Varuna.20120102 Occultation January 02, 2012

(last updated 2011 12 31)

OBSERVER NOTES

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

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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