Varuna.20110210 Occultation February 10, 2011

(last updated 2011 02 08)

OBSERVER NOTES

Report Your Observations

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 3 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)

2011 February 10 12:37:47± 00:01:181 UT
Minimum Geocentric Separation 0.162± 0.0291 arcsec
Position Angle (Varuna relative to the star; measured north through east) 9.56 degrees
Geocentric Velocity 22.20 km/sec
Occultation Star UCAC2 magnitude 15.52
Occultation Star BVR2 magnitudes B=15.340, V=15.100, R=15.220
KBO Visual Magnitude 20.2
KBO Angular Radius 0.011 arcseconds (approximate)
1One standard deviation of random error.
2The UCAC bandpass (579-642nm) is between V and R. BVR magnitudes obtained from NOMAD Catalog.
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.20110210 Catalog 07 35 38.8650± 0.0961 26 16 06.471± 0.092
Varuna.20110210 Measured3 07 35 38.8564± 0.0192 26 16 06.470± 0.015
from 21 USNO 61-inch frames and 8 CTIO SMARTS 0.9m frames
Table 3: Projected KBO Offsets4 from Reference Ephemeris at the Time of the Event
Body RA (arcsec) Dec (arcsec)  
Varuna

+0.0107± 0.0541

 –0.071± 0.024 See Notes 5 and 6

3Measured position corresponds to RA offset of –0.129 and Dec. offset of –0.001.

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 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 Varuna: (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.

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)
Fairbanks, AK
-147 42 59
64 50 13
0.14
64 N.
22.08
Columbia Basin College
-119 07 36
46 15 08
0.124
5 S.
21.96
Univ. of Washington (Seattle)
-122 20 02
47 36 08
0.0
39 S.
21.97
Palmer, AK
-149 00 35
61 32 42
0.0
119 S.
22.09
Anchorage, AK
-149 43 07
61 08 09
0.0
158 S.
22.36
Bend, OR
-121 18 54
44 03 27
3.6
193 S.
21.96
Lick
-121 38 12
37 20 36
1.290
616 S.
21.96
Breit Ideas
-121 42 10
37 06 47
0.282
635 S.
21.96
Cabrillo College
-121 55 26
36 59 34
0.282
651 S.
21.96
Riverside Astronomical Society
-117 23 43
33 57 11
0.899
683 S.
21.93
Palomar
-116 51 54
33 21 24
1.706
703 S.
21.92
Novosibirsk
+82 55 40
55 02 19
0.1
1700 S.
22.17
Lake Baikal
+107 49 01
53 14 44
1.00
2212 S.
22.26
Hokkaido, Japan
+141 20 52
43 03 48
0.0
3227 S.
22.36
Haleakala
-156 15 24
20 42 24
3.054
3517 S.
22.20
Windward Community College
-157 48 54
21 24 36
0.06
3524 S.
22.21
Leeward Community College
-157 59 04
21 23 28
0.02
3534 S.
22.21
IRTF
-155 28 29
19 49 46
4.182
3564 S.
22.20
Beijing (NAOC)
+117 34 30
40 23 39
0.96
3611 S.
22.42
Sendai, Japan
+141 20 52
38 15 59
0.0
3738 S.
22.38
Nishi-Harima Astronomical Obs.
+134 20 08
35 01 31
0.0
4162 S.
22.40
Yunnan
+100 01 51
26 42 32
3.193
4923 S.
22.34
Lulin Observatory (Taiwan)
+120 28 29
23 28 07
2.862
5484 S.
22.42
Geocenter
----------
---------
center of Earth
4989 S.
22.02

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 ±2720 km (three 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.20110210 Occultation Predictions for Individual Sites

Site
Varuna Immersion (UT)9
UT Mid-Time
KBO Altitude
Solar Altitude9

Varuna Emersion (UT)9
Anchorage, AK
12:35:53
12:36:14
34°
–36°
12:36:36
Beijing (NAOC)
-----------
12:39:36
63°
–34°
-----------
Bend, OR
12:34:32
12:34:52
15°
–29°
12:35:13
Breit Ideas, CA
-----------
12:34:26
13.1°
–29°
-----------
Cabrillo College
-----------
12:34:26
13.2°
–30°
-----------
Columbia Basin College
12:34:40
12:35:03
14.8°
–27°
12:35:25
Fairbanks, AK
12:36:07
12:36:30
32°
–33°
12:36:52
Haleakala
-----------
12:34:05
37°
-----------
-----------
Hokkaido, Japan
-----------
12:38:11
73°
-----------
-----------
IRTF
-----------
12:34:01
36°
-----------
-----------
Lake Baikal
-----------
12:39:51
52°
–26°
-----------
Leeward Community College
-----------
12:34:10
38°
-----------
-----------
Lick
12:34:08
12:34:27
14°
-----------
12:34:32
Lulin Observatory (Taiwan)
-----------
12:39:28
69°
-----------
-----------
Nishi-Harima Astronomical Obs.
-----------
12:38:34
77°
-----------
-----------
Novosibirsk
-----------
12:40:38
38°
–11°
-----------
Palmer, AK
12:35:54
12:36:16
34°
–36°
12:36:38
Palomar
-----------
12:34:17
8°
-----------
-----------
Riverside
-----------
12:34:18
8.6°
–26°
-----------
Sendai, Japan
-----------
12:38:08
77°
-----------
-----------
Yunnan
-----------
12:40:47
52°
–21°
-----------
University of Washington (Seattle)
12:34:44
12:35:07
17°
-----------
12:35:29
Windward Community College
-----------
12:34:10
38°
-----------
-----------
Geocenter
-----------
12:37:47
------
-----------
-----------

9The errors on all times are ±1:18 (1 minutes and 18 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) 2011-02-08 2:30

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