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The 2006 June 12 occultation of the star P384.2 (2UCAC 26039859) by Pluto was observed from five sites in southeastern Australia with high-speed imaging photometers that produced time-series CCD images. Light curves were constructed from the image time series and fit by least-squares methods with model light curves. A new modeling procedure is presented that allows a simultaneous fit of the atmospheric parameters for Pluto and the astrometric parameters for the occultation to all of the light curves. Under the assumption of a clear atmosphere and using this modeling procedure to establish the upper atmosphere boundary condition, immersion and emersion temperature profiles were derived by inversion of the Siding Spring light curve, which had our best signal-to-noise ratio. Above ∼1230 km radius, atmospheric temperatures are ∼ 100 K and decrease slightly with altitude - the same as observed in 1988 and 2002. Below 1210 km, the temperature abruptly decreases with altitude (gradients ∼2.2 K km-1), which would reach the expected N2 surface-ice temperature of ∼40 K in the 1158-1184 km radius range. This structure is similar to that observed in 2002, but a much stronger thermal gradient (or stronger extinction) is implied by the 1988 light curve (which shows a "kink" or "knee" at 1210 km). The temperature profiles derived from inversion of the present data show good agreement with a physical model for Pluto's atmosphere selected from those presented by Strobel et al. (1996). Constraints derived from the temperature profiles (and considering the possibility of a deep troposphere) yield a value of 1152 ± 32 km for Pluto's surface radius. This value is compared with surface-radius values derived from the series of mutual occultations and eclipses that occurred in 1985-1989, and the limitations of both types of measurements for determining Pluto's surface radius are discussed. The radius of Pluto's atmospheric shadow at the half-intensity point is 1207.9 ± 8.5 km, the same as

Observations of the 2006 June 12 occultation of P384.2 (McDonald & Elliot, AJ 120, 1599; aka UCAC2-26039859) were attempted at five sites by the MIT-Williams occultation group. Four were successful: the 0.8-m telescope at the Star Castle Observatory in Black Springs, the 1 m at the Mt. Canopus Observatory in Hobart, the 1.8 m at Mt. Stromlo, and the 2.3-m ANU telescope at Siding Spring. The data were recorded with our Portable Occultation, Eclipse, and Transit Systems (POETS; Souza et al., in preparation). These telescopes were located on both sides of the centerline and yielded light curves of good to excellent signal-to-noise ratio, in spite of Pluto being located 15º deg from a 15.7 day-old-moon. Above the 0.50 stellar flux level (and somewhat below it), Pluto's atmosphere is well described by an isothermal model, having the same scale height (within the errors) at all of our stations. Thus the 0.50 flux level provides a well-defined, consistent fiducial for measuring the radius of Pluto's atmosphere. All eight occultation timings (immersion and emersion at each station) were used in a least-squares fit for the radius. Results will be compared with Pluto's atmospheric size in 2002 (Person et al., Icarus, submitted), which had expanded significantly from that reported in 1988 (Elliot et al., Nature 424, 165). Pluto's atmospheric structure as derived from these data is discussed in the abstract by Gulbis et al. and the use of these data to probe for unknown satellites and debris in the Pluto-Charon system is discussed in the abstract by Pasachoff et al.

Observations of the 2006 June 12 occultation by Pluto of P384.2 (McDonald & Elliot, AJ 120, 1599; UCAC2 26039859) were attempted by the MIT-Williams College collaboration from five sites in Australia and New Zealand. Four sites were successful: Black Springs, South Australia (0.8m); Mt. Canopus, Tasmania (1m); Mt. Stromlo, Australian Capital Territory (1.8m); and Siding Spring, New South Wales (2.3m). Data were recorded using Portable Occultation, Eclipse, and Transit Systems (POETS; Souza et al., in preparation). Using these data, we characterize Pluto's atmosphere and compare our results to previous occultation observations. Above half-light level, the light curves exhibit the signature of an isothermal atmosphere. The scale height is consistent at 60 km, equivalent to a temperature of 110 K for an N2 atmosphere. Below half-light level, the light curves resemble those obtained in 2002 (Pasachoff et al., AJ 129, 1718) more than 1988 (Elliot et al., Icarus 77, 148). The data drop significantly below the isothermal curve at this level, due either to a thermal gradient or extinction (or some combination); however, the drop is not as abrupt as in 1988. Data from 2002 demonstrated that at least some extinction is at work, due to the wavelength dependence of the residual flux at the bottom of the light curves (Elliot et al., Nature 424, 165). Unfortunately, we do not have multi-wavelength observations for P384.2. Our highest signal-to-noise ratio data, from the 2.3m, exhibit spikes caused by density variations in Pluto's atmosphere and interesting structure in the bottom of the light curve, when the star is probing around the limb more than vertically. Data from this event are also discussed in Elliot et al., a derivation of Pluto's atmospheric size, and Pasachoff et al., a search for satellites, rings and debris.

We examined our data runs from four sites for the 2006 July 12 occultation of the star P384.2 (McDonald & Elliot, AJ 120, 1599, 2000; UCAC2 26039859), to search for moons, rings, or other debris in the Pluto system. Our data runs extended 80 minutes, or 115,200 km. Motivated by the discovery of P1 (Hydra) and P2 (Nix), each approximately 50 km in diameter and thought to result from the same collision that formed Charon, S. A. Stern et al. (Nature 439, 946-948, 2006) suggested that such matter might be detectable. Though their first estimate was unobservably low at 5×10-6, it could change by a factor of 10,000 or more in either direction (Stern, private communication). Our cloudless data sets, in declining order of S/N, used our Portable Occultation, Eclipse, and Transit Systems (POETS; Souza et al., in preparation) and include those from the 2.3-m ANU telescope at Siding Spring, Australia; 0.8-m Black Springs telescope near Adelaide, and the 1.8-m EOS telescope at Mt. Stromlo; though the atmospheric observation time at the 1-m Mt. Canopus Telescope at Hobart could be recovered from the comparison stars, cloudy intervals prevent full recovery during the ring/debris possible interval. Our observing with the 1-m Mt. John University Observatory in New Zealand was rendered impossible by the lack of electricity resulting from a major snowstorm. For the ring/debris search, we also evaluated data from past Pluto (Pasachoff et al., AJ 129, 1718-1723, 2005) and Charon (Gulbis et al., Nature 439, 48-51, 2006) occultations. See also Elliot et al. and Gulbis et al. (this meeting).