| Summary: | 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.
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