55636.20091009 Occultation October 09, 2009

(last updated 2009 10 08)

 

 

Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of 55636's shadow. The northern and southern limits correspond to a radius of 405 km (using an assumed albedo of 0.1). The upper and lower dashed lines indicate the effects of unknown systematic errors such as catalog zone errors. Previous KBO appulse analyses have shown the observed error to be 1.5-2 times that of the prediction's random 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 55636, (ii) to probe for a tenuous atmosphere of 55636, and (iii) to detect possible nearby satellites of 55636.

Observations are worthwhile and encouraged from any location at which the event 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 systematic effect uncertainties shown.

 

Table 1: Prediction Details
Geocentric Mid-time (yyyy month dd hh:mm:ss)

2009 October 09 10:30:07± 00:00:081 UT

Minimum Geocentric Separation 0.0593± 0.00631 arcsec
Position Angle (55636 relative to the star; measured north through east) 158.90 degrees
Geocentric Velocity 25.29 km/sec
Occultation Star UCAC2 magnitude 13.12
KBO Visual Magnitude 19.6
KBO Angular Radius 0.013 arcseconds (approximate)
Prediction Version 55636.20091009-AST-13.0
1One standard deviation of random error.
2The UCAC bandpass (579-642nm) is between V and R.

 

Table 2: Reference Star Position
Reference star position:
(UCAC2, at epoch of event)
RA (h:m:s; J2000) Dec (d:m:s; J2000) Notes
55636.20091009 Catalog 00 37 13.6103± 0.0028 28 22 22.981± 0.092
55636.20091009 Measured3 00 37 13.6193± 0.0002 28 22 23.023± 0.002
From 11 USNO 40-inch telescope frames and 58 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)  
55636

+0.2654± 0.0075

–0.073± 0.006 See Notes 5 and 6

3Measured position corresponds to RA offset of +0.1341'' and Dec. offset of +0.041''.

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 55636 is that given by JPL Horizon's ephemeris (55636 source file: JPL#7; Earth center source file: DE405).

6Data from the SMARTS 0.9m (35 frames) , USNO 40-inch (7 frames), and USNO 61-inch (28 frames) 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 55636: (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
East Longitude
Latitude

Site Altitude6

(km)

Distance7

(km)

Velocity

(km/s)

Behlen Observatory (Nebraska U.)
–96 26 48
41 10 18
0.362
2812 N.
25.47
Fickle Hill Observatory
–123 59 09
40 48 08
0.61
2407
25.49
Puckett Observatory
–84 55 00
33 45 00
0.30
2381 N.
25.42
Lick Obs.
–121 38 12
37 20 36
1.29
2032 N.
25.58
Fremont Peak
–121 29 55
36 45 36
0.84
1968 N.
25.59
USNO
–111 44 24
35 11 00
2.31
1881 N.
25.55
M.R.O.
–107 11 05
33 58 36
2.22
1818 N.
25.54
Pomona College
–117 42 35
34 05 51
0.35
1698 N.
25.58
Puerto Rico (Arecibo)
–66 45 12
18 20 36
0.50
1643 N.
25.31
Mt. Graham (VTT)
–109 53 21
32 42 04
3.19
1635 N.
25.56
Palomar
–116 51 54
33 21 24
1.71
1623 N.
25.58
Arizona Sky Village (David Churchill)
–109 07 33
31 56 49
1.4
1565 N.
25.55
Arizona Sky Village (Jack Newton)
–109 07 08
31 55 30
1.4
1562 N.
25.55
McDonald Observatory (Mt. Locke)
–104 01 21
30 40 17
2.08
1520 N.
25.53
Guillermo Haro Obs.
–110 23 05
31 03 10
2.480
1447 N.
25.58
San Pedro Martir, Mexico
–115 27 49
31 02 39
2.83
1382 N.
25.58
Brownsville, Texas
–97 29 22
25 56 47
0.121
1171 N.
25.51
Leeward Community College
–157 59 04
21 23 28
0.02
743 N.
25.70
Windward Community College
–157 48 54
21 24 36
0.06
740 N.
25.70
Haleakala
–156 15 24
20 42 24
3.05
620 N.
25.70
IRTF
–155 28 29
19 49 46
4.18
506 N.
25.70
Mauna Kea Mid-Level
–155 27 15
19 45 36
2.8
499 N.
25.70
Tonantzintla Observatory
–98 18 50
19 01 58
2.2
420 N.
25.52
Acapulco
–99 53 16
16 51 33
0.0
152 N.
25.54
Obs. Ast. de la UNAN - Managua (Nicaragua)
–86 16 14
12 06 25
0.25
127 N.
25.69
Cairns, Australia
145 46 28
–16 55 25
0.08
1 N.
25.50
Townesville
146 45 00
–19 15 00
0.0
254 S.
25.24
Black Springs
138 53 18
–33 53 58
0.47
994 S.
25.43
Toowoomba
151 57 00
–27 34 12
0.69
1218 S.
25.51
Siding Spring
149 03 44
–31 16 17
1.21
1337 S.
25.49
Grove Creek Obs. (Sydney)
149 21 59
–33 49 46
0.90
1538 S.
25.48
Mount Stromlo
149 03 44
–35 18 57
0.81
1624 S.
25.48
Hobart
147 26 24
–42 48 18
0.04
2042 S.
25.45
Auckland
174 46 42
–36 54 24
0.80
2943 S.
25.59
Mt. John
170 27 50
–43 59 22
1.04
3108 S.
25.54
Geocenter
----------
---------
center of Earth
1758 S.
25.29

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 55636's shadow in the shadow plane. The errors on all closest approach distances are ±184 km (one standard deviation). "S." means the site is south of the center of 55636's shadow. "N." means the site is north of the center of 55636's shadow.

Table 5: 55636.20091009 Occultation Predictions for Individual Sites

Site
55636 Immersion (UT)9
UT Mid-Time
KBO Altitude
Solar Altitude9

55636 Emersion (UT)9

Acapulco
10:26:21
10:26:36
27°
-----------
10:26:51
Arizona Sky Village (Jack Newton)
-----------
10:26:58
41°
-----------
-----------
Arizona Sky Village (David Churchill)
-----------
10:26:58
41°
-----------
-----------
Auckland
-----------
10:32:25
24°
-----------
-----------
Behlen Observatory (Nebraska U.)
-----------
10:26:40
33°
-----------
-----------
Black Springs
-----------
10:33:50
11°
-----------
-----------
Brownsville, Texas
-----------
10:26:30
30°
-----------
-----------
Cairns, Australia
10:33:27
10:33:42
27°
-----------
10:33:58
Fickle Hill Observatory
-----------
10:27:40
52°
-----------
-----------
Fremont Peak
-----------
10:27:32
51°
-----------
-----------
Guillermo Haro Obs.
-----------
10:27:01
42°
-----------
-----------
Grove Creek Obs. (Sydney)
-----------
10:33:31
17°
-----------
-----------
Haleakala
-----------
10:29:40
78°
-----------
-----------
Hobart
-----------
10:33:25
-----------
-----------
Leeward Community College
-----------
10:29:40
78°
-----------
-----------
Lick Obs.
-----------
10:27:33
51°
-----------
-----------
M.R.O.
-----------
10:26:55
40°
-----------
-----------
IRTF
-----------
10:29:38
76°
-----------
-----------
Mauna Kea Mid-Level
-----------
10:29:38
76°
-----------
-----------
McDonald Observatory (Mt. Locke)
-----------
10:26:46
37°
-----------
-----------
Mt. Graham (VTT)
-----------
10:27:00
41°
-----------
-----------
Mt. John
-----------
10:32:35
17°
-----------
-----------
Mt. Stromlo
-----------
10:33:30
15°
-----------
-----------
Obs. Ast. de la UNAN - Managua (Nicaragua)
10:25:57
10:26:12
15°
-16°
10:26:27
Palomar
-----------
10:27:19
46°
-----------
-----------
Pomona College
-----------
10:27:21
48°
-----------
-----------
Puckett Observatory
-----------
10:26:15
21°
-15°
-----------
Puerto Rico (Arecibo)
-----------
10:25:54
21°
-----------
San Pedro Martir, Mexico
-----------
10:27:14
46°
-----------
-----------
Siding Spring
-----------
10:33:33
18°
-----------
-----------
Tonantzintla Observatory
-----------
10:26:32
28°
-----------
-----------
Toowoomba
-----------
10:33:28
23°
-----------
-----------
Townsville
10:33:28
10:33:41
25°
-----------
10:33:53
USNO
-----------
10:27:06
42°
-----------
-----------
Windward Community College
-----------
10:29:45
78°
-----------
-----------
Geocentric
-----------
10:30:07
-----------
-----------

9The errors on all times are ±0:08 (8 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 Michael J Person (mjperson@mit.edu) 2009-10-08 14:00

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