September 23, 1999 CfA Colloquium

Title: X-Ray Spectra of Photoionized Plasmas

Speaker: Dr. Steven M. Kahn

Abstract: X-ray photoionized plasmas are produced in cosmic accretion-powered sources, such as X-ray binaries and active galactic nuclei, where an intense X-ray continuum irradiates much cooler surrounding gas. X-ray spectra of such systems reveal characteristic discrete emission features produced primarily via radiative cascade following recombination. I will review some of the intricacies of this process, and illustrate the diagnostic potential of future high resolution spectroscopic observations planned for Chandra, XMM, and ASTRO E. I will also discuss thermal instability in X-ray photoionized plasmas, and present some new calculations of the discrete X-ray spectra expected from reflection off of cold irradiated gas.

Student Lunch: Thursday 9/23 at 12:00 in A-101.

Further Reading:

• D.A. Liedahl, S.M. Kahn, A.L. Osterheld, and W.H. Goldstein, "X-Ray Spectral Signatures of Photoionized Plasmas", Ap. J. (Letters), 350, L37 (1990).
• C.J. Hess, S.M. Kahn, and F.B.S. Paerels, "Properties and Spectroscopic Implications of Thermal Instability in X-Ray Binary and AGN Accretion Flows," Ap. J., 478, 94 (1997).
• D.W. Savin, T. Bartsch, M.H. Chen, S.M. Kahn, D.A. Liedahl, J. Linkemann, A. Muller, S. Schippers, M. Schmitt, D. Schwalm, and A. Wolf, "Dielectronic Recombination in Photoionized Gas: The Importance of Fine-Structure Core Excitations," Ap. J. (Letters), 489, L115 (1997).
• M. Sako, D.A. Liedahl, S.M. Kahn, and F. Paerels, "The X-Ray Spectrum and Global Structure of the Stellar Wind in Vela X-1", Ap. J., 525, in press.