Title page for ETD etd-1031103-154611


Type of Document Dissertation
Author Valencic, Lynne Angela
URN etd-1031103-154611
Title The Extinction Properties of Reddened Galactic OB Sightlines
Degree Doctor of Philosophy (Ph.D.)
Department Physics & Astronomy
Advisory Committee
Advisor Name Title
Geoffrey Clayton Committee Chair
A.R.P. Rau Committee Member
Arlo Landolt Committee Member
Joel Tohline Committee Member
John Wefel Committee Member
Samuel Bentley Committee Member
Keywords
  • interstellar dust
  • interstellar medium
  • interstellar extinction
Date of Defense 2003-09-02
Availability unrestricted
Abstract
A solid understanding of dust grains and their extinction properties is needed to better remove the effects of extinction from data and to comprehend the nature of the processes which modify grains. This requires a large sample of Galactic sightlines, extending far beyond the solar neighborhood, sampling not only a large volume of space but also a wide variety of environments. To fulfill this requirement, a database of sightlines toward 426 young, reddened stars was constructed using extinction curves based on IUE spectra. The curves were fit and the Fitzpatrick-Massa (FM) parameters were found. FM parameters allow for a quantitative analysis of curve characteristics. IR photometry was also

obtained for these sightlines, and thus R(V) (=A(V)/E(B-V)) was found. Links between the environment and various grain populations responsible for different components of

the extinction curve were sought, as were relationships between different FM parameters, especially those which describe the 2175 Angstrom absorption feature (the "bump").

A search for sightlines which cannot be described by the R(V)-dependent extinction law of Cardelli, Clayton, & Mathis (1989; hereafter CCM) was also undertaken. The main results are: (1.) The CCM extinction relation is accurate for the vast majority of Galactic sightlines. Thus, processes which lead to a CCM-like extinction curve dominate the ISM and the grain populations responsible for the extinction are modified efficiently and systematically. (2.) The central wavelength of the bump does not shift, and the bump width is environment-dependent, being narrow along diffuse sightlines and broadening with increasing density. These provide constraints on grain mantle materials. (3.) The Galaxy can support environments that lead to Magellanic Cloud-like extinction; this emphasizes the importance of local environment in determining extinction properties. (4.) Reddened Galactic sightlines which do not adhere to the standard

extinction relation tend to be dense and molecule-rich.

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