Pluto Occultation March 18, 2007

The northern limit, centerline, and southern limit of Pluto's shadow are shown by the three lines across the globe pictured above. The shaded area represents where the sun is more than 12 degrees below the horizon.	P445.3 Prediction (as of: 2007 03 16)
Geocentric Mid-time (yyyy month dd hh:mm:ss)	2007 March 18 10:55:51 ± :01:39 UT
Minimum Geocentric Separation	0.252± 0.032 arcsec
Position Angle (Pluto relative to the star; measured north through east)	–15.99 degrees
Geocentric Velocity	7.1 km/sec
Prediction Version	P445.3-AST-1.7

Discussion

On March 18th, 2007, Pluto will occult P445.3 (= 2UCAC 25823784; as originally published in McDonald & Elliot, 2000; Table). The above map and the following prediction results are from the analysis of 32 strip scans obtained at the Lowell Observatory Astrograph by MIT observers during 2005-2007 (the strip scans from earlier years did not contain Pluto-Charon images).

Proper motion of the star has been applied up to the time of the occultation (according to the UCAC2 catalog, dRA: –10.8 ± 8.0 mas/yr, dDec: –21.4 ± 7.9 mas/yr). The offsets between the measured RA and Dec of P445.3 and its UCAC2 values at the time of the event are also given in the table.

Pluto and Charon are unresolved on the strip scans, so a point-spread function (PSF) model is fit to the blended image, with Charon's position and light ratio set as fixed parameters. The resulting Pluto positions are then compared with the light-time corrected, geocentric JPL Horizons ephemeris (System DE413 - Pluto source file; PLU013; Earth center source file; DE405), and the measured offsets from the ephemeris are calculated. The offsets are folded at Charon's period about Pluto and fit with a Fourier series of three terms (mean, sine, and cosine coefficients). The resulting Fourier model is then used to calculate the model offset in the position of Pluto (and its error) from its ephemeris at the time of the occultation. These are the RA and Dec offets listed for Pluto in the above table.

Prediction Notes

• A Charon to Pluto light ratio of 0.15 and Charon to Pluto mass ratio of 0.12 are used to calculate the prediction.
• The separation between the center line and each of the limb lines is an estimated Pluto radius of 1200 km for a flux drop of 50% for a partial occultation by the atmosphere.
• Independent predictions for this event are given on the websites of Leslie Young (map given here) and Bruno Sicardy

Archive of all P445.3 occultation predictions based on alternate sources of data, including past predictions

P445.3 Occultation Predictions for Individual Sites

³"Distance" refers to the closest approach distance of the "Site" to the center of Pluto's shadow in the shadow plane. The errors on all closest approach distances are ±736 km (one standard deviation).

⁴The errors on all times are ±1:39 (1 minute and 39 seconds; one standard deviation)

Last updated by Carlos A Zuluaga (czuluaga@mit.edu) 2007-03-16 09:00

Please direct all inquiries to Planetary Astronomy Lab (planetary-astronomy@mit.edu)

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