P20130504; May 04, 2013

³Measured position corresponds to RA offset of +0.0584'' and Dec. offset of +0.3413''.

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 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.

⁷Pluto position adjusted by an additional ~60mas (not included in these values) to correct for the offset observed at the 22 March 2013 appulse, as measured from Keck2, Lowell 42-inch, Lowell DCT, NOFS 61-inch, NOFS 1.3-m, and SARA-S.

Table 1: Prediction Details
Pluto Geocentric Mid-time (yyyy month dd hh:mm:ss)	2013 May 04 08:21:32± 00:01:37¹ UT
Pluto Minimum Geocentric Separation	0.004± 0.039¹ arcsec
Position Angle (Pluto relative to the star; measured north through east)	+174.21 degrees
Geocentric Velocity	10.21 km/sec
Occultation Star UCAC2 magnitude	14.25²

Table 2: Reference Star Position
Reference star position: (UCAC2, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
P20130504 Catalog	18 47 52.5286± 0.183	–19 41 24.7272± 0.173
P20130504 Measured³	18 47 52.5327± 0.014	–19 41 24.3859± 0.017	From 51 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	–0.1441± 0.041	+0.206± 0.031	See Notes 5, 6, and 7
³Measured position corresponds to RA offset of +0.0584'' and Dec. offset of +0.3413''. 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 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. ⁷Pluto position adjusted by an additional ~60mas (not included in these values) to correct for the offset observed at the 22 March 2013 appulse, as measured from Keck2, Lowell 42-inch, Lowell DCT, NOFS 61-inch, NOFS 1.3-m, and SARA-S.

Site	East Longitude	Latitude	Site Altitude⁸ (km)	Pluto Distance⁹ (km)	Velocity (km/s)
Cerro Pachon	–70 40 12	–30 14 26	2.783	1003 S.	10.62
Cerro Tololo	–70 48 54	–30 09 54	2.2	994 S.	10.61
Flagstaff	–111 44 23	+35 11 02	2.3	5140 N.	10.47
La Silla	–70 43 48	–29 15 24	2.3	895 S.	10.62
Las Campanas	–70 42 00	–29 00 30	2.3	868 S.	10.61
Llano del Hato	–70 52 74	+8 47 18	3.6	3170 N.	10.67
McDonald Observatory	–104 01 21	+30 40 17	2.1	4935 N.	10.52
Santiago	–70 32 10	–33 23 45	0.9	1345 S.	10.60
Geocenter	----------	---------	center of Earth	103 N.	10.21

Site	Pluto Immersion (UT)¹⁰	Pluto Mid-Time (UT)	Pluto Emersion (UT)¹⁰	Pluto Altitude	Solar Altitude¹⁰
Cerro Pachon	08:20:56	08:22:28	08:24:00	-----------	-----------
Cerro Tololo	08:20:57	08:22:30	08:24:03	-----------	-----------
Flagstaff	-----------	08:26:41	-----------	-----------	-----------
La Silla	08:20:47	08:22:28	08:24:10	-----------	-----------
Las Campanas	08:20:45	08:22:28	08:24:11	-----------	-----------
Llano del Hato	-----------	08:21:58	-----------	-----------	-----------
McDonald Obs	-----------	08:26:09	-----------	-----------	-----------
Santiago	08:21:52	08:22:29	08:23:06	-----------	-----------
Geocenter	08:19:15	08:21:32	08:23:49	-----------	-----------

P20130504 Occultation May 04, 2013