RASNZ Occultation Section - Io Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (85) IO - 2003 AUG 02

[Edwin Goffin's Prediction + Finder Charts]

UPDATE: 2003 JUL 05, 19:00 UT

THE UPDATED PATH

(Note: The time given in the line below is for the midpoint of the path as it crosses the Earth - please see the minute markers on the map to determine the approximate the time for your location)

On 2003 Aug 02 UT, the 154 km diameter asteroid (85) Io will occult a 10.6 mag star in the constellation Delphinus for observers along a path across the South Island of New Zealand.

In the case of an occultation, the combined light of the asteroid and the star will drop by 0.5 mag to 10.1 mag (the magnitude of the asteroid) for at most 21.4 seconds. (NOTE: This magnitude drop is very near the limit of visibility for visual observers).

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, TMO astrometry for the asteroid kindly provided by Bill Owen, historical astrometry from AstDys, and the UCAC catalog for the star position.

Additional details of this and other events are available at Steve Preston's website at http://www.asteroidoccultation.com/

EVENT DETAILS SUMMARY :

Event Rank : 99
(The event Rank is a measure of the likelihood of observing an event, and is equal to
the probability of at least one successful observation by a team of two observers spaced 1/8 path
width just inside opposite sides of the predicted path).
Date and approx. UT time of event : 2003 Aug 02, 11:55 - 11:59 UT
(Refer to map(s) for your own location)
Magnitude of target star : 10.6
Magnitude drop [mag] : 0.5
Estimated maximum duration [s] : 21.4
Phase of moon, angular distance : 20 % sunlit, 127° distance
Sun : 158° distance
Rough path description : New Zealand

Data for the target star :

Name : TYC 0520-02100-1
Constellation : Delphinus
J2000 position [h,m,s ; °,',"]: RA: 20 46 09.9096 DE: +03 53 41.401
Position source : Pos: UCAC2, pm: UCAC2, pi:
Standard error : RA,DE ["]: ( .016, .016 )
V mag [mag] : 10.6
Remarks : (none)

Data for the minor planet :

Number, name : (85) Io
Approx. diameter [km] : 154
Approx. diameter [arcsec] : .181
Source of used astrometry : FASTT TMO Astdys
Number of used observations : 749
Number of rejected observations : 89
Time covered by the observations : 1904 Oct 09 - 2003 Jun 16
1 sigma uncertainty ellipse (major, minor, PA) : 0.035, 0.024, 80°
Remarks :
Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).

The Occultation Path :

Approximate projected width [km] : 201
Uncertainty interval [path widths] : +/- 0.16 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .038 +/- .029) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .038", .029", 82° ) (1 sigma)
Remarks :
Path Co-ordinates :

                  Centre              Star  Star   Sun      Path Limits           Error Limits
  E. Longitude   Latitude      U.T.    Alt    Az   Alt    Limit 1    Limit 2    Limit 3    Limit 4
      o  '  "     o  '  "    h  m  s     o     o     o    o  '  "    o  '  "    o  '  "    o  '  "
                                                         Latitude   Latitude   Latitude   Latitude
    160  0  0   -48 51 28   11 58 53    34    26   -54  -47 49 38  -49 54 24  -47 49 38  -49 54 24
    161  0  0   -48 29 25   11 58 45    35    25   -55  -47 27 32  -49 32 24  -47 27 32  -49 32 24
    162  0  0   -48  7  8   11 58 36    35    24   -56  -47  5 12  -49 10  9  -47  5 12  -49 10  9

    163  0  0   -47 44 36   11 58 28    36    23   -56  -46 42 38  -48 47 40  -46 42 38  -48 47 40
    164  0  0   -47 21 51   11 58 19    37    22   -57  -46 19 50  -48 24 57  -46 19 50  -48 24 57
    165  0  0   -46 58 52   11 58  9    37    21   -58  -45 56 50  -48  2  0  -45 56 50  -48  2  0
    166  0  0   -46 35 41   11 58  0    38    20   -58  -45 33 38  -47 38 51  -45 33 38  -47 38 51
    167  0  0   -46 12 18   11 57 51    38    19   -59  -45 10 13  -47 15 28  -45 10 13  -47 15 28

    168  0  0   -45 48 42   11 57 41    39    17   -60  -44 46 38  -46 51 53  -44 46 38  -46 51 53
    169  0  0   -45 24 56   11 57 31    40    16   -60  -44 22 51  -46 28  7  -44 22 51  -46 28  7
    170  0  0   -45  0 58   11 57 21    40    15   -61  -43 58 54  -46  4 10  -43 58 54  -46  4 10
    171  0  0   -44 36 51   11 57 11    41    14   -62  -43 34 46  -45 40  1  -43 34 46  -45 40  1
    172  0  0   -44 12 33   11 57  0    41    13   -62  -43 10 30  -45 15 43  -43 10 30  -45 15 43

    173  0  0   -43 48  7   11 56 50    42    12   -63  -42 46  5  -44 51 15  -42 46  5  -44 51 15
    174  0  0   -43 23 32   11 56 39    42    11   -63  -42 21 31  -44 26 38  -42 21 31  -44 26 38
    175  0  0   -42 58 48   11 56 28    43     9   -64  -41 56 50  -44  1 53  -41 56 50  -44  1 53
    176  0  0   -42 33 58   11 56 17    43     8   -65  -41 32  1  -43 37  0  -41 32  1  -43 37  0
    177  0  0   -42  9  0   11 56  5    44     7   -65  -41  7  6  -43 12  0  -41  7  6  -43 12  0

    178  0  0   -41 43 56   11 55 54    44     6   -66  -40 42  5  -42 46 53  -40 42  5  -42 46 53
    179  0  0   -41 18 47   11 55 42    45     4   -66  -40 16 59  -42 21 40  -40 16 59  -42 21 40
    180  0  0   -40 53 32   11 55 31    45     3   -67  -39 51 48  -41 56 22  -39 51 48  -41 56 22

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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