Quaoar.20120710; July 10, 2012

³Measured position corresponds to RA offset of –0.2109 and Dec. offset of +0.254.

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 Haumea are those given by JPL Horizon's ephemeris (Quaoar source file: JPL16; Earth center source file: DE405).

⁶Data from the USNO 61-inch, SMARTS 0.9m, and Lowell 42-inch telescopes over the span of 3 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 Quaoar: (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. The model was propagated to obtain the predicted position and error of the KBO at the time of the occultation. The errors listed for the KBO are 1 standard deviation.

Table 1: Prediction Details
Quaoar Geocentric Mid-time (yyyy month dd hh:mm:ss)	2012 July 10 08:21:04± 00:00:31¹ UT
Quaoar Minimum Geocentric Separation	0.065± 0.016¹ arcsec
Position Angle (Quaoar relative to the star; measured north through east)	–1.09545 degrees
Geocentric Velocity	22.87 km/sec
Occultation Star USNO-B Rmagnitude	15.9²

Table 2: Reference Star Position
Reference star position: (UCAC2, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
Quaoar.20120710 Catalog	17 29 09.9733± 0.098	–15 22 47.800± 0.09
Quaoar.20120710 Measured³	17 29 09.9588± 0.005	–15 22 47.546± 0.003	From 3 USNO 61-inch Telescope frames
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body	RA (arcsec)	Dec (arcsec)
Quaoar	–0.2927± 0.0022	–0.098± 0.016	See Notes 5 and 6
³Measured position corresponds to RA offset of –0.2109 and Dec. offset of +0.254. 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 Haumea are those given by JPL Horizon's ephemeris (Quaoar source file: JPL16; Earth center source file: DE405). ⁶Data from the USNO 61-inch, SMARTS 0.9m, and Lowell 42-inch telescopes over the span of 3 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 Quaoar: (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. The model was propagated to obtain the predicted position and error of the KBO at the time of the occultation. The errors listed for the KBO are 1 standard deviation.

Site	East Longitude	Latitude	Site Altitude⁶ (km)	Distance⁷ (km)	Velocity (km/s)
IRTF	-155 28 29	19 49 46	4.182	1692 N.	22.31
Lowell	-111 39 54	35 12 12	2.219	2558 N.	22.15
Magdalena Ridge Obs.	-107 11 05	33 58 36	2.22	2388 N.	22.14
McDonald Observatory	–104 01 21	30 40 17	2.08	2065 N.	22.13
Table Mountaint	-117 40 50	34 22 55	2.29	2590 N.	22.18
Geocenter	----------	---------	center of Earth	1978 S.	21.87

Site	KBO Immersion (UT)⁹	UT Mid-Time	KBO Altitude	Solar Altitude⁹	KBO Emersion (UT)⁹
IRTF	-----------	08:21:20	55	-----------	-----------
Lowell	-----------	08:18:30	27	-----------	-----------
Magdalena Ridge Obs.	-----------	08:18:14	25	-----------	-----------
McDonald Observatory	-----------	08:17:58	26	-----------	-----------
Table Mountaint	-----------	08:18:48	31	-----------	-----------
Geocenter	-----------	08:21:04	-----------	-----------	-----------

Quaoar.20120710 Occultation July 10, 2012