Sedna.20121225 Occultation December 25, 2012

(last updated 2012 11 27)

OBSERVER NOTES

 

Across the globe pictured above, the three solid lines correspond to the northern limit, centerline, and southern limit of Sedna's shadow. The northern and southern limits correspond to a radius of 928 km. The upper and lower dashed lines indicate 3-sigma errors. The shaded area represents where the sun is more than 12 degrees below the horizon.
Table 1: Prediction Details
Sedna Geocentric Mid-time (yyyy month dd hh:mm:ss)

2012 December 25 03:32:51± 00:03:141 UT

Sedna Minimum Geocentric Separation 0.072± 0.0561 arcsec
Position Angle (Sedna relative to the star; measured north through east) –1.62 degrees
Geocentric Velocity 19.18 km/sec
Occultation Star USNOB R magnitude 18.712

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
Sedna.20121225 Catalog 03 33 12.9280 ± 0.1530 +06 46 51.140 ± 0.071
Sedna.20121225 Measured3 03 33 12.9295 ± 0.0120 +06 46 50.814 ± 0.005
From 3 USNO 61-inch frames
Table 3: Projected KBO Offsets from Reference Ephemeris at the Time of the Event
Body RA (arcsec) Dec (arcsec)  
Sedna

0.0613 ± 0.0595

–0.037 ± 0.056 See Notes 5 and 6

3Measured position corresponds to RA offset of +0.0218 and Dec. offset of –0.326.

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 (Sedna source file: JPL18; 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 4: Site Information

Site
East Longitude
Latitude

Site Altitude6

(km)

Distance7

(km)

Velocity

(km/s)

Wallace
–71 29 06
42 36 36
0.11
793 N.
19.50
Geocenter
----------
---------
center of Earth
4489 N.
19.18

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 Sedna's shadow in the shadow plane. The errors on all closest approach distances are ±3608 km (one standard deviation). "S." means the site is south of the center of Sedna's shadow. "N." means the site is north of the center of Sedna's shadow.

Table 5: Sedna.20130110 Occultation Predictions for Individual Sites

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

KBO Emersion (UT)9

Wallace
03:30:50
03:31:15
-----------
-----------
03:31:39
Geocenter
-----------
03:32:51
-----------
-----------
-----------

9The errors on all times are ±3:14 (3 minutes, 14 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.


Last updated by Carlos Zuluaga (czuluaga@mit.edu) 2012-11-27 12:38

Please direct all inquiries to PAL (planetary-astronomy@mit.edu)