How are stars formed? This is one of the most fundamental questions in astronomy. It is therefore ironic that to date, no object has been unambiguously identified as a true protostar; an object which derives the bulk of its luminosity from accretion. While this may be ironic, it is not surprising. Stars are believed to form as a result of the gravitational collapse of a portion of a molecular cloud. Theory predicts that the cloud core in which the star is formed will be cold, dense and possess hundreds of magnitudes of extinction, rendering it opaque at visible and near-infrared wavelengths. Continuum observations at far-infrared, submillimeter, and millimeter wavelengths can be used to identify candidate protostars, but spectroscopic observations are needed to detect infall. The difficulties arise when there are systematic velocity fields present in the cloud core which are not the result of infall, such as would be produced by either a molecular outflow or rotation. In this dissertation we use both observations and theoretical models to sort through these problems and develop a strategy which could be used to identify and study protostars.

We have conducted a CS survey of the 10 outflows and 30 IRAS sources identified by Margulis (1987) in the Mon OB1 dark cloud to study the relationship between outflows, YSOs, and dense cores in this cloud. We have found that the CS J = 2 → 1 transition traces a large portion of the dense, low-velocity components of the outflows in Mon OB1. We find the mass of this component to be nearly an order of magnitude greater than previous estimates of the outflow "core" component. We detected little CS gas around the quiescent sources in this cloud. CS 2 → 1 temperatures and integrated intensities are 2 to 7 and 2 to 14 times higher, respectively, in the vicinities of IRAS sources associated with outflow activity than about the quiescent sources. This implies CS abundances, temperatures and/or densities are enhanced in regions where outflows impact the ambient cloud. The CS 2 → 1 emission is concentrated in two regions encompassing 6 of the 10 previously identified outflows in this cloud. Four of these six outflows are identifiable in CS. Two, previously identified as monopolar outflows, exhibit bipolar structure in CS. We have detected the CS J = 5 → 4 transition in the vicinity of 4 of the 10 outflows in this cloud, and around none of the quiescent IRAS sources. The CS 5 → 4 emission is extended around two of the outflow sources and has been mapped in these regions. CS J = 7 → 6 emission has been mapped about the brightest outflow source in this cloud. The morphology of the 7 → 6 region suggests it may have been part of the collimating structure for the outflow associated with this sources. The velocity structure and binding energies of the 5 → 4 and 7 → 6 cores suggest the outflows are disrupting these cores. The addition of the low-velocity CS outflow component to previous estimates of outflow energetics implies multiple generations of outflows need not be required to support this cloud against collapse. Our results neither support nor rule out the existence of fossil outflows in this cloud. A full-cloud, unbiased survey is required to search for such outflows.

We have studied the properties of molecular clouds and the stellar population associated with 10 H II regions. We used the James Clerk Maxwell Telescope (JCMT) to make 12CO(2-1) maps in order to study the structure of the cloud and to identify the dense clumps within the cloud. In half of our sources we found that molecular gas appears to have been pushed and compressed into the shells around the expanding ionized gas and fragmented into clumps. Most of these clumps have higher temperature and density compared to the other clumps within the mapped regions. We made pointed observations in 13CO(2-1) and CS(5-4) at the peak of 12CO(2-1) within each clump to measure and calculate the physical properties of the clumps such as line width, excitation temperature, density and mass. Two gas components were selected in the cloud associated with S175 to investigate the influence of the H II region on the molecular gas: S175A is adjacent to the ionization fronts and probably affected by the expanding H II region while S175B is too distant to be affected. Contrary to our expectation S175B was a turbulent region with broadened line profiles. We made a sub-map in 12CO(3-2) using HARP at the JCMT to search for the source of turbulence and identified a proto-stellar outflow in S175B. We examined the relationship between gas parameters derived for the clumps within the entire sample. The identified clumps were found to be divided into two categories: “type I” sources in which we can find a relationship between size and line width and “type II” sources where there is no relation. We found that the power law indices for type I sources are generally larger than the previous studies. Larger line widths and consequently larger indices seems to be an initial environmental characteristic of massive star forming regions We found that mass and column density increase with line width for both type I and type II sources. We did not find any relation between the size and column density. The influence of the H II region on temperature and line widths was examined and we found that the temperature decreases with distance from the ionized fronts but no change was found for the line width. Although most of the clumps within the compressed shells around the H II region have generally larger line widths, from this test we may conclude that the internal dynamics of the cloud beyond the compressed shells is not much influenced by the expanding H II region. Finally, our near IR study of the stellar populations using 2MASS data, shows that in half of the regions the exciting star belongs to a cluster. We also found that star formation is consistent with triggering by the expansion of the ionized gas in some of sources in our sample. At least two young embedded clusters have been identified at the same position as the dense clumps within fragmented shells around H II regions. These clumps have high temperature and density and large line widths. We identify some other hot and dense clumps very similar in molecular gas properties as candidates of cluster or massive star formation. Most of the active star forming regions associated with H II regions have a population of massive newborn stars compared to a star forming cloud which is distant from the massive star and the ionized gas. We conclude that more massive stars form in the molecular cloud at the peripheries of H II regions but it is not clear f this is a result of the initial conditions that have formed the massive, exciting star of the H II region or a feedback of the massive star itself and the expanding H II region.

We have studied the properties of molecular clouds and the stellar population associated with 10 H II regions. We used the James Clerk Maxwell Telescope (JCMT) to make 12CO(2-1) maps in order to study the structure of the cloud and to identify the dense clumps within the cloud. In half of our sources we found that molecular gas appears to have been pushed and compressed into the shells around the expanding ionized gas and fragmented into clumps. Most of these clumps have higher temperature and density compared to the other clumps within the mapped regions. We made pointed observations in 13CO(2-1) and CS(5-4) at the peak of 12CO(2-1) within each clump to measure and calculate the physical properties of the clumps such as line width, excitation temperature, density and mass. Two gas components were selected in the cloud associated with S175 to investigate the influence of the H II region on the molecular gas: S175A is adjacent to the ionization fronts and probably affected by the expanding H II region while S175B is too distant to be affected. Contrary to our expectation S175B was a turbulent region with broadened line profiles. We made a sub-map in 12CO(3-2) using HARP at the JCMT to search for the source of turbulence and identified a proto-stellar outflow in S175B. We examined the relationship between gas parameters derived for the clumps within the entire sample. The identified clumps were found to be divided into two categories: “type I” sources in which we can find a relationship between size and line width and “type II” sources where there is no relation. We found that the power law indices for type I sources are generally larger than the previous studies. Larger line widths and consequently larger indices seems to be an initial environmental characteristic of massive star forming regions We found that mass and column density increase with line width for both type I and type II sources. We did not find any relation between the size and column density. The influence of the H II region on temperature and line widths was examined and we found that the temperature decreases with distance from the ionized fronts but no change was found for the line width. Although most of the clumps within the compressed shells around the H II region have generally larger line widths, from this test we may conclude that the internal dynamics of the cloud beyond the compressed shells is not much influenced by the expanding H II region. Finally, our near IR study of the stellar populations using 2MASS data, shows that in half of the regions the exciting star belongs to a cluster. We also found that star formation is consistent with triggering by the expansion of the ionized gas in some of sources in our sample. At least two young embedded clusters have been identified at the same position as the dense clumps within fragmented shells around H II regions. These clumps have high temperature and density and large line widths. We identify some other hot and dense clumps very similar in molecular gas properties as candidates of cluster or massive star formation. Most of the active star forming regions associated with H II regions have a population of massive newborn stars compared to a star forming cloud which is distant from the massive star and the ionized gas. We conclude that more massive stars form in the molecular cloud at the peripheries of H II regions but it is not clear f this is a result of the initial conditions that have formed the massive, exciting star of the H II region or a feedback of the massive star itself and the expanding H II region.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1986. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 62-63).

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, June 1997. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Optical absorption line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A2II -X2E+ (1,0) and (2,0) bands of the red system are reported, and are compared with observations of the blue system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photo -processes still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.

Thesis (M.S.)--University of Toledo, 2009. / Typescript. " As partial fulfillment of the requirements for the Master of Science in Physics." "A thesis entitled"--at head of title. Bibliography: leaves 21-22.