This dissertation is composed of two parts. The first part is a description of the Mid-Infrared Array Camera (MIRAC), a new camera for ground-based astronomy. The second part of this dissertation is an infrared study of planetary nebulae utilizing observations with the new camera. MIRAC is a collaborative effort among the University of Arizona, Smithsonian Astrophysical Observatory, and Naval Research Laboratory. It currently utilizes a Hughes 20 x 64 Si:As IBC detector array, which is sensitive to infrared (IR) radiation from 2 to 26 μm. The camera is equipped with 10% bandwidth filters at 2.2, 3.8, 4.6, 8.8, 9.8, 11.7, and 12.5 μm, and a wide band 8.0 to 12.8 μm "N" filter. There is also a 20% filter at 20.5 μm, and a 8-14 μm CVF with a resolution of 1.8%. The MIRAC electronics provides timing signals and coadds successive frames at a maximum rate of 10 KHz for the full array, and higher rates for a partial array readout. The data are transferred via a serial interface to a PC for storage and further processing. The camera recently achieved a NEFD of.010 Jy/arcsec² at 8.8, 11.7, and 12.5 μm for a 900 second on-source integration on the Steward Observatory 1.5 m telescope. Planetary Nebulae (PN) are formed when a star is in the post-Asymptotic Giant Branch stage of evolution. The ejection of circumstellar material is an important enrichment mechanism for the interstellar medium. In many PN, there is an excess of emission in the IR, indicating the presence of dust. There are several different components seen in the IR emission, including a family of unidentified IR (UIR) emission features at 3.3, 6.2, 7.7, and 11.3 μm. Images in the near- and mid-IR are presented here for the following PN: IC 418, BD + 30°3639, J 900, NGC 2392, NGC 6543, AFGL 2688, and M 2-9. In IC 418 and BD + 30°3639, the SiC and UIR emission is seen to be spatially distinct from the IR continuum. In NGC 2392 and NGC 6543, evidence for excess emission is seen in the distribution of the near-IR flux. In the bipolar nebulae AFGL 2688 and M 2-9, structures in the IR emission are seen that could be related to the equatorial density enhancements that have caused the bipolar morphology.

Recent improvements in infrared detector arrays make it possible for the first time to conduct detailed spectroscopic studies of a complete range of objects in the 0.9-1.35 μm region. In this dissertation, I examine the 0.9-1.35 μm spectra of planetary and proto-planetary nebulae, M dwarfs, young stellar objects, Seyfert galaxies, an H II region, and a Wolf-Rayet star. Line identifications are made for each of these objects, and extensive line lists are presented. I also investigate what the lines can tell us about each object. The 0.9-1.35 μm spectrum of the proto-planetary nebula AFGL 618 is dominated by recombination lines, low-ionization, shock-excited lines, and thermal and fluorescent H₂ lines. We use ratios of forbidden lines to show that there are two distinct physical regions in the lobes of AFGL 618, including one which must have been excited by shocks. We also show that the H₂ lines in the 0.9-1.35 μm region are ideal for detecting low levels of fluorescent H₂ emission, even when a strong thermal component is present. We present 0.6-1.5 μm spectra for M dwarfs ranging from M2 through M9. These spectra are compared with recent theoretical models, and a temperature scale is determined. In late-M dwarfs, the shape of the infrared spectrum and the depth of the 1.35 μm H₂O feature are good temperature indicators. The temperatures we derive for the M dwarfs are higher than the temperatures found in earlier studies and are in closer agreement with theoretical tracks of the lower main sequence. We present 0.9-1.35 μm spectra for 7 young stellar objects. These objects exhibit a wide variety of behavior, including strong fluorescent emission. We show that the infrared spectra can be used to study all of the regions that are detected with visible and red spectra. As a result, 0.9-1.35 μm spectroscopy should be quite useful for studying heavily embedded sources. The 0.9-1.35 μm spectra of high-excitation objects include a number of distinctive features including He II lines, several high ionization lines, and very strong (S III) lines. We find that the excitation level of a source can be estimated based on these features alone.

This thesis explains and develops the design of a compact 3-5μm catadioptric optical imaging system. This system is intended for use with a two-dimensional array detector that replaces the need for the scan mirrors of a traditional FLIR system. This design also illustrates the complete optical design process. From the basic system requirements, to a complete design with consideration to such items as assembly and alignment, cost, and maintaining focus for a change in the environmental temperature.

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