55636.20091009 Occultation October 09, 2009

(last updated 2009 10 08)

Across the globe pictured above, the three solid 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 (using an assumed albedo of 0.1). The upper and lower dashed lines indicate the effects of unknown systematic errors such as catalog zone errors. Previous KBO appulse analyses have shown the observed error to be 1.5-2 times that of the prediction's random error. The shaded area represents where the sun is more than 12 degrees below the horizon. The scientific goals of this event are (i) to accurately determine the diameter of 55636, (ii) to probe for a tenuous atmosphere of 55636, and (iii) to detect possible nearby satellites of 55636. Observations are worthwhile and encouraged from any location at which the event is visible. Due to the possibilities of the occultation star being a multiple star system or the KBO having a satellite; either of these could move the event by more than the systematic effect uncertainties shown.

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 59 frames obtained using the United States Naval Observatory 61-inch and 40-inch telescopes taken by Stephen Levine and Trudy Tilleman, and the SMARTS 0.9m telescope taken by Joselino Vasquez. The 70 frames, taken between August 2007 and September 2009, were used to develop an ephemeris correction 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. With this approach, the error in the JPL ephemeris does not enter into our prediction error, since the ephemeris is used only as a reference ephemeris for our correction model.


For the occultation star, 69 frames obatined using the United States Naval Observatory 61-inch and 40-inch taken by Stephen Levine and Trudy Tilleman were used to calculate the RA and Dec position.

Previous Prediction of 55636.20091009.

Table 4: 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 ±184 km (one standard deviation). "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.

Table 5: 55636.20091009 Occultation Predictions for Individual Sites

⁹The errors on all times are ±0:08 (8 seconds; one standard deviation). The solar altitude is given for locations where it is relevant (solar altitude greater than -18°). No entry in the immersion and emersion columns indicates that the occultation is not predicted to be visible at that site. But due to unknown effects (stellar or KBO duplicity), 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 Michael J Person (mjperson@mit.edu) 2009-10-08 14:00

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

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