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Narrowband filter photometry observations of Comet Hyakutake (1996 B2) were used to investigate this comet's short-term variability as well as its behavior for the apparition as a whole. Utilizing measurements obtained on a total of 13 nights between February 9, 1996, and April 14, 1996, we find that the heliocentric distance ([r.sub.H]) dependence of the production rates of OH and NH were much shallower than those for either the carbon-bearing species or the visible dust. Based on the OH measurements, the derived water [r.sub.H]-dependence was also significantly less steep than expected from a basic water vaporization model and required an effective active surface area of about 29 [km.sup.2] at [r.sub.H] = 1.8 AU, 16 [km.sup.2] at [r.sub.H] = 1 AU, and only 13 [km.sup.2] at [r.sub.H] = 0.6 AU. This decrease in active area may be due to seasonally induced variations of a heterogeneous surface, or due to a decreasing contribution of gas from icy grains in the innermost coma. The relative abundances of the minor gas species place Hyakutake into the 'typical' category of comets in the A'Hearn et al. (1995, Icarus 118, 223-270) taxonomic classification system. The spectrum is generally redder at shorter wavelengths throughout the apparition; however, the dust color progressively changes from being significantly reddened (37%/1000 A [Angstrom]) at large [r.sub.H] to near-solar at small [r.sub.H]. This change of color with distance implies a significant change in grain sizes or a changing proportion between two or more grain populations. A major outburst was initiated near March 19.9, just prior to the comet's close approach to Earth. The characteristic recovery from the outburst differed among the observed species, with OH recovering most rapidly, essentially returning to its baseline values by March 25. The spatial radial fall-off of OH throughout this interval was consistent with the expected nominal spatial distribution, while CN and [C.sub.2] displayed fall-offs consistent with a distributed source, and the dust fall-off was significantly less steep than 1/[rho], possibly due to fragmenting grains. Rotational lightcurve amplitudes were largest for the OH, NH, and dust, again consistent with the carbon-bearing species primarily originating from a distributed source. Significant variations were observed in the lightcurve amplitude and phase shifts as functions of aperture size. Finally, a refined value for the rotation period of 0.2614 [+ or -] 0.0003 day was determined. Key Words: Hyakutake; comets; photometry; composition; rotation.

Narrowband photometry of Comet Hyakutake (1996 B2) revealed periodic variability in the production of dust and gas during the comet's close approach to Earth in March 1996. The photometry alone was insufficient to unambiguously discriminate among several possible periods, but a unique period determination was possible by utilizing repeating morphological features in CCD images obtained simultaneously with the photometry on the nights of March 23-25. In particular, a large puff or blob of material was seen to be released in the sunward direction every 6.23 [+ or -] 0.03 h. This periodic release of material, presumably from a single dominant active region on the surface, was the source of the observed lightcurve variations. A second, much smaller morphological feature also repeats each cycle, confirming the value of 6.23 h for Hyakutake's synodic rotational period. Key Words: Hyakutake; comets; photometry; imaging; rotation.

A study shows that asteroid 4015 Wilson-Harrington has size, rotation period and lightcurve amplitude similar to those of near-earth asteroids (NEA) and small main-belt asteroids. The results suggest that some of the NEAs have NEAs have originated from comets. The size calculated is larger than previous values. The observations are made using CCD photometry.

The production rates of OH, CN, C2, C3 and NH along with NH2, in the Comet P/Wolf-Harrington, is obtained by a narrowband filter photometry of the comet during its 1984 and 1990/91 apparitions from the Lowell Observatory. The Multiple Mirror Telescope at Mount Hopkins was used for the single spectrophotometric observation of the comet. A measure of the comet's dust production Af-rho is also determined using the data. Determination of chemical elements in the comet enables the study of its origin and evolution. A comparison of the abundance of elements in comet P/Wolf-Harrington with other comets reveals that it contains less carbon Nh and NHZ and more OH and CN. This indicates that the comet and its constituent parts evolved at different temperatures, locations and times.

The groundbased narrowband photometry data on nine candidate comets obtained over the last 15 years were examined. Measured production rates of hydroxide and cyanide, measures of dust production, production rate ratios and heliocentric distance dependencies for each comet are involved in this investigation. Comets were compared to Halley and other comets in the data base. The utility of groundbased data was demonstrated.