Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 58, Number 12
Friday–Saturday, October 18–19, 2013; Denver, Colorado
Session D2: Astrophysics II |
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Chair: Shane Larson, Northwestern University Room: 254 |
Friday, October 18, 2013 2:00PM - 2:24PM |
D2.00001: Invited talk - Astrophysics Invited Speaker: Chip Kobulnicky |
Friday, October 18, 2013 2:24PM - 2:36PM |
D2.00002: How do massive stars form? Virginie Montes, Peter Hofner Massive stars play a key role in the evolution of their host galaxies, but their formation remains not well understood. Two main competitive theories try to explain it: the turbulent core model, which is an extension of the low-mass star formation model, and models involving competitive accretion or stellar collisions. The study of the massive star-forming region IRAS 20126$+$4104 with combined data can help us to characterize the population of that cluster (age and mass of the stars) and be used to discriminate between theories. This region was observed with the X-ray space telescope CHANDRA. We detected 150 sources, and a spectroscopic analysis of each source was performed. To determine the cluster characteristics, X-ray data were combined with radio observations done with the JVLA, infrared counterparts from the survey 2MASS and the space telescope SPITZER, and optical counterparts from the TYCHO catalog. A stellar population simulation was done to determine the expected foreground and background population in the cluster (contamination). This study shows that most of the stars are in the WTTS stage and all stars except the main source are low-mass protostars. I will discuss implications of those results and the future work planned for the cluster. [Preview Abstract] |
Friday, October 18, 2013 2:36PM - 2:48PM |
D2.00003: Observing the Variations of Interacting Solar Winds in a Massive Binary Star System Darren McKinnon, Theodore Gull Eta Carinae, a massive, highly-eccentric binary star system with enormous colliding solar winds, boasts an astronomical laboratory of great interest. It is an exceptional example of a pre-supernova environment, having survived a non-terminal stellar explosion in the 1800's that left behind the incredible bipolar Homunculus nebula. The central interacting stellar winds are resolvable using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). Using HST/STIS, several three-dimensional (3D) data cubes (2D spatial, 1D velocity) have been collected at several phases during Eta Carinae's 5.54-year orbital cycle. The data cubes were collected by mapping with a spatially-resolvable long slit, while focusing on selected spectral lines that form in the colliding wind regions. By applying differencing techniques to these data cubes, we can compare and measure temporal changes in the interactions between the two massive winds. Initial evaluation of these changes supports current 3D hydrodynamical models of Eta Carinae's colliding winds. The observations can also be used to help constrain Eta Carinae's recent mass-loss history, which is important for determining the current and future states of this likely nearby supernova progenitor. [Preview Abstract] |
Friday, October 18, 2013 2:48PM - 3:00PM |
D2.00004: A Direct Measurement of the Mean Occupation Function of Quasars: Breaking Degeneracies between Halo Occupation Distribution Models My Nguyen, Suchetana Chatterjee, Adam Myers, Zheng Zheng Recent work on quasar clustering suggests a degeneracy in the halo occupation distribution constrained from two-point correlation functions. To break the degeneracy, we make the first direct measurement of the mean occupation function (MOF) of quasars at $z \sim 0.2$ by matching quasar positions with clusters in the MaxBCG sample. We fit a power law and a 4-parameter model to the MOF. The number distribution of quasars in host halos is close to Poisson, and the slopes obtained for the power law case favor a monotonically increased MOF with halo mass. The best-fit slopes are $0.53 \pm 0.04$ for the power law model and $1.03\pm 1.12$ for the 4-parameter model. The radial distribution of quasars within halos is described by a power law with a slope $-2.3 \pm 0.4$. The conditional luminosity function (CLF) of quasars shows no evidence of luminosity evolution with host halo mass, similar to the inferences drawn from clustering measurements. Although the conditional black hole mass function (CMF) is consistent with no evolution, we observe a slight indication of downsizing of the black hole mass function. The lack of evolution in the CLF and the CMF shows that quasars, residing in clusters have a characteristic mass and luminosity scale independent of their host halos. [Preview Abstract] |
Friday, October 18, 2013 3:00PM - 3:12PM |
D2.00005: Differential Proper-Motion Measurements of The Cygnus Egg Nebula; The Presence of Fast Equatorial Outflows Rachael Tomasino, Toshiya Ueta, Brian Ferguson We present the results of differential proper-motion analyses of the dust shell structure in the Egg Nebula (RAFGL 2688, V1610 Cyg), based on the archived two-epoch imaging-polarimetric data in the optical taken with the Hubble Space Telescope. We measured the amount of motion of local structures and the signature concentric arcs in the nebula by determining their relative shifts over an interval of 7.25 yr. We discovered that the optical polarization characteristics of the Egg Nebula was influenced by the marginal optical thickness of the circumstellar shell and the illumination of the nebula was done in two-step mechanism - most of the nebula is illuminated by the secondary/dust-scattered starlight emanating from the bipolar lobes themselves due to the central concentration of dust grains of more than 10$^3$ AU diameter that regulates the seepage of the starlight from the central region. Nevertheless, based on two types of differential proper-motion analyses we revealed interesting dynamics of the lobes and concentric arcs, which should provide solid constraints on the subsequent theoretical/numerical investigations. [Preview Abstract] |
Friday, October 18, 2013 3:12PM - 3:24PM |
D2.00006: What is the singular behavior of the gravitational field near generic big-bang type events? Ellery Ames, James Isenberg, Florian Beyer While specific examples of solutions to the Einstein equations are well-known and provide useful physical models, significantly less is known about the behavior of general solutions to the these equations. One outstanding set of questions concerns the behavior of general solutions in their singular regions. We consider certain classes of solutions to the Einstein equations in the cosmological setting, and show that within these classes there are families of solutions whose singular behavior can be well-understood using analytical techniques. These results are based on a so-called ``Fuchsian method,'' which we develop, for investigating the behavior of solutions to singular hyperbolic partial differential equations. Similar techniques should be adaptable for broader applicability in physics. [Preview Abstract] |
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