Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session 10HE: Radiation and Supernovae |
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Sponsoring Units: HEDP HEDLA Chair: Steve Rose, Imperial College Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Promenade F |
Sunday, April 13, 2008 11:00AM - 11:25AM |
10HE.00001: Supernova remnants Invited Speaker: Supernova remnants are of general interest for astrophysics for two main reasons: 1) By studying supernova remnants we study the remains of an exploded star, thereby giving new data on explosive nucleosynthesis, explosion asymmetries, and explosion kinematics. 2) Supernova remnants offer an interesting mix of interesting physical process: non-equilibrium ionization, non-equilibration of temperatures, and, currently a hot topic, cosmic ray acceleration. I will discuss several of these aspects, mainly from an observational point of view. A prominent place in this talk is reserved for the bright remnant Cas A, which shows evidence for radio-active Ti-44 in its interior, a bipolar explosion, and cosmic ray acceleration. [Preview Abstract] |
Sunday, April 13, 2008 11:25AM - 11:50AM |
10HE.00002: Observations of Supernovae during and after Shock Breakout Invited Speaker: Supernovae (SNe) are some of the most energetic explosion since the birth of the universe. Over the past few years, space-based observatories have allowed detailed studies of these energetic events in previously unexplored wavelength regimes. NASA's \textit{Swift} observatory is particularly suited to probe the early emission of SNe due to its fast response, flexible scheduling capabilities, and large wavelength band coverage, ranging from the optical, UV, and X-ray to the Gamma-ray bands. By studying the outgoing SN shocks with material in its surroundings, the explosion physics and nature of progenitor stars can be studied. Furthermore, monitoring the X-ray emission of SNe with space-based X-ray observatories is being used to map the density structure in SN environments out to large radii from the sites of the explosions ($>$10$^{20}$ cm, 10,000 times larger than our solar system), the transition of a SN into an old supernova remnant can be studied, and the mass-loss rates of the progenitor stars can be probed over significant timescales ($>$10$^{4}$ years) in the stellar wind history. In combination, these observations give unprecedented insights into the nature of energetic explosions and their environments. During this talk, I will present highlights from recent observations, among them the first observation of a SN \textit{during} the actual explosion with \textit{Swift}. [Preview Abstract] |
Sunday, April 13, 2008 11:50AM - 12:15PM |
10HE.00003: Analytic Approach to the Stability of Standing Accretion Shocks Invited Speaker: We explore an analytic model of the accretion shock in the postbounce phase of a core-collapse supernova explosion. We find growing oscillations of the shock in the $l=1$ and 2 modes, in agreement with a variety of existing numerical simulations. For modest values of the ratio of the outer accretion shock to that of the inner boundary to the shocked flow, the instability appears to derive from the growth of trapped sound waves, whereas at higher values, postshock advection clearly plays a role. Thus, the model described here may relate to the different mechanisms of instability recently advocated by Blondin \& Mezzacappa and by Foglizzo and collaborators. [Preview Abstract] |
Sunday, April 13, 2008 12:15PM - 2:00PM |
10HE.00004: LUNCH BREAK
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Sunday, April 13, 2008 2:00PM - 2:25PM |
10HE.00005: Radiative shock theory, experiments, and connections to astrophysics Invited Speaker: This work concerns both radiative shocks (RS) in astrophysics and in laboratory. Accurate RS models are attempted to understand stellar evolution where they are always involved. Two extreme types of RS can be considered: in optically thin and thick medium. A third type is an intermediate regime. In astrophysics, observed RS arise generally in optically thin material. Thus, radiation escapes without interaction with the surrounding gas and it can be modeled by a cooling function $\Lambda $. In this case only the post-shock region is structured by the radiation cooling. We have solved the hydrodynamic equations including $\Lambda \propto \rho ^\varepsilon P^\zeta x^\theta $ for arbitrary values of $\varepsilon ,\;\,\zeta ,\,\;\theta $. Moreover introducing this cooling function in hydro-code HADES, we are able to simulate astrophysical shocks under optically thin conditions and recover analytical calculations. Our models are validated by confrontation with experimental results. We performed RS experiments using LULI2000 laser facility, in which the plasma is more or less optically thick. Consequently, these high-Mach number RS present a radiative precursor. Specific radiation hydrodynamic codes, including radiative terms (flux, pressure, energy density), are used to examine the structure of this kind of RS. In addition, we obtain analytical solutions describing the post-shock structure of RS growing both in astrophysical environment and in laboratory. Therefore, we can study this region experimentally and compare its structure with astrophysical shocks. This theoretical work is motivated by new very high-power experimental facilities, as LIL (France) for which we propose to probe the downstream zone. Experimental results related to the cooling in the downstream flow will allow to validate and to check our astrophysical code HADES. Finally, we attempt to predict the precursor length of steady laboratory RS, using now $\Lambda $ as a radiation flux propagating towards the upstream flow in the precursor. [Preview Abstract] |
Sunday, April 13, 2008 2:25PM - 2:50PM |
10HE.00006: Radiative Transfer in Type Ia Supernovae Invited Speaker: Some white dwarf stars die in a thermonuclear runaway leading to complete stellar disruption within seconds -- a Type~Ia supernova. The material ejected in that explosion will shine brightly for months, powered by the decay of freshly synthesized radioactive isotopes. Multi-physics hydrodynamical codes are now simulating the first violent seconds of the event, and a treatment of the subsequent radiation transport is needed to calculate predictions of the observable light curves, spectral evolution, and spectropolarization. Here I discuss Monte Carlo techniques for addressing multi-group time-dependent radiative transfer in 3-dimensional, rapidly expanding plasmas, where the densities are low and non-LTE effects can be important. I compare our model calculations directly to astronomical observations, and discuss how the simulations are helping us understand the progenitors and explosion mechanism of Type~Ia supernovae, as well as refining their applicability as probes of cosmological expansion. [Preview Abstract] |
Sunday, April 13, 2008 2:50PM - 3:10PM |
10HE.00007: BREAK
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