Visible and Near-IR Observations of the 2007 March 18 Occultation by Pluto

The predicted shadow path for the 2007 March 18 occultation of a 15.3 magnitude star by Pluto crossed western and central United States and northern Mexico, including several large, fixed telescopes with infrared instrumentation, with a slow sky-plane velocity (6.8 km/s, roughly three times slower than typical). The PHOT (portable high-speed occultation telescope) group used nineteen instruments at ten sites, with wavelengths ranging from B to K. Our goal was multi-wavelength observations to constrain atmospheric opacity, taking advantage of the decrease of opacity with wavelength for photochemical hazes. We obtained lightcurves from Red Buttes Observatory in Laramie WY (I), Lick Observatory (H), Lowell Observatory (R, I, H), Palomar Observatory (I, K), Mount Lemmon (I), Table Mountain Observatory (I), Kitt Peak National Observatory (I, R, H, Ks), and San Pedro Martir (I, K). Weather prevented observations at Apache Point Observatory and McDonald Observatory. Our northernmost site, Red Buttes, was south of the central line, but still reached the zero stellar flux level, and even our southernmost site, San Pedro Martir, observed a grazing event. We see little difference between visible and infrared observations. We see, for the first time, well-defined high-altitude spikes caused by local refocusing of starlight by small-scale density variations. We will present the results of this varied dataset, including limits on or evidence for hazes in Pluto's lower atmosphere.