A new series of observation of the Crab Nebula in TeV gamma rays using an improved camera on the Whipple Observatory 10 m Optical Reflector is reported. The smaller pixel size results in a lower energy threshold for gamma-ray detection than that reported in WEA89. The improvement in SNR compared with the original camera (Cawley et al., 1990) is a

Ionospheric modification using photochemically reactive vapors is studied with a one-dimensional, multiion, fluid model of plasma flow along magnetic field lines. The magnitudes of ion and electron density changes are determined by considering both chemical processes (i.e., photoionization, ion-molecule reactions, dissociative recombination

The evolution of supernova remnants in preexisting cavities is examined by means of 1D and 2D numerical studies of the phenomenon and the fragmentation of ejecta. The analytical approach involves approximating the cavity produced by an adiabatic blast with a power-law density distribution. The numerical studies that follow model a single supernova

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An intriguing bipolar mass outflow and a faint envelope were detected spectroscopically in the planetary nebula NGC 6751 by Gieseking and Solf (1986). To study the physical structure, deep CCD images of this nebula have been obtained which detect not only the morphological counterparts of the aforementioned features but also additional faint halos

A theoretical model of the polarization properties of a Gregory-coude telescope is calculated to predict the behavior of the German Gregory-coude telescope installed at the Observatorio del Teide (Spain). Measurements of the real effects produced by this telescope acting upon light of known polarization are compared with the model. An uncertainty