INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter free, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note wiU indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Infonnaticn Company 300 North Zeeb Road, Ann Aitwr MI 48106-1346 USA 313/761-4700 800/521-0600 EMISSION SPECTRA AND IONIZATION STRUCTURE OF IRON IN GASEOUS NEBULAE AND PARTIALLY IONIZED ZONES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Manuel A. Bautista, B.Sc. ***** The Ohio State University 1997 Dissertation Committee: Professor Anil K. Pradhan, Adviser Professor Darren L. DePoy Adviser Professor Richard W. Pogge Department of Astronomy ÜHI Number; 9801640 UMI Microform 9801640 Copyright 1997, by UMI Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 © Copyright by Manuel A. Bautista 1997 ABSTRACT The emission spectra and the ionization structure of the low ionization stages of iron, Fe I-IV, in gaseous nebulae are studied. This work includes: (i) new atomic data; (ii) detailed study of excitation mechanisms for the [Fe II], [Fe III], and [Fe IV] emission, and spectroscopic analysis of the observed IR, optical, and UV spectra; (iii) study of the physical structure and kinematics of the nebulae and their ionization fronts. Spectral analysis of the well observ^ed Orion nebula is carried out as a test case, using extensive collisional-radiative and photoionization models. It is shown that the [Fe II] emission from the Orion nebula is predominantly excited via electron collisions in high density partially ionized zones; fluorescence is relatively much less effective. Further evidence for high density zones is derived from the [O I] and [Ni II] spectral lines, [Fe II]/[O I] and [Fe II]/[Ni II] correlations, and the kinematic measurements of ionic species in the nebula. The ionization structure of iron in Orion is modeled using the newly calculated atomic parameters, showing some significant differences from previous models. The new model suggests a fully ionized H II region at densities of the order of 10^ cm"^, and a dynamic partially ionized H II/H I region at densities of 10'’ — 10' cm~^ . The gas phase iron abundance in Orion is estimated from observed spectra, including recently observed [Fe IV] lines. 11 To Maggie, for all the good and the difficult moments that we have lived and for the life that we have ahead, together. in ACKNOWLEDGMENTS There are several people who contributed very much to my present achievement. The most influencing have been my parents, Manolo y Gloria, who gave me all their love and support since I was born. They taught me about the importance of honesty, hard work, and perseverance. My parents are to me real life heroes and I love them. I like to recognize also my grandmothers, Ligia y Margot, who also cared for me so much. They were very important to me during my early years and accompanied me for a good part of my education. Various good teachers influenced my life and inspired me to pursue these studies. -A.mong them, I regard special gratitude and appreciation for Celso Luis Ladera, Claudio Mendoza, and .A.nil K. Pradhan (my present adviser). Luis was the best teacher that I had as undergraduate at the Universidad Simon Bolivar. He trusted me, motivated me, and gave me enough freedom to take my first steps in research. At the same time, he was a counselor and friend. Claudio introduced me to the scientific areas that I like the most, from the use of computers to atomic physics to spectroscopy and astrophysics. He offered me many opportunities and guided me to take the right decisions, which have led me to this point. Anil has been the best adviser that there is. He is, in addition to a very good scientist, one of the most patient, caring, and generous persons that I have ever met. He has been also a friend since the first day IV that I arrived to Columbus and he received me in his home and helped me to start a new life so different and far away from my country. In addition to good teachers, good collaborators and team mates were also part of my experience. Sultana N. Nahar and Hongling Zhang encouraged me all along this work and sheared with me a lot of their expertise and knowledge. They also provided a very supportive and friendly environment to work. I feel also lucky for having Don Osterbrock as a collaborator. Don is, without a doubt, one of the greatest astronomers of this time as well as one of the nicest persons in the field. Don’s com m ents and suggestions have been fundamental throughout the present work and his words of wisdom and encouragement were most inspiring. I am grateful to the faculty and staflf members of the Department of .Astronomy for their support, instruction, and guidance. I thank in particular Rick Pogge and Darren DePoy for their many useful discussions and for teaching me almost everything that I know about observational astronomy. I thank the entire crew of the Ohio Supercomputer Center for their help and instruction in the use of supercomputers and massive parallel processors. Apart from studies and work, my time at the department was filled with pleasant moments in the company of my graduate students fellows. I especially appreciate all the help that my compadre Ani Thakar and his family gave me since my arrival to Columbus. I thank my lunch and soccer partners Cheongho Han and Mark Everett for their sincere friendship and the good times that we had together, including the arrest on the Sunset Crater in Arizona. I thank Bob Blum, Glen Tiede, Mark Houdashelt, Anita Krishnamurthi, Mike Owen, and Solange Ramirez, to mention just a few, for occasional “get-aways”, tea time senseless discussions, soccer, tennis, and softball games, etc. I also thank Joao Santos, Ignaz Wanders, Kevin Uchida, and the rest of the department’s postdoctoral fellows for many good moments. Finally, I thank with all my heart my son Manuel Antonio (Mantonio) and my wife Maggie for all their sacrifices and courage in following me here in chase of my dreams. Mantonio and Maggie have given me the moral support that took me throughout the most difficult moments. Maggie has been also my counselor and confident and she has helped me a lot with her talents and wisdom. Mantonio and Maggie are the most important people in my life and the source of my happiness. I hope being able to make everything that they have given for me worthy. Support for this work was provided in part by an educative loan of the Fundacion Gran Marizcal de .A.yacucho (Venezuela), the Department of .\stronomy of the Ohio State University, and the U.S. National Science Foundation (PHY-9421898) grant for the Iron Project. The computations were carried out in part on the Cray Y-MP, Cray T3D, and IBM SP2 at the the Ohio Supercomputer Center (OSC). VI VITA May 20, 1968 ..........................................................Bogota - Colombia 1990 ...........................................................................B.Sc. Physics, Universidad Simon Bolivar, Venezuela 1990-1991 ................................................................Research Associate, IBM Scientific Center, Venezuela 1991-present ............................................................Physics Specialist, Centro Nacional para el Mejoramiento de la Ensenanza de la Ciencia (CENAMEC), Ministery of Education of Venezuela 1993-present ............................................................Graduate Teaching .Associate, T he Ohio State University Publications Research Publications Nahar, S.N., Bautista, M.A., & Pradhan, A.K., "Total electron-ion recombination of FeF Astrophysical 7., 479, 497 (1997). Bautista, M. A., “Atomic data from the Iron Project XIX. Photoionization Cross Sections and Oscillator Strengths for Fe I” Astron. and Astrophys. SuppL, 122. 167 (1997). Bautista, M. A., “Atomic data from the Iron Project XVI. Photoionization Cross Sections and Oscillator Strengths for Fe V” Astron. and Astrophys. SuppL, 119, 115 (1996). Bautista. M. A., Peng, J.,& Pradhan, A. K., “Excitation of [Nill] and [Fell] lines in gaseous nebulae” Astrophysical J., 460, 372 (1996). Bautista, M. A. &: Pradhan, .A.. K., “Atomic data from the Iron Project XIV. Electron Excitation Rates and Emissivity Ratios for Forbidden Transitions in Nill and Fell” Astron. and Astrophys. SuppL, 115, 551 (1996). vii Bautista, M. A.. Nahar, S. N., Peng, J., Pradhan, A. K., & Zhang, H. L.. “The Iron Project: Atomic data for Fel - FeVI” Astrophysics in the Extreme Ultraviolet, eds. S. Bowyer and R.F. Malina (Kluwer Academic Publishers), 577 (1996). Bautista, M. A., Pogge, R.