List of Past Astronomy Colloquia : 01-Jan-2002 to 01-Jun-2002

Date:   Wednesday 6-Feb-2002
Speaker:   Dr. Philip Armitage (University of Colorado, Boulder)
Title:  "Population synthesis of extrasolar planets and brown dwarfs"

Date:   Wednesday 13-Feb-2002
Speaker:   Prof. Chris Reynolds (UMd-Astronomy)
Title:  "X-ray bubbles and shells: the hydrodynamics of radio-galaxy/cluster interactions"


X-ray observations by ROSAT and, most recently, Chandra are revealing direct signatures of the interaction between radio galaxies and the diffuse hot X-ray medium of their host galaxy or galaxy cluster. I will discuss these observations with particular emphasis on one such system, the cluster Abell 4059 which hosts the radio galaxy PKS2354-35. I will then discuss how these observations can be used, together with detailed hydrodynamic simulations, to constrain the evolution of radio-loud AGN activity.

Date:   Wednesday 20-Feb-2002
Speaker:   Dr. Wes Huntress (CANCELLED!)
Title:  "Discussion on `The Next Steps in Exploring Deep Space' (CANCELLED!)"

We regret that this colloquium has been cancelled.

Date:   Wednesday 27-Feb-2002
Speaker:   Dr. Namir Kassim (NRL)
Title:  "Emerging from the confusion: a quiet renaissance in low-freq radio astronomy"

Date:   Wednesday 6-Mar-2002
Speaker:   Prof. Vera Rubin (DTM)
Title:  "How far does the dark halo of our Galaxy extend?"


There are presently a few methods for studying the extent and shape of the Galaxy dark halo. A comparison of numerical simulations with the observed properties of satellite galaxies, of stellar streams in the halo, of tidal tails, and of weak gravitationally lensed background galaxies, reveal a few details of the structure, extent, and mass of our halo, or of generic spiral halos. I will discuss what we presently know or expect to know soon, about the extent of the dark halo of the Galaxy.

Date:   Wednesday 13-Mar-2002
Speaker:   Prof. David Spergel (Princeton)
Title:  "Beyond HST : Optical Terrestial Planet Finder"

Date:   Wednesday 20-Mar-2002
Speaker:   Dr. John Hibbard (NRAO)
Title:  "Gaseous Substructures in Tidal Tails"


A range of luminous or gaseous sub-structures have been identified within the tidal debris of interacting galaxies, and are often referred to as "Tidal Dwarf Galaxies". It is claimed that these structures will evolve into long-lived autonomous dIrr-sized companions to the merger remnant, and that tidal dwarf formation may be a significant path to the formation of dwarf galaxies. However, the only firm measurements supporting the kinematic autonomy of candidate tidal dwarfs have been made for detached systems which may be pre-existing dwarf companions. No such measurements have been made for substructures entrained within a tidal tail. Using recent high-resolution VLA HI spectral line observations of the proto-typical tailed merger "The Antennae" (NGC 4038/9), I attempt to remedy this situation.

Date:   Wednesday 3-Apr-2002
Speaker:   Prof. Caty Pilachowski (Indiana)
Title:  "Heavy Metal from Ancient Superstars"


Old stars in the Milky Way Galaxy record the history of nucleosynthesis in our part of the Universe stretching back almost to the beginning of time. From studies of the compositions of low mass stars which formed more than 10 billion years ago, we can trace the origin of the elements and identify sites of nucleosynthesis.

The origin of heavy metals at the earliest times in the history of the Galaxy is uncertain, but the weak s-process operating in massive stars may have contributed some of the lighter neutron captures elements (Sr-Y-Zr). The onset of the main r-process can be seen at [Fe/H]=-2.9, producing Ba, Eu, and other lanthanides; this onset is consistent with the suggestion that Type II supernovae from 8-10 Msun stars are responsible for the r-process. Until a metallicity of [Fe/H]=-2.4, the abundance pattern of the heavy (Z>56) n-capture elements in most giants is well-matched to a dominant r-process nucleosynthesis pattern, rather than the traditional mix of r- and s-process products. Contributions from the s-process can first be seen in some stars with metallicities as low as [Fe/H]=-2.75, and are present in most stars with metallicities [Fe/H]>-2.3. The appearance of s-process contributions as metallicity increases reflects the longer stellar evolutionary timescale of the (low-mass) s-process nucleosynthesis sites. The abundances of the heavy metals in these metal poor stars show clear evidence for a large star-to-star dispersion in the heavy element-to-iron ratios. This condition must have arisen from individual nucleosynthetic events in rapidly evolving halo progenitors that injected newly manufactured n-capture elements into an inhomogeneous early Galactic halo interstellar medium.

Date:   Wednesday 10-Apr-2002
Speaker:   Prof. Jeffrey Linsky (University of Colorado)
Title:  "The Local Interstellar Medium: Structure, Physical Properties, and Interaction with Stellar Winds"


High resolution spectroscopy and theory are now pointing the way to a deeper understanding of the interstellar medium in the local region of the Galactic disk. Within about 100 pc of the Sun, the ISM consists of warm gas clouds surrounded by hot gas. The material is flowing from the Sco-Cen association, but the warm clouds appear to have individual properties with different velocity vectors, temperatures, and depletions. I will summarize what we are learning about the kinematics of these clouds from analysis of GHRS, STIS, and ground-based data. The physical properties of the local warm clouds may not be in agreement with ionization equilibrium models. The interaction of the interstellar gas flows with stellar winds provides the first information on astrospheres (stellar analogs of the heliosphere) and the mass loss rates of nearby stars.

Date:   Wednesday 17-Apr-2002
Speaker:   Dr. Spiro Antiochos (NRL)
Title:  "The Formation and Destruction of Solar Prominences"


Solar prominences/filaments are among the most fascinating and mysterious forms of solar activity; they are certainly the most beautiful. In addition, prominence magnetic fields are believed to be the underlying drivers of the giant disruptions of the Sun's atmosphere known as coronal mass ejections/eruptive flares. In this talk I will present recent observations and theory that address the three central questions regarding prominences that have long puzzled astrophysicists:

Why does cool prominence mass form in the Sun's hot corona? How is the dense prominence mass supported against gravity? What causes prominences to erupt into interplanetary space?

Date:   Wednesday 24-Apr-2002
Speaker:   Dr. Nicholas White (LHEA/NASA-GSFC)
Title:  "The X-ray Evolution of Galaxies"

Date:   Wednesday 1-May-2002
Speaker:   Prof. Alyssa Goodman (Harvard)
Title:  "Order from Chaos: Star Formation in a Dynamic Interstellar Medium"

Date:   Wednesday 8-May-2002
Speaker:   Dr. Andrew Young (UMd)
Title:  "Chandra observations of nearby galaxies and clusters"

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