Multiwavelength study of photodissociation regions and a near-infrared image

Young Owl, Rolaine Chandler

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https://hdl.handle.net/2142/79030 Copy

Description

Title

Multiwavelength study of photodissociation regions and a near-infrared image

Author(s)

Young Owl, Rolaine Chandler

Issue Date

1999-03-31

Director of Research (if dissertation) or Advisor (if thesis)

Meixner, Margaret

Department of Study

Astronomy

Discipline

Astronomy

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D. (doctoral)

Degree Level

Dissertation

Keyword(s)

• Photodissociation regions
• Interstellar medium
• Photon-dominated regions
• Nitrogen Chemistry Model
• Far-infrared spectra

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 involves adding 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 an introduction to this work and presents the motivation for the multiwavelength approach. 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. Besides demonstrating the morphology of the molecular gas in the Orion Bar, we 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-density PDRs. We describe the analysis of far-infrared continuum and fine-structure line emission from the PDRs in several reflection nebulae. We found that the observed. line intensities and predicted densities fall within the regime defined by the low-density model of Hollenbach, Takahashi & Tielens. We also found that varying the stellar type of the illuminating source has little effect on the heating efficiency of the PDR gas, which agrees with the color temperature model of Spaans, Tielens, van Dishoeck & Bakes. Chapter 4 describes the construction and operation of the Near-Infrared lmager (NIRIM), which was commissioned at the Mt. Laguna 1-meter telescope in August 1995. Also described is the use of the NIRIM to obtain high-resolution wide-field images 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 appears much more diffuse.

Type of Resource

text

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