Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session J4: Atomic and Molecular Collisions Related to Astrophysical Applications |
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Sponsoring Units: GEC Chair: Murtadha Khakoo, California State University, Fullerton Room: Regency Ballroom |
Thursday, May 27, 2010 8:00AM - 8:30AM |
J4.00001: Laboratory astrophysics with ion-beams: Cross sections for dielectronic recombination, photoionization and electron-impact ionization from heavy-ion storage-rings and synchrotron light-sources Invited Speaker: Laboratory experiments yield vitally needed benchmarks of atomic data for plasma modeling. An effort to provide rate coefficients for dielectronic recombination (DR) and electron impact ionization (EII) of highly charged atomic ions is being carried out at the Heidelberg heavy-ion storage ring TSR\footnote{E. W. Schmidt et al., ApJL 641 (2006) L157; A\&A 492 (2008) 265; M. Lestinsky et al., ApJ 698 (2009) 648 and references therein.}. Popular compilations of DR data sometimes underestimate low-temperature DR rate coefficients by orders of magnitude as has already been suspected e.g.\ for Fe-M shell ions on the basis of the modeling of x-ray spectra from active galactic nuclei\footnote{H. Netzer, ApJ 604 (2004) 551; S. Kraemer et al., Apj 604 (2004) 556.}. Even modern theoretical calculations often deviate strongly from our experimental results. This is due to the fundamental difficulty to calculate low-energy DR resonance positions of complex ions with sufficient accuracy. For these ions, storage-ring DR experiments are the only reliable source for low-temperature DR data. Astrophysically relevant results from storage-ring EII measurements and photon-ion experiments at synchrotron light sources will also be presented. [Preview Abstract] |
Thursday, May 27, 2010 8:30AM - 9:00AM |
J4.00002: Lab Astro and the Origins of the Chemical Elements Invited Speaker: Interpretation of the spectra of metal-poor Galactic halo stars is dependent on AMO laboratory data [1,2]. Metal-poor Galactic halo stars were born when the Milky Way was young and they provide a record of the chemical evolution of the Galaxy. Elements heavier than iron are produced via r(apid)-process and s(low)-process n(eutron)-capture mechanisms. The s-process mechanism, which occurs in certain AGB stars, is relatively well understood. The explosive r-process is not well understood. The r-process n-capture mechanism was dominant early in the Galaxy's history [3]. New large aperture telescopes make it possible to record high-resolution spectra with high signal-to-noise ratios on a growing number of metal-poor stars. In addition to mapping the chemical evolution of the Galaxy, these studies are yielding an increasingly well-defined r-process elemental abundance pattern which constrains models of r-process nucleosynthesis [1]. The next phase of this ongoing research will address challenges in modeling stellar photospheres. Peculiar trends in abundances of specific Fe-group elements as a function of stellar age or metallicity may be due to limitations in traditional one dimensional (1d) local thermodynamic equilibrium (LTE) models of stellar photospheres or may be due to poorly understood nucleosynthesis [4]. Efforts are now underway to test the Saha or ionization equilibrium in a variety of stellar atmospheres for several Fe-group elements using the best available spectroscopic data for selected transitions. More comprehensive spectroscopic data of improved accuracy and accurate collisional data, especially for inelastic collisions of H atoms with metal atoms and ions, will be needed to fully develop 3d/non-LTE models of photospheres [e.g. 5]. \\[4pt] [1] C. Sneden, J. E. Lawler, J. J. Cowan, I. I. Ivans, and E. A. Den Hartog, Astrophys. J. Suppl. Ser. 182, 80-96 (2009). \\[0pt] [2] J. E. Lawler, C. Sneden, J. J. Cowan, I. I. Ivans, and E. A. Den Hartog, Astrophys. J. Suppl. Ser. 182, 51-79 (2009). \\[0pt] [3] J. Simmerer, C. Sneden, J. J. Cowan, J. Collier, V. M. Woolf, and J. E. Lawler, Astrophys. J. 617, 1091-1114 (2004). \\[0pt] [4] A. McWilliam, Ann. Rev. Astron. {\&} Astrophys. 35, 503 (1997). \\[0pt] [5] M. Asplund, Ann. Rev. Astron. {\&} Astrophys. 43, 481 (2005). [Preview Abstract] |
Thursday, May 27, 2010 9:00AM - 9:30AM |
J4.00003: Atomic Astrophysics in 3-D: Discovery, Data and Diagnostics Invited Speaker: For the foreseeable future, new ground- and space-based instruments, with higher spectroscopic resolution and greater sensitivities, will discover new astronomical phenomena, creating a continuing demand for rigorous atomic and molecular studies to provide understanding of the underlying astrophysics. In order to deduce the physical conditions of astronomical objects, astronomers use diagnostics such as spectral line ratios for key atomic or ionic species, together with increasingly complex models, involving millions of spectral lines. Atomic physics data of unprecedented accuracy is critical to this enterprise. Several recent examples of atomic collision processes important to understanding astronomical observations will be given. [Preview Abstract] |
Thursday, May 27, 2010 9:30AM - 10:00AM |
J4.00004: The Atomic and Molecular Universe: Collisions in Hot Plasmas to the Building Blocks of Life Invited Speaker: Basic atomic and molecular collision phenomena are operative at the core of an enormous range of astrophysical plasmas, including the interstellar medium (ISM), protostellar regions, stars, our Sun, and planetary atmospheres, ionospheres, \& magnetospheres. Laboratory measurements of cross sections and lifetimes are needed to establish plasma charge-state distributions. A required database includes absolute electron- impact excitation, ionization, and recombination cross sections in highly-charged ions (HCIs); photoionization cross sections; and absolute single- and multiple charge-exchange cross sections between a neutral target and an HCI, as when a solar/stellar wind meets a circumstellar cloud or passing comet to generate X- rays via charge exchange. Since satellites and spacecraft often detect photons from the astronomical object, the infrared-to-X- ray emissions are governed by a balance between collisional excitation and radiative decay, so that accurate lifetimes, branching fractions, and Einstein A and B coefficients are also needed. On yet another level, observations in the infrared-to- millimeter wave region from, for example, the Green Bank Telescope, Spitzer, Sofia, Herschel, and the James Webb Telescope provide information on molecular formation in the ISM and protostellar regions. Over 144 atomic, molecular, and ionic species have been identified to date. Recent laboratory results will be given on formation of some of these polyatomic molecules in superthermal, ground-state H- and O-atom collisions with simple, grain-adsorbed species, and results compared to the impressive array of space spectroscopic data. [Preview Abstract] |
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