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OCCULTATION OF TYC 7803-01437-1 BY 89 Julia
2012 April 20

This event has been updated 2012 May 15 - See below.

Two positive chords were initially recorded by widely spaced observers Chris Chad and Jacquie Milner, using video OSD technique.

View the updated prediction.

  1    C Chad, Gunnedah, NSW,AU
  2    J Milner,Glen Forrest, Western Australia, AU
  3(P) Prediction


Julia occultation - 2012 April 20


The ellipse above was plotted at the best fit to the two chords. This reults in an area about 81% of the predicted circle of 175km. With two chords we can be confident of the path of Julia and that it was very close to the predicted line.

Julia occultation - 2012 April 20
The Damit 3D model above has been overlaid on the measured ellipse and rotated to give a good fit to the chords. This may or may not be the correct orientaion at the time and this will be reviewed when the correct orientation is known.

The figure below shows the Chris' Tangra light curve of the occultation.

Julia occultation - 2012 April 20

The figure below shows the Jacquie's Tangra light curve of the occultation.

Julia occultation - 2012 April 20

A great result!

However - there was some discussion as to whether Jacquie's curve was real or noise. Also a correct for time DAMIT model was obtained which implies that her chord is very near to a graze as seen below.

Julia occultation - 2012 April 20

Her data was put through Occular which gave very slightly different times from the original but gave it high confidence even though the magnitude drop that Occular measured was only about half the predicted drop. Other plots using normalisation gave similat but not so confident results.
After further discussion we decided we could not be fully confident that the data represents an occultation.
Points For:
- There appears to be a small dip over a long period
- Occular agrees with location
- The times look in good agreement with the prediction, the DAMIT model and Chris' time.

Points Against:
- Mag drop does not agree with prediction (but could be caused by graze)
- Other Occular runs are not so confident
- Signal to noise ratio < 1

So the conclusion is that for archival purposes we do not feel 100% confident that Jacqui's chord is real and so it will be reported to MPC as a singlechord event with the object circle of 175 km diameter,centered on Chris' chord. Because of the doubt the object has not been drawn using Jacquie's chord as a constraint and we cannot be sure which side of Chris' chord it lies.

Julia occultation - 2012 April 20
This write up serves to record the doubt.

Observational Data:

Observation details for MP ( 89 ) Julia
By Star              TYC 7803-01437-1
On 2012-04-20  at 16:35:40.0


Observer   Chris Chad
Location   Gunnedah, New South Wales
Longitude  +150:15
Latitude   -30:59
Altitude   315 m
Datum      WGS84
Telescope Newtonian
Aperture   15 cm
Seeing     Slight flickering Clear
Camera Type  Other integrating            NTSC/EIA
Camera Delay 0
Timing     GPS - time inserted Video with frame analysis
Disappearance  16:35:36.86
Reappearance   16:35:45.07
Comments: My first ever positive (I'm chuffed)!
Low magnitude drop and still noisy,
so not 100% confident with times. Samsung SCB-2000 (modded) -
waits one frame before sending signal, so 34ms subtracted from times.
Rolling interference in video (possibly from mount - yet to be resolved)


Observer   Jacquie Milner
Location   Glen Forrest, Western Australia, AU
Longitude  +116:05
Latitude   -31:54
Altitude   262 m
Datum      WGS84
Telescope SCT including Cass and Mak
Aperture   20 cm
Seeing     Steady Clear
Camera Type
Camera Delay
Timing     GPS - time inserted Video with frame analysis
Disappearance  16:39:37.56 (Occular 16:39:38.027)
Reappearance   16:39:42.68 (Occular 16:39:43.300)
[But will be treated as a Miss (see above) ]
Comments: Focal reducer used, 4x integration used and
a -0.110 second correction applied to times. S/N 0.9

Return to 2012 occultation results

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