A Mid-Infrared Study of Dust Evolution: Protoplanetary Disks, Circumstellar Envelopes, and Lmircam Development

Astrophysical dust plays a major role in the formation and evolution of stellar systems. Evolved stars collectively act as the main factories of dust production and enrichment of the interstellar medium (ISM). After processing in the ISM, this dust is recycled into another cycle of star formation and stellar evolution. During the early stages of star formation, a circumstellar disk forms as direct consequence of conservation of angular momentum during gravitational collapse of a molecular cloud core. As the suspected birthplace of planets, extensive studies of dust in these circumstellar disks reveal the processes involved in the formation and evolution of planetary systems. Circumstellar material in thermal equilibrium with the environmental radiation field has a temperature distribution such that the majority of the spectral energy distribution emits in the mid-infrared (mid-IR). This thesis utilizes mid-IR spectra (5 − 40 µm) from the Spitzer Space Telescope Infrared Spectrograph (IRS) to study the dust production and condensation of AGB stars within different metallicity environments. By quantifying the composition of this dust, we obtain direct information on the chemical makeup of the dominant type of material injected into the ISM. In addition, a multi-epoch Spitzer IRS study of the dust constituents around young, low mass stars in the Taurus-Auriga star formation region attempts to identify the physical mechanisms responsible for the large spread in dust composition and disk morphologies observed for this coeval region. Finally, this thesis describes the development and implementation of the L/Mband (3−5 µm) Infrared Camera (LMIRcam), which is on the verge of exploiting the full capabilities of the Large Binocular Telescope Interferometer (LBTI). The LBTI combines the beams of two 8.4-meter mirrors, delivering the sensitivity comparable to iii a single 11.8-meter mirror and the resolving power equivalent to a 22.8-meter aperture. LMIRcam's 30 milli-arcsecond resolution and coronagraphic system will produce true Fizeau images of unprecedented resolution and sensitivity. In addition, two grisms will deliver a spectral resolution of R∼400, allowing LMIRcam to characterize spectral features of extended circumstellar shells around evolved stars, protoplanetary disks, and even extrasolar planets.

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