55636.20091009 Occultation October 09, 2009

(last updated 2009 09 08)

Across the globe pictured above, the three lines correspond to the northern limit, centerline, and southern limit of 55636's shadow. The northern and southern limits correspond to a radius of 405 km (from kboOccCandByAndRad.1.5.csv). The error in the prediction (3 Standard Deviations from the limb of the KBO) is depicted by the upper and lower dashed lines. The shaded area represents where the sun is more than 12 degrees below the horizon.
Geocentric Mid-time (yyyy month dd hh:mm:ss)	2009 October 09 10:30:23± 00:00:351 UT
Minimum Geocentric Separation	0.0546± 0.02491 arcsec
Position Angle (55636 relative to the star; measured north through east)	158.90 degrees
Geocentric Velocity	25.29 km/sec
Prediction Version	555636.20091009-AST-11.0

Discussion

On 2009 October 9th, 55636 (2002 TX300) will occult will occult 2UCAC number 41650964. The above map and the following prediction results are from the analysis of 52 frames obtained using the United States Naval Observatory 61-inch and 40-inch, and the SMARTS 0.9m telescope. The 52 frames, which range from August 2007 to August 2009, were used to develop a model to fit the residuals from our measured positions compared to that of the object's JPL ephemeris. The model includes the first-order effects of errors in the orbital elements of 55636: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, and (iii) sinusoidal terms with the Earth's orbital period.
For the occultation star, 29 frames obatined using the United States Naval Observatory 61-inch and 40-inch were used to calculate the RA and Dec offsets from the UCAC2 values.

Precise Astrometry of KBOs is difficult to carry out due to their faint magnitudes and small angular radii. In the case of 55636, which has a visual magnitude of 19.6 and angular radius of 0.013 arcseconds (from an assumed radius of 405 km), accurately predicting an occultation can be difficult.

Site Information

The sites in the table below are listed in order of their distance from the predicted centerline, starting with the most northern site.

⁶Altitude of each observatory is measured in kilometers above sea level.

⁷"Distance" refers to the closest approach distance of the "Site" to the center of 55636's shadow in the shadow plane. The errors on all closest approach distances are ±734 km (three standard deviations). "S." means the site is South of the center of 55636's shadow. "N." means the site is North of the center of 55636's shadow.

55636.20091009 Occultation Predictions for Individual Sites

⁹The errors on all times are ±0:35 (35 seconds; Three standard deviations). In parenthesis is the elevation of the body above the celestial horizon in degrees. The Solar altitude is given for locations where it is relevant (past astronomical twilight). No entry in the Immersion and Emersion columns indicates that the occultation is not predicted to be visible at that site. But because the errors are large, some of these sites may see an occultation event that would be centered on the time in the "UT Mid-Time" column.

Last updated by Carlos A Zuluaga (czuluaga@mit.edu) 2009-09-08 10:00

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

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