3. GENERAL DATABASES AND CENTERS

Compilation and evaluation of atomic data is carried out at several locations listed below. Apart from astronomy, perhaps the largest user of atomic data is the nuclear fusion community which is served by some of these data centers.

• The Controlled Fusion Atomic Data Center at Oak Ridge National Laboratory; data include electron impact ionization and charge transfer cross sections and rates and analytic fits thereof.

• National Institute of Fusion Science, Nagoya, Japan; data includes fits to excitation, ionization and charge transfer rate coefficients.

• International Atomic Energy Agency, Vienna, Austria; database includes excitation, ionization and charge exchange data. Janev et al. (1988, 1989) and Janev (1992) describe the atomic and molecular database relevant to fusion, which is obtainable in the ALADDIN database system (Hulse 1990). Limited data is available for electron and neutral H collisions with H and H, He^q+, Li^q+, Be^q+, B^q+, C^q+, O^q+, Si^q+, Ti^q+, Fe^q+, Cr^q+, Ni^q+, Mo^q+, W^q+ ions, and with H₂, H₂⁺, CH₄, CH₄⁺, C_mH_n, C_mH_n⁺, O₂, O₂⁺, CO, CO⁺, H₂O, H₂O⁺ molecules (Phaneuf 1993).

• The wavelengths and energy levels continue to be provided by the National Institute for Standards and Technology, Gaithersburg, Maryland. An electronic database is in preparation and can be accessed on Internet (IP: atm.phy.nist.gov; username: asd).

• TOPBASE: This is the most extensive electronic database containing radiative data, oscillator strengths and photoionization cross sections, from the Opacity Project (Seaton et al. 1994; Cunto et al. 1993).

The latest version 0.7 of TOPBASE may be accessed from two nodes:

• Centre de Donnees Astronomique de Strasbourg (CDS);
  IP: 130.79.128.5, login: topbase, pw: Seaton+

• NASA-NSSDC Goddard Space Flight Center;
  IP: 128.183.101.54, login: topbase, pw: Seaton+
  (Note the uppercase `S' in the password). An on-line manual is available at http://heasarc.gsfc.nasa.gov/topbase/topbase.html, or from http://www.astronomy.ohio-state.edu/~pradhan.

Some of the TOPBASE data is being upgraded through new calculations by the Iron Project, in particular for the important low ionization stages of Iron (Fe I - V). The photoionization cross sections obtained using the low energy close coupling approximation with the R-matrix method, and incorporated in TOPBASE, are of high accuracy in the important near-threshold region containing the extensive autoionizing resonance structures. However, in the high energy region the cross sections are often inaccurate owing to the presence of pseudo resonances. Thus the TOPBASE photoionization cross sections were fitted to a simple ^-3 ``tail'' above all thresholds of ionization included in the close coupling calculations; these are not reliable for applications that need such data (e.g. X-ray opacities that involve inner-shell ionizations). A new effort is under way to improve the high energy ``tails'' of the photoionization cross sections and will be incorporated into TOPBASE in due course.

Further extensions of TOPBASE are also planned to include collisional data from the Iron Project (TIPBASE), as well as data for electron-ion recombination rate coefficients.