COMETARY ACTIVITY IN 2060-CHIRON

We present the results of a 2 yr investigation of cometary activity in 2060 Chiton. The investigation is based on charge-coupled device (CCD) photometry and spectroscopy taken at the Mauna Kea, Kitt Peak, and MDM Observatories, with Chiron in the 11.2≤R≤12.6 AU heliocentric distance range. The new photometry includes an image of 20 000 s effective integration, a new rotational light curve, the surface brightness profile of the coma at three epochs, and near-ultraviolet narrowband photometry taken to search for Rayleigh scattering from small particles in the coma. The spectroscopy from 1989 and 1990 was obtained to search for molecular emissions, and to study the shape of the reflected continuum of the nucleus and coma. Major results include the detection of impulsive brightening on a timescale of hours (to be distinguished from the slow rise in the total light observed in 1987-1990), evidence for a secular change in the blue portion of the reflectivity spectrum of the nucleus, no evidence for Rayleigh scattering in the near ultraviolet, and an upper limit to the column density of CO+ ions in the coma. We also find that the surface brightness gradient of the coma of Chiron is steep and variable: it cannot be matched by steady-state models, compatible with our detection of transient mass loss at high rates. The photometric range of the rotational light curve is diminished in proportion to the local cross section of the coma, showing that the coma of Chiron is optically thin. We find that the mean mass loss rate needed to produce the observed coma is of order 1 kg s-1, and that this rate can be supplied by sublimation of ices with the volatility of CO or CO2 from a small fraction of the nucleus surface.