ASTROMETRIC UPDATE:
OCCULTATION BY (85) IO - 2003 MAY 02
[Edwin Goffin's Prediction + Finder Charts]
UPDATE: 2003 APR 25, 21:45 UT
THE UPDATED PATH
On the evening of 2003 May 02 UT (before dawn on the 3rd), the 154 km diameter asteroid (85) Io will occult a 11.0 mag star in the constellation Aquila for observers along a path across Australia.
In the case of an occultation, the combined light of the asteroid and the star will drop by 1.2 mag to 11.8 mag (the magnitude of the asteroid) for at most 7.8 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.
Additional details of this and other events are available at Steve Preston's website at http://www.asteroidoccultation.com/
EVENT DETAILS SUMMARY :
- Event Rank : 99
(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 : 2003 May 02, 20:01 - 2003 May 02, 20:12 UT
(Refer to map for your own location)
- Magnitude of target star : 11.0
- Magnitude drop [mag] : 1.2
- Estimated maximum duration [s] : 7.8
- Phase of moon, angular distance : 2 % sunlit, 107° distance
- Sun : 93° distance
- Rough path description : Australia
The Occultation Path :
- Approximate projected width [km] : 158
- Uncertainty interval [path widths] : +/- 0.27 (1 sigma)
- Uncertainty interval approx RA,DE ["] : (+/- .037 +/- .028) (1 sigma)
- Uncertainty ellipse (major, minor, PA) : ( .037", .028", 84° ) (1 sigma)
- Remarks :
Data for the target star :
- Name : TAC +04#13968
- Constellation : Aquila
- J2000 position [h,m,s ; °,',"]: RA: 20 31 55.1749 DE: -04 57 06.932
- Position source : Pos: UCAC, pm: Preston, pi:
- Standard error : RA,DE ["]: ( .024, .022 )
- V mag [mag] : 11.0
- Remarks : (none)
Data for the minor planet :
- Number, name : (85) Io
- Approx. diameter [km] : 154
- Approx. diameter [arcsec] : .109
- Source of used astrometry : FASTT TMO Astdys
- Number of used observations : 743
- Number of rejected observations : 88
- Time covered by the observations : 1904 Oct 09 - 2002 Jul 21
- 1 sigma uncertainty ellipse (major, minor, PA) : 0.028, 0.018, 80°
- 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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