RASNZ Occultation Section - Bettina Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (250) BETTINA - 2000 MAY 30

THIS UPDATE REPLACES THE PREVIOUS UPDATE OF 20 MAY.

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[Prediction by Edwin Goffin]

[Prediction using OCCULT software]

[Detailed finder chart by Jan Manek]

Goffin's path runs to the south of Fiji and New Caledonia before crossing the western parts of the Tasman Sea. The south east extremety of Tasmania including Hobart lie within its boundary. The path given by OCCULT lies around two path widths to the north-west with little change in time, passing to the north of Fiji and crossing the southern tip of New Caledonia. The extreme southern coast of New South Wales and the extreme eastern sections of the Gippsland area in Victoria are also covered. The path then covers the north-western portions of Tasmania.

UPDATE: 27 May 2000

This prediction update has been computed by Jan Manek of the Stefanik Observatory based on astrometry from Ron Stone of the US Navel Observatory - Flagstaff Station and Bill Owen of TMO. The Tycho-2 position of the target star has been used.

Summary:

This update indicates a shift to the north-west of around 5 path widths and around 2 minutes earlier than that given by Goffin. The path clips the northern tip of New Caledonia (12:24 UT), passes very close to Brisbane and includes the Gold Coast/Tweed area (12:30 UT). Further south, the path passes near Dubbo (12:33 UT), Swan Hill (12:37 UT) and between Portland and Mount Gambier (12:38 UT). Observers in Sydney should concentrate on times around 12:33 UT and Melbourne observers around 12:37 UT - both of these cities lie near the edge of the error bands for this update.

Observers should note that the asteroid will be moving very slowly at the time of the occultation (amplifying errors in this update calculation). They are therefore urged to monitor this event for as long a time period as possible. When reading the map below, it is important to note that the circles represent the predicted path, NOT the lines with the time graduations.

THE EVENT AT A GLANCE:

Date and approx. UT time of event: May 30, 2000 @ 12:33 UT
Magnitude of target star: 10.1
Magnitude drop [mag]: 3.0
Estimated maximum duration [s]: 25.0
Path description: See above.
Goffin's original chart reference: A00_0514

The Occultation Path:

Approximate width [km]: 110
Uncertainty [path widths]: 2.5
Uncertainty in time [s]: 50
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 4956 835 = PPM 195933

Constellation: Virgo

J2000 position [h,m,s; ^o,',"]: 12h 53m 16.084s; -07^o 29' 19.25"

Position source: Tycho 2

Estimated accuracy ["]: 0.05" (0.04", 0.04")

V mag [mag]: 10.11

B-V [mag]: +1.20

Remarks:

The target star is in central Virgo around 2 degrees north of psi Virginis (magnitude = 4.8). It is also around 8.8 degrees north-west of Spica (alpha Virginis - magnitude = 1.1) and 6.6 degrees south south-east of gamma Virginis (magnitude = 2.7)
To see a detailed finder chart, click here.

Data for the minor planet:

Number, name: (250) Bettina
Approx. diameter [km]: 86
Source of used astrometry: US Navel Observatory - Flagstaff Station (Ron Stone), TMO (Bill Owen)
Number of used observations: 57 USNO, 2 TMO
Number of rejected observations: 3 USNO, 1 TMO
Time covered by the observations: 1998 09 30 - 2000 05 11
RMS residuals ["] (RA,DE): 0.06", 0.06"
Estimated positional accuracy at epoch of event ["]: 0.06"

Data for the event:

UT date and time of least geocentric approach: 2000 May 30, 12:35.9 UT
Approx. V mag of minor planet at event [mag]: 13.0
Geocentric parallax of minor planet ["]: 3.446
Magnitude drop [mag]: 3.0
Estimated maximum duration [s]: 25.0
Apparent motion of minor planet ["/h]: 6.69
Angular distance to moon, phase of moon [deg,%]: 167, 13%
Update computed by: Jan Manek - Stefanik Observatory - Prague, Czech Republic.

Bettina 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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