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A 0.36 second occultation was recorded by Dave Herald at Beacon, WA, Australia, using video and GPS technique.
View the updated prediction.
Observers: 1 D Herald, Beacon, WA, Australia
Discussion:
The circle above is plotted at the expected 24km diameter of Graff. With only one chord it is not possible to determine whether Dave was north or south of the central line of the event. However, assuming the updated prediction was approximately correct would suggest that the chord might lie across the southern portion of the asteroid.
Observational Data:
Observer's Name : D Herald
Aperture (cm) : 20cm
Focal length (cm) : 200cm
Type (e.g. SCT; Newtonian) : SCT
Magnification : -
Observing site name : Beacon, WA
Longitude (DD MM SS ; East +ve) : 117 52 04.1
Latitude (DD MM SS ; South -ve) : -30 26 59.5
Height above Sealevel (metres) : 373
Geodetic Datum (e.g.WGS84,NZ1949): WGS84
Height Datum (if known) : WGS84
Sky Transparency (Delete two) : Good
Star Image Stability (Delete two): Good
Other Conditions:
TIMINGS: (PLEASE REPORT IN UNIVERSAL TIME)
Time Source (e.g. WWVH, GPS) : GPS
Recording method (e.g. tape) : Video
Could you see the Asteroid? : no
Approx. Limiting Magnitude :
| Estimated |
Universal Time | Reaction | Accuracy, Remarks
h m s | Time (sec) |
Started Observing :
Star and Object Merged :
Disappearance At : 16 56 29.56 to 29.72
Reappearance At : 16 56 30.32 to 30.88
Star and Object Separated :
Stopped Observing :
ADDITIONAL COMMENTS: Definite non-instantaneous events. R much longer than D.
Estimated star diameter is 0.00093". Expected diameter of asteroid 0.010".
So gradual event is from stellar diameter.
Earlier comments:
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I've just recorded an occultation of a mag 6 star by the 24km asteroid 3202 Graff,
from where I'm staying in Western Australia. I was almost 1 sigma north of the predicted
path - which means the occultation would have been visible in Brisbane & Towoomba. Maximum
duration was predicted to be 1.8 secs.
The occultation was quite short - about 1 second. It appears as though I had a near-grazing
event. The light curve is very interesting. The D was gradual over 0.16 secs, while the R
was gradual over 0.56secs. The light curve is continuous - not a stepped event. The star is
very red (Mv 6.15, Mb 7.15) and the parallax reasonably large (0.0130") so I was almost certainly
seeing the effects of the stellar diameter.
Later comments:
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In my model, the different durations can be explained on the basis of a significantly elliptic
asteroid - such that on ingress the star path was much closer to the normal to the surface than
for the egress. I shall have to play around with the data, but I'm thinking that an ellipticity
of the asteroid might be derivable - assuming an average diameter....