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RESEARCH INTERESTS
TEACHING INTERESTS

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Department of Natural Sciences
University of Michigan-Dearborn
4901 Evergreen Rd.
Dearborn, MI 48128
(313) 593-5277   FAX: (313) 593-4937

e-mail:  dbord@umd.umich.edu
Office:  2210 CW  (313) 593-5483
Lab:  33 SB   (313) 593-3501 

WHAT'S NEW!

In an effort to meet a long-standing need for more and better astronomical instrumentation and a permanent observing site to support our introductory and upper-level astronomy offerings, we are developing plans for a new observatory as part of a nearly $10 million project to enhance science facilities on campus. The proposal, partial funding for which will be sought from the NSF's Course, Curriculum, and Laboratory Instrumentation program, includes a 16-inch Schmidt-Cassegrain telescope, a grating spectrograph with a CCD detector, and a high resolution video camera to permit downloading astronomical images in real time to laboratory and class rooms across the campus via an existing fiber optic backbone. An integral part of the plan includes cooperation with neighboring Henry Ford Community College and provides for regular access to their planetarium facilities for our students in exchange for access to our observatory for theirs. The observatory will be located on the roof of the campus' parking structure, and its design will be patterned after a similar student facility at the University of Nebraska-Lincoln. The location and design of the observatory will permit it to be completely accessible by persons with physical disabilities, one of only a few such installations of its kind in southeastern Michigan. A sketch of the proposed observatory facility is available by clicking here. 

Chuck Cowley and I continue our studies of chemically peculiar (CP) stars (see below), and we are now engaged in a study of broad flux depressions in magnetic CP stars with Dr. Glenn Wahlgren at Lund University in Sweden. Our hope is to explain (at least in part) the features at 4200 A and 5200 A in terms of line absorption by the third spectra of rare-earth elements like neodymium and praeseodymium. For more details, click here. In addition, I am just completing some ab initio calculations of energy levels in Ho II to to permit a re-evaluation of the partition function (as a function of temperature) for this ion. These results will be used to re-determine the abundance of holmium in the Sun in an attempt to reconcile the meteoritic and photospheric abundances for this element. 

RESEARCH INTERESTS:

My current research focusses on determining the abundances of heavy and rare-earth elements (REEs) in the Sun and chemically peculiar (CP) stars. This work has been done primarily in collaboration with Prof. Charles R. Cowley at the University of Michigan-Ann Arbor and our students, but it has also benefitted from the advice and assistance of colleagues at LANL, the University of Wisconsin, the Lund University in Sweden, Moscow State University, Vanderbilt University, the European Southern Observatory, and Case Western Reserve University.

CP stars comprise about 20% of main sequence stars of spectral type A-F in the Galaxy, and are generally characterized by abundance patterns for elements beyond the iron peak which depart significantly (by factors of ~10 to more than 10⁴) from those found in the Sun and other "normal" stars. The best current theory to account for the existence of these stars is one that invokes the process of radiation-pressure driven diffusion to concentrate these elements in the upper atmospheres of these objects where they can be observed in their spectra. Validation of this theory first requires that accurate predictions of the abundance patterns for these stars be made and then that they be compared with abundances derived from observed stellar spectra. Both aspects of this program demand large quantities of highly accurate atomic data (wavelengths, energy levels, transition probabilities, Landé factors, etc.) to permit the model calculations and spectral analyses to be performed reliably.

My efforts contribute to both aspects of this problem. In particular, to establish the abundances of first and second ionized lanthanide REEs (like La, Ce, Nd, Pr, Dy, and Lu) in CP stars by comparing high resolution, high signal-to-noise observations of these objects with synthetic spectra, we must employ atomic line data like that noted above. However, for many of the species of interest, these data are limited in number, poorly known, or lacking entirely. For this reason, we have undertaken ab initio calculations of some of these quantities, notably the gf-values and Landé factors, using a code developed by Dr. Robert Cowan at LANL, to obtain the needed information. Recent work has included computation of transition probabilities for La II, Ce III, Nd III, Pr III, and Lu II, as well as partition functions for most of the 2nd and 3rd spectra of the lanthanide REEs. A goodly share of these data are now part of the database maintained by the University of Vienna (VALD) and available for use by the astronomical community in calculating model stellar atmospheres and performing typical spectral synthesis and radial velocity analyses. The data for Nd III recently appeared in a paper in Astronomy and Astrophysics Supplements, 144, 517 (2000).

We have used these data in the analysis of abundances in several stars, including the Sun for which we were able to finally reconcile the photospheric abundance of lutetium with that determined from meteoritic studies (see Publications). We are have recently completed an investigation of HD101065 ("Przybylski's star"), arguably the most extreme CP star known in the Galaxy. The visual spectrum of this "rapidly oscillating peculiar A-star" (roAp star) is dominated by lines of 2nd and 3rd spectra of the REEs in such a way as to nearly mask the presence of more common elements like Fe, Cr, and Mn. So complex is its spectrum that controversy still surrounds such fundamental stellar parameters as its effective temperature and surface gravity. Based on fits to the Balmer line profiles in high-resolution echelle spectra obtained with the 3-meter New Technology Telescope at the ESO using Kurucz model atmospheres, we have adopted a model with T = 6600 K and log g = 3.5. Using this model and up-to-date atomic parameters, including our own calculations, we have derived abundances for all reliably identified species, including Fe I, Fe II, Pr II, Pr III, and the first three ionization stages of Nd. The results generally confirm the earlier work of Wegner and collaborators in that the iron peak elements appear to be at or slightly below the solar abundance, while the REEs are generally overabundant relative to the Sun by factors of about 10⁴. Additional details of these results may be found in an article in The Monthly Notices of the Royal Astronomical Society, 317, 299 (2000).

TEACHING INTERESTS:

My primary teaching interests lie in the areas of astronomy and astrophysics, and closely related subjects. In the past few years, I have taught Astrophysics (P421), Optics (P405), Quantum Mechanics (P453), and Atomic & Nuclear Physics (P457). In each of these offerings, I have tried to incorporate recent developments based on research in physics education to enhance the teaching and learning environment; among those that have been used regularly with success are group problem-solving activities, concept mapping exercises, one-minute essays focussed on identifying the most important and the "muddiest" concepts, and "demonstration" and "dissection" projects. I also regularly teach the introductory astronomy lab (P131), where I have revised the course to include a roughly 50-50 split between outdoor activities including visual and telescopic observing exercises and indoor microcomputer-based labs modeled after the CLEA exercises. We have recently acquired a 7.5-ft small radio telescope (SRT) that we have mounted on the roof of our science building. I am currently developing exercises for the astronomy lab and for our advanced physics lab (P460) that will utilize this new instrument.

In addition, I have had an abiding interest in improving the quality and maintaining the relevancy of conceptual physics and astronomy courses. It was this commitment that motivated my collaboration with Vern Ostdiek of Benedictine College (Atchison, KS) and led to our writing Inquiry into Physics, the 5th edition of which was just published by Brooks-Cole. This book is designed expressly to be used in a one-semester, introductory course for non-science majors, and it emphasizes conceptual understanding and application of physics principles in everyday life. In addition to long-standing pedagogical features like concept maps, "Physics Potpourris," and learning checks, the latest edition features an expanded set of "Explore-It-Yourself" activities. These elements are carefully placed at the beginning of most sections to encourage readers to investigate in a "hands-on" fashion certain physical phenomena in order to form their own conclusions before reading about their accepted interpretations or explanations. In this way, students have a chance to discover knowledge for themselves and confont their misunderstanding or confirm their assessments. Moreso than in any previous edition of the book, we have worked hard to emphasize the "inquiry" approach to physics that is advertised in its title.