Varuna.20120102 Occultation January 02, 2012

(last updated 2011 12 31)

Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of Varuna's shadow. The northern and southern limits correspond to a radius of 500 km. The upper and lower dashed lines indicate 1 sigma 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 Varuna, (ii) to probe for a tenuous atmosphere of Varuna, and (iii) to detect possible nearby satellites of Varuna.

Observations are worthwhile and encouraged from any location at which the star 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 random uncertainties shown.

Table 1: Prediction Details
Geocentric Mid-time (yyyy month dd hh:mm:ss)	2012 January 02 13:17:13± 00:01:15¹ UT
Minimum Geocentric Separation	0.004± 0.053¹ arcsec
Position Angle (Varuna relative to the star; measured north through east)	14.27 degrees
Geocentric Velocity	25.39 km/sec
Occultation Star USNOB Rmagnitude	15.95
KBO Visual Magnitude	20.2
KBO Angular Radius	0.011 arcseconds (approximate)

¹One standard deviation of random error.

Table 2: Reference Star Position
Reference star position: (UCAC2, at epoch of event)	RA (h:m:s; J2000)	Dec (d:m:s; J2000)	Notes
Varuna.20120102 Catalog	07 44 35.5733± 0.073	26 15 48.480± 0.074
Varuna.20120102 Measured³	07 44 35.5893± 0.003	26 15 48.466± 0.015	from 69 USNO61, Lowell 42-inch, SMARTS 0.9m frames
Table 3: Projected KBO Offsets⁴ from Reference Ephemeris at the Time of the Event
Body	RA (arcsec)	Dec (arcsec)
Varuna	–0.0079± 0.0562	–0.074± 0.050	See Notes 5 and 6
³Measured position corresponds to RA offset of +0.2394 and Dec. offset of –0.013. 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 position for Varuna is that given by JPL Horizon's ephemeris (Varuna source file: JPL#19; Earth center source file: DE405). ⁶Data from the USNO 61-inch, SMARTS 0.9m, and Lowell 42-inch telescopes over December 2011 were reduced with respect to stars in the UCAC2 catalog.

Discussion

On 2012 January 2nd, Varuna will occult USNO-B1.0 star number 1162-0144973. The above map and the following prediction results are from the analysis of 69 frames of the occultation star and KBO were obtained using the Lowell 42-inch, USNO-61 inch, and SMARTS 0.9m telescope. Data was taken during the month of December, 2011.

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.

Site	Longitude	Latitude	Site Altitude⁶ (km)	Distance⁷ (km)	Velocity (km/s)
Akaiwa Ryuten Observatory	+134 00 08	34 53 38	0.47	473 N.	25.69
Beijing	+116 24 10	39 54 08	0.1	1266 N.	25.98
Dominion Astrophysical Obs.	-123 25 05	48 31 13	0.23	4016 N.	25.52
Faulkes North	-156 15 24	20 42 24	3.05	237 N.	25.76
Hiroshima University Observatory	+132 46 36	34 22 39	0.51	427 N.	25.69
IRTF	-155 28 29	19 49 46	4.18	182 N.	25.76
Kagoshima University Observatory	+130 26 25	31 44 57	0.55	163 N.	25.69
Leuschner Obs.	-122 09 18	37 55 35	0.	3323 N.	25.43
Lowell Obs.	111 39 54	35 12 12	2.22	3580 N.	25.48
Lulin Observatory & TAOS	+120 52 25	23 28 07	2.86	592 S.	25.66
Magdalena Ridge Obs.	–107 11 05	33 58 36	3.22	3689 N.	25.40
Mt. Wilson	-118 03 26	34 13 32	1.74	3222 N.	25.53
Nayoro-shiritsu Observatory	+142 28 59	44 22 27	0.15	1464 N.	25.68
Sendai-shi Observatory	+140 45 18	38 15 22	0.17	803 N.	25.71
Sendai Space Hall	+130 20 23	31 49 26	0.25	172 N.	25.69
Yunnan	+100 01 51	26 42 32	3.1	328 N.	25.53
Geocenter	----------	---------	center of Earth	141 S.	25.40

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 Varuna's shadow in the shadow plane. The errors on all closest approach distances are ±1649 km (one standard deviations). "S." means the site is south of the center of Varuna's shadow. "N." means the site is north of the center of Varuna's shadow.

Table 5: Varuna.20120102 Occultation Predictions for Individual Sites

Site	Varuna Immersion (UT)⁹	UT Mid-Time	KBO Altitude	Solar Altitude⁹	Varuna Emersion (UT)⁹
Akaiwa Ryuten Observatory	13:19:31	13:19:38	54°	-----------	13:19:44
Beijing	-----------	13:20:16	40°	-----------	-----------
Dominion Astrophysical Obs.	-----------	13:15:24	38°	-----------	-----------
Faulkes North	13:15:06	13:15:23	64°	-----------	13:15:40
Hiroshima University Observatory	13:19:31	13:19:42	53°	-----------	13:19:52
IRTF	13:15:01	13:15:19	63°	-----------	13:15:37
Kagoshima University Observatory	13:19:31	13:19:50	51°	-----------	13:20:08
Leuschner Obs.	-----------	13:14:46	37°	-----------	-----------
Lowell Obs.	-----------	13:14:27	28	–16	-----------
Lulin Observatory & TAOS	-----------	13:20:20	42°	-----------	-----------
Magdalena Ridge Obs.	-----------	13:14:21	25	–12	-----------
Mt. Wilson	-----------	13:14:30	33	–21	-----------
Nayoro-shiritsu Observatory	-----------	13:19:08	58°	-----------	-----------
Sendai-shi Observatory	-----------	13:19:16	59°	-----------	-----------
Sendai Space Hall	13:19:32	13:19:50	51°	-----------	13:20:08
Yunnan	13:20:46	13:21:01	25°	-----------	13:21:15
Geocenter	-----------	13:17:18	------	-----------	-----------

⁹The errors on all times are ±1:15 (1 minute and 15 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 Carlos Zuluaga (czuluaga@mit.edu) 2011-12-31 19:50

Please direct all inquiries to pal (pal@mit.edu)

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