RASNZ Occultation Section - Phyllis Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (556) PHYLLIS - 2002 FEB 26

UPDATE: 2002 FEB 19, 04:42 UT

THE UPDATED PATH

On the evening of February 26 the 37 km diameter asteroid (556) Phyllis will occult a 11.0 mag star in the constellation Leo for observers along a path across New Zealand (where the path is likely to cross south Auckland, Hamilton, Tauranga and Whakatane and pass not far from Gisborne around 12:37 UT) and Australia (eastern New South Wales around 12:41 UT).

In the case of an occultation, the combined light of the asteroid and the star will drop by 1.7 mag to 12.4 mag (the magnitude of the asteroid) for at most 4.1 seconds.

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, 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 :

Date and approx. UT time of event : 2002 Feb 26, 12:32 - 12:50 UT (Refer to map for your own location)
Magnitude of target star : 11.0
Magnitude drop [mag] : 1.7
Estimated maximum duration [s] : 4.1
Phase of moon, angular distance : 99 % sunlit, 11° distance
Sun : 166° distance
Rough path description : New Zealand, Australia

The Occultation Path :

Approximate projected width [km] : 47
Uncertainty interval [path widths] : +/- 1.11 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .043 +/- .037) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .043", .037", 102° ) (1 sigma)
Remarks :

Data for the target star :

Name : TYC 0242-01450
Constellation : Leo
J2000 position [h,m,s ; °,',"]: RA: 09 43 01.6232 DE: +06 53 55.113
Position source : Pos: UCAC, pm: Tycho-2, pi:
Standard error : RA,DE ["]: ( .030, .030 )
V mag [mag] : 11.0
Remarks :

Data for the minor planet :

Number, name : (556) Phyllis
Approx. diameter [km] : 37
Approx. diameter [arcsec] : .039
Source of used astrometry : FASTT Astdys
Number of used observations : 347
Number of rejected observations : 30
Time covered by the observations : 1907 Sep 06 - 2002 Feb 15
1 sigma uncertainty ellipse (major, minor, PA) : 0.031, 0.022, 113°
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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