Update for (88) Thisbe - August 8/9, 2000

Jan Manek's update

                    IOTA/IOTA-ES occultation update for
           (88) Thisbe / GSC 0599.1001 event on August 8/9, 2000
           visible from SW Madagascar, central and NE Africa, 
                       Turkey, Bulgaria and Romania


Summary 

In the morning of August 8/9, 2000 a faint 11.7 mag star GSC 0599.1001 will be occulted by a large 232 km asteroid (88) Thisbe. This update is based on USNO/Flagstaff, TMO, Geneva and Gnosca astrometry for the asteroid and Geneva+Gnosca star position.

The updated path shows large ~1.0" east shift with time ~5 minutes earlier compared to Edwin Goffin's nominal prediction. This shift was result mainly of the new star position used.

The path of this occultation runs over SW Madagascar ~1:45 UT to north, over central Africa to Egypt ~2:20 UT. Crete is in path ~2:25 UT, egerian coast of Turkey ~2:27 UT, Bulgaria ~2:30 UT and Romania ~2:32 UT where twilight will start to be a problem. South Africa, which was in path of the nominal prediction has no chance.

GSC magnitude is approximately visual and asteroid is ~0.7 magnitude brighter than target star, so brightness drop is under 0.5 magnitude - the event is NOT suitable for visual observations. Expected errors are rather large, but the asteroid is also large.

The event at one glimpse:
 * date and approx. UT time of event: August 9, 2000 @ 02:30 UT (Europe)
 * magnitude of target star: 11.7
 * magnitude drop [mag]: 0.5
 * estimated maximum duration [s]: 87.5
 * path description: given above
 * Goffin's original chart reference: B00_0805

The occultation path:
 * approximate ground width [km]: 240
 * uncertainty [path widths]: 1.3
 * uncertainty in time [s]: 2 minutes (!)
 * map: below
 * remarks: Path uncertainities are given according to nominal star
    position errors and expected asteroid positional accuracy.
    !!!!!!!
    Circles along path indicates the centerline for this event.
    They are more accurate than the path limit lines.
    !!!!!!!

Data for the target star:
 * name: GSC 0599.1001
 * constellation: Pisces
 * J2000 position [h,m,s; o,',"]: 00h 24m 17.487s; +10o 33' 26.91"
 * position source: Gnosca (MPC station 143), Geneva (MPC station 517)
 * estimated accuracy ["]: 0.12"
 * V mag [mag]: 11.7
 * B-V [mag]: +?.??
 * remarks: 
     Tycho-2 relative position of star was measured by Raoul Behrend (517) 
     on 3 of his own images and 9 of Stefano Sposetti (143). The value used 
     was computed as weighted mean from all these positions.

     Target star is in middle Pisces, about 5 degrees SE of 2.8 mag star
     gamma Pegasi. There is slightly brighter star GSC 599.0521 only 2.2'
     NE of target star.

Close finding chart (prepared in GUIDE7):
 * occulted star is in center - labeled with cross
 * field is 3.0x3.0 degrees
 * limiting magnitude is 12.5
 * labeled stars have indicated SAO numbers





Data for the minor planet:
 * general information:
     number, name: (88) Thisbe
     approx. diameter [km]: 232
 * orbital information
     orbit source: calculation Manek
     source of used astrometry: USNO/Flagstaff (Ron Stone), TMO (Bill Owen),
                      Geneva Obs.(Raoul Behrend), Gnosca (Stefano Sposetti)
     number of used observations: 51 USNO, 13 TMO, 6(2)Geneva, 9(1) Gnosca
     number of rejected observations: 2 USNO
     time covered by the observations: 1998 02 26 - 2000 08 08
     rms residuals ["] (RA,DE): 0.08", 0.07"
     estimated positional accuracy at epoch of event ["]: 0.12"
     remarks: There 3(mean) this year's positions, so estimated accuracy
       is somewhat larger than RMS values of solution.

Data for the event:
 * UT date and time of least geocentric approach: 02:09.5  UT
 * approx. V mag of minor planet at event [mag]: 11.0
 * geocentric parallax of minor planet ["]: 5.349
 * magnitude drop [mag]: 0.5
 * estimated maximum duration [s]: 87.5
 * apparent motion of minor planet ["/h]: 8.01
 * angular distance to moon, phase of moon [deg,%]: 119, 69%
 * remarks: 

Calculator(s): Jan Manek








Path coordinates:
                                       Altitude
  E. Longitude    Latitude     U.T.    star  sun
   ........ shortened ..........................
      o  '  "     o  '  "    h  m  s     o     o
     26 22 38    34  0  0    2 24 11    63   -14
     26 13 52    35  0  0    2 24 50    62   -13
     26  5 33    36  0  0    2 25 28    61   -13
     25 57 42    37  0  0    2 26  6    61   -12
     25 50 19    38  0  0    2 26 44    60   -12
     25 43 26    39  0  0    2 27 21    59   -11
     25 37  4    40  0  0    2 27 58    58   -10
     25 31 15    41  0  0    2 28 35    57   -10
     25 26  0    42  0  0    2 29 11    56    -9
     25 21 21    43  0  0    2 29 47    55    -9
     25 17 20    44  0  0    2 30 22    54    -8
     25 13 58    45  0  0    2 30 57    53    -8
     25 11 19    46  0  0    2 31 32    52    -7
     25  9 23    47  0  0    2 32  6    51    -6
     25  8 15    48  0  0    2 32 40    51    -6
     25  7 56    49  0  0    2 33 13    50    -5
     25  8 31    50  0  0    2 33 46    49    -5
   ........ shortened ..........................

----------------------------------------------------------------------------
Jan Manek
Stefanik Observatory                Private :
Petrin 205                          Werichova 950
118 46  Praha 1                     152 00  Praha 5 - Barrandov     |_|_|
Czech Republic                      Czech Republic                  /   \
Internet : jmanek@mbox.vol.cz                                      |-O-O-|
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