RASNZ Occultation Section - Ekard Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (694) EKARD - 2000 APRIL 29

THIS UPDATE REPLACES THE PREVIOUS UPDATE OF 21 APRIL.

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[Prediction by Edwin Goffin]

[Prediction using OCCULT software]

[Detailed finder chart by Jan Manek]

Goffin's predicted path crosses the southern Western Australian coast just east of Esperence passing to the northwest leaving the coastline in the Karratha/Onslow area. The path predicted by OCCULT lies around three path widths to the east crossing the coasts near the South Australia border and exiting near Pardoo east of Port Hedland. There is little difference in the predicted times for the two paths.

UPDATE: 26 April 2000

This prediction update is supplied by Jan Manek of the Stefanik Observatory, Prague, and is based on USNO/Flagstaff astrometry for the minor planet and the TYC-2 star position.

Summary:

This update places the path around 0.4" to the north-east of the path given by Goffin near that given by OCCULT and about 40 seconds earlier. The path runs now just to the west of Tasmania (19:48 UT), crosses the Western Australian southern coast just west of the South Australia border (19:52:50 UT) passing to the north-west crossing the coast again just to the east of Port Hedland (19:55:15 UT). The path then crosses Java and Surakarta (15:59 UT) and between Borneo and Sumatra (20:10 UT). The path then crosses Thailand east of Krungh Thep (20:04 UT) before crossing eastern Burma, far eastern India, central China and Russia at low altitude.

The target star is the brighter component of the double star STN 34. See further comments below.

THE EVENT AT ONE GLIMPSE:

Date and approx. UT time of event: April 29, 2000 @ 19:53 UT (Australia), 20:07 UT (Asia)
Magnitude of target star: 9.4
Magnitude drop [mag]: 3.6
Estimated maximum duration [s]: 12.5
Path description: See above.
Goffins original chart reference: A00 0427

The Occultation Path:

Approximate width [km]: 85 km
Uncertainty [path widths]: 1.7
Uncertainty in time [s]: 25
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: HIP 84523 = SAO 160417 = PPM 232858 = TYC 6237 00517-1

Constellation: Ophiuchus

J2000 position [h,m,s; ^o,',"]: 17h 16m 42.437s; -17^o 09' 11.50"

Position source: Tycho 2

Estimated accuracy ["]: 0.04" (0.03", 0.03")

Johson V mag [mag]: 9.43

B-V [mag]: +1.16

Remarks:

The target star is in southern Ophiuchus around 2.1 degrees south east of 2.4 mag star eta Ophiuchi and 1.5 degrees north-northwest of the globular cluster Messier 9 (M9). There is also a 7.6 mag star (SAO 160404) around 16' to the west southwest of the target. Be careful when identifying and observing the target star as it is the brighter component of a double star system (STN 34). The secondary component is mag 10.3 at PA 289 with a seperation of 17". Observers with smaller telescopes or using low magnification may not resolve the pair and the magnitude drop for the combined system will be only about 1 mag. Observers are therefore urged to use as high a magnification as practicable and concentrate only on the brighter component of the pair (if possible).
To see a detailed finder chart, click here.

Data for the minor planet:

Number, name: (694) Ekard
Approx. diameter [km]: 93
Source of used astrometry: USNO/Flagstaff (Ron Stone)
Number of used observations: 35 USNO
Number of rejected observations: 3 USNO
Time covered by the observations: 1998 02 12 - 2000 04 17
RMS residuals ["] (RA,DE): 0.10", 0.11"
Estimated positional accuracy at epoch of event ["]: 0.11"

Data for the event:

UT date and time of least geocentric approach: 2000 April 29, 19:57.5 UTC
Approx. V mag of minor planet at event [mag]: 13.0
Geocentric parallax of minor planet ["]: 5.408
Magnitude drop [mag]: 3.6
Estimated maximum duration [s]: 12.5
Apparent motion of minor planet ["/h]: 22.79
Angular distance to moon, phase of moon [deg,%]: 83, 23%
Update computed by: Jan Manek

Ekard Update

Ekard Update - North

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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