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The research presented in this thesis investigates several aspects of the evolutionary processes of T Tauri stars and their accompanying circumstellar disks. The versatile Monte Carlo radiation transfer technique, with several modifications and extensions, is used throughout to study the structure and constitution of both the circumstellar disk at large and the changeable and dynamic inner disk regions. The photopolarimetric variability of AA Tau in the Taurus star forming region is modelled in a fully 3D manner. I find that a magnetospherically induced warp in the accretion disk at roughly the stellar co-rotation radius occults the star and reproduces both the observed period and duration and the required brightness and polarisation variations. The model SEDs allow estimates of the disk mass, radial extent and large- scale density structure. Using a modified SPH code we find the interaction of a 5.2kG stellar magnetic field inclined at 30° to the rotation axis with the disk, is capable of generating a warp of the size and shape needed to reproduce the observed variations. Modified Monte Carlo models capable of incorporating any number of dust particle grain sizes distributed throughout the disk in vertical and radial distributions, in a fully 3D manner are presented. This versatile tool allows the investigation of evolutionary processes such as dust settling and grain growth predicted to occur in T Tauri sources as they age. A Mie Scattering code was also adapted and incorporated into the models allowing us to determine optical properties for dust grains and distributions of any size. I present model SEDs fitting the latest publicly available IR data for a number of T Tauri sources and reproduce the observational effects of dust grain growth and settling with a high degree of success. The fits are by no means unique and the structural parameters required to produce them are quite uncertain but it is possible to determine useful information on the larger scale structure and bulk constituents of these disks. A fully 3D non-LTE radiative transfer code using CO line emissions as a tracer of the disk dynamics and able to simulate any disk structure or geometry, either analytical or imported from a hydrodynamic simulation, is presented. Signatures attributed to the disk dynamics and spiral density structure derived from hydrodynamic simulations of massive disks are investigated and resolved. Line profiles and contour maps of the velocity of the emitting material are generated and compared with observations.

Many important elements of galaxy structure and star formation are invisible or lessened in brightness in optical images. Newly formed stars which shine incredibly bright have most of their emitted light absorbed by interstellar dust. Old, cool stars that make up interesting galaxy structures like stellar bars are outshone by bright star forming regions. In order to understand these fundamental features of galaxies infrared light is needed.Near-infrared (NIR) light can help observe light obscured or attenuated at other wavelengths. NIR light can indirectly observe light from newly born stars. When the dust grains which attenuated the high-energy light cool, that light is reprocessed into the infrared. Using a combination of high energy and infrared light a star formation rate can be calculated. In Ch. 2 I present 2′′ resolution galaxy-wide dust attenuation and star formation rate measurements for nearby, face-on galaxies NGC 5194 and NGC 6946. These measurements are calculated using two different ionizing states of Hydrogen at 6562.8 A(Hα) and 1.282 μm (Paβ). I find that attenuation drops with radius, with a bright, high attenuation inner region, and I calculate the best-fit empirical coefficients to correct for attenuation by combining Hα with 8, 12, 24, 70, or 100μm.NIR light can also help observe stellar bars, which are outshone by brighter star-forming regions in optical light. NIR light is less affected by nearby star formation. Additionally, any dust attenuation in the stellar bar would be less in the NIR than at optical wavelengths. Chapters 3 and 4 use NIR images to analyze bars. In chapter 3 I trained a convolutional neural network to identify stellar bars in galaxies. In chapter 4 I used LASSO regression, a type of an ordinary least squares regression with a penalizing term, to identify which bar and galaxy variables are the most correlated with centrally enhanced star formation.The half-light radius is the radius within half of the light of the galaxy is contained. For nearby galaxies this measurement has been well studied at optical wavelengths. In Chapter 5 I present my work measuring the half-light radius for nearly ~ 10, 000 galaxies at wavelengths that go from the mid-infrared to the far ultraviolet. I find that the mass-metallicity relation, and therefore the change of dust with mass, fundamentally affects how the half-light radius changes with wavelength.

Silicates analogous to cosmic dust were synthesized, modified, and analyzed utilizing ion-beam techniques with Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Silicate dust is a common constituent in interstellar space, with an estimated 50% of dust produced in the stellar winds of M class Asymptotic Giant Branch (AGB) stars. Silicate dust acts as a surface upon which other chemicals may form (water ice for example), increasing significance in the cosmochemistry field, as well as laboratory astrophysics. Silicate formation in the stellar winds of AGB stars was simulated in the laboratory environment. Three sequential ion implantations of Fe-, MgH2-, and O- with thermal annealing were used to synthesize a mixture appropriate to silicate dust in the surface layers of a p-type Si substrate. Post implantation He+ irradiation was shown to preferentially induce crystalline formation in the analogue prior to thermal annealing. This effect is believed to originate in the ion-electron interaction in the Si substrate. The effects of ionization and ion energy loss due to electronic stopping forces is believed to precipitate nucleation in the amorphous media. For annealing temperatures of 1273 K, predominant quartz formation was found in the substrate, whereas lower annealing temperatures of 1000 K formed enstatite without post-implantation He+ irradiation, and olivine with He+ irradiation. Post annealed crystalline phase modification was investigated via x-ray diffraction and elemental compositions were investigated utilizing RBS. Finally, the interdiffusion of Fe and Mg at temperatures of 900-1100 K was investigated with RBS, and activation energies for interdiffusion were extracted for the transition from amorphous to crystalline phase in the silicate analogues. Fe had an interdiffusion energy of 1.8 eV and Mg 1.5eV. The produced analogues have similar properties to those inferred from infrared spectroscopy of the stellar winds of M-class AGB stars with an oxygen-rich outflow. This work established a method of silicate production using ion beam modifications, explored He+ irradiation effects in the annealed structures, and derived interdiffusion activation energies for Fe and Mg in the amorphous structure. Grain sizes were

Glassy spherules from three Transantarctic Mountain sediments were geochemically analyzed and at two of these sites (Mt. Raymond (RY) in the Grosvenor Mountains and Meteorite Moraine (MM) in Walcott Neve, in the Beardmore Glacier region of Antarctica) Australasian microtektites were discovered. The microtektites were identified based on their pale yellow appearance and confirmed geochemically; they have high concentrations of silica (SiO2 = 60.0 +/- 6.9 wt%) and alumina (Al2O3 = 23.0 +/- 4.0 wt%) and all have K2O/Na2O > 1, characteristic of microtektites and distinct from spherules of meteoritic origin. Additionally, the trace element pattern matches the upper continental crust with enrichments in refractory elements and depletions in volatile elements, most likely as a result of melting and vaporization of the source material. The presence of Australasian microtektites in RY sediment confirms the recent Australasian strewnfield extension to Antarctica (Folco et al., 2008) and the presence of highly-depleted microtektites (Van Ginneken et al., 2018). In addition to microtektites, thousands of chondritic spherules and a few unique cosmic spherules were identified in RY, MM, and Jacobs Nunatak (JA) sediments. These sites are evidently successful cosmic dust and impact debris collectors, and thus their usefulness in recording influx events is explored.

Interstellar dust plays an important role in the physics of the interstellar medium, as well as the formation and evolution of stars. The presence of dust is often indicated in optical images by dark lanes which bisect spiral galaxies, or seen directly as reflection nebulosity around stars or emission nebulosity if sufficient heating is present. Of interest in this thesis is the dust that is associated with bipolar outflow sources. Bipolar outflows can occur in either evolved stars or in young stellar objects, and are so named because they consist of two lobes which are thought to be due to out-flowing dust and gas, with a dark lane between them due to thick dust in a circumstellar disk or shell which often blocks the light from the central star. The spatial distribution of the properties of dust around bipolar outflow sources has been examined using a combination of theoretical and observational techniques. To aid the interpretation of observations of bipolar outflow sources, we have modelled the wavelength dependence of light from 0.36 to 22\um, scattered by dust particles with varying characteristics. The results were then presented in the form of colour excess ratios. These model ratios can be applied to observations if the contribution due to the central star is able to be removed, such that all that remains in the image is the effect of the dust particles. The scattering of light by dust particles was modelled by varying six different characteristics: grain material, size (particle radius from 0.002 to 0.75\um), mantle temperatures and thicknesses, shape, and orientation. Of those characteristics, the largest variation in the colour excess ratios resulted from varying grain composition and size. Different scattering angles also produce a noticeable variation in the colour excess ratios, however the effect is difficult to distinguish from the general extinction due to dust around the source. Water ice mantles were also found to significantly change the colour excess ratios. Grain shape and orientation produced only small variations in the colour excess ratios. Three bipolar outflow sources were studied as part of this thesis, two evolved objects, OH~231.8+4.2 and Mz\,3, and the young T-Tauri object Rno\,91. The observations involved multi-wavelength imaging in the infrared, from which colours and colour excess ratios were obtained at various points of the bipolar outflows and then compared to the predictions made in the modelling. The most extensive data set analysed was seven images of the object OH~231.8+4.2 which were used in a multi-wavelength study in the infrared H to N bands (1.25--12\um). The central source position of the object has been confined to less than an arcsec using the longer wavelength images and an L--M colour image. The two peaks which dominate the lobes in the shorter wavelength images were found to be scattering peaks where the light from the central source is scattered from the walls of the lobes. The spatial distribution of water ice in the nebula has also been constrained to the circumstellar disk which has a torus or disk shape rather than being a spherical shell. The colour excess ratios derived for the nebula from the images also suggest slightly different dust properties between the circumstellar disk, lobe walls and within the lobe cavities. The young T-Tauri star Rno\,91 also contains ice, and was observed between J and L. The central star which illuminates the nebula was shown to be coincident with the brightest point in these images. Using colour excess ratio results for various parts of the nebula, it was shown that the dust close to the central star is likely to contain larger grains than the diffuse ISM, but with a similar composition. Moving away from the central star, the dust becomes more like that observed in the diffuse ISM. The presence of water ice on dust close to the central star was confirmed using images centred in the ice band. The protoplanetary bipolar outflow source Mz\,3 is slightly more evolved than OH 231.8+4.2, and does not have evidence of any water ice in the circumstellar disk. Images of this object were obtained between J and 10\um. The presence of warm dust throughout the inner bipolar lobes of this object is noticeable by the brightness of the lobes in the image at 10\um. Line profiles through the position of the central source of the 10\um\ image demonstrate that there is a circumstellar shell close to the central source which has an inner radius of $\lta\,375$\,AU. Colour excess ratio results for the bipolar lobes suggest that the dust associated with Mz\,3 is generally smaller than that found in the diffuse ISM. The properties of the dust in the bipolar lobes were also observed to be different to the dust closer to the central source and lying in the circumstellar disk. The small sizes for dust in Mz\,3 is consistent with the high velocity outflows that have been associated with the object.