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 ACT/TRC star position.

Summary:

• Using the ACT star position gives a time ~1.4 minutes later than Goffin's nominal prediction, with a path location virtually the same as his.
• Using the TRC 1.0 star position gives the same time as for the ACT position, but 1 full path width further south.
• The regions of Melbourne and Canberra lie within the area of uncertainty, together with Tasmania and possibly even the very north of New Zealand.

THE EVENT AT ONE GLIMPSE:

• Date and approx. UT time of event: May, 27, 1999 @ 16:31 UT
• Magnitude of target star: 10.5
• Magnitude drop [mag]: 3.2
• Estimated maximum duration [s]: 11.9
• Path description: Path runs ~4 path widths north of New Zealand at ~16:25 UT and runs just off the coast of SE Australia and over Bass Strait at ~16:31 UT. The path based on the TRC 1.0 position runs 1 path width further south with NW Tasmania on the southern limit.

• Approximate width [km]: 90
• Uncertainty [path widths]: 3
• Uncertainty in time [s]: 35
• Map: See below
• Remarks: Uncertainities are given on the basis of the nominal errors in the observations.
• Circles along the path are OCCULT calculated exact centerline points.

• Name: TYC 6872 00112
• Constellation: Sagittarius
• J2000 position [h,m,s; o,',"]: 18h 51m 42.397s; -28o 22' 35.27"
• Position source: ACT
• Estimated accuracy ["]: 0.07" (0.05", 0.04")
• V mag [mag]: 10.51
• B-V [mag]: +1.29
• Remarks:
  1. The TRC 1.0 gives end figures 42.396s and 35.21" with nominal errors 0.07" and 0.07" respectively. TYCHO gives quality flag 7 (low), Z flag (no investigation for duplicity) and X flag (dubious astrometric reference star). Earlier events in which such a combination of flags occured showed that the star position error may be 0.2" or even larger.
  2. The target star is 4.0' south-west of the mag 9.3 star SAO 187371. This is in the middle of Sagittarius, about 1.9 degrees SE of the mag 3.2 star Phi Sgr.

• Number, name: (160) Una
• Approx. diameter [km]: 85
• Orbit source: calculation Manek
• Source of used astrometry: USNO/Flagstaff (Ron Stone)
• Number of used observations: 19 USNO
• Number of rejected observations: 0
• Time covered by the observations: 1998 03 10 - 1995 05 19
• Rms residuals ["] (RA,DE): 0.10", 0.09"
• Estimated positional accuracy at epoch of event ["]: 0.10"

• UT date and time of least geocentric approach: 16:29:20 UT
• Approx. V mag of minor planet at event [mag]: 13.6
• Geocentric parallax of minor planet ["]: 4.397
• Magnitude drop [mag]: 3.2
• Estimated maximum duration [s]: 11.9
• Apparent motion of minor planet ["/h]: 17.73
• Angular distance to moon, phase of moon [deg,%]: 66, 93%

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.