The Abundances of Light Neutron-Capture Elements in Planetary Nebulae III. The Impact of New Atomic Data on Nebular Selenium and Krypton Abundance Determinations

The detection of neutron(n)-capture elements in several planetary nebulae (PNe) has provided a new means of investigating s-process nucleosynthesis in low-mass stars. However, a lack of atomic data has inhibited accurate trans-iron element abundance determinations in astrophysical nebulae. Recently, photoionization and recombination data were determined for Se and Kr, the two most widely detected n-capture elements in nebular spectra. We have incorporated these new data into the photoionization code Cloudy. To test the atomic data, numerical models were computed for 15 PNe that exhibit emission lines from multiple Kr ions. We found systematic discrepancies between the predicted and observed emission lines that are most likely caused by inaccurate photoionization and recombination data. These discrepancies were removed by adjusting the Kr$^+$--Kr$^{3+}$ photoionization cross sections within their cited uncertainties and the dielectronic recombination rate coefficients by slightly larger amounts. From grids of models spanning the physical conditions encountered in PNe, we derive new, broadly applicable ionization correction factor (ICF) formulae for calculating Se and Kr elemental abundances. The ICFs were applied to our previous survey of near-infrared [Kr III] and [Se IV] emission lines in 120 PNe. The revised Se and Kr abundances are 0.1-0.3 dex lower than former estimates, with average values of [Se/(O, Ar)]=0.12$\pm$0.27 and [Kr/(O, Ar)]=0.82$\pm$0.29, but correlations previously found between their abundances and other nebular and stellar properties are unaffected. We also find a tendency for high-velocity PNe that can be associated with the Galactic thick disk to exhibit larger s-process enrichments than low-velocity PNe belonging to the thin disk population.Comment: 73 pages, 6 figures, 18 tables, accepted for publication in ApJ

Understanding the Telecommunications Act of 1996

Books Reviewed: Guidebook to the Telecommunications Act of 1996; by Charles D. Ferris, Frank W. Lloyd, and Howard J. Symons; Matthew Bender & Co., Inc. (1996); 298 pages The Telecommunications Act of 1996: Special Report; by Peter W. Huber, Michael K. Kellogg, and John Thorne; Little, Brown & Co. (1996); 428 pages Telecommunications Act Handbook: A Complete Reference For Business; by Leon T. Knauer, Ronald K. Machtley, and Thomas M. Lynch; Government Institutes (1996); 620 pages Legal Guide to Broadcast Law and Regulation; by the National Association of Broadcasters (5th ed. 1996); 700 pages The Telecommunications Act of 1996: What It Means to Local Governments; by Miller, Canfield, Paddock & Stone, PLC; National League of Cities (1996); 38 pages National Regulatory Research Institute (NRRI) Series on the 1996 Telecommunications Act (all 1996): The Eligible Telecommunications Carrier: A Strategy for Expanding Universal Service; by Phyllis Bernt; 87 pages Determining When Competition is Workable : A Handbook for State Commissions Making Assessments Required by the Telecommunications Act of 1996; by David Chessler; 103 pages Convergence and Controversy in Early Interconnection Agreements; by Vivian Witkind Davis and Michael E. Clements; 43 pages State Commission Mediation and Arbitration of Interconnection Agreements: Procedures and Status Under the Telecommunications Act of 1996; by Vivian Davis and Nancy Zearfoss; 43 pages Competition-Enhancing Costing and Pricing Standards for Telecommunications Interconnection; by David Gabel; 44 pages State and Federal Number Portability Policies; by Raymond Lawton and Nancy Zearfoss; 16 pagesRights-of-Way and other Customer-Access Facilities: Issues, Policies, and Options for Regulators; by Edwin Rosenberg and Stella Rubia; 138 page

Working the System

Book Review: FCC Lobbying: A Handbook of Insider Tips and Practical Advice, Erwin G. Krasnow, David R. Siddall, and Michael D. Berg, Washington: Telecommunications Reports International, 2001, 225 pages

Understanding the Telecommunications Act of 1996

Books Reviewed: Guidebook to the Telecommunications Act of 1996; by Charles D. Ferris, Frank W. Lloyd, and Howard J. Symons; Matthew Bender & Co., Inc. (1996); 298 pages The Telecommunications Act of 1996: Special Report; by Peter W. Huber, Michael K. Kellogg, and John Thorne; Little, Brown & Co. (1996); 428 pages Telecommunications Act Handbook: A Complete Reference For Business; by Leon T. Knauer, Ronald K. Machtley, and Thomas M. Lynch; Government Institutes (1996); 620 pages Legal Guide to Broadcast Law and Regulation; by the National Association of Broadcasters (5th ed. 1996); 700 pages The Telecommunications Act of 1996: What It Means to Local Governments; by Miller, Canfield, Paddock & Stone, PLC; National League of Cities (1996); 38 pages National Regulatory Research Institute (NRRI) Series on the 1996 Telecommunications Act (all 1996): The Eligible Telecommunications Carrier: A Strategy for Expanding Universal Service; by Phyllis Bernt; 87 pages Determining When Competition is Workable : A Handbook for State Commissions Making Assessments Required by the Telecommunications Act of 1996; by David Chessler; 103 pages Convergence and Controversy in Early Interconnection Agreements; by Vivian Witkind Davis and Michael E. Clements; 43 pages State Commission Mediation and Arbitration of Interconnection Agreements: Procedures and Status Under the Telecommunications Act of 1996; by Vivian Davis and Nancy Zearfoss; 43 pages Competition-Enhancing Costing and Pricing Standards for Telecommunications Interconnection; by David Gabel; 44 pages State and Federal Number Portability Policies; by Raymond Lawton and Nancy Zearfoss; 16 pagesRights-of-Way and other Customer-Access Facilities: Issues, Policies, and Options for Regulators; by Edwin Rosenberg and Stella Rubia; 138 page

Working the System

Book Review: FCC Lobbying: A Handbook of Insider Tips and Practical Advice, Erwin G. Krasnow, David R. Siddall, and Michael D. Berg, Washington: Telecommunications Reports International, 2001, 225 pages

Churchill and Strategic Dilemmas before the World Wars:Essays in Honor of Michael I. Handel,

One of three volumes of essays (two fo- cus on different aspects of strategy) pub- lished in Handel’s memory, this work is based on a conference held in Newport, Rhode Island. It offers four scholarly pa- pers on Churchill’s assessment of the German naval challenge before the First World War, Pacific security and the lim- its of British power between the wars, Churchill and the German threat in the late 1930s, and Churchill’s views of tech- nology. Each assesses a different aspect of Churchill’s changing role