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 AbstractA 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.
Filename Size Approximate Download Time (Hours:Minutes:Seconds)
28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access Valencic_dis.pdf 1.49 Mb 00:06:55 00:03:33 00:03:06 00:01:33 00:00:07