RASNZ Occultation Section - Diotima Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (423) DIOTIMA - 2001 AUGUST 22

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[Prediction using OCCULT software + finder charts]

The path given by Occult crosses the Cook Strait area of New Zealand including Wellington.

UPDATE: 19 August 2001

This prediction update has been computed by Steve Preston of Medina, Washington (state) in the United States based on astrometry from Ron Stone of the US Naval Observatory - Flagstaff Station supplemented with data from the AstDys database. The UCAC position of the target star has been used combined with proper motion information from Tycho 2.

Summary:

This updated path lies around two path widths to the south of that given by Occult and around 10 seconds earlier. The new path covers the south island of New Zealand between Timaru and Balclutha including Dunedin around 7:09:15 UT.

While the error tolerance for this calculation is among the smaller seen so far, there are reasonable chances of seeing an occultation from any point of the South Island south of around Christchurch. (The uncertainty circle on the graphic below is the 1 sigma limit).

Observers should note that the target star is faint (magnitude = 12.1). The magnitude drop for this event is only 1.4 and any observer who can comfortably monitor the target star may well see the asteroid during any occultation.

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: August 22, 2001 @ 7:09 UT
Magnitude of target star: 12.1
Magnitude drop [mag]: 1.4
Estimated maximum duration [s]: 6.3
Path description: See above.

The Occultation Path:

Approximate width [km]: 276
Uncertainty [path widths]: 0.4 (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 4973-00537-1 = GSC 4973 537
Constellation: Virgo
J2000 position [h,m,s; ^o,',"]: 13h 43m 42.3654s; -5^o 55' 20.994"
Position source: UCAC position + Tycho 2 proper motion
Estimated accuracy ["]: 0.042" (0.030", 0.030")
V mag [mag]: 12.1
Remarks:
The target star is in central Virgo. It lies 7 degrees northeast of Spica (alpha Virginis - magnitude = 1.1) and two degrees east-southeast of 80 Virginis (magnitude = 5.7).
A set of finder charts are available with the Occult prediction and can be viewed by clicking here.

Data for the minor planet:

Number, name: (423) Diotima
Approx. diameter [km]: 208
Source of used astrometry: US Naval Observatory - Flagstaff Station (Ron Stone), AstDys
Number of used observations: 700
Number of rejected observations: 46
Time covered by the observations: 1904 03 12 - 2001 06 15
Uncertainy Ellipse ["] (major axis, minor axis, PA): 0.019", 0.017", 134°.

Data for the event:

UT date and time of least geocentric approach: 2001 August 22, 7:06.9 UT
Approx. V mag of minor planet at event [mag]: 13.2
Geocentric parallax of minor planet ["]: 2.570
Magnitude drop [mag]: 1.4
Estimated maximum duration [s]: 6.3
Apparent motion of minor planet ["/h]: 42.00
Angular distance to moon, phase of moon [deg,%]: 12, 15%
Update computed by: Steve Preston, Medina, Washington, USA. (OrbFit)

Diotima 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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