RASNZ Occultation Section - Echo Occultation Update

ASTROMETRIC UPDATE:
OCCULTATION BY (60) ECHO - 2015 Sep 12

Event Rank : 60

(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 2015 Sep 12 UT, the 59 km diameter asteroid (60) Echo will occult a 11.5 mag star in the constellation Sagittarius for observers along a path across Australia, across eastern Northern Territory and eastern South Australia to Adelaide.

In the case of an occultation, the combined light of the asteroid and the star will drop by 1.6 mag to 12.8 mag (the magnitude of the asteroid) for at most 30.4 seconds.

This update is based on UNSO/Flagstaff astrometry for the asteroid kindly provided by Alice Monet, 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 : 60
Date and approx. UT time of event : 2015 Sep 12, 11:58 - 2015 Sep 12, 12:32
(Refer to map(s) for your own location)
Magnitude of target star : 11.5
Magnitude drop [mag] : 1.6
Estimated maximum duration [s] : 30.4
Phase of moon, angular distance : 1 % sunlit, 130° distance
Sun : 121° distance
Rough path description : Japan, Australia

Data for the target star :

Name : TYC 6301-00510-1
Constellation : Sagittarius
J2000 position with proper motion to date of event [h,m,s ; °,',"]: RA: 19 26 21.0515 DE: -17 41 57.310
Position source : mpos:UCAC4 pm:UCAC4
Standard error : RA,DE ["]: ( .040, .033 )
V mag [mag] : 11.5
B mag [mag] : 11.7
Remarks : (none)

Data for the minor planet :

Number, name : (60) Echo
Approx. diameter [km] : 59
Approx. diameter [arcsec] : .039
Distance from Earth [AU] : 2.10900
Source of used astrometry : FASTT MPC (via Astdys)
Number of used observations : 1385
Number of rejected observations : 167
Time covered by the observations : 1914 Apr 15 - 2015 Aug 14
1 sigma uncertainty ellipse (major, minor, PA) : 0.008, 0.007, 81°
Remarks : (none)
Orbital Elements for (60) Echo :
Update computed by : Steve Preston, Medina, Washington, USA. (OrbFit).

The Occultation Path :

Approximate projected width [km] : 61
Uncertainty interval [path widths] : +/- 1.04 (1 sigma)
Uncertainty interval [seconds] : +/- 26.7 (1 sigma)
Uncertainty interval approx RA,DE ["] : (+/- .041 +/- .034) (1 sigma)
Uncertainty ellipse (major, minor, PA) : ( .041", .034", 90° ) (1 sigma)
Approx speed of asteroid's shadow [km/s]: 1.9439
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
    135 33 40   -10  0  0   11 58 35    74   240   -46  135 17  3  135 50 19  134 42 32  136 24 59
    135 32 31   -11  0  0   11 59 34    74   243   -46  135 15 49  135 49 13  134 41 10  136 24  2
    135 31 44   -12  0  0   12  0 32    74   247   -46  135 14 58  135 48 31  134 40 10  136 23 30
    135 31 21   -13  0  0   12  1 30    75   250   -46  135 14 30  135 48 13  134 39 32  136 23 22

    135 31 23   -14  0  0   12  2 29    75   254   -47  135 14 27  135 48 21  134 39 17  136 23 41
    135 31 52   -15  0  0   12  3 27    75   258   -47  135 14 50  135 48 55  134 39 28  136 24 28
    135 32 48   -16  0  0   12  4 26    75   261   -47  135 15 40  135 49 58  134 40  6  136 25 44
    135 34 13   -17  0  0   12  5 25    74   265   -47  135 16 58  135 51 29  134 41 11  136 27 30
    135 36  9   -18  0  0   12  6 24    74   268   -47  135 18 47  135 53 32  134 42 45  136 29 47

    135 38 37   -19  0  0   12  7 22    74   272   -47  135 21  7  135 56  8  134 44 49  136 32 39
    135 41 38   -20  0  0   12  8 21    74   275   -47  135 24  0  135 59 17  134 47 26  136 36  6
    135 45 15   -21  0  0   12  9 20    73   278   -47  135 27 28  136  3  3  134 50 36  136 40  9
    135 49 28   -22  0  0   12 10 19    73   281   -47  135 31 33  136  7 26  134 54 22  136 44 52
    135 54 21   -23  0  0   12 11 18    72   284   -47  135 36 16  136 12 28  134 58 45  136 50 15

    135 59 56   -24  0  0   12 12 17    72   286   -47  135 41 40  136 18 13  135  3 47  136 56 22
    136  6 13   -25  0  0   12 13 16    71   289   -47  135 47 46  136 24 41  135  9 31  137  3 14
    136 13 16   -26  0  0   12 14 14    70   291   -47  135 54 38  136 31 56  135 15 59  137 10 53
    136 21  7   -27  0  0   12 15 13    70   293   -46  136  2 17  136 40  0  135 23 12  137 19 23
    136 29 49   -28  0  0   12 16 12    69   295   -46  136 10 46  136 48 55  135 31 14  137 28 47

    136 39 25   -29  0  0   12 17 10    68   297   -46  136 20  7  136 58 45  135 40  7  137 39  6
    136 49 57   -30  0  0   12 18  8    67   298   -46  136 30 25  137  9 32  135 49 54  137 50 24
    137  1 29   -31  0  0   12 19  6    67   299   -46  136 41 41  137 21 20  136  0 39  138  2 46
    137 14  5   -32  0  0   12 20  4    66   301   -46  136 54  0  137 34 12  136 12 23  138 16 13
    137 27 48   -33  0  0   12 21  2    65   302   -46  137  7 25  137 48 13  136 25 12  138 30 52

    137 42 42   -34  0  0   12 22  0    64   303   -45  137 22  1  138  3 26  136 39  9  138 46 45
    137 58 52   -35  0  0   12 22 57    63   304   -45  137 37 51  138 19 56  136 54 19  139  3 57
    138 16 22   -36  0  0   12 23 55    62   305   -45  137 55  0  138 37 48  137 10 44  139 22 35
    138 35 19   -37  0  0   12 24 52    61   305   -45  138 13 34  138 57  7  137 28 32  139 42 42
    138 55 46   -38  0  0   12 25 49    60   306   -44  138 33 38  139 17 59  137 47 46  140  4 26

    139 17 52   -39  0  0   12 26 45    59   307   -44  138 55 18  139 40 31  138  8 34  140 27 53
    139 41 43   -40  0  0   12 27 42    58   307   -44  139 18 41  140  4 50  138 31  1  140 53 10
    140  7 26   -41  0  0   12 28 38    57   307   -43  139 43 54  140 31  2  138 55 14  141 20 26
    140 35  9   -42  0  0   12 29 34    56   308   -43  140 11  6  140 59 18  139 21 22  141 49 49
    141  5  3   -43  0  0   12 30 29    55   308   -43  140 40 26  141 29 46  139 49 32  142 21 31

    141 37 17   -44  0  0   12 31 25    54   308   -42  141 12  4  142  2 37  140 19 56  142 55 41
                                                         Latitude   Latitude   Latitude   Latitude
    142  0  0   -44 39 42   12 32  1    53   308   -42  -45 23  4  -43 55 23  -46 50 29  -42 19 46
    143  0  0   -46 15 52   12 33 29    52   308   -42  -46 56  0  -45 34 58  -48 17 16  -44  7 16
    144  0  0   -47 41 26   12 34 47    50   308   -41  -48 18 57  -47  3 18  -49 35 11  -45 41 52
    145  0  0   -48 58 21   12 35 57    49   307   -40  -49 33 42  -48 22 30  -50 45 43  -47  6 12

Uncertainty in time = +/- 32 secs

Prediction of 2015 Aug 20.0

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