Conventional narrowband photoelectric photometry of Comet Hale-Bopp (1995 O1) was obtained on 99 nights from mid-1995 to early-2000, yielding gas and dust production rates over an unprecedented range of time and distance. The appearance of Hale-Bopp (H-B) presented a prime opportunity for active comet studies, and its inherent brightness and orbital geometry allowed the characterization of its long-term activity. Throughout the apparition, H-B released, by far, more gas and dust than any other comet ever measured. As a very high dust-to-gas ratio object, dust production was successfully measured throughout the apparition, with the dust consistently slightly red in color. All five gas species including OH and NH were detected just inside of 5 au inbound, while C2 and C3 were detected to just past 5 au outbound, and CN was followed until nearly 7.7 au. Heliocentric distance dependencies ranged between -1.2 and -2.7 in log-log space, with the extremes magnified by the large extrapolations in Haser model parameters at large distances. H-B's enormous size and associated extremely high outgassing resulted in a much larger collisional zone, which in turn yielded outflow velocities more than 2x higher than ever previously measured at comparable distances. Even so, volatile composition remained within the "typical" classification, consistent with most Oort Cloud comets, and water production follows the expected curve based on a standard water vaporization model. However, seasonal effects provided evidence for inhomogeneities among the major source regions on the surface of the nucleus. Preliminary modeling of the nucleus and coma successfully matches this seasonal behavior.

We present preliminary results from our on-going observational campaign of Comet LINEAR (2000 WM1). These ground-based observations include both narrowband photometry and CCD imaging. We began monthly photometric observations of LINEAR in August 2001 (r H = 2.7 AU) using the Hall 1.1-m telescope at Lowell Observatory. These continued from Lowell until mid-December, when LINEAR became a southern hemisphere object and observations began from the 0.6-m Planetary Patrol telescope at Perth Observatory. Production rates for the measured gas species and for dust (see A’Hearn et al., 1995 for model parameters) are shown in Figure 1 for dates ranging from 23 August 2001 to 11 January 2002, only eleven days prior to perihelion (0.56 AU). Our most recent production rate for OH was obtained on 13 December (1.05 AU), with a Haser value of 3.8 × 1028mol/s, corresponding to a vectorial equivalent water production rate of 5.2 × 1028mol/s. (The near-UV OH and NH bands are not measured from Perth due to its relatively low elevation.) The r H-dependence of water closely follows a standard ice vaporization model (cf. Cowan and A’Hearn, 1979), and the water production implies an effective active area of 10 km2.This corresponds to a lower limit of the effective nucleus radius of about 0.9 km. Relative abundances of the minor species yield a classification of “typical” in the A’Hearn et al. (1995) database.

The Apollo asteroid 4179 Toutatis passed within 0.0242 AU of Earth in December 1992, and photometry was obtained by observers from at least 25 sites around the world, at solar phase angles between 121° and 0.2°. The phase curve is well described in the H, G system with a mean H of 15.3 and a slope parameter G of 0.10 ± 0.10. However, the rotational lightcurve is very unusual. The amplitude is large (1.2 magnitudes) and the rotation period is extremely long (several days). Most remarkably, the lightcurve does not appear to be periodic: it is unlikely that a single rotation period can account for the lightcurve even when the rapidly changing viewing and illumination geometry during the close Earth approach is taken into account, though strong lightcurve minima recurred approximately every 7.3 days. The likely explanation is that Toutatis has complex, tumbling, rotation with a characteristic period between 3 and 7 days. As noted by A. W. Harris (1994 Icarus 107, 209-211), the damping time scale from complex to simple rotation for a small, slowly rotating asteroid like Toutatis is so long that complex rotation is expected, but Toutatis is the first asteroid to show such strong observational evidence for complex rotation.

Narrowband filter photometry of Comet Levy (1990c) was obtained on 51 nights in the interval from 3 June 1990 to 19 April 1991. The emission bands of OH, NH, CN, C3, and C2 were isolated, in addition to continuum points at 3650 and 4845 Å. Relative abundances among the species were typical of most comets previously observed. All species showed pronounced asymmetry about perihelion, with production rates for most species being about twice as large before perihelion as after over the heliocentric distance range of 1.0–3.0 AU. The OH production rate's asymmetry was nearly double that observed for the other species, with maximum production occuring more than a month before other species. Periodic variations having a single-peaked lightcurve period of 18.9 hr or a double-peaked lightcurve period of 37.8 hr were observed during late-August 1990. Observations by Feldman et al. (1991) only 3 weeks later using the IUE satellite require a period 7% shorter than the value we found. Neither period determination is consistent with both data sets, implying that the rotational period charged between the two sets of observations.