2007 Pluto Occultation

Pluto OccultationOn March 18, 2007, Pluto occulted a 15th magnitude star (UCAC2 25823784), and the resulting shadow crossed the central U.S. I was able to record this event from Colorado at 4:55 AM MDT (UT 10:55). I observed a drop in brightness of about 0.45 magnitude when Pluto blocked the light of the star. The duration of the occultation was about five minutes. These data were collected under extremely poor seeing conditions (FWHM 5.5"), so the photometric signal is noisy. At the scale of the images, Pluto and the star it occults cannot be resolved as separate sources. The magnitude scale on the plot is approximate; the camera was unfiltered. You can watch a streaming video of the occultation, and the dimming of the pair is easy to detect visually (you may also view or download the video as a 857 KB GIF).

Images were collected over 25 minutes with an SBIG ST-8 camera binned 2x2, attached to a 300 mm aperture, 2306 mm focal length SCT (1.61"/pixel). The exposure time of each image is 5 seconds. The light curve is normalized against 8 surrounding reference stars.

Initial analysis (March 26) shows that the shadow path was significantly north of the original predictions, indicating that the ephemeris model used for Pluto needs some correction, and probably should be updated every year or two.

Light Curve
  (Mouse over for data fit, derived from Bruno Sicardy's analysis)

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© Copyright 2007, Chris L Peterson. All rights reserved.