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Abstracts for ISM Seminars Feb. 4 (Zhu): "Mass Flows in Cometary Ultracompact HII Regions" Abstract: High spectral and spatial resolution mid-IR fine structure line observations toward two ultracompact HII (UCHII) regions (G29.96~-0.02 and Mon~R2) allow us to study the structure and kinematics of cometary UCHII regions. In our earlier study of Mon~R2, we showed that highly organized mass motions accounted for most of the velocity structure in that UCHII region. In this work, we show that the kinematics in both Mon~R2 and G29.96 are consistent with motion along a parabolic shell. We model the velocity structure seen in our mapping data and test the stellar wind bow shock model for such parabolic flows. The observations and the simulation indicate that the ram pressures of the stellar wind and ambient interstellar medium cause the accumulated mass in the bow shock to flow along the surface of the shock. A relaxation code reproduces the mass flow's velocity structure as derived by the analytical solution. It further predicts that the pressure gradient along the flow can accelerate ionized gas to a speed higher than that of the moving star. In the original bow shock model, the star speed relative to the ambient medium was considered to be the final speed of ionized gas in the shell. Feb. 11 (Linsky): "What is the total deuterium abundance in the local Galactic disk?" Abstract: Accurate measurements of the deuterium/hydrogen (D/H) ratio provide critically important tests of models of primordial nucleosynthesis, Galactic chemical evolution, and the chemical properties of the intergalactic medium. Among all of the light elements, deuterium provides the most stringent test of our understanding of these three critically important topics. I will describe our recent measurements of the D/H ratio in the Galactic disk based on analyses of far ultraviolet spectra obtained with the FUSE satellite. Beyond the Local Bubble (extending to roughly 100 pc), the D/H ratios have a wide range of values which we believe is due to depletion of deuterium on to grains. As a result, the total deuterium abundance in the nearby Galactic disk is significantly larger than previously assumed. I will discuss the implications of the new larger D/H ratio. Feb. 18 (Lester): "SAFIR - Planning a Future Great Observatory" Abstract: The Single Aperture Far InfraRed telescope has been identified by the National Academy as a high priority for space science, and has been tagged a future Vision Mission. This 10m far-IR and submm observatory would build on results from Spitzer and Herschel. This talk reviews the SAFIR design study now being undertaken by NASA with partners in the science community and industry. Science goals, observatory architecture, and instrumentation will be covered, as well as technology challenges. See http://safir.jpl.nasa.gov. An increasingly important challenge for this work is understanding how future exploration efforts could be enabling for SAFIR science. I will briefly cover conference highlights of the second Loya Jirga on in-space capabilities, as well as noteworthy parts of the NASA FY06 budget drop. |
28 January 2005
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
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Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
prospective student inquiries: studentinfo@astro.as.utexas.edu
site comments: www@www.as.utexas.edu