will demonstrate that the interface between low temperature techniques and materials synthesis provides an ideal environment for driving advances in condensed matter physics.

References:

1. R. E. Baumbach, X. Lu, F. Ronning, J. D. Thompson, and E. D. Bauer, "Pressure tuned ferromagnetism in CeRu2M2X (M = Al, Ga ; X = B,C)," Journal of Physics: Condensed Matter 24, 325601 (2012)
2. R. E. Baumbach, T. Shang, M. Torrez, F. Ronning, J. D. Thompson, and E. D. Bauer, "Local moment ferromagnetism in CeRu2Ga2B," Journal of Physics: Condensed Matter 24, 185702 (2012)
3. R. E. Baumbach, H. Chudo, H. Yasuoka, F. Ronning, E. D. Bauer, and J. D. Thompson, "CeRu2Al2B: A local-moment 4f magnet with a complex T-H phase diagram," Physical Review B 85, 094422 (2012)

January 11 Densitometry and Thermometry of Starburst Galaxies
Jeff Mangum (NRAO)

Measurements of the physical conditions within the star formation regions of external galaxies, specifically the spatial density and kinetic temperature, remain illusive. The main difficulty lies with finding a dense gas probe whose sensitivity to these physical conditions can be accurately isolated. To this end we have investigated the spatial density and kinetic temperature probing properties of the formaldehyde (H2CO) and ammonia (NH3) molecules, respectively, within a sample of mainly starburst galaxies. Using the NRAO Green Bank Telescope (GBT) and Very Large Array (VLA) we have measured the H2CO 1(10)-1(11) and 2(11)-2(12) emission from a sample of mainly nearby galaxies (Mangum etal. 2008, 2013), showing that H2CO is a reliable and accurate density probe for extragalactic environments where the kinetic temperature is known. Characterization of the kinetic temperatures in the dense star forming gas in our external galaxy sample has been made using GBT measurements of the NH3 emission toward our external galaxy sample. Our GBT measurements of the H2CO and NH3 emission toward starburst galaxies have provided a uniform characterization of the dense gas properties in these objects. Our VLA measurements of the H2CO emission toward several of these galaxies has allowed us to determine their dense gas structure. In this presentation I will describe how the H2CO and NH3 molecules are used to measure the spatial density and kinetic temperature in dense molecular enironments, describe their application to the measurement of dense gas physical conditions in external galaxies, and summarize the results from our studies of the H2CO and NH3 emission in starburst galaxies.

February 1 U-Pb baddeleyite dating of basaltic meteorites and mafic terrestrial rocks through non-destructive, in-situ secondary ion mass spectrometry
Kevin Chamberlain (University of Wyoming)

Our newly developed in-situ U-Pb method for dating basaltic meteorites and mafic terrestrial rocks is ideal for samples that contain baddeleyite (ZrO2) crystals that are too small to separate physically, or samples that are too rare and precious to crush for mineral separation. We've successfully dated grains as small as 3 microns using the CAMECA ims1270 secondary ion mass spectrometer (SIMS) at UCLA. The method requires only portions of polished thin sections and is relatively non-destructive, as it preserves the analyzed sections largely intact and still suitable for additional types of analyses. X-ray mapping, energy-dispersive spectrometry and backscattered electron imaging (BSE) are used to locate and image the grains and have added benefits of identifying alteration-free grains, armoring relationships, and mineral growth mechanisms. The SIMS U-Pb dating method can be integrated with in-situ nanobeam surface microstructural techniques to resolve magmatic ages and the timing of shock melting associated with meteorite ejections from other planets. Age precisions range from 0.5 to 1% for 207Pb/206Pb dates from rocks that are > 1000 million years, and 3 to 8% for 238U/206Pb dates from rocks that are < 1000 million years. Examples include eucritic, lunar and martian meteorites. A detailed study of the highly shocked basaltic shergottite NWA 5298 determines the true age of shergottite crystallization on Mars, resolves a decades-long conundrum in martian geochronology, and places a 22+/-2 mllion year upper limit on the launch age and interplanetary travel time.

February 22 Physics, astronomy, and the power of critical thinking build the foundation for many career options in industry
Justin Schaefer (SEAKR Engineering Inc.)

I will discuss how interests and an academic background in physics, astronomy, and related areas provide the right skill sets that contribute to building a foundation for a career in industry. I will structure the discussion on 3 different parts. Part I will be my background and the things I learned in college that have transferred over to industry, including how I made that leap to industry. Part II will be a discussion on my current position; what I am doing in industry, what skills I am using, and what topics/skills I could have benefitted from having explored more during my college years. Part III will be an industry-wide overview of potential career opportunities available to those with our background; there will be an emphasis on career opportunities in the aerospace sector.

March 1 Turbulence in Protoplanetary Disks: Defining the Environment for Planet Formation
Jacob Simon, (UC Boulder)

I will discuss the nature of turbulence in protoplanetary disks driven by the magnetorotational instability and how this turbulence may affect the very earliest stages of planet formation. In particular, I will present a series of high resolution gas dynamics simulations that are focused on several radial regions in a model protoplanetary disk. Close to the star where the gas is fully ionized, strong features named "zonal flows" appear in the gas pressure; these features could potentially trap small dust particles for long periods of time, playing a significant role in early planet formation processes. At larger disk radii where the ionization levels are lower, there exist "dead" regions (also important for planet formation) where the MRI is inefficient at producing significant levels of turbulence. By applying representative ionization models to our simulations, I will show that beyond a few tens of AU, the geometry and strength of the global magnetic field plays an important role in setting the level of turbulence and the properties of the dead regions. Finally, I will present a series of turbulent velocity distributions calculated from these simulations for comparison with sub-mm observations; such comparisons can be used to constrain our models for protoplanetary disk structure and evolution. These various studies all aim to explore the conditions under which planets first begin to form.

March 8 Interferometry 101: Measuring the Radii, Temperatures, and Masses of Stars
- or -
How I Learned to Stop Worrying and Love Fringes
Gerard van Belle (Lowell Observatory)

One of the most straightforward things an array of telescopes, or 'interferometer', can do is measure the sizes of stars. Such measurements allow us to directly establish the basic properties of these building blocks of the universe around us - their sizes, and their temperatures. The speaker aims to describe the mystical principles underlying a functional stellar interferometer, in a way that is understandable to the lay person - or at least, no more confusing than it is to astronomers.

Dr. van Belle began working on optical interferometers with graduate work at U. Wyoming in the mid 1990's, working with Mel Dyck on the IOTA interferometer on Mt. Hopkins, AZ, collaborating with colleagues from lesser-known institutions such as Harvard and U. Mass. Upon completion of his PhD at the University of Wyoming in 1996, he joined NASA's Jet Propulsion Laboratory as an instrument architect for the Keck Interferometer, expanding his portfolio to include work with the largest telescopes in the world. At JPL he also made scientific use of the Palomar Testbed Interferometer and published extensively on stellar radii and temperatures, and made the first-ever direct measures of non-spherical stellar shapes. In 2002 he transferred to Caltech, where he continued work on PTI and also contributed to the GSU CHARA Array commissioning, while administering the NASA Keck time and the Michelson Fellowship program. From 2007 until July 2011 he was with ESO, working as the Instrument Scientist for PRIMA, an advanced dual-star combiner undergoing commissioning for the 1.8m and 8.2m apertures of the VLTI. In August of 2011, he moved back to the United States to take a position at Lowell Observatory in Flagstaff, AZ, where he is Lowell's PI for the Navy Precision Optical Interferometer.

March 22 SPRING BREAK, NO COLLOQUIUM
March 29 EASTER, NO COLLOQUIUM
April 12 The Multiwavelength View of Mass Loss and Transfer in Massive Binaries Stars
Jamie Lomax (University of Denver)

Massive binary stars possess strong stellar winds and undergo periods of active mass transfer; the resulting mass loss affects their subsequent evolution. Eclipsing systems provide unique opportunities to illuminate the detailed properties of this process. I will present results from optical spectropolarimetric and X-ray studies aimed at constraining the location and characteristics of the circumstellar material within several eclipsing Roche-lobe overflow and colliding-wind binary systems. Using broadband and spectropolarimetric analysis, I derive new information about the geometric structures of material within these systems. Using X-ray spectral analysis, I probe the regions of shocked gas for new information about their winds and wind collision regions. The combination of these two methods will improve our understanding of the 3D nature of mass loss in massive binary stars and shed light on the relationship between mass loss and the late stages of binary stellar evolution.

April 19 Some Adventures in Applied Physics
Lowell J. Burnett (Quasar Federal Systems Inc.; SDSU)

How do we utilize our knowledge of fundamental physical phenomena to produce new technologies? Despite 150 years of continuous (and at times intensive) effort, classical electrodynamics remains a fertile field for technological development. Examples of recent advances include: (a) ultrasensitive electric field and magnetic field (E-field and B-field) sensors enabling such diverse applications as sniper detection and the onset of fatigue; (b) Poynting vector receivers for radio direction finding and oil exploration, and (c) magnetic resonance scanning systems designed to detect explosives in packages, people, and plastic-cased mines. In each case, we will start with a discussion of the fundamental physical principle, and then follow it to the ultimate application.

April 26 Surface-Plasmon Assisted Exciton and Charge Carrier Transport in One-Dimensional Nanostructures
Andrei Piryatinski (Los Alamos National Lab)

The ability to precisely control optical and transport properties of nanostructured materials opens up possibility of their use as functional materials in a broad range of electronic and optoelectronic applications. Low-dimensional semiconductor materials (e.g., quantum dots, quantum wires, carbon nanotubes) posses electronic structures affected by the size-quantization allowing one to control light absorption/emission properties as well as the charge carriers and exciton transport. Metal nanoparticles also show tunable optical responses of the coherent charge oscillations called surface-plasmon modes. The nanoscale (near-field) interactions between confined carriers/excitons and surface-plasmons in the hybrid semiconductor-metal nanostructures leads to emergent physical properties. This talk will discuss our theoretical study on charge carrier and exciton motion in one-dimensional semiconductor nanostructures (e.g., carbon nanotubes) in the presence of a localized surface-plasmon mode associated with a proximal metal nanoparticle. To treat the effect of the charge-surface-plasmon interactions, we use analogy with the polaron problem and calculate zero-point dynamical quantum correction to the charge-image potential. This leads to the formation of a tunneling barrier controlling the charge transmission through the one-dimensional nanostructure. Considering the exciton transport, we show that the problem maps on the problem of exciton scattering on an impurity state. Most interesting we demonstrate that the surface-plasmon resonance leads to the formation of a bound band-gap state. The emission properties of the exciton are affected by the interaction with the surface-plasmon mode. In particular, the bound state dramatically influences exciton-plasmon radiation pattern.

May 3 Advanced spintronic materials for generation and control of spin current
Koki Takanashi, Institute for Materials Research, Tohoku University

Abstract, TBD

June 03 PHAT Clusters: Obtaining a Complete View of Stellar Clusters in M31
L. Cliff Johnson, U. Washington

The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going Hubble Space Telescope multi-cycle program that is mapping the resolved stellar content for one-third of the nearby galaxy M31, with wavelength coverage from the ultraviolet to the near-infrared. The resultant data products will include a stellar catalog of over 100 million resolved sources, as well as one of the largest and most complete samples of stellar clusters to date. I will give an overview of the current status of PHAT observations and stellar cluster work, including results derived from the Andromeda Project citizen science website. HST's superior resolution and sensitivity has allowed us to identify thousands of new clusters, pushing well into intermediate and low mass regimes. These data provide a unique opportunity to explore the attributes of a stellar cluster population across a range of environments in a large disk galaxy. I will discuss our efforts to explore the environmental dependencies of stellar cluster formation and destruction, and show how we hope to employ this knowledge to back-out characteristics of past star formation within galaxies.


Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006 Spring 2007 Fall 2007 Spring 2008 2008-09 2009-10 2010-11 2011-12
Contact for program information: Adam Myers