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JD17 will take place on July 22, and the Panel Discussion on Atomic Data and Databases will be held on July 23, 9-10:30, jointly with Commission 14 (C14) - (Note different location)

AIMS AND DESCRIPTION

Atomic data are crucial to the analysis of X-ray observations. Space observatories, the X-Ray Multi-Mirror Mission (XMM-Newton) and the Chandra X-ray Observatory (CXO), complemented by others such as BeppoSaX and the Rossi X-ray Timing Explorer (RXTE), are providing not only an astonishing wealth of spectroscopic data of a variety of astronomical sources, but also reveal tantalizing features of heretofore unobserved astrophysical phenomena.

Among the types of objects being studied are Stellar coronae, winds, and flares, Supernovae, Active Galactic Nuclei, X-ray binaries, and Gamma-ray bursters. The unprecedented spectral resolution of the new instruments reveals immense complexity representative of the emitting regions in these objects, from relatively well understood coronae of stars to the largely unknown physics of accretion discs of massive black holes thought to be the central engines of AGN. Answers to fundamental questions related to general relativity and atomic plasmas under extreme conditions, such as in the vicinity of black holes, possibly lie buried in the vast amount of X-ray spectroscopic data now being accumulated.

X-ray spectra of these diverse objects and the enormous range of conditions within them have made it abundantly clear that atomic physics plays a vital role, not only in spectral formation generally, but especially in specific wavelength regions that display anomalous features requiring careful interpretation. It is essential to disentangle atomic processes, plasma effects, and physical phenomena such as relativistic red-shifts and geometry. Accurate and extensive atomic data are the key to eliminating the uncertainties in astrophysical models, thereby allowing the real nature of observed sources to be determined.

As the X-ray spectroscopic observations and data analysis progress from discovery to diagnostics, astronomers are discovering that the available fundamental laboratory data do not match the task at hand. This situation is in spite of, not due to lack of, considerable recent progress in atomic theory, experiments, and astrophysical modeling. Large-scale calculations of accurate atomic data are now being carried out by groups of international collaborators; elaborate experiments using electron beam ion traps (EBIT) and synchroton ion storage rings are capable of detailed studies of excitation processes underlying X-ray emission; numerical simulations of plasma enviroments with new codes and data are becoming increasingly extensive and precise in the description of astrophysical sources.

The aim of this Joint Discussion is to bring together these distinct, but intimately related, components of X-ray astronomy -- astronomical X-ray observers and modellers, and experimental and theoretical atomic physicists -- with the goal of discussing atomic data needs and availablity.

Outstanding Issues And Themes

I. New X-ray Observations

• The JD will begin with reports from ongoing space missions. These would address some of the following issues and themes.

• Among the most intriguing observations of X-ray objects are the K-alpha complexes - "neutral" and "ionized" components in accretion disc and warm absorber regions. For example, The iron K-alpha lines are prominent -- nearly ubiquitous -- in X-ray sources, yet their interpretation is controversial. These features generally manifest themselves with strong components at 6.4 keV and 6.7 to 6.9 keV, corresponding to low or highly ionized states of Fe, respective signatures of cold or hot plasma. In AGN, their spectral formation may be dominated by any or all of the following factors: "neutral" ionization states of Fe I to XVI, and/or "ionized" components from Fe XVII to XXVI; relativistically broadened spectra in the inner accretion disc of a massive black hole; reflection from an ionized or neutral plasma; absorption/emission from the "warm absorber" region; radiative transfer; abundances; geometry; and temporal variability of the source. Similar considerations also appear to affect K-alpha complexes of other elements such as C, N, and O, which, though simpler, are nonetheless difficult to analyze completely. In particular, attention has focused on an AGN MCG-6-30-15 that has become the rosetta stone of X-ray astronomy, and therefore extensively observed by CXO, XMM-Newton, and RXTE.

  
  Chandra observations of the Seyfert 1 active galactic nucleus of MCG-6-30-15 (Lee etal. 2001)

  
  XMM-Newton spectrum of the active Seyfert 2 galaxy NGC 1068 (Kinkhabwala et al. 2002)

• X-ray spectra of strong flares in RS CVn stars indicate intense magnetic activity and anomalous abundances, such as overabundance of neon with respect to iron.

• The detailed X-ray spectra of supernova remnants reveal the kinematics of the shocked ejecta and the colder circumstellar gas, thus providing valuable information on the dynamics, abundances, and history of SNR's.

• Gamma-Ray bursts and X-ray/UV afterglows as signatures of progenitors such as hypernovae.

  II. Theoretical Computations

• Recent advances in theoretical atomic physics enable accurate atomic computations to be carried out efficiently. Large computational programs such as the Opacity Project and the Iron Project, using the powerful R-matrix method and its relativistic extensions, are producing huge amounts of atomic data with unprecedented accuracy for nearly all atomic processes of interest - excitation, photoionization, electron-ion recombination, radiative transitions and resonance spectroscopy. However, the ab-initio methods are intensive and laborious. The benchmarking and availability of such data is a high priority item.

  
  K-alpha resonances in X-ray absorption by Oxygen ions (Pradhan,Chen,Delahaye,Nahar,Oelgoetz 2002)

• More approximate and semi-empirical methods are capable of generating extensive sets of data efficiently and rapidly, and enable large atomic models to be constructed for applications. The main problem from the point of view of theory is therefore a compromise or a choice between accuracy and completeness. It is essential to compare the results from the two types of theoretical methods, for many processes and applications, in order to ascertain the reliability and validity of different datasets currently in use in astrophysical models.

  III. Laboratory Measurements

  A number of major experimental programs are under way in X-ray laboratory astrophysics: electron-beam-ion-traps, synchrotron ion storage rings, tokamaks, and magnetic Z-pinch devices. These are capable of very high-resolution measurements of cross sections to calibrate theoretical calculations, and diagnostic line ratios for comparison with models. Furthermore, spectral observations over extended wavelength ranges of several ionization states of different elements may be observed under controlled laboratory conditions. The JD would highlight the state-of-the-art in experimental atomic physics of X-ray spectroscopy.

  
  LLNL EBIT measured cross sections and comparison with theory (courtesy, P. Beiersdorfer)

  
  SAO-NIST EBIT measured x-ray spectrum (courtesy, E. Silver)

  
  (Merged-beams recombination rate coeffcient of Li-like Ni25+ measured at the heavy-ion storage ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg, Schippers et al., Phys. Rev. A 62, 022708 (2002).)

  IV. Numerical Simulations and Databases

• As mentioned, the accuracy and completeness of atomic data are the the main problem facing astrophysical modeling codes. Currently available codes generally employ either photoionization equilibrium or collisional (coronal) equilibrium approximations. The validity of these approximations needs to be ascertained for different classes of objects. Accurate spectral analysis often requires complex non-LTE models. This will be one of the main thrust areas that the JD should be able to address.

• While the modeling codes are capable of spectral simulations under various plasma conditions, new and more efficient methods need to be developed to not only interface with the huge amount of needed atomic data, but also to consider effects particular to a given source. Radiative transfer is inextricably linked to atomic physics. At present such codes and techniques are under development and greater coordination is needed between atomic physicists and astrophysicists engaged in X-ray modeling.

• There are several atomic databases. Although most are general, there are deficiencies that users need to be aware of. The JD will attempt to review the accuracy of data sources and databases.

  FORMAT

  The JD will comprise of 2 half-day sessions, divided into 4 parts covering (I) New X-Ray Observations, (II) Atomic Theory, (III) Laboratory Measurements, and (IV) Plasma Modeling and Atomic Databases. Each part will consist of three 30-minute revies talks and a few other oral presentations. Interposed between the two sessions will be a poster session for contributed papers. The JD will include presentations from various databases and a Panel Discussion on July 23 or 24.

  This JD is the only meeting at the IAU General Assembly dedicated to X-ray Astronomy, and the SOC welcomes poster contributions on all aspects thereof.

  There will be a book of Proceedings for participants, in the IAU Highlights of Astronomy series to submit articles based on their presentations and related material.

  Scientific Organising Committee

  N. Brickhouse (USA), H. Hasan (USA), J. Houck (USA), A. Fabian (UK), J. Kaastra (Netherlands), F. Keenan (UK), S. Kahn (USA), T. Kallman (USA), H. Netzer (Israel), A.K. Pradhan (USA, Chair), P.L. Smith (USA), K.Yamashita (Japan).

  PROGRAM

  Invited Speakers and Data Panelists:

  Ehud Behar (Israel), Peter Beiersdorfer (USA), Nancy Brickhouse (USA), Andy Fabian (UK), Rajmal Jain (India), Jelle Kaastra (Netherlands), Steve Kahn (USA), Tim Kallman (USA), Enrico Landi (Italy), Julia Lee (USA), Duane Liedahl (USA), Brendan McLaughlin (UK), Patrick Palmeri (France), Izumi Murakami (Japan), Anil Pradhan (USA), Stefan Schippers (Germany), Eric Silver (USA), Bill Martin (USA)

  Session Chairs:

  Bob Williams, Hagai Netzer, Peter Smith, Ken Pounds, Mike Dopita

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  ABSTRACTS FOR CONTRIBUTED PRESENTATIONS TO JD17 MAY BE SUBMITTED AT: ABSTRACT SUBMISSION

  Please consult the IAU website at: www.iau.org, or XXVth IAU GENERAL ASSEMBLY for more information on the site.

  Site and Travel:

  The JD will take place all day Tuesday July 22, with a Panel Discussion on July 23 or 24, during the General Assembly to be held in the Convention and Exhibition Centre at Darling Harbour, Sydney. A number of other Joint Discussions and Symposia are being organised all throughout the two-week duration of the GA.

  Limited funds from the IAU are available to assist with travel costs for participants without much other support. However, these grants are generally small and cover only a small fraction of the total cost. The application forms are available from the IAU website.

  Deadlines:

  Abstract Submission Deadline 1 March 2003 (Post-deadline abstracts can be accepted)

  Applications for IAU Travel Grants: 15th February 2003

  Abstract deadline: 15th February 2003

  Successful Travel Grant applicants notified: 15th March 2003

  Early Registration deadline: 30th April 2003

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  Revised: 2002 November 26