AAS 204th Meeting, June 2004
Session 61 Structures in the Interstellar Medium
Poster, Wednesday, June 2, 2004, 10:00am-7:00pm, Ballroom

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[61.14] The Contribution of H II Regions to PDR Line Intensity Diagnostics

N. P. Abel, G. J. Ferland (University of Kentucky)

Photodissociation Regions (PDR’s), regions surrounding stars where hydrogen makes the transition from ionized to atomic and then finally to molecular, comprise a majority of all the mass in the galaxy. This fact makes the study of PDR’s paramount to our understanding of the ISM and star forming regions. The classical approach to the study of PDR’s is to observe line intensities that are thought to originate in the PDR, many of which are in the infrared. These observations are combined with theoretical calculations that attempt to reproduce the observations by varying the hydrogen density and intensity of the UV radiation field. Calculations of PDR’s almost always ignore radiation >13.6eV, since a PDR is operationally defined to begin where the H II region ends. Some line intensities that are observed in the study of PDR’s, however, can also have a significant contribution emerging from the adjacent H II region, which leads to an underestimate of the intensities of these lines. A separate calculation of the H II region is then desired, but calculating the properties of these two regions separately ignores the fact that they are dynamically linked.

We present here another approach to this problem, and that is to calculate the intensity of PDR lines by modeling the PDR and H II region in a single self-consistent calculation. By making the assumption of constant gas pressure between the PDR and H II region, we will be able to predict the H II region contribution to the intensity of commonly used PDR diagnostics. This calculation will be performed for a wide range of densities and radiation field strengths. Ultimately our calculations can be used to determine the “correction factor” that standard PDR calculations need to use to account for neglecting the H II region over a wide range of parameter space.

The author(s) of this abstract have provided an email address for comments about the abstract: npabel2@uky.edu

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