ALBERT

Description: We have obtained high velocity and spatial resolution long-slit H alpha spectra of comets Austin (1989c1) and Levy (1990c). Spectra of both comets clearly show the existence of a low velocity thermalized component of hydrogen gas. The amount of slow hydrogen is estimated for comet Austin. The Levy spectrum shows an unusual high-velocity spatially-confined blob of hydrogen emission of unknown origin.

Description: An explicit test of the ability of the galaxy two-point correlation function to be recovered from the Lick counts of galaxies (Shane and Wirtanen, 1967) is reported. High-fidelity simulations are created, starting with the distribution of galaxies in space. These distributions are projected onto a set of simulated Lick plates which are reduced to a uniform limiting magnitude with the method of Seldner et al. (1977). The simulated catalogs are then analyzed with the methods of Groth and Peebles (1977). The resulting correlation functions are found to reproduce accurately the correlation functions that were built in during the first step of the simulations.

Description: We present direct ground based observations of the plasma flow sunward and tailward of the nucleus of Comet P/Swift-Tuttle. The observations are long-slit high resolution spectra of the H2O(+) emission centered at 6199 A with a velocity resolution of about 7 km/s FWHM and a spatial resolution of about 10 exp 4 km at the comet. Emission is visible from just inside the predicted position of the cometopause on the sunward side of the nucleus out to 5 x 10 exp 5 km on the tailward side. The deceleration of the solar plasma on the sunward side is clearly observed as is the acceleration of cometary ions into the tail. These observations show the effectiveness of ground based methods for the systematic study of cometary plasmas and point to the need for a better theoretical understanding of their acceleration mechanisms.

Description: We have obtained long-slit high resolution spectra of the H2O(+) 6199 A complex in the near tail of comet P/Swift-Tuttle. The observations were made using the Hamilton echelle spectrometer fed by the Lick Observatory 0.6 m coude auxiliary telescope. For most of our observations, the spectral slit was aligned along the Sun-tail axis and the cometary nucleus was placed at one end of the slit, giving us spectra having the spatial and spectral resolution needed to measure the radial velocity and velocity dispersion continuously down the cometary tail out to a distance of 4X10(exp 5) km. The radial velocities confirm the earlier more restricted observations by Rauer & Jockers (1993) and by Wyckoff & Lindholm (1994) showing that the tail motions are indeed bulk flows in the antisolar direction. Out to 3X10(exp 5) km in the tail typical bulk flows are at a speed of approximately 30 km/s. The velocity dispersion, (sigma(sub r)), of the H2O(+) lines follows a pattern that is quite systematic; sigma(sub r) is smallest near the cometary nucleus, and steadily increases down the tail. The highest velocity dispersions are found ahead of the nucleus and off the tail axis. These velocity dispersions are equivalent to ion temperatures ranging from 10(exp 5) to 10(exp 6) K. We note a clear anticorrelation between the H2O(+) line intensities (related to the ion density) and the bulk flow and dispersion velocities; direct mass loading of the solar wind by the observed water ions may be responsible. We discuss several approximate equipartition methods used to infer local magnetic fields induced by the interaction of the cometary ions with the solar wind particle/field stream. Typical fields derived are near 50 nT. The measured tailward accelerations are consistent with this order of magnitude B field.

Description: The Hamilton Echelle spectrograph on the 3-m Shane telescope at Lick Observatory was used to obtain high-velocity and spatial resolution 2D spectra of H-alpha 6563-A emission in Comets Austin and Levy. The presence of the components expected from water dissociation and collisional thermalization in the inner coma is confirmed by the hydrogen velocity distribution. In Comet Austin, the potential high-velocity hydrogen includes velocities of up to about 40 km/s and is spatially symmetric with respect to the nucleus. In Comet Levy, the high-velocity hydrogen reaches velocities of up to 50 km/s and is situated exclusively on the sunward side of the nucleus. The two distinct signatures of high-velocity hydrogen imply two distinct sources.