Part I: How Did We Get Here? College Students' Preinstructional Ideas on the Topic of Planet Formation, and the Development of the Planet Formation Concept Inventory; Part II: Evidence for Magnetically Driven Protoplanetary Disk Winds
AdvisorImpey, Christopher D.
Buxner, Sanlyn R.
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractThis dissertation includes two independent research projects, one in astronomy education research and the other in planetary science/astrophysics research. In the first research effort, we investigate college students' conceptual and reasoning difficulties on the topic of planet formation pre-instruction. Through an analysis of over 1,000 responses to open-ended questions, we find that these students lack an understanding of fundamental topics in astronomy (e.g. gravity, basic definitions of a planet or solar system, mass versus density). The results from this analysis laid the foundation for the development of the Planet Formation Concept Inventory (PFCI), an educational research tool that can be used like a diagnostic test to assess students' pre- and post-instructional knowledge. Using iterative design and statistical processes consistent with Classical Test Theory (CTT), we are able to confirm that the PFCI is a reliable and valid instrument that can be utilized to measure college students' learning on the topic of planet formation over time. In the second research effort, we analyze forbidden lines (predominantly the [O I] line at 6300 Å) from a sample of 33 T-Tauri stars with disks spanning a range of evolutionary stages. After removing a high-velocity component (HVC) associated with microjets, we focus our efforts on studying the low-velocity component (LVC) to better elucidate its origin. The LVC can be attributed to slow disk winds that are either thermally or magnetically driven. We find that the LVC itself can be resolved into two distinct components: a broad component (FWHM > 40 km/s) and a narrow component (FWHM < 40 km/s). Additionally, we find that the FWHM of both components correlates with the disk inclination, consistent with Keplerian broadening from radii of 0.05 to 0.5 AU for the BC and 0.5 to 5 AU for the NC. Since the BC emission arises inward of 0.5 AU where the gravity of the star/disk system is strong, we eliminate the possibility that the BC traces a thermally-driven wind, and instead suggest that it traces the base of a magnetohydrodynamic (MHD) wind. For the NC, half of the features we observe have centroid velocities consistent with the stellar velocity, and the other half have blueshifts between -2 and -5 km/s. For this component of the LVC, the origin remains more elusive, and we cannot exclude the possibility that the NC arises in a photoevaporative wind.
Degree ProgramGraduate College