RASNZ Occultation Section - Rotraut Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (874) ROTRAUT - 2002 MAY 04

UPDATE: 2002 APR 23, 01:19 UT

THE UPDATED PATH

On 2002 May 04 UT (morning of May 5), the 56 km diameter asteroid (874) Rotraut will occult a 11.3 mag star in the constellation Aquarius for observers along a path across Tasmania (running between LAUNCESTON and HOBART) and New Zealand (directly crossing HAMILTON, ROTORUA and WHAKATANE). Auckland and Gisborne lie within the formal path uncertainty.

When the occultation occurs the combined light of the asteroid and the star will drop by 4.7 mag to 16.0 mag (the magnitude of the asteroid) for at most 3.1 seconds. As the star is only 15 degrees from a 47% sunlit moon larger telescopes may be required.

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, historical astrometry from AstDys, and the UCAC and Tycho-2 catalogs for the star position.

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 : 38
(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 04, 15:33.7 (Tasmania) - 2002 May 04, 15:34.7 (New Zealand) UT
(Refer to map for your own location)
Magnitude of target star : 11.3
Magnitude drop [mag] : 4.7
Estimated maximum duration [s] : 3.1
Phase of moon, angular distance : 47 % sunlit, 15° distance
Sun : 86° distance
Rough path description : Tasmania, New Zealand

The Occultation Path :

Approximate projected width [km] : 57
Uncertainty interval [path widths] : +/- 1.76 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .060 +/- .041) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .060", .041", 83° ) (1 sigma)
Remarks :

Data for the target star :

Name : TYC 5201-00781
Constellation : Aquarius
J2000 position [h,m,s ; °,',"]: RA: 21 09 14.8779 DE: -04 57 50.525
Position source : Pos: UCAC, pm: Tycho-2, pi:
Standard error : RA,DE ["]: ( .030, .030 )
V mag [mag] : 11.3
Remarks : (none)

Data for the minor planet :

Number, name : (874) Rotraut
Approx. diameter [km] : 56
Approx. diameter [arcsec] : .025
Source of used astrometry : FASTT Astdys
Number of used observations : 289
Number of rejected observations : 11
Time covered by the observations : 1917 May 25 - 2001 Jul 16
1 sigma uncertainty ellipse (major, minor, PA) : 0.052, 0.028, 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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