ASTROMETRIC UPDATE:
OCCULTATION BY (86) SEMELE - 2002 AUG 12
[Edwin Goffin's Prediction + Finder Charts]
UPDATE: 2002 JUL 17, 20:07 UT
THE UPDATED PATH
On the evening of 2002 Aug 12 UT (morning of August 13 Australian time), the 120 km diameter asteroid (86) Semele will occult a 9.6 mag star in the constellation Pisces for observers along a path across south-central Australia. For observers on the east coast the event will be too close to dawn while the path passes north of Perth on the west coast.
When the occultation occurs, the combined light of the asteroid and the star will drop by 3.4 mag to 12.9 mag (the magnitude of the asteroid) for at most 17.1 seconds.
This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, TMO astrometry for the asteroid kindly provided by Bill Owen, historical astrometry from AstDys, and the following catalogs for the star position: UCAC, Tycho-2.
Additional details of this and other events are available at Steve Preston's website at http://www.oz.net/~stevepr/Asteroids/asteroid.htm
EVENT DETAILS SUMMARY :
- Event Rank : 96
(The event Rank is a measure of the likelihood of observing an event. Currently, the Rank equals
the probability of at least one successful observation by a team of two observers spaced 1/8 path
width just inside opposite sides of the predicted path. This probability is a function of the size
of the asteroid in the sky (in arc seconds), the uncertainty in the position of the asteroid, and
the uncertainty in the position of the star. Eventually, the Rank will also consider factors such
as the brightness of the star, the magnitude drop, and the duration of the event).
- Date and approx. UT time of event : 2002 Aug 12, 20:20 - 20:30 UT
(Refer to map for your own location)
- Magnitude of target star : 9.6
- Magnitude drop [mag] : 3.4
- Estimated maximum duration [s] : 17.1
- Phase of moon, angular distance : 22 % sunlit, 171° distance
- Sun : 115° distance
- Rough path description : Australia
The Occultation Path :
- Approximate projected width [km] : 143
- Uncertainty interval [path widths] : +/- 0.40 (1 sigma)
- Uncertainty interval approx RA,DE ["] : (+/- .068 +/- .038) (1 sigma)
- Uncertainty ellipse (major, minor, PA) : ( .073", .029", 68° ) (1 sigma)
- Remarks :
Data for the target star :
- Name : TYC 0032-00514-1
- Constellation : Pisces
- J2000 position [h,m,s ; °,',"]: RA: 01 40 44.9378 DE: +03 44 20.960
- Position source : Pos: UCAC, pm: Tycho-2, pi:
- Standard error : RA,DE ["]: ( .021, .017 )
- V mag [mag] : 9.6
- Remarks : (none)
Data for the minor planet :
- Number, name : (86) Semele
- Approx. diameter [km] : 120
- Approx. diameter [arcsec] : .086
- Source of used astrometry : FASTT TMO Astdys
- Number of used observations : 420
- Number of rejected observations : 40
- Time covered by the observations : 1907 May 18 - 2001 Sep 02
- 1 sigma uncertainty ellipse (major, minor, PA) : 0.070, 0.024, 66°
- Remarks :
- Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).
IMPORTANT NOTE!
Astrometric updates such as these should not be taken as definitive, but rather only as an indication of where the true track may lie relative to the original predicted track. Observers must bear in mind that later astrometry, in which the target star is measured in the same field as the asteroid, may still reveal substantial changes to the predicted track and time of the event. For this reason it is most important that observers far from the predicted track still monitor the event.
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