The Structure of Pluto's Atmosphere from the 2002 August 21 Stellar Occultation

We have observed the 2002 August 21 occultation by Pluto of the R=15.7 mag star P131.1, using 0.5 s cadence observations in integrated white light with the Williams College frame-transfer, rapid-readout CCD at the 2.24 m University of Hawaii telescope. We detected an occultation that lasted 5 minutes, 9.1+/-0.7 s between half-light points. The ``kinks'' in the ingress and egress parts of the curve that were apparent in 1988 had become much less pronounced by the time of the two 2002 occultations that were observed, indicating a major change in the structure of Pluto's atmosphere. Analysis of our light curves shows that the pressure in Pluto's atmosphere has increased at all the altitudes that we probed. Essentially, the entire pressure scale has moved up in altitude, increasing by a factor of 2 since 1988. Spikes in our light curve reveal vertical structure in Pluto's atmosphere at unprecedentedly high resolution. We have confirmation of our spikes at lower time resolution as part of observations of the emersion made at 1.4 s and 2.4 s cadence with the 3.67 m AEOS telescope on Maui.