C20130615; June 15, 2013

³Measured position corresponds to RA offset of –0.6957'' and Dec. offset of –0.182''.

⁴All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction.

⁴Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation.

⁵The reference positions for Pluto and Charon are those given by JPL Horizon's ephemeris (Pluto source file: PLU017; Earth center source file: DE405). Our residual model is based on the assumption that the same offsets in RA and Dec apply to both Pluto and Charon.

⁶Data from the du Pont 2.5m, USNO 61-inch, and Lowell Astrograph telescopes over the span of 6 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of Pluto: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, (iii) sinusoidal terms with the Earth's orbital period, and (iv) sinusoidal terms with the Pluto-Charon mutual orbit. The model was propagated to obtain the predicted position and error of the Pluto at the time of the occultation. The errors listed for the Pluto are the RMS of the models fitted.

Table 1: Prediction Details
Charon Geocentric Mid-time (yyyy month dd hh:mm:ss)	2013 June 15 06:19:36 + 00:00:57¹ UT
Charon Minimum Geocentric Separation	0.291 + 0.023¹ arcsec
Position Angle (Charon relative to the star; measured north through east)	–7.16 degrees
Geocentric Velocity	22.66 km/sec
Occultation Star UCAC4 magnitude	14.86²

Table 2: Reference Star Position
Reference star position: (UCAC4, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
C20130615 Catalog	18 44 37.9835 ± 0.0800	-19 46 43.442 ± 0.081
C20130615 Measured³	18 44 37.9397 ± 0.0029	-19 46 43.590 ± 0.005	From 5 USNO 61-inch Telescope frames. See note 4.
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body	RA (arcsec)	Dec (arcsec)
Pluto	–0.1361± 0.058	+0.240± 0.022	See Notes 5 and 6
³Measured position corresponds to RA offset of –0.6957'' and Dec. offset of –0.182''. ⁴All "offsets" are defined in the ("corrected" – "reference") or ("observed" – "calculated") sense. The offsets should be added to reference positions to get the measured positions, which we use to calculate the prediction. ⁴Data analyzed using UCAC2 reference network. A weighted average of the data from the two telescopes was used to calculate the RA and DEC. The errors given are 1 standard deviation. ⁵The reference positions for Pluto and Charon are those given by JPL Horizon's ephemeris (Pluto source file: PLU017; Earth center source file: DE405). Our residual model is based on the assumption that the same offsets in RA and Dec apply to both Pluto and Charon. ⁶Data from the du Pont 2.5m, USNO 61-inch, and Lowell Astrograph telescopes over the span of 6 years were reduced with respect to stars in the UCAC2 catalog. A model was developed to fit the residuals obtained from our measured positions compared to that of the object's JPL ephemeris. All residuals obtained from the different telescopes were consistent with the model. The model includes the first-order effects of errors in the orbital elements of Pluto: (i) constant offsets in RA and Dec, (ii) linear (in time) offsets in RA and Dec, (iii) sinusoidal terms with the Earth's orbital period, and (iv) sinusoidal terms with the Pluto-Charon mutual orbit. The model was propagated to obtain the predicted position and error of the Pluto at the time of the occultation. The errors listed for the Pluto are the RMS of the models fitted.

Site	East Longitude	Latitude	Site Altitude⁶ (km)	Pluto Distance⁷ (km)	Velocity (km/s)
SVH	–74 56 45	40 57 41	0.22	1178 S.	23.01
Wallace	–71 29 06	42 36 36	0.11	1132 S.	23.00
Williams	–73 12 06	42 42 42	0.22	1105 S.	23.00
Geocenter	----------	---------	center of Earth	5125 S.	22.67

Site	Charon Immersion (UT)⁹	Charon Mid-Time (UT)	Charon Emersion (UT)⁹	Charon Altitude	Solar Altitude⁹
SVH	-----------	06:18:58	-----------	-----------	-----------
Wallace	-----------	06:18:45	-----------	-----------	-----------
Williams	-----------	06:18:51	-----------	-----------	-----------
Geocenter	-----------	06:19:36	-----------	-----------	-----------

C20130615 Occultation June 15, 2013