{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/85196"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/85196","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Multiwavelength Study of Photodissociation Regions and a Near -Infrared Imager","abstract":"In this thesis, observations of photodissociation regions (PDRs) in the millimeter, far-infrared, and near-infrared wavelength regimes are interpreted in the context of PDR theory. Three modifications to the standard Tielens & Hollenbach PDR model are considered. The first modification adds nitrogen chemistry to the TH model (Wolfire & Tielens). The second modification extends the TH model to lower-density and lower-excitation conditions (Hollenbach, Takahashi & Tielens). The third accounts for the effects of the color temperature of the illuminating field (Spaans, Tielens, van Dishoeck & Bakes). Chapter 1 is the introduction and presents the motivation for this work. In Chapter 2, high-resolution millimeter-wavelength maps of the high-density PDR in the Orion Bar were used to evaluate the PDR nitrogen chemistry model calculated by Tielens & Wolfire. The morphology of the molecular gas is demonstrated. We also found that the production of HCN and HCO+ occurs mainly in dense clumps near the PDR surface. Chapter 3 focuses on the energetics of lower-excitation PDRs. We describe a far-infrared analysis of the PDRs in several reflection nebulae. We found that the observed line intensities and predicted gas densities fall within the range of the low-density model of Hollenbach, Takahashi & Tielens. We also found that varying the stellar type of the illuminating star has little effect on the heating efficiency of the PDR, which agrees with the color temperature model of Spaans, Tielens, van Dishoeck & Bakes. Chapter 4 describes the construction and operation of the Near Infrared Imager (NIRIM), which was commissioned at the Mt. Laguna 1-meter telescope in August 1995. NIRIM was used for high-resolution wide-field imaging of the PDR in the reflection nebula NGC 2023. We found that the fluorescent molecular hydrogen in NGC 2023 has a filamentary structure, whereas recombination emission from neutral atomic carbon is more diffuse.","abstract_html":"In this thesis, observations of photodissociation regions (PDRs) in the millimeter, far-infrared, and near-infrared wavelength regimes are interpreted in the context of PDR theory. Three modifications to the standard Tielens & Hollenbach PDR model are considered. The first modification adds nitrogen chemistry to the TH model (Wolfire & Tielens). The second modification extends the TH model to lower-density and lower-excitation conditions (Hollenbach, Takahashi & Tielens). The third accounts for the effects of the color temperature of the illuminating field (Spaans, Tielens, van Dishoeck & Bakes). Chapter 1 is the introduction and presents the motivation for this work. In Chapter 2, high-resolution millimeter-wavelength maps of the high-density PDR in the Orion Bar were used to evaluate the PDR nitrogen chemistry model calculated by Tielens & Wolfire. The morphology of the molecular gas is demonstrated. We also found that the production of HCN and HCO+ occurs mainly in dense clumps near the PDR surface. Chapter 3 focuses on the energetics of lower-excitation PDRs. We describe a far-infrared analysis of the PDRs in several reflection nebulae. We found that the observed line intensities and predicted gas densities fall within the range of the low-density model of Hollenbach, Takahashi & Tielens. We also found that varying the stellar type of the illuminating star has little effect on the heating efficiency of the PDR, which agrees with the color temperature model of Spaans, Tielens, van Dishoeck & Bakes. Chapter 4 describes the construction and operation of the Near Infrared Imager (NIRIM), which was commissioned at the Mt. Laguna 1-meter telescope in August 1995. NIRIM was used for high-resolution wide-field imaging of the PDR in the reflection nebula NGC 2023. We found that the fluorescent molecular hydrogen in NGC 2023 has a filamentary structure, whereas recombination emission from neutral atomic carbon is more diffuse.","abstract_has_math":false,"creators":["Young Owl, Rolaine Chandler"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Astronomy","degree_department":null,"school":null,"contributors":["Margaret M. Meixner"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-09-25T22:35:42Z","date_published":"2015-09-25T22:35:42Z","updated_at":"2026-07-22T22:26:24Z","subjects":["Physics, Astronomy and Astrophysics"],"languages":["eng"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["(MiAaPQ)AAI9945038"],"render_values":[{"text":"(MiAaPQ)AAI9945038","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/85196","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Margaret M. 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Three modifications to the standard Tielens & Hollenbach PDR model are considered. The first modification adds nitrogen chemistry to the TH model (Wolfire & Tielens). The second modification extends the TH model to lower-density and lower-excitation conditions (Hollenbach, Takahashi & Tielens). The third accounts for the effects of the color temperature of the illuminating field (Spaans, Tielens, van Dishoeck & Bakes). Chapter 1 is the introduction and presents the motivation for this work. In Chapter 2, high-resolution millimeter-wavelength maps of the high-density PDR in the Orion Bar were used to evaluate the PDR nitrogen chemistry model calculated by Tielens & Wolfire. The morphology of the molecular gas is demonstrated. We also found that the production of HCN and HCO+ occurs mainly in dense clumps near the PDR surface. Chapter 3 focuses on the energetics of lower-excitation PDRs. We describe a far-infrared analysis of the PDRs in several reflection nebulae. We found that the observed line intensities and predicted gas densities fall within the range of the low-density model of Hollenbach, Takahashi & Tielens. We also found that varying the stellar type of the illuminating star has little effect on the heating efficiency of the PDR, which agrees with the color temperature model of Spaans, Tielens, van Dishoeck & Bakes. Chapter 4 describes the construction and operation of the Near Infrared Imager (NIRIM), which was commissioned at the Mt. Laguna 1-meter telescope in August 1995. NIRIM was used for high-resolution wide-field imaging of the PDR in the reflection nebula NGC 2023. We found that the fluorescent molecular hydrogen in NGC 2023 has a filamentary structure, whereas recombination emission from neutral atomic carbon is more diffuse.","Made available in DSpace on 2015-09-25T22:35:42Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 9945038.pdf: 5639042 bytes, checksum: b48c1f916b317a5993c73022562efc0b (MD5) Previous issue date: 1999","Embargo set by: Seth Robbins for item 86477 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","115 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1999."]},{"key":"dc:title","label":"Title","values":["Multiwavelength Study of Photodissociation Regions and a Near -Infrared Imager"]}]}],"canonical_facts":{"dc:contributor":["Margaret M. Meixner"],"dc:creator":["Young Owl, Rolaine Chandler"],"dc:date":["2015-09-25T22:35:42Z","10000-01-01","1999"],"dc:description":["In this thesis, observations of photodissociation regions (PDRs) in the millimeter, far-infrared, and near-infrared wavelength regimes are interpreted in the context of PDR theory. Three modifications to the standard Tielens & Hollenbach PDR model are considered. The first modification adds nitrogen chemistry to the TH model (Wolfire & Tielens). The second modification extends the TH model to lower-density and lower-excitation conditions (Hollenbach, Takahashi & Tielens). The third accounts for the effects of the color temperature of the illuminating field (Spaans, Tielens, van Dishoeck & Bakes). Chapter 1 is the introduction and presents the motivation for this work. In Chapter 2, high-resolution millimeter-wavelength maps of the high-density PDR in the Orion Bar were used to evaluate the PDR nitrogen chemistry model calculated by Tielens & Wolfire. The morphology of the molecular gas is demonstrated. We also found that the production of HCN and HCO+ occurs mainly in dense clumps near the PDR surface. Chapter 3 focuses on the energetics of lower-excitation PDRs. We describe a far-infrared analysis of the PDRs in several reflection nebulae. We found that the observed line intensities and predicted gas densities fall within the range of the low-density model of Hollenbach, Takahashi & Tielens. We also found that varying the stellar type of the illuminating star has little effect on the heating efficiency of the PDR, which agrees with the color temperature model of Spaans, Tielens, van Dishoeck & Bakes. Chapter 4 describes the construction and operation of the Near Infrared Imager (NIRIM), which was commissioned at the Mt. Laguna 1-meter telescope in August 1995. NIRIM was used for high-resolution wide-field imaging of the PDR in the reflection nebula NGC 2023. We found that the fluorescent molecular hydrogen in NGC 2023 has a filamentary structure, whereas recombination emission from neutral atomic carbon is more diffuse.","Made available in DSpace on 2015-09-25T22:35:42Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 9945038.pdf: 5639042 bytes, checksum: b48c1f916b317a5993c73022562efc0b (MD5) Previous issue date: 1999","Embargo set by: Seth Robbins for item 86477 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs","U of I Only","115 p.","Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1999."],"dc:identifier":["http://hdl.handle.net/2142/85196","(MiAaPQ)AAI9945038"],"dc:language":["eng"],"dc:subject":["Physics, Astronomy and Astrophysics"],"dc:title":["Multiwavelength Study of Photodissociation Regions and a Near -Infrared Imager"],"dc:type":["text"],"thesis:degree_discipline":["Astronomy"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:26:24Z"}