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We use Spitzer Space Telescop and Heinrich Hertz Telescope(HHT) observations to study the earliest stages of low--mass starformation. Using spatially resolved absorption features, termedshadows, we study the cold cloud cores where stars form.We study Barnard 335, a prototypical isolated Bok globule with anembedded Class 0 protostar. We discover an 8 micron shadow in theinner regions of the core; using this feature we measure the densecore structure and mass. Using HHT observations we detect a rotatingstructure, a flattened molecular core, with a diameter~ 10,000 AU. The flattened molecular core is likely to be thesame structure as that generating the 8 micron shadow, and isexpected from theoretical simulations. This structure has not beenrobustly detected in previous observations although there have beensome prior indications of its presence.We study dense starless core structure through longer wavelengthobservations of shadows; we present Spitzer observations of 8 micron,24 micron, and 70 micron\ shadows of 14 cores in total. Combined withHHT observations of 12CO 2--1 and 13CO 2--1, we derive core sizes,masses, study core structure, and investigate the collapse status ofeach core. Our study of starless core CB190 reveals that the core islikely to be stable against collapse if magnetic pressure is presentat a reasonable level in the core. Our study of the 70 micron shadowassociated with the starless core L429 reveals that this object isvery likely to be collapsing. Finally, we study a sample of 12starless cores selected to have prominent 24 micron shadows. We findthat about 2/3 of these sources are likely to be collapsing.Additionally, we find indications that 1/2 of the cores revealed to becollapse candidates show indications of having 70 micron shadows. Weconclude that all cores dense enough to produce 70 micron shadows arecollapse candidates, and that the presence of a shadow at 24 micronis an indicator that the core is likely (60% probability)to be collapsing.

Herbig Ae/Be (HAeBe) stars are the pre-main sequence progenitors of main sequence A and B stars, and are characterized observationally by strong emission in spectral lines and significant infra-red excess that results from their presence in dust-obscured regions. These stars are usually surrounded by a complex environment composed of gas and dust and often a significant stellar wind and a circumstellar disc. This complex circumstellar environment can have a significant affect on their spectral energy distributions, leading to large systematic uncertainties in determinations of their effective temperatures from photometric methods. In an attempt to improve temperature determinations for HAeBe stars, we have conducted an experiment to evaluate the potential of high-resolution spectra to constrain their atmospheric parameters. To this end, high-resolution (R~68 000) and low-resolution (R~1500) spectra obtained using the ESPaDOnS spectropolarimeter (at the Canada-France-Hawaii telescope) and the FORS1 spectropolarimeter (at the Very Large Telescope) have been used with an automatic spectrum fitting procedure. This procedure compares spectroscopic data to a grid of synthetic LTE, solar abundance spectra, spanning a range in effective temperature, surface gravity, and micro-turbulence. This analysis was applied to the spectra of a sample of twelve previously well-studied HAeBe stars. Our temperatures were found to be consistent with previously published values, while providing much lower uncertainties - in some cases about 5 times smaller. Numerous methods were investigated to obtain these quantitative uncertainties (chi-squared statistics, Bayesian analysis, Monte Carlo bootstrap method, individual temperature sensitive line region analysis). We conclude that our method can be used to efficiently and effectively obtain temperatures of HAeBe stars in addition to providing us with a characterization of the degree of departure of the spectrum from solar abundance, LTE photospheric models. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-02-13 10:23:04.9

The thesis goes on to extend the work of Bretherton (2003) and Moore et al. (2007) on the W3 Giant Molecular Cloud, by performing NH3 follow up of a sample of the cores discovered in the 850um SCUBA map and observing the whole cloud in 13CO(J=1-0) and C18O(J=1-0). - The NH3(1,1) and NH3(2,2) observations of the SCUBA cores used the fact that NH3 only traces the densest regions of the cloud, and hence can be used to find the temperature and kinematics of the cores themselves. This was used to test if the individual cores were virially bound, and from this find if cores in the more densely star-forming region of the cloud (High-Density Layer, HDL) were more likely to be bound than those in the Low-Density Layer (LDL). There are a mixture of virially bound and unbound cores in both the HDL and the LDL but no statistical difference in ratio of these between the two regions. This has an important bearing on models of environmentally-dependent star-formation, which divide into two categories; those, such as Collect and Collapse (Dale et al., 2007), which state that external pressures create dense structure, and those such as Radiatively- Driven Instability (RD I) (Bertoldi, 1989), which state that those external pressures cause dense structure to collapse. The evidence from this thesis favours models in which dense structure is created according to the Collect and Collapse scenario.

A sample of K stars has been taken from several objective-prism plates. This sample will be studied photometrically to answer two basic questions. First, is it feasible to subclassify these stars as K1, K2, K3, ... etc., which reflect temperature differences? This has been done by determining color indices of the stars in the sample and taking an average color index for stars in each subclass. Standard deviations were used to ascertain if differences between the means are statistically significant. Second, are there any red giant stars in our sample? If so, is giant contamination related to temperature classification? The B-V and V-I color indices for the program stars were compared to those of known dwarf and giant stars in a two-color diagram. The results of this study will permit more informed decisions about the value of spectral classes for K stars. Also distances (photometric parallaxes) were computed from the photometric data obtained. / Department of Physics and Astronomy

In this thesis we investigate the effect of shear on radiating stars undergoing gravitational collapse. The interior spacetime is described by the most general spherically symmetric line element in the absence of rotation. The energy momentum tensor for the stellar interior is taken to be an anisotropic fluid with heat flux. The thermodynamics of a relativistic fluid is reviewed for the Eckart and causal theories. Since the star is radiating energy to the exterior in the form of a radial heat flux, the atmosphere is described by Vaidya's outgoing solution. We provide the matching conditions required for the continuity of the momentum flux across the boundary, which determines the temporal evolution junction conditions for the metric functions. We provide a general method to obtain shearing solutions of the Einstein field equations describing a radiating, collapsing sphere. A particular exact solution satisfying the boundary condition and field equations is found. The validity of this specific model is investigated by employing a causal heat transport equation which yields the temperature profile within the stellar core. The energy conditions are studied and yield interesting features of this particular model which are absent in the shear-free case. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2011.

This Thesis is concerned with the physical nature of the outer atmospheres of the 'hybrid' bright giants. These stars show C IV emission and evidence of cool, fast winds - unlike giants of similar effective temperature, which possess only cool chromospheres. The K3 II star ι Aur is studied in detail. Chapter 1 discusses the importance of these stars in the context of the HR diagram. Chapter 2 examines the evolutionary status of the 'hybrid' bright giants and sets out the physical parameters which are adopted in the atmospheric modelling. In Chapter 3, the high and low resolution IUE data extracted for ι Aur are discussed. In Chapter 4, the emission line fluxes and profiles are analysed and an emission measure distribution is calculated. Simple hydrostatic models of the transition region and corona are constructed. Chapter 5 describes the methodology employed to construct model chromospheres using non-LTE radiative transfer. In Chapter 6, computations of the chromospheric structure of a 'hybrid' star are presented for the first time. Calculations made for the first time show that the excitation of the Fe I y⁵G^o₃ level by the Mg II k line can produce the observed emission in other transitions from the J = 3 level. In Chapter 7, non-isothermal Alfvén wave driven wind models are calculated. It is shown that ι Aur proves to be a severe test of these models and that the transition region and the cool wind are physically separate. A brief resumé, and possible future research topics are given Chapter 8.