RASNZ Occultation Section - Theobalda Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (778) THEOBALDA - 2003 SEP 17

UPDATE: 2003 SEP 09, 15:34 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 Sep 17 UT, the 64 km diameter asteroid (778) Theobalda will occult a 9.9 mag star in the constellation Pegasus for observers along a path across central Australia.

Note: This path crosses the region of Alice Springs, NT and Bundaberg, Qld.

In the case of an occultation, the combined light of the asteroid and the star will drop by 4.1 mag to 14.0 mag (the magnitude of the asteroid) for at most 4.9 seconds.

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, astrometry for the asteroid kindly provided by Gordon Garradd, historical astrometry from the MPC files (via AstDys), and the following catalogs for the star position: UCAC.

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

EVENT DETAILS SUMMARY :

Event Rank : 69
(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 Sep 17, 16:39.5 - 2003 Sep 17, 16:45 UT
(Refer to map(s) for your own location)
Magnitude of target star : 9.9
Magnitude drop [mag] : 4.1
Estimated maximum duration [s] : 4.9
Phase of moon, angular distance : 60 % sunlit, 70° distance
Sun : 165° distance
Rough path description : Australia

Data for the target star :

Name : TYC 1177-01532-1
Constellation : Pegasus
J2000 position [h,m,s ; °,',"]: RA: 23 52 20.2043 DE: +12 46 20.893
Position source : Pos: UCAC2, pm: UCAC2, pi:
Standard error : RA,DE ["]: ( .015, .015 )
V mag [mag] : 9.9
Remarks : (none)

Data for the minor planet :

Number, name : (778) Theobalda
Approx. diameter [km] : 64
Approx. diameter [arcsec] : .043
Source of used astrometry : FASTT Garradd MPC (via Astdys)
Number of used observations : 268
Number of rejected observations : 23
Time covered by the observations : 1923 Sep 09 - 2003 Aug 31
1 sigma uncertainty ellipse (major, minor, PA) : 0.051, 0.029, 58°
Remarks : (none)
Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).

The Occultation Path :

Approximate projected width [km] : 82
Uncertainty interval [path widths] : +/- 0.85 (1 sigma)
Uncertainty interval [seconds] : +/- 5.6 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .048 +/- .038) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .053", .032", 60° ) (1 sigma)
Important Note regarding Accuracy:
The uncertainty interval in path widths given above (and shown as a 1-sigma uncertainty ellipse on the plot) refers to RMS deviation and is applied as a +/- range. In other words, a path uncertainty of 1.0 path widths means that the actual center of the asteroid's shadow path should fall within plus or minus 1 path width of the plotted path center. However path errors larger than 1 sigma have been observed so observers should be alert for primary occultations within plus or minus 3 sigma of the updated path.
Further, almost all asteroidal satellites discovered so far have been found within 10 diameters of the asteroid (since this distance is deep enough within the gravitational well to be stable over long timescales). Therefore, if monitoring for secondary events, observing out to about 10 path-widths either side of the predicted track remains worthwhile.
We therefore recommend that you monitor for events if your observing location is up to +/- 10 path-widths from the predicted track. If not monitoring for occultations by secondary bodies you should observe from locations within 3 sigma of the nominal path.
In terms of time, the predictions are now usually accurate to about +/- 0.3 minute so you should be most attentive during the predicted minute of the event. However if intending to catch a potential satellite occultation you should start observing at least 10 times the predicted central duration before the predicted closest approach time for your location, and continue for a similar period afterwards.
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
     97  0  0   -27 57 10   16 46 24    47    19   -63  -27 34 38  -28 19 48  -27 34 38  -28 19 48
     98  0  0   -27 47 25   16 46 17    48    18   -63  -27 24 55  -28 10  3  -27 24 55  -28 10  3
     99  0  0   -27 37 54   16 46 10    48    17   -64  -27 15 25  -28  0 30  -27 15 25  -28  0 30
    100  0  0   -27 28 36   16 46  3    49    15   -64  -27  6  8  -27 51 11  -27  6  8  -27 51 11
    101  0  0   -27 19 31   16 45 56    49    14   -64  -26 57  4  -27 42  6  -26 57  4  -27 42  6

    102  0  0   -27 10 40   16 45 49    49    13   -65  -26 48 14  -27 33 13  -26 48 14  -27 33 13
    103  0  0   -27  2  3   16 45 42    50    11   -65  -26 39 38  -27 24 35  -26 39 38  -27 24 35
    104  0  0   -26 53 40   16 45 35    50    10   -65  -26 31 16  -27 16 11  -26 31 16  -27 16 11
    105  0  0   -26 45 30   16 45 27    50     9   -65  -26 23  7  -27  8  0  -26 23  7  -27  8  0
    106  0  0   -26 37 35   16 45 20    50     7   -66  -26 15 13  -27  0  5  -26 15 13  -27  0  5

    107  0  0   -26 29 55   16 45 13    51     6   -66  -26  7 34  -26 52 23  -26  7 34  -26 52 23
    108  0  0   -26 22 29   16 45  5    51     4   -66  -26  0  9  -26 44 56  -26  0  9  -26 44 56
    109  0  0   -26 15 17   16 44 58    51     3   -66  -25 52 58  -26 37 44  -25 52 58  -26 37 44
    110  0  0   -26  8 21   16 44 51    51     1   -66  -25 46  2  -26 30 46  -25 46  2  -26 30 46
    111  0  0   -26  1 39   16 44 43    51   360   -66  -25 39 22  -26 24  4  -25 39 22  -26 24  4

    112  0  0   -25 55 13   16 44 36    51   358   -66  -25 32 56  -26 17 37  -25 32 56  -26 17 37
    113  0  0   -25 49  1   16 44 28    51   357   -66  -25 26 45  -26 11 24  -25 26 45  -26 11 24
    114  0  0   -25 43  5   16 44 21    51   355   -66  -25 20 50  -26  5 28  -25 20 50  -26  5 28
    115  0  0   -25 37 25   16 44 13    51   354   -66  -25 15 10  -25 59 46  -25 15 10  -25 59 46
    116  0  0   -25 32  0   16 44  6    51   352   -65  -25  9 46  -25 54 21  -25  9 46  -25 54 21

    117  0  0   -25 26 50   16 43 58    51   350   -65  -25  4 37  -25 49 11  -25  4 37  -25 49 11
    118  0  0   -25 21 57   16 43 51    51   349   -65  -24 59 44  -25 44 16  -24 59 44  -25 44 16
    119  0  0   -25 17 19   16 43 44    51   347   -65  -24 55  7  -25 39 38  -24 55  7  -25 39 38
    120  0  0   -25 12 57   16 43 36    51   346   -64  -24 50 45  -25 35 15  -24 50 45  -25 35 15
    121  0  0   -25  8 51   16 43 29    51   344   -64  -24 46 40  -25 31  9  -24 46 40  -25 31  9

    122  0  0   -25  5  1   16 43 21    51   343   -63  -24 42 51  -25 27 19  -24 42 51  -25 27 19
    123  0  0   -25  1 27   16 43 14    51   342   -63  -24 39 17  -25 23 44  -24 39 17  -25 23 44
    124  0  0   -24 58 10   16 43  7    50   340   -63  -24 36  0  -25 20 27  -24 36  0  -25 20 27
    125  0  0   -24 55  9   16 42 59    50   339   -62  -24 32 59  -25 17 25  -24 32 59  -25 17 25
    126  0  0   -24 52 24   16 42 52    50   337   -61  -24 30 15  -25 14 40  -24 30 15  -25 14 40

    127  0  0   -24 49 56   16 42 45    49   336   -61  -24 27 47  -25 12 11  -24 27 47  -25 12 11
    128  0  0   -24 47 44   16 42 38    49   335   -60  -24 25 35  -25  9 59  -24 25 35  -25  9 59
    129  0  0   -24 45 48   16 42 30    49   333   -60  -24 23 40  -25  8  3  -24 23 40  -25  8  3
    130  0  0   -24 44  9   16 42 23    48   332   -59  -24 22  1  -25  6 24  -24 22  1  -25  6 24
    131  0  0   -24 42 47   16 42 16    48   331   -59  -24 20 39  -25  5  2  -24 20 39  -25  5  2

    132  0  0   -24 41 41   16 42  9    48   329   -58  -24 19 33  -25  3 56  -24 19 33  -25  3 56
    133  0  0   -24 40 52   16 42  2    47   328   -57  -24 18 44  -25  3  7  -24 18 44  -25  3  7
    134  0  0   -24 40 20   16 41 55    47   327   -57  -24 18 12  -25  2 34  -24 18 12  -25  2 34
    135  0  0   -24 40  4   16 41 48    46   326   -56  -24 17 56  -25  2 19  -24 17 56  -25  2 19
    136  0  0   -24 40  5   16 41 41    46   325   -55  -24 17 57  -25  2 20  -24 17 57  -25  2 20

    137  0  0   -24 40 23   16 41 34    45   323   -54  -24 18 15  -25  2 38  -24 18 15  -25  2 38
    138  0  0   -24 40 57   16 41 28    45   322   -54  -24 18 49  -25  3 12  -24 18 49  -25  3 12
    139  0  0   -24 41 49   16 41 21    44   321   -53  -24 19 40  -25  4  4  -24 19 40  -25  4  4
    140  0  0   -24 42 56   16 41 14    43   320   -52  -24 20 48  -25  5 12  -24 20 48  -25  5 12
    141  0  0   -24 44 21   16 41  8    43   319   -51  -24 22 12  -25  6 37  -24 22 12  -25  6 37

    142  0  0   -24 46  3   16 41  1    42   318   -51  -24 23 54  -25  8 18  -24 23 54  -25  8 18
    143  0  0   -24 48  1   16 40 55    42   317   -50  -24 25 51  -25 10 17  -24 25 51  -25 10 17
    144  0  0   -24 50 16   16 40 49    41   316   -49  -24 28  6  -25 12 32  -24 28  6  -25 12 32
    145  0  0   -24 52 47   16 40 42    40   315   -48  -24 30 37  -25 15  4  -24 30 37  -25 15  4
    146  0  0   -24 55 35   16 40 36    40   314   -47  -24 33 25  -25 17 52  -24 33 25  -25 17 52

    147  0  0   -24 58 40   16 40 30    39   314   -47  -24 36 29  -25 20 58  -24 36 29  -25 20 58
    148  0  0   -25  2  1   16 40 24    38   313   -46  -24 39 49  -25 24 19  -24 39 49  -25 24 19
    149  0  0   -25  5 39   16 40 18    38   312   -45  -24 43 27  -25 27 58  -24 43 27  -25 27 58
    150  0  0   -25  9 33   16 40 13    37   311   -44  -24 47 20  -25 31 52  -24 47 20  -25 31 52
    151  0  0   -25 13 44   16 40  7    36   310   -43  -24 51 30  -25 36  4  -24 51 30  -25 36  4

    152  0  0   -25 18 10   16 40  1    36   309   -42  -24 55 57  -25 40 31  -24 55 57  -25 40 31
    153  0  0   -25 22 54   16 39 56    35   309   -42  -25  0 39  -25 45 15  -25  0 39  -25 45 15
    154  0  0   -25 27 53   16 39 50    34   308   -41  -25  5 38  -25 50 15  -25  5 38  -25 50 15
    155  0  0   -25 33  9   16 39 45    33   307   -40  -25 10 53  -25 55 32  -25 10 53  -25 55 32
    156  0  0   -25 38 40   16 39 40    33   307   -39  -25 16 23  -26  1  4  -25 16 23  -26  1  4

    157  0  0   -25 44 28   16 39 35    32   306   -38  -25 22 10  -26  6 52  -25 22 10  -26  6 52
    158  0  0   -25 50 31   16 39 30    31   305   -37  -25 28 13  -26 12 57  -25 28 13  -26 12 57
    159  0  0   -25 56 51   16 39 25    30   304   -36  -25 34 31  -26 19 17  -25 34 31  -26 19 17
    160  0  0   -26  3 25   16 39 20    29   304   -35  -25 41  5  -26 25 53  -25 41  5  -26 25 53
    161  0  0   -26 10 16   16 39 15    29   303   -35  -25 47 55  -26 32 44  -25 47 55  -26 32 44

    162  0  0   -26 17 22   16 39 11    28   303   -34  -25 55  0  -26 39 51  -25 55  0  -26 39 51
    163  0  0   -26 24 43   16 39  6    27   302   -33  -26  2 20  -26 47 13  -26  2 20  -26 47 13
    164  0  0   -26 32 20   16 39  2    26   301   -32  -26  9 55  -26 54 51  -26  9 55  -26 54 51
    165  0  0   -26 40 11   16 38 58    25   301   -31  -26 17 46  -27  2 43  -26 17 46  -27  2 43
    166  0  0   -26 48 18   16 38 54    25   300   -30  -26 25 51  -27 10 51  -26 25 51  -27 10 51

    167  0  0   -26 56 39   16 38 50    24   300   -29  -26 34 11  -27 19 13  -26 34 11  -27 19 13
    168  0  0   -27  5 15   16 38 46    23   299   -28  -26 42 46  -27 27 51  -26 42 46  -27 27 51
    169  0  0   -27 14  5   16 38 42    22   298   -28  -26 51 36  -27 36 42  -26 51 36  -27 36 42
    170  0  0   -27 23 10   16 38 39    21   298   -27  -27  0 39  -27 45 48  -27  0 39  -27 45 48
    171  0  0   -27 32 29   16 38 35    20   297   -26  -27  9 57  -27 55  8  -27  9 57  -27 55  8

    172  0  0   -27 42  2   16 38 32    19   297   -25  -27 19 29  -28  4 42  -27 19 29  -28  4 42
    173  0  0   -27 51 48   16 38 29    19   296   -24  -27 29 14  -28 14 30  -27 29 14  -28 14 30
    174  0  0   -28  1 49   16 38 26    18   296   -23  -27 39 13  -28 24 32  -27 39 13  -28 24 32
    175  0  0   -28 12  3   16 38 23    17   295   -22  -27 49 26  -28 34 47  -27 49 26  -28 34 47
    176  0  0   -28 22 29   16 38 20    16   295   -21  -27 59 51  -28 45 15  -27 59 51  -28 45 15

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