ALBERT

Description: The non-asteroidal brightening of (2060) Chiron, first noted by Tholen in 1988 is now ascribed to cometary activity. Photometry since 1988 has revealed a broad surge in brightness that peaked in 1989 about 1.0 mag above the brightness in the mid-1980s. The surge is evidently due to sporatic formation of dust coma, which is itself driven by the presence of extremely volatile ices at or near the surface. CN emission was recently reported. Since Chiron is now nearing perihelion, there is interest in determining whether it has exhibited anomalous brightening in the past, particularly at greater heliocentric distances. Photographic plates dating back to 1895 are known to contain images of Chiron. Using some of these archival material, the initial results are presented for a project to determine Chiron's brightness history over orbital timescales. A particularly homogeneous and high-quality set of plates taken prior to and around the time of Chiron's discovery in Oct. 1977 at the 1.2 m Oschin Schmidt telescope at Mt. Palomar Observatory were examined. Images of Chiron were identified and digitized using a PDS microdensitometer, and images of field stars around Chiron were both similarly digitized and photometrically calibrated using recently acquired B and V band CCD frames. As a result of the present work, eleven new data, including estimated errors, were added between 1969 and 1977. The implications that Chiron can be active at any heliocentric distance in its present orbit suggest that the active volatile is either N2, CH4, or CO, and that a substantial degree of mantling may have developed. Further historical data is presented, the error bars discussed, and possible mechanisms suggested for the observed activity.

Description: Production rates of OH, CN, C2, C3, NH, and NH2 were derived from different data sets for the Comet P/Wolf-Harrington, and a dust production measure was calculated. This comet is found to be depleted by more than an order of magnitude in its pure carbon species compared with OH and CN. The data obtained suggest that a nonnegligible fraction of comets or their constituent components formed at a different temperature and thus at a different location and/or time than the majority of comets.

Description: Periodic variations in Comet Halley's production of gas and dust during its 1910 apparition were searched for using measurements from a homogeneous set of photographic plates obtained at the National Observatory of Argentina at Cordoba. After applying corrections to the observations to compensate for geometric and heliocentric distance effects, the data, spanning the two months immediately following perihelion, were split into two sections for analysis. Of the possible periods indicated in either half of the dataset, only those in the range of 7.3-7.8 days were present in both halves. The additional constraint of similarity in the shape of the resulting, phased light curves further constrained the period from about 7.35 to 7.60 days. Allowing for the inherent limitations of the 1910 data, comparison of these light curves to the equivalent 1986 light curve indicates that a match in features between the two apparitions is made possible by utilizng one of two phase shifts. While not conclusive, this ability to match features suggests long-term stability in many aspects of Halley's intrinsic activity.