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 C2: Astrophysics I |
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Chair: Pearl Sandick, University of Utah Room: 254 |
Friday, October 18, 2013 11:00AM - 11:24AM |
C2.00001: New Views of Stellar Explosions: The Supernova Spectropolarimetry Project Invited Speaker: Jennifer L. Hoffman Nearly all supernovae possess spectropolarimetric signatures that indicate the presence of aspherical morphologies. These asphericities may include, for example, global asymmetries in the ejecta's shape or velocity structure, clumpy distributions of ejected material, or interactions between the supernova and surrounding inhomogeneous circumstellar material. Interpreting spectropolarimetric signatures and their variations over time can give rise to unprecedentedly detailed information about the explosion mechanism, the physical processes that shape the ejecta, and the properties of the progenitor star. The Supernova Spectropolarimetry Project (SNPOL) is a recently formed collaboration between observers and theorists that focuses on understanding the complex, time-dependent spectropolarimetric behavior of supernovae of all types. Using the CCD Imaging/Spectropolarimeter (SPOL) at the 61" Kuiper, the 90" Bok, and the 6.5-m MMT telescopes, we have obtained multi-epoch observations of 21 supernovae of various types. I will present early observational results from this project and discuss ongoing modeling efforts. Initial analysis reveals strong, time-variable line polarization signatures that probe the distributions of different chemical species and thereby trace the detailed structure of the ejecta as these supernovae evolve. Our continuing observations will form the most comprehensive survey to date of supernovae in polarized light, allowing us to illuminate previously obscured relationships among subtypes and build a more well-rounded picture of the supernova population as a whole. [Preview Abstract] |
Friday, October 18, 2013 11:24AM - 11:36AM |
C2.00002: Finding the First Cosmic Explosions: Hypernovae and Pair-Instability Supernovae Brandon Wiggins The cosmic Dark Ages ended with the formation of the first stars at $z \sim 20$, or $\sim 200$ Myr after the Big Bang. Because they literally lie at the edge of the observable universe Pop III stars will be beyond the reach of even next generation observatories like JWST and the Thirty-Meter Telescope. But primordial supernovae could soon directly probe the properties of the first stars because they can be observed at high redshifts and their masses can be inferred from their light curves. I will present results from numerical simulations of Pop III hypernovae and pair-instability supernovae and their light curves computed with the Los Alamos National Laboratory's RAGE and SPECTRUM codes. We find that these two types of explosions will be visible at $z \sim 10 - 15$, revealing the positions of ancient dim galaxies on the sky and tracing their star formation rates. [Preview Abstract] |
Friday, October 18, 2013 11:36AM - 11:48AM |
C2.00003: Cross Section Measurements for 34S($\alpha $,$\gamma )$ Patrick O'Malley, Devin Connolly, Ulrike Hager, Uwe Greife, Sergey Ilyushkin, Fred Sarazin, Charles Akers, Alan Chen, Greg Christian, Jennifer Fallis, Brian Fulton, Dave Hutcheon, Alison Laird, Chris Ruiz, Kiana Setoodehnia, Barry Davids Some massive stars will go through a stage of~explosive oxygen burning which commences with conversion of $^{16}$O and $^{24}$Mg to~$^{28}$Si. When the $^{24}$Mg becomes exhausted, a network of reactions ranging from $^{28}$Si to $^{40}$Ca is initiated. Final abundances of most of the neutron-rich nuclides in this mass region depend in varying amounts on the cross sections of reactions involving $^{34}$S and $^{38}$Ar, particularly those of $\alpha $-capture. Astrophysical reaction rates are dominated by the isolated resonances within the Gamow windows. Often statistical modeling is used instead for reaction rate calculations though there is typically a large discrepancy between these calculations and experimental determinations. For $\alpha $-capture onto $^{34}$S there are discrepancies between experimental measurements that have never been resolved. Also, unstudied states exist around the Gamow window that could be resonances for alpha capture. A recent measurement was done using DRAGON at TRIUMF to resolve these discrepancies and to search for new resonances. Experimental data will be shown and preliminary results discussed. [Preview Abstract] |
Friday, October 18, 2013 11:48AM - 12:00PM |
C2.00004: Convective Origins of Active Longitudes on Solar-like Stars Maria Weber, Yuhong Fan, Mark Miesch Using a thin flux tube model in a rotating spherical shell of turbulent, solar-like convective flows, we find that the distribution of emerging flux tubes in our simulation is inhomogeneous in longitude, with properties similar to those of active regions on the Sun and other solar-like stars. The large-scale pattern of flux emergence our simulations produce exhibits preferred longitudinal modes of low order, drift with respect to a fixed reference system, and alignment across the equator at low latitudes. We suggest that these active-longitude-like emergence patterns are the result of columnar, rotationally aligned giant cells present in our convection simulation at low latitudes. If giant convecting cells exist in the bulk of solar and stellar convection zones, this phenomenon, along with differential rotation, could in part provide an explanation for the behavior of active longitudes. [Preview Abstract] |
Friday, October 18, 2013 12:00PM - 12:12PM |
C2.00005: Chromospheric activity and stellar winds in supergiant stars Kathleen Geise Emission lines in the ultraviolet (UV), such as the doublet lines of Mg II, and in the visible part of the spectrum, such as Ca II H \& K, may be good indicators of chromospheric activity in supergiant stars. Some of these lines may also be used to infer the presence of stellar winds, especially when blue-shifted absorption is present in the line profile. Stellar winds are an important mechanism for mass loss in supergiant stars. We seek to show that mass loss from slow winds may be common in F supergiant stars and that variability in spectral lines such as H alpha may be used as an indicator of stellar wind. We compared archival UV and visible spectra of type F supergiant stars in order to distinguish between chromospheric activity and stellar winds in these stars. Variable or asymmetric H alpha lines were found in spectra of supergiant stars that also exhibited wind or chromospheric signatures in UV Mg II lines. [Preview Abstract] |
Friday, October 18, 2013 12:12PM - 12:24PM |
C2.00006: Understanding the Relation of Progenitors and Supernovae through the Study of Circumstellar Material (CSM) Manisha Shrestha, Jennifer L. Hoffman, Hilding R. Neilson, Richard Ignace Circumstellar material (CSM) around supernovae helps us to uncover the evolutionary connections between these supernovae and their massive progenitor stars. This CSM arises from stellar winds, outflows, or eruptions from the massive star before it explodes and can be detected with polarimetric observations. We use a Monte Carlo-based radiative transfer code (SLIP) to investigate the polarization created by different models for the CSM surrounding Type IIn supernovae. We vary parameters such as the shape, optical depth, temperature, and brightness of the CSM and compare the simulated flux and polarization behavior with observational data. We present results from new simulations that assume a bow shock shape for the CSM. Bow shocks are commonly observed around massive stars; this shape forms when a star moving more quickly than the speed of sound in the local interstellar medium emits a stellar wind that drives a shock wave into the ISM. Since a bow shock projects an aspherical shape onto the sky, light from the central source that scatters in the shock region becomes polarized. We present electron-scattering polarization maps for this geometry and discuss the behavior of observed polarization with viewing angle in the unresolved case. [Preview Abstract] |
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