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J. M. Pasachoff (Williams College), J. L. Elliot (MIT), B. A. Babcock, D. R. Ticehurst (Williams College), D. J. Tholen (U. of Hawaii), M. J. Person (MIT)
We observed a 304-s FWHM occultation of the 15th magnitude (R) star P131.1 by Pluto on 2002 August 21 (UT) with the University of Hawaii's 2.2-m telescope on Mauna Kea. We used a Princeton Instruments/Roper front-illuminated CCD in frame-transfer mode at a 0.5 s cadence, with no filter in order to maximize the signal-to-noise ratio. Seeing was 0.4 arcsec; Charon was distinctly visible throughout alongside Pluto. We obtained images with our 0.2 arcsec pixels for astrometric purposes at various times before and after the occultation on the night of the occultation and on the preceding night. In our occultation run of 20 min, we binned 5\times5 and obtained 2400 images. A nearby double star allowed monitoring of the sky transparency. The light curve shows the occultation at a higher cadence than the visible and infrared light curves obtained at adjacent telescopes. We discuss the fully reduced and calibrated light curve, the implications for models of haze in Pluto's atmosphere from the lack of complete occultation even at full depth, and the interpretation of positive spikes in the light curve during the emersion as waves or turbulence in Pluto's atmosphere. We compare these white-light observations with the infrared results obtained simultaneously and discuss implications for Pluto's current atmospheric structure.
This work was supported by Research Corporation, by NASA through its New Horizons project, and by Williams College. The CCD is part of NSF-supported solar-eclipse research. We thank A. Pickles for assistance with scientific arrangements at Mauna Kea and S. P. Souza for help with preliminary data reduction and other aspects of the expedition.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.