C20130715; July 15, 2013

³Measured position corresponds to RA offset of +1.2409'' and Dec. offset of –0.1777''.

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.

⁶The 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.

⁷Data from the du Pont 2.5m, USNO 61-inch, and Lowell Astrograph telescopes over the span of 8 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
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)	2013 July 15 03:15:46± 00:01:02¹ UT
Charon Geocentric Mid-time (yyyy month dd hh:mm:ss)	2013 July 15 03:10:55± 00:01:02¹ UT
Pluto Minimum Geocentric Separation	0.333± 0.045 arcsec
Charon Minimum Geocentric Separation	0.307± 0.045¹ arcsec
Position Angle (Pluto relative to the star; measured north through east)	171.20 degrees
Geocentric Velocity	23.43 km/sec
Measured magnitude (approx. r')	16.2

Table 2: Reference Star Position
Reference star position: (USNOB, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
PC20130715 Catalog	18 41 29.9807 ± 0.3690	–19 52 59.800 ± 0.192
PC20130715 Measured³	18 41 30.0647 ± 0.0486	–19 52 59.978 ± 0.038	From Lowell 42-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	–0.1373 ± 0.041	+0.256± 0.031	See Notes 6 and 7
³Measured position corresponds to RA offset of +1.2409'' and Dec. offset of –0.1777''. 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. ⁶The 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. ⁷Data from the du Pont 2.5m, USNO 61-inch, and Lowell Astrograph telescopes over the span of 8 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 Altitude⁸ (km)	Pluto Distance⁹ (km)	Charon Distance⁹ (km)	Velocity (km/s)
SVH Observatory	–74 56 45	40 57 41	0.220	1999 S.	12635 N.	23.61
Wallace	–71 29 06	42 36 36	0.107	1941 S.	12697 N.	23.61
Williams	–73 12 06	42 42 42	0.215	1923 S.	12713 N.	23.61
Geocenter	----------	---------	center of Earth	7609 S.	7018 N.	23.27

Site	Charon Immersion (UT)¹⁰	Charon Mid-Time (UT)	Charon Emersion (UT)¹⁰	Pluto Immersion (UT)¹⁰	Pluto Mid-Time (UT)	Pluto Emersion (UT)¹⁰	Pluto Altitude	Solar Altitude¹⁰
SVH Observatory	-----------	03:11:11	-----------	-----------	03:15:56	-----------	-----------	-----------
Wallace	-----------	03:10:57	-----------	-----------	03:15:42	-----------	-----------	-----------
Williams	-----------	03:11:03	-----------	-----------	03:15:48	-----------	-----------	-----------
Geocenter	-----------	03:10:55	-----------	-----------	03:15:46	-----------	-----------	-----------

PC20130715 Occultation July 15, 2013