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OCCULTATION OF TYC 1879-00902-1 BY 158 Koronis
2012 January 19

A 3.68 second occultation was recorded by Patrick Purcell, using Video OSD technique.

And a 4.2 second occultation was recorded by Diana Watson, using Visual technique.

The predicted maximum time was 3.5 seconds.

This event has proved very interesting to analyse.

View the updated prediction.

  1    D Watson,Thornton near Whakatane, NZ
  2    P Purcell,CHAPMAN, ACT, AU, revised
  3(P) Prediction, Jan 15


Koronis occultation - 2012 January 19


The ellipse above is plotted at the same area as the predicted circle of 35 km. With two independant chords we can be confident of the path of Koronis and that it was just north of the predicted line. The ISAM 3D model has been overlaid on the measured ellipse and shows a good fit.
Diana had said her visual timing may have been a bit slow so when I first saw the times I thought that might explain the offset between the chords. When I looked more closely and got the ISAM 3D model overlaid it became clear that the offset is mainly real due to the shape of the rock and the longer than expected times are due to the orientation.

Patrick's Limovie light curve below shows an interesting step during the R at about 50% light intensity which lasts for 2 integration periods. Normally we would ask for 3 periods at the intermediate level to indicate a new double star.

Koronis occultation - 2012 January 19

If we assume that it is a double star then the following plot shows the fit to 2 stars.

Koronis occultation - 2012 January 19

This gives a separation of 4.3 milliarcseconds and PA of 169 degrees.
Diana's report of slow visual changes can also be understood by this solution.

On balanace the evidence for a double while tantalising but probably not good enough to make a formal claim how ever it is worth flagging this star as a "Possible Close Double".

Observational Data:

Observation details for MP (158) Koronis
By Star              TYC 1879-00902-1
On 2012-01-19  at 12:03:28.0


Observer   Diana Watson
Location   Thornton near Whakatane, NZ
Longitude  +176:51
Latitude   -37:55
Altitude   3 m
Datum      Other
Telescope SCT including Cass and Mak
Aperture  20 cm
Seeing     Steady Thin cloud < 2
Camera Type
Camera Delay
Timing     Tape Recorder + time signal Visual, no PE applied
Disappearance  12:03:28.00
Reappearance   12:03:32.20
Comments: After minute 5 thin cloud causing star to flicker in ond out
sevaral times and wipe out after 9th minute.
My feeling is that the D was hesitant but the return reasonably fast.

Observer   Patrick Purcell
Location   CHAPMAN, ACT, AU
Longitude  +149:02
Latitude   -35:21
Altitude   642 m
Datum      WGS84
Telescope SCT including Cass and Mak
Aperture   20 cm
Seeing     Slight flickering Broken cloud
Camera Type
Camera Delay
Timing     GPS - other linking Video with frame analysis
Disappearance  12:07:24.19 (revised to 12:07:24.42)
Reappearance   12:07:27.87 (revised to 12:07:28.01)
    (Or if we assume a double the 12:07:27.94 for r1 and 12:07:28.26 for r2)
Comments: Watec N120+ video camera with integration set to 4.
VTI used. Some broken cloud but clear at time of event.


Return to 2012 occultation results

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