RASNZ Occultation Section - Lanzia Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (683) LANZIA - 2002 MAY 28

UPDATE: 2002 MAY 04, 05:20 UT

THE UPDATED PATH

On the evening of 2002 May 28 UT, the 82 km diameter asteroid (683) Lanzia will occult a 10.8 mag star in the constellation Sagittarius for observers along a path across northern New Zealand, Australia. The path includes Gisborne, the Bay of Plenty area trough to Auckland and further north. The event will be very difficult to monitor due to the near full moon only 5 degrees from the target star.

In the case of an occultation, the combined light of the asteroid and the star will drop by 2.3 mag to 13.0 mag (the magnitude of the asteroid) for at most 6.5 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.oz.net/~stevepr/Asteroids/asteroid.htm

EVENT DETAILS SUMMARY :

Event Rank : 67
(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 May 28, 09:46 - 2002 May 28, 09:59 UT
(Refer to map for your own location)
Magnitude of target star : 10.8
Magnitude drop [mag] : 2.3
Estimated maximum duration [s] : 6.5
Phase of moon, angular distance : 95 % sunlit, 5° distance
Sun : 160° distance
Rough path description : N New Zealand, Australia

The Occultation Path :

Approximate projected width [km] : 107
Uncertainty interval [path widths] : +/- 0.88 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .058 +/- .042) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .059", .041", 80° ) (1 sigma)
Remarks :

Data for the target star :

Name : TYC 6828-00429
Constellation : Sagittarius
J2000 position [h,m,s ; °,',"]: RA: 17 47 25.3458 DE: -23 04 45.800
Position source : UCAC
Standard error : RA,DE ["]: ( .031, .031 )
V mag [mag] : 10.8
Remarks : (none)

Data for the minor planet :

Number, name : (683) Lanzia
Approx. diameter [km] : 82
Approx. diameter [arcsec] : .054
Source of used astrometry : FASTT TMO Astdys
Number of used observations : 298
Number of rejected observations : 16
Time covered by the observations : 1913 Apr 03 - 2002 May 03
1 sigma uncertainty ellipse (major, minor, PA) : 0.050, 0.026, 76°
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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