Bulletin of the American Physical Society
2007 Joint Fall Meeting of the Texas Sections of the APS and AAPT; Zone 13 of SPS
Volume 52, Number 16
Thursday–Saturday, October 18–20, 2007; College Station, Texas
Session B4: AS1: Astrophysics, Space Physics, Astronomy and Cosmology |
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Chair: Kevin Krisciunas, Texas A&M University Room: Rudder Tower 510 |
Friday, October 19, 2007 10:40AM - 10:52AM |
B4.00001: Testing a New Method of Detecting RR Lyrae Variable Stars W. Lee Powell Jr., Ronald Wilhelm, Gwen Armstrong, Stephen Torrence Our group has submitted two papers for publication describing a new method of detecting RR Lyrae variable stars using only a single epoch of both photometry and spectroscopy taken from the Sloan Digital Sky Survey (SDSS). The method takes advantage of clear departures from the template norm for stars that have photometry and spectroscopy taken out of phase. This paper describes observations taken at McDonald Observatory to test the method's accuracy. I will discuss how and why the method works, our McDonald observations, and some statistical methods for determining the variability of stars that lack complete light curves. [Preview Abstract] |
Friday, October 19, 2007 10:52AM - 11:04AM |
B4.00002: Investigation of Element Processing in the Crab Nebula Tim Satterfield, Gordon MacAlpine Heavy elements are manufactured in stars. In particular, exploding stars are very effective at distributing heavy nuclei into the interstellar medium, where they may form into new stars, planets, and life. Young supernova remnants can provide our best means for detailed studies of how elements are processed in stars before, during, and after the explosions. The Crab Nebula, the remnant of a supernova observed from Earth in 1054, is ideal for this type of investigation. We are using a numerical photoionization code to analyze the physical and chemical properties at different locations of the Crab Nebula's gaseous debris field. Results of calculations are compared with optical and infrared spectrum measurements in order to understand chemical abundances and the range of nuclear processing. It is found that some gas has apparently not been processed significantly beyond the CNO-cycle, whereby roughly 90{\%} of the material is helium by mass fraction. In addition, much of the nebula has undergone partial helium-burning, leading to a large increase in the amount of carbon, along with conversion of nitrogen into neon. Furthermore, regions with significantly increased products of oxygen-burning can be effectively modeled; and extremely high apparent concentrations of nickel contain mixtures of elements consistent with the recent suggestion that winds may carry iron-peak nuclei away from the surface of the young neutron star in the Crab Nebula. [Preview Abstract] |
Friday, October 19, 2007 11:04AM - 11:16AM |
B4.00003: VI CCD Photometry of the Old Open Clusters IC 361 and Berkeley 78. Amy Jones, Randy Phelps Open clusters are important test particles for probing the formation and evolution of the Milky Way disk. We have undertaken VI CCD photometry of the poorly studied open clusters IC 361 and Berkeley 78. Ages, reddenings [E(V-I)], Heliocentric distances [d], apparent distance moduli [(m-M)v], true distance moduli [(m-M)o], Galactocentric radii [R$_{GC}$], and vertical distances for the plane [z] for these clusters have been determined using the Girardi et al.(2002, A{\&}A, 391, 195) isochrones. [Preview Abstract] |
Friday, October 19, 2007 11:16AM - 11:28AM |
B4.00004: Untangling the M Cloud Within the Local Supercluster Mike Fanelli, Lindsay Anderson The Local Supercluster (LSC) contains a number of galaxy groups with varying morphological content. Untangling the three dimensional structure of the LSC requires accurate distance measures to in individual galaxies. Distance assessments are greatly complicated by the effects of the Virgo Cluster, the dynamical center of the LSC, which perturbs the Hubble flow, introducing uncertainties in distance estimates. Discerning the content of the Virgo Cluster itself is affected; background galaxies projected onto the cluster cannot easily be distinguished from cluster members. We have analyzed the content of the M cloud, a galaxy group located on the periphery of the Virgo Cluster, using new data from the Sloan Survey and modern distance estimators. The M Cloud contains $\sim$30 galaxies, located at approximately twice the distance to Virgo. [Preview Abstract] |
Friday, October 19, 2007 11:28AM - 11:40AM |
B4.00005: A Search for Parsec-scale Radio Jets in Faint Quasar and Radio Galaxy Nuclei David Hough, Christian Aars Parsec-scale radio jets in bright active galaxy nuclei have been well-studied, but they are generally directed toward Earth. To test relativistic jet models over a wide range in orientation, we are studying nuclei 10-1000 times weaker. Observations of four very faint nuclei in classical doubles were made at 8.4 GHz in December 2004 and March 2006 using the High Sensitivity Array (HSA). The radio galaxy 3C132 has a 5- mJy elliptical structure, but it is not clear if this might represent a one- or two-sided jet. The radio galaxy 3C34 shows a 1.5-mJy circular core with no jet. The radio galaxy 3C441 was not detected ($<$ 1 mJy). The quasar 3C68.1 has a 1.2-mJy circular core with no jet. Thus, despite the HSA's extreme sensitivity, we have not made a clear detection of a single jet. This is somewhat surprising based on an extrapolation of a known core-jet brightness correlation to fainter nuclei, but core and jet Lorentz factors of 5-10 could explain the missing jets if a substantial fraction of the core emission is unbeamed at large orientation angles. [Preview Abstract] |
Friday, October 19, 2007 11:40AM - 11:52AM |
B4.00006: Simulations of the Cleft Ion Fountain outflows resulting from the passage of Storm Enhanced Density (SED) plasma flux tubes through the dayside cleft auroral processes region James Horwitz, Wen Zeng Foster et al. [2002] reported elevated ionospheric density regions convected from subauroral plasmaspheric regions toward noon, in association with convection of plasmaspheric tails. These Storm Enhanced Density (SED) regions could supply cleft ion fountain outflows. Here, we will utilize our Dynamic Fluid Kinetic (DyFK) model to simulate the entry of a high-density ``plasmasphere-like'' flux tube entering the cleft region and subjected to an episode of wave-driven transverse ion heating. It is found that the O$^{+}$ ion density at higher altitudes increases and the density at lower altitudes decreases, following this heating episode, indicating increased fluxes of O$^{+}$ ions from the ionospheric source gain sufficient energy to reach higher altitudes after the effects of transverse wave heating. Foster, J. C., P. J. Erickson, A. J. Coster, J. Goldstein, and F. J. Rich, Ionospheric signatures of plasmaspheric tails, \textit{Geophys. Res. Lett.}, $29$(13), 1623, doi:10.1029/2002GL015067, 2002. [Preview Abstract] |
Friday, October 19, 2007 11:52AM - 12:04PM |
B4.00007: Compact representations of high-latitude ionospheric outflows James Horwitz, Wen Zeng Realistic compact representations of the ionospheric outflow bulk parameters and their relationships to putative drivers are needed for global magnetospheric modeling. Recent satellite data analyses have obtained formula fits for the measurement-based relationships of the outflows levels to parameterizations for electron precipitation and Poynting fluxes, which are expected to be among the principal drivers for the ionospheric outflows. Here, an extensive set of systematic simulation runs with our Dynamic Fluid Kinetic (DyFK) simulation code for ionospheric plasma field-aligned transport is employed to obtain O$^{+}$ and H$^{+}$ densities and flow velocities at altitudes corresponding to typical inner boundary levels for prominent current global magnetospheric models. These O$^{+}$ and H$^{+}$ densities and parallel flow velocities are represented versus parameterizations for precipitation electrons, the BBELF waves which transversely heat ionospheric ions, and solar zenith angle. [Preview Abstract] |
Friday, October 19, 2007 12:04PM - 12:16PM |
B4.00008: Formation of O$^{+}$ trough zones in the polar cap ionosphere-magnetosphere coupling region: Dynamic Fluid-Kinetic Simulations James Horwitz, Wen Zeng, Fajer Jaafari Thermal ion measurements by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft show that the O$^{+}$ densities in the polar cap near 6000 km altitude display structured variations featuring low-density trough regions. For this presentation, the UT Arlington Dynamic Fluid-Kinetic (DyFK) model is utilized to investigate such O$^{+}$ density profiles. Using available measured solar wind parameters to drive a time-varying high-latitude convection model and incorporating auroral processes of soft electron precipitation and wave-driven ion heating, we simulate the evolving high-latitude ionospheric plasma transport and associated parameter profiles for several convecting flux tubes in the high-latitude ionosphere-magnetosphere system. The modeled densities near 6000 km altitudes are compared with multiple trough events featuring POLAR/TIDE-measured O$^{+}$ densities for inside and outside of such trough regions. [Preview Abstract] |
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