RASNZ Occultation Section - Merapi Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (536) MERAPI - 2005 OCT 13

Event Rank : 94

(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. An event rank of 100 indicates that the prediction is expected to be very accurate).

THE UPDATED PATH

Note: The duration given in the line below is the interval during which the occultation shadow sweeps across the Earth - please see the minute markers on the map to determine the approximate time for your location.

On 2005 Oct 13 UT, the 151 km diameter asteroid (536) Merapi will occult a 11.9 mag star in the constellation Auriga for observers along a path across the eastern part of Western Australia.

In the case of an occultation, the combined light of the asteroid and the star will drop by 2.2 mag to 13.9 mag (the magnitude of the asteroid) for at most 18.9 seconds.

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Ron Stone, 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 : 94
Date and approx. UT time of event : 2005 Oct 13, 20:16 - 2005 Oct 13, 20:41 UT
(Refer to map(s) for your own location)
Magnitude of target star : 11.9
Magnitude drop [mag] : 2.2
Estimated maximum duration [s] : 18.9
Phase of moon, angular distance : 82 % sunlit, 118° distance
Sun : 112° distance
Rough path description : W Australia

Data for the target star :

Name : TYC 1875-01630-1
Constellation : Auriga
J2000 position with proper motion to date of event [h,m,s ; °,',"]: RA: 05 52 39.4793 DE: +28 46 31.775
Position source : UCAC2
Standard error : RA,DE ["]: ( .021, .023 )
V mag [mag] : 11.9
B mag [mag] : 0.0
Remarks : (none)

Data for the minor planet :

Number, name : (536) Merapi
Approx. diameter [km] : 151
Approx. diameter [arcsec] : .072
Distance from Earth [AU] : 2.89500
Source of used astrometry : FASTT MPC (via Astdys)
Number of used observations : 572
Number of rejected observations : 30
Time covered by the observations : 1904 Jul 14 - 2005 Feb 04
1 sigma uncertainty ellipse (major, minor, PA) : 0.028, 0.015, 76°
Remarks : (none)
Orbital Elements for (536) Merapi :
Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).

The Occultation Path :

Approximate projected width [km] : 163
Uncertainty interval [path widths] : +/- 0.46 (1 sigma)
Uncertainty interval [seconds] : +/- 7.7 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .035 +/- .028) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .035", .028", 81° ) (1 sigma)
Approx speed of asteroid's shadow [km/s]: 8.0076
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  '  "
                                                        Longitude  Longitude  Longitude  Longitude
    125  1 20   -35  0  0   20 17 52    26   356    -9  125 54 24  124  8 27  126 43 25  123 19 58
    125  9 35   -34  0  0   20 17 59    27   356    -9  126  2  3  124 17 19  126 50 30  123 29 22
    125 18  3   -33  0  0   20 18  6    28   356    -9  126  9 57  124 26 21  126 57 52  123 38 56
    125 26 44   -32  0  0   20 18 13    29   356   -10  126 18  5  124 35 35  127  5 30  123 48 40
    125 35 38   -31  0  0   20 18 21    30   356   -10  126 26 28  124 44 59  127 13 25  123 58 32

    125 44 45   -30  0  0   20 18 28    31   355   -10  126 35  6  124 54 35  127 21 35  124  8 35
    125 54  4   -29  0  0   20 18 36    32   355   -10  126 43 57  125  4 22  127 30  2  124 18 47
    126  3 37   -28  0  0   20 18 44    33   355   -10  126 53  4  125 14 20  127 38 44  124 29 10
    126 13 22   -27  0  0   20 18 53    34   355   -10  127  2 24  125 24 30  127 47 42  124 39 42
    126 23 20   -26  0  0   20 19  1    35   354   -10  127 11 59  125 34 51  127 56 56  124 50 24

    126 33 31   -25  0  0   20 19 10    36   354   -10  127 21 49  125 45 24  128  6 25  125  1 17
    126 43 56   -24  0  0   20 19 19    37   354   -10  127 31 53  125 56  9  128 16 10  125 12 21
    126 54 33   -23  0  0   20 19 28    38   353   -10  127 42 12  126  7  6  128 26 12  125 23 36
    127  5 25   -22  0  0   20 19 38    39   353   -10  127 52 45  126 18 16  128 36 29  125 35  2
    127 16 30   -21  0  0   20 19 47    40   353   -10  128  3 34  126 29 38  128 47  2  125 46 39

    127 27 50   -20  0  0   20 19 57    41   352   -10  128 14 38  126 41 13  128 57 53  125 58 28
    127 39 24   -19  0  0   20 20  7    42   352   -10  128 25 58  126 53  1  129  8 59  126 10 30
    127 51 13   -18  0  0   20 20 17    43   351   -10  128 37 34  127  5  3  129 20 23  126 22 44
    128  3 16   -17  0  0   20 20 28    44   351   -10  128 49 26  127 17 19  129 32  4  126 35 11
    128 15 36   -16  0  0   20 20 39    45   351   -10  129  1 34  127 29 49  129 44  3  126 47 51

    128 28 11   -15  0  0   20 20 49    46   350   -10  129 14  0  127 42 34  129 56 19  127  0 45
    128 41  3   -14  0  0   20 21  0    47   350   -10  129 26 43  127 55 34  130  8 54  127 13 54
    128 54 11   -13  0  0   20 21 12    48   349   -10  129 39 44  128  8 50  130 21 48  127 27 17
    129  7 37   -12  0  0   20 21 23    48   348   -10  129 53  3  128 22 23  130 35  2  127 40 55
    129 21 20   -11  0  0   20 21 35    49   348   -10  130  6 41  128 36 12  130 48 35  127 54 50

    129 35 22   -10  0  0   20 21 47    50   347   -10  130 20 38  128 50 18  131  2 29  128  9  1

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