RASNZ Occultation Section - Fortuna Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (19) FORTUNA - 2006 FEB 26

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. 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 2006 Feb 26 UT, the 124 km diameter asteroid (19) Fortuna will occult a 8.4 mag star in the constellation Taurus for observers along a path across the central parts of the North Island of New Zealand, approximately between Palmerston North and Hamilton.

In the case of an occultation, the combined light of the asteroid and the star will drop by 3.4 mag to 11.7 mag (the magnitude of the asteroid) for at most 4.7 seconds. The visibility of this event may be hampered by late stages of evening twilight.

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 the MPC files (via AstDys), and the following catalogs for the star position: Hipparcos .

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
Date and approx. UT time of event : 2006 Feb 26, 07:42 - 2006 Feb 26, 07:46 UT
(Refer to map(s) for your own location)
Magnitude of target star : 8.4
Magnitude drop [mag] : 3.4
Estimated maximum duration [s] : 4.7
Phase of moon, angular distance : 5 % sunlit, 102° distance
Sun : 77° distance
Rough path description : New Zealand

Data for the target star :

Name : HIP 16416
Constellation : Taurus
J2000 position with proper motion to date of event [h,m,s ; °,',"]: RA: 03 31 24.4630 DE: +17 48 40.687
Position source : Hipparcos
Standard error : RA,DE ["]: ( .024, .015 )
V mag [mag] : 8.4
B mag [mag] : 9.4
Remarks : (none)

Data for the minor planet :

Number, name : (19) Fortuna
Approx. diameter [km] : 124
Approx. diameter [arcsec] : .080
Distance from Earth [AU] : 2.13700
Source of used astrometry : FASTT TMO MPC (via Astdys)
Number of used observations : 1322
Number of rejected observations : 249
Time covered by the observations : 1900 Feb 12 - 2006 Feb 02
1 sigma uncertainty ellipse (major, minor, PA) : 0.008, 0.006, 79°
Remarks : (none)
Orbital Elements for (19) Fortuna :
Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).

The Occultation Path :

Approximate projected width [km] : 258
Uncertainty interval [path widths] : +/- 0.20 (1 sigma)
Uncertainty interval [seconds] : +/- 1.4 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .025 +/- .016) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .025", .016", 89° ) (1 sigma)
Approx speed of asteroid's shadow [km/s]: 26.2629
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
    171  0  0   -39 30  6    7 44 53    26   328    -5  -40 42 35  -38 20 21  -41 12 25  -37 53  9
    172  0  0   -39 24 34    7 44 56    26   327    -6  -40 36 55  -38 14 56  -41  6 42  -37 47 46
    173  0  0   -39 19 42    7 44 59    25   326    -7  -40 31 56  -38 10 11  -41  1 40  -37 43  3
    174  0  0   -39 15 31    7 45  2    25   325    -7  -40 27 39  -38  6  5  -40 57 20  -37 38 59
    175  0  0   -39 12  0    7 45  5    25   324    -8  -40 24  3  -38  2 38  -40 53 42  -37 35 34

    176  0  0   -39  9  9    7 45  7    24   323    -9  -40 21  8  -37 59 51  -40 50 45  -37 32 49
    177  0  0   -39  6 59    7 45 10    24   322   -10  -40 18 54  -37 57 44  -40 48 30  -37 30 43
    178  0  0   -39  5 29    7 45 13    23   321   -10  -40 17 22  -37 56 16  -40 46 56  -37 29 16
    179  0  0   -39  4 39    7 45 16    23   320   -11  -40 16 31  -37 55 28  -40 46  5  -37 28 28

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