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 2HE: Accretion and Photoionized Plasmas |
Hide Abstracts |
Sponsoring Units: HEDP HEDLA Chair: Roberto Mancini, University of Nevada-Reno Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Promenade F |
Friday, April 11, 2008 11:15AM - 11:40AM |
2HE.00001: Photoionized Plasma and Opacity Experiments on the Z Machine Invited Speaker: Laboratory experiments at Z use high energy density to create plasma conditions similar to extreme astrophysical environments, including stellar interiors and accretion powered objects. The importance of radiation unifies these topics, even though the plasmas involved are very different. Understanding stellar interiors requires knowledge of radiation transport in dense, hot, collision-dominated plasma. A Z x-ray source was used to measure iron plasma transmission at 156 eV electron temperature, 2x higher than in prior work. The data provide the first experimental tests of absorption features critical for stellar interior opacity models and may provide insight into whether the present discrepancy between solar models and helioseismology originates in opacity model deficiencies or in some other aspect of the solar model. In contrast, accretion physics requires interpretation of x-ray spectra from lower density photoionization-dominated plasma. Exploiting astrophysical spectra requires a spectral model that connects the observations with a model that describes the overall picture of the astrophysical object. However, photoionized plasma spectral models are largely untested. Z-pinch radiation was used to create photoionized iron and neon plasmas with photoionization parameter 5-25 erg cm /s. Comparisons with the data improve x-ray photoionization models and promote more accurate interpretation of spectra acquired with astrophysical observatories. The prospects for new experiments at the higher radiation powers provided by the recently upgraded Z facility will be described.* In collaboration with scientists from CEA, LANL, LLNL, Oxford, Prism, Queens University, Swarthmore College, U. Nevada Reno, and Sandia ++Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000. [Preview Abstract] |
Friday, April 11, 2008 11:40AM - 12:05PM |
2HE.00002: Current Challenges of Astrophysical Photoionized Plasmas Invited Speaker: Photoioniation and photoexcitation has been known to be important in astrophysical plasmas since the early study of emission line nebulae, and the study of optical and UV emission lines is a classical subject. Recently, this has broadened to include emission in other wavelength bands. In the X-ray band, Chandra and XMM-Newton have revealed rich spectra from active galaxies and compact binaries, and this has motivated new efforts at modeling these plasmas. This has led to insights about a component of the gas in these systems which had been previously unknown, observationally, and which has implications for our understanding of the global mass budget. In this talk I will review the observational data on these plasmas, and discuss some recent results on modeling. [Preview Abstract] |
Friday, April 11, 2008 12:05PM - 12:30PM |
2HE.00003: Astrophysics of Accretion onto Compact Objects Invited Speaker: The most energetic phenomena in the universe are systems powered by gravity through accretion. For compact stars such as white dwarfs, neutron stars, and especially black holes, the energy released per unit mass accreted can significantly exceed that released by nuclear reactions. Over the last half century a growing body of observations has revealed a plethora of environments in which accretion plays a significant or even dominant role. Our theoretical understanding of accretion disk systems has not kept pace. Until recently theory has been based primarily on a one-dimensional time-steady model consisting of an optically thick, vertically-thin, Keplerian disk with an unknown, parameterized internal stress. While these analytic models have served us well to understand many properties of a wide variety of accretion systems, their limitations are now well-known, and the observation data demand moving beyond this standard. Space- and ground-based observations are providing increasingly detailed evidence that accretion systems are dynamic. For example, the spectral energy distribution and luminosity for sources such as X-ray binaries and AGN are strongly variable, often with substantial amplitudes. The timescales for variability are rapid, often comparable to the dynamical times associated with orbits near the central black hole. This variability must arise not from secular changes in the accretion rate (the only process accessible to time-stationary analytic disk models) but from processes that occur within the disk. Numerical simulations provide a way to investigate the dynamics of accretion flows directly with far fewer limitations compared to analytic models. Because magnetic fields are fundamentally important for jets and disks, and because we now know that magnetic turbulence accounts for the internal stress, the governing equations are those of compressible magnetohydrodynamics (MHD). Accretion disk dynamics can thus be investigated using three-dimensional MHD simulation codes that employ both global and local computational domains. Although it is not yet possible to do fully global time-dependent radiation transport in disk models, the observational implications of these simulations can be investigated using simple emission and absorption models coupled with relativistic ray tracing. The time and length-scales involved make such simulations challenging, but even the first results are intriguing. They have revealed details about time-dependent properties of disks, magnetic disk dynamos, jet launching mechanisms, and the dynamical properties of systems other than the standard thin disk. As the capabilities of computational hardware increase, and the development of advanced numerical codes continues, our theoretical understanding of accretion physics will substantially increase. [Preview Abstract] |
Friday, April 11, 2008 12:30PM - 12:55PM |
2HE.00004: Radiation transfer experiments using high-power lasers. Invited Speaker: Experiments using high-power lasers that investigate radiation transfer have been undertaken for many years. We shall summarise different experimental approaches that have been used and consider what has been learned from those experiments which include studies of diffusive energy flow and line radiation transfer both in static plasmas and where there is a large plasma velocity gradient. We shall conclude with a discussion of recent theoretical work studying the effect of plasma geometry on line radiation transfer, together with its application to astrophysical observations and laboratory experiments. [Preview Abstract] |
Friday, April 11, 2008 12:55PM - 2:25PM |
2HE.00005: LUNCH BREAK
|
Friday, April 11, 2008 2:25PM - 2:50PM |
2HE.00006: Experimental and Computational Analysis of Photo-ionized Non-LTE Plasma Produced by Intense Laser Invited Speaker: Two types of photo-ionized plasma experiments have been carried out with Gekko-XII laser in Osaka and Shingang-II laser in Shanghai as joint experiment with China. One is spectroscopic measurement of self emission from nitrogen plasma and the other is absorption by silicon plasma both heated by almost Planckian radiation with Tr = 80 eV in gold cavities heated by lasers. Experimental data are analyzed with two different codes developed in Japan and China. The code coupled with rate equation solver and HULLAC says that the nitrogen gas line emission can be explained when we assume the electron temperature is much lower than Tr and we obtained a good agreement with the electron temperature 20 eV. It is pointed out that this spectrum can be reproduced even if we assume the plasma and radiation is in LTE with Tr = Te = 60 eV. This suggests careful analysis is required in analyzing observational spectra from Universe. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700