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Department Library

1998

Maureen Lyn Hintz (Masters Thesis, August 1998, Advisor: Clark Christensen )

Abstract

The hk index had been used as a metallicity indicator for RR Lyrae variable stars. It is now being applied to the shorter period δ Scuti variables. In order to find a method of using the hk index to find [Fe/H] values, standard stars with well-defined spectroscopic abundances along with stellar atmosphere models are used to calibrate the index. A 3-D interpolation calculates [Fe/H], log g and Teff from intrinsic (b-y), c1 and hk values. The results for 11 δ Scuti stars are presented.

1990

Stephen M. Setzer (Honors Thesis, July 1990, Advisor: Clark Christensen )

Abstract

1989

Fabrizio Pinto (PhD Dissertation, August 1989, Advisor: Clark Christensen )

Abstract

The formation of globular clusters was a key cosmological process related to the physical state of the universe shortly after the Big Bang. For this reason, globular clusters can be used as probes to study the environments where galaxies formed, and, in order to better understand the formation of these objects, we approached the problem from two different points of view. The former approach has been that of using young globular clusters in the Large Magellanic Cloud as a laboratory to study the formation of massive star clusters. An analytic model has been derived to describe these objects. An estimate of the star formation efficiency has bene obtained which is in agreement with the observations. Even if these results can be extended to the primeval case only with great causation, this approach has been quite fruitful in helping constrain the values of some otherwise arbitrary parameters. The latter approach has been that of modeling in greater detail some important phases of star formation and dynamical evolution in the Galaxy. In particular, the phase of gas expulsion from a newly formed cluster has been studied analytically in the impulsive approximation. This has yielded interesting new results concerning the roles possibly played by the magnetic field and by the turbulence in protoclouds. We also devised a theoretical model to describe the formation of star clusters based on the hypothesis that the process is triggered by cloud-cloud collisions. This model has helped better clarify what physical parameters may have had an important role in shaping the cluster population.

1988

Mario Ruben Perez (PhD Dissertation, August 1988, Advisor: Clark Christensen )

Abstract

Northern Monoceros is a region rich in emission nebulosity, opaque clouds, dark globules, and young open clusters and could be considered a good environment and laboratory to detect and study young stellar objects. From this region we have studied the young open clusters NGC 2244 (C0629 + 049) and NC 2264 (C0638+099), known to be sites of very active star formation and which are among the youngest in the Galaxy (tage ͌ 4-6x106 yr). We have secured stellar data in the cluster fields with different photometric systems (Stromgren, Walraven, Johnson, Cousins, and near-infrared) and the spectroscopic system, IDS, in three observing seasons (1985, 86, and 87). These new data allowed us to assess membership, spectral types and to estimate extinctions, distances, abundances, variability, cluster ages and masses, and several other important astrophysical parameters. The picture that emerges from the analysis is that the cluster NGC 2244 seems to be formed only by massive stars (OB-type), whereas, two well differentiated groups of massive stars (some Herbig Ae/Be and main sequence stars with moderate or small infrared excesses) and low-mass stars (emission lines and T Tauri stars) appear to form NGC 2264. It was also found that the clusters lie in different arms of the Galaxy and they have been originated by dissimilar mechanisms in different epochs.

David Wayne Thomas (Masters Thesis, December 1988, Advisor: Clark Christensen )

Abstract

Three new 4.25 x 4.25 star fields-MF17, M18, and MF19- have been selected by B.E. Westerlund top supplement the Warner and Swasey Luminosity Function fields F 2 through 15. We have partially covered the field MF17 with VRI photometry, and by combining our data with data obtained from The (unpublished), have calculated the infrared absorption and the space density distribution of M giants for the two fields MF17 and MF18. The absorption in MF17 increases to 1.4 magnitudes at 0.7 kpc, then slowly increases to 1.7 magnitudes at 3.0 kpc. The absorption in MF18 increases to 0.8 magnitudes at 0.4 kpc, then slowly increases to 1.4 magnitudes at 3 kpc. The Malmquist-Schalen method is used to calculate the space densities of M2-M4 and M5-M6 giants in MF17 and M0-M1, M2-M4, and M5-Mg giants in MF18. There is some indication of structure in the direction of MF17 because if peaks in space densities of both groups of giants at distances of 0.4 to 0.8 kpc.