RASNZ Occultation Section - Polyxo Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (308) POLYXO - 2001 JUNE 20

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[Prediction by Edwin Goffin]

[Prediction using OCCULT software]

The path given by Edwin Goffin runs from the Sydney/Canberra area west across northern Victoria and southern New South Wales and includes most of South Australia south and east of Adelaide. The path given by Occult lies around 1.5 path widths to the south and around 1 minute earlier. This path includes much of central Victoria including metropolitan Melbourne as well as the southeastern extremeties of New South Wales and South Australia.

UPDATE: 15 June 2001

This prediction update has been computed by Steve Preston of the Medina, Washington (state) in the United States based on astrometry from Ron Stone of the US Naval Observatory - Flagstaff Station supplemented with historical data from the AstDys database. The UCAC position of the target star has been used combined with Tycho proper motion and parallax data.

Summary:

This update indicates a shift of around 1.5 path widths to the south and around 90 seconds earlier than that given by Goffin. The path misses the northern tip of the North Island of New Zealand (16:04:30 UT) before crossing the Tasman Sea to the New South Wales coastline. It covers the coastline between Bermagui and Cape Howe (16:06:20 UT) running west to cover the Victorian high country and metropolitan Melbourne at 16:07 UT. Further west, the path includes Ballarat and Hamilton in Victoria and Mount Gambier in South Australia (16:07:30 UT) before passing into the Southern Ocean.

Observers should note that the magnitude fall for this event is only 1.4. In this case, if the target star is comfortably visible then the asteroid will most likely also be visible in the event of an occultation - ie. a complete disappearence of the asteroid/star image at the time of the occultation is unlikely.

Additional details of this and other events are available at Steve Preston's website at http://www.oz.net/~stevepr/Asteroids/asteroid.htm

THE EVENT AT ONE GLIMPSE:

Date and approx. UT time of event: 20 June 2001 @ 16:06 UT
Magnitude of target star: 11.04
Magnitude drop [mag]: 1.4
Estimated maximum duration [s]: 18.7
Path description: See above.
Goffin's original chart reference: A01_0622

The Occultation Path:

Approximate width [km]: 160
Uncertainty [path widths]: 0.5 (1 sigma error band)
Map: See below
Remarks: Uncertainities are given on the basis of the nominal star position errors and the expected asteroid positional accuracy.
Circles along the path are OCCULT calculated exact centerline points !!!!

Data for the target star:

Name: TYC 5623-00707-1
Constellation: Scorpius
J2000 position [h,m,s; ^o,',"]: 16h 03m 04.760s; -14^o 16' 31.38"
Position source: UCAC 1 + Tycho 2 proper motion and parallax
Estimated accuracy ["]: 0.042" (0.030", 0.030")
V mag [mag]: 11.04
B-V [mag]: +0.49
Remarks:
The target star is in northwestern Scorpius near the border with Libra. It lies 1.1 degrees east of 48 Librae (magnitude = 4.7).

Data for the minor planet:

Number, name: (308) Polyxo
Approx. diameter [km]: 148.0
Source of used astrometry: US Naval Observatory - Flagstaff Station (Ron Stone), AstDys
Number of used observations: 714
Number of rejected observations: 66
Time covered by the observations: 1902 10 07 - 2001 06 07
Uncertainy Ellipse ["] (major axis, minor axis, PA): 0.019", 0.018", 91°.

Data for the event:

UT date and time of least geocentric approach: 2001 June 20, 16:16.4 UT
Approx. V mag of minor planet at event [mag]: 12.11
Geocentric parallax of minor planet ["]: 5.09
Magnitude drop [mag]: 1.4
Estimated maximum duration [s]: 18.7
Apparent motion of minor planet ["/h]: 22.67
Angular distance to moon, phase of moon [deg,%]: 163, 1%
Update computed by: Steve Preston, Medina, Washington, USA. (OrbFit)

Polyxo Update

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.

Use these links for further information:
[Planetary Occultations] [Using the Predictions]
[Observing Details] [Timing Details] [Reporting Details] [Report Form]
[Asteroid Occultation Results]

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