University of Minnesota
University of Minnesota
Colloquia and Seminars

Astrophysics Colloquium

Spring 2010 - Coordinated by Terry J. Jones
Held in Physics 210 at 3:35pm on Fridays
(unless otherwise noted)

January 22 No Colloquium
January 29 Dr. Johannes Staguhn, NASA Goddard Space Flight Center
Title: The Search for the Earliest Dusty Galaxies and Dark Matter Halos with a 2mm Bolometer Camera
Abstract: We have built the 2mm bolometer camera GISMO for astronomical observations at the IRAM 30m telescope on Pico Veleta in Spain. The camera is optimized to observe dusty galaxies at the highest redshifts. With its sensitivity, observations of high-z galaxies with 1011 L will be possible. Such observations will allow us to trace dark matter halos in the early universe.
Host: A. Kovacs
February 5 Dr. Terry J. Jones, U Minnesota, Astronomy
Title: In Search of Grain Alignment
Abstract: Interstellar polarization is widely used to measure the projected geometry of the magnetic field in the ISM. Yet, despite over 50 years of work, the grain alignment mechanism is still not understood, perhaps not even at the most basic level. Recent observations of interstellar polarization in dense molecular clouds may provide clues to the alignment mechanism and help better establish interstellar polarization as a useful tool for studying magnetic fields.
February 12 Dr. Daniel Keefe, U Minnesota, Comp. Science and Eng.
Title: Picturing Time: Visualizing and Analyzing Scientific Motion Data
Abstract: From studying biomechanics to blood flow, scientists in almost every discipline need to analyze time-varying data. In this talk, I will describe my group's current research in developing and studying interactive visualization tools to facilitate analysis of motion data. The initial work I'll describe is driven by recent studies in orthopedics and evolutionary biology. With the advent of new imaging technologies, our collaborators in these fields have new abilities to collect high-resolution motion data (e.g. the 3D motion of bones in animals and humans while performing different actions). Analyzing these data poses a major challenge. Building upon a rich history of using pictures to depict motion, our work uses a combination of 2D and 3D computer graphics coupled with interactive techniques, such as coordinated multi-view visualization, to support data exploration. Much of our initial work has been driven by studies in evolutionary biology of animal biomechanics designed to gain insight into evolution and historical diversification among animals. I'll show some compelling videos of bats flying and pigs eating from this work. I will also touch on our current work studying the mechanics of the human spine, in collaboration with orthopedists at the Univ. of Minnesota. We believe this work will ultimately have implications for visualizing and analyzing a variety of other time-varying data sets, for example, fluid flows. I'll finish by mentioning some of the other current work in our lab, including interactive visualization of blood flow and medical device design using emerging technologies, such as multii-touch interactive surfaces and haptic virtual reality displays.
Host: T.J. Jones
February 19 No Colloquium
February 26 Dr. Dan Clemens, Boston U
Title: The Galactic Plane Infrared Polarization Survey (GPIPS)
Abstract: Since 1999, Boston University has been the main partner with Lowell Observatory in the use of the 1.83m Perkins telescope located on Anderson Mesa outside Flagstaff, Arizona. Two instruments for use on the Perkinds were developed at Boston University: PRISM, an optical imager, spectrometer, and polarizer, and Mimir, the infrared twin of PRISM which supplies the same three light analysis functions. Mimir saw "first light" in 2004 and—with PRISM—has been in regular use ever since. Our group has been using Mimir on the Perkins for the past 4+ years to conduct a major new survey of the inner disk of the Milky Way to reveal the Galactic magnetic field with unprecedented angular resolution and depth. This Galactic Plane Infrared Polarization Survey, or GPIPS, has already covered about 50% of the same 76 square degree region already surveyed by 2MASS, the GLIMPSE mid-infrared imaging project for the Spitzer Space Telescope, and the BU-based Galactic Ring Survey for 13CO spectral line emission. This talk will review the GPIPS project and present a sampling of images and early findings from GPIPS.
Host: T.J. Jones
March 5 Dr. Jonathan Fortney, U California, Santa Cruz
Title: Extreme Planetary Atmospheres: Modeling Close-in Planets
Abstract: The Spitzer Space Telescope has allowed astronomers to detect thermal emission from the close-in gas giant planets known as "hot Jupiters." Modeling these hot atmospheres requires an understanding of radiative transfer, chemistry, cloud formation (of rock and iron!), and atmospheric dynamics. These planets are quite diverse in terms of the measured fluxes from their day and night sides. Via spectroscopy, molecules that have been detected include H2O, CH4, CO, and CO2. I will discuss 1D and 3D models of these atmospheres, and our growing understanding of these planets as a class of astronomical objects. The next frontier, low-mass "Super Earth" planets, is also now at hand.
Host: R.D. Gehrz
March 12 Dr. Sebastian Heinz, U Wisconsin — Madison
Title: Black Hole Exhaust: An Environmental Impact Study of Microquasars
Abstract: We have known about the large scale impact of jets from supermassive black holes for decades and have successfully used knowledge gained from the kpc scale radio structures they inflate to study black hole growth and jet formation. In recent years, it has become increasingly clear that stellar mass black holes in X-ray binaries do exactly the same tricks their supermassive cousins do: they produce powerful jets that interact with the ISM, inflating bubbles, producing shocks, and leaving behind cosmic ray laced, magnetized exhaust. I will discuss how we can use this exhaust to constrain important aspects of accretion and jet physics.
Host: P. Mendygral
March 19 No Colloquium — Spring Break
March 26 Dr. Daniel Lennon, Space Telescope Science Institute
Title: Spitzer SAGE Studies of Massive Stars in the Magellanic Clouds: Looking for stuff around massive stars
Abstract: We have compiled catalogs of massive stars in the Magellanic Clouds with known reliable spectral types as derived from either slit or fiber spectra. These catalogs span the full range of massive star types; Wolf-Rayet stars, LBVs, Be stars, B[e] stars, supergiants of various types as well as numerous normal main sequence stars. We have cross-correlated these catalogs with data in the Spitzer SAGE catalogs of the LMC and SMC and have found several thousand matches and have constructed color-magnitude and color-color diagrams for the Spitzer data to investigate trends in both galaxies. These data are used to investigate IR excesses due to stellar winds, circumstellar gaseous disks, and dust around massive stars in both galaxies. We find that LBVs and B[e] stars are among the brightest objects in both galaxies in the IR. Comparing LMC and SMC samples we present estimates of mass-loss rates for red supergiants, discuss global Oe/Be stars fractions, and comment on a number of early-type stars with peculiar mid-IR excesses.
Host: R. Humphreys
April 2 Dr. Claudia Scalata, IPAC, Caltech
Title: High redshift Lya blobs and escape of Lya photons from dusty galaxies

The mechanism powering Lyman alpha (Lya) emission in extended Lya nebulae (Lya blobs) discovered at high redshifts is still elusive.

These nebulae are similar to those observed around high redshift radio galaxies, but they are not associated with either radio or Xray sources. Various mechanisms have been proposed to power the emission, including photoionization by a dust enshrouded AGN, interaction between the IGM and the super winds produced in a starburst, and cooling radiation from gas falling onto a galaxy potential well (so called cold accretion).

I will present recent results based on mid-IR imaging and spectroscopy of a sample of z>2 Lya blobs. These data suggest that the majority of the infrared-bright galaxies associated with Lya blobs are powered by star-formation, rather than AGN. I will discuss in detail one extended Lya nebula, associated with both a dusty sturburst and a type 2 AGN. Using a combination of rest-frame UV and mid-IR spectroscopy and imaging to constrain the source of energy, I find that the mechanism that best reproduces all the observed properties of this peculiar object is cold accretion. I will present some preliminary results based on a study of the polarization of Lya radiation in one of the brightest Lya blobs.

Based on a new sample of z~0.3 Lya emitters, I will also discuss the escape of Lya photons from dusty galaxies. I will show that in these galaxies Lya photons escape through clean line of sights, following similar paths as those traveled by Balmer and continuum (non resonant) photons.

April 9 Dr. Etienne Artigau, Gemini Observatory
Title: NICI and Beyond: the Search for Giant Planets at Gemini
Host: R. Humphreys
April 16 Dr. James Jackson, Boston U
Title: High-Mass Star Formation in Filamentary Infrared Dark Clouds
Abstract: Infrared Dark Clouds (IRDCs) are identified as extinction features in the mid-infrared. They are cold (T=10 K), dense (n > 104 cm-3), and extremely opaque (AV > 30). IRDCs have masses ~3,000 M and sizes ~2 pc, comparable to molecular clumps such as Orion associated with the formation of high-mass stars and star clusters. They are located primarily in spiral arms. IRDCs contain compact cores of mass ~100–1,000 M, about 1/3 of which show evidence for high-mass star formation. Thus, IRDCs are the birthplaces of high-mass stars; they are the high-mass equivalent to Bok globules. Their morphology is typically filamentary. One extremely filamentary IRDC, the "Nessie" nebula, shows a periodic spacing between its compact cores of order 5 pc. This spacing probably arises from the "sausage" fluid instability, which predicts the observed clump spacing. The mass of star clusters may be controlled primarily by the "sausage" instability.
Host: E. Skillman
April 23 Dr. B-G Andersson, Sofia Science Center
Title: Interstellar Grain Alignment – Astronomy's String Theory?
Abstract: Interstellar polarization was discovered over 60 years ago independently by John Hall and Albert Hiltner. It was very soon realized that the polarization had to be associated with asymmetrical dust grains aligned with the magnetic field. Over the intervening years several theories have been proposed to explain how such an alignment takes place, but very limited quantitative observational testing has been available. However, in the last decade, significant progress have been made, both on the theoretical and observational front. I will discuss how we can now devise direct tests of the quantitative predictions made available by the new grain alignment theory, developed by Alex Lazarian and his coworkers. I will thus try to convince you that interstellar grain alignment is no longer the string theory of astronomy – a beautiful theory with no experimental support.
Host: T.J. Jones
April 30 Dr. Nate Bastian, Inst. of Tech., U Cambridge
Title: A Universal Stellar Initial Mass Function? A Critical Look at Variations
Abstract: Few topics in astronomy initiate such vigorous discussion as whether or not the initial mass function (IMF) of stars is universal, or instead sensitive to the initial conditions of star formation. The distinction is of critical importance: the IMF influences most of the observable properties of stellar populations and galaxies, and detecting variations in the IMF could provide deep insights into the process by which stars form. In this talk, I will review the evidence for and against a varying IMF, concentrating on "extreme" environments, from massive star clusters to high redshift starburst galaxies. Despite indications of "non-standard" IMFs in specific local and extragalactic environments (which clearly warrant further study), there is currently no clear evidence that the IMF varies strongly and systematically after the first few generations of stars.
Host: D. Weisz
May 7