Update for (257) Silesia - December 21/22, 1999

Jan Manek's update

                     IOTA/IOTA-ES occultation update for
         (257) Silesia / PPM 96143 event on December 21/22, 1999
                     visible from Sardegna and SW France


Summary 

In the night December 21/22, 1999 (in fact morning of December 22) a bright 7.9 mag star PP 96143 will be occulted by a 74 km asteroid (257) Silesia. This update is based on USNO/Flagstaff astrometry for the asteroid and ACT star position.

The updated path shows ~4 path widths northern shift with time ~1.4 minutes earlier compared to Edwin Goffin's nominal prediction.

The path now runs over Sicilia in morning twilight at ~5:31.5 UT, Sardegna few seconds later and then over France. Marseille is on the northern limit at ~5:32 UT and path runs to NW with Bordeaux south of the path at ~5:32.5 UT. Centerline then runs along northen coast of Biskai Bay in France up to ~5:33 UT. SW tips of England and Ireland are just off the path.

Full Moon is only 17 degrees away from target star so this may make the location of star harder, however as the star is bright, occultation should be easily visible.

The event at one glimpse:
 * date and approx. UT time of event: December 22, 1999 @ 05:32 UT
 * magnitude of target star: 7.9
 * magnitude drop [mag]: 5.4
 * estimated maximum duration [s]: 6.5
 * path description: given above

The occultation path:
 * approximate ground width [km]: 100
 * uncertainty [path widths]: 1.7
 * uncertainty in time [s]: 15
 * map: attached 
 * remarks: Path uncertainities are given according to nominal star 
    position errors and expected asteroid positional accuracy. 
    !!!!!!!
    Circles along the path are OCCULT exactly calculated centerline points. 
    !!!!!!!

Data for the target star:
 * name: SAO 78483 = PPM 93143 = TYC 1887 00862 1
 * constellation: Auriga
 * J2000 position [h,m,s; o,',"]: 06h 33m 04.906s; +28o 04' 54.57"
 * position source: ACT
 * estimated accuracy ["]: 0.04" (0.01", 0.04")
 * V mag [mag]: 7.90
 * B-V [mag]: +0.18
 * remarks: TYCHO gives quality flag 2(=very high) with 'no duplicity' flag.

     Target star is in SE Auriga, close to Gemini border. There is 8.4 mag
     star SAO 78488 only 3.2' east of target with declination difference
     only 13" which may be a problem for drift scan observations with
     such a bright stars. There is also 7.5 mag star SAO 78496 about 10' SE 
     of target and a bright 5.3 mag star 49 Aurigae = SAO 78524 about 28' 
     east of target. 
     
Data for the minor planet:
 * general information:
     number, name: (257) Silesia
     approx. diameter [km]: 73.5
 * orbital information
     orbit source: calculation Manek
     source of used astrometry: USNO/Flagstaff (Ron Stone)
     number of used observations: 34 USNO
     number of rejected observations: 7 USNO
     time covered by the observations: 1998 08 02 - 1999 12 14
     rms residuals ["] (RA,DE): 0.10", 0.07"
     estimated positional accuracy at epoch of event ["]: 0.08"
     remarks: 

Data for the event:
 * UT date and time of least geocentric approach: 05:38:01 UT
 * approx. V mag of minor planet at event [mag]: 13.3
 * geocentric parallax of minor planet ["]: 4.837
 * magnitude drop [mag]: 5.4
 * estimated maximum duration [s]: 6.5
 * apparent motion of minor planet ["/h]: 31.29
 * angular distance to moon, phase of moon [deg,%]: 17, 99%
 * remarks: 

Calculator(s): Jan Manek





Path coordinates:
                                       Altitude
  E. Longitude    Latitude     U.T.    star  sun
   ........ shortened ..........................
   + 17 00 00   + 35 52 50    5 31 11   15    -6
   + 15 00 00   + 37 04 06    5 31 17   16    -8
   + 13 00 00   + 38 15 12    5 31 25   18   -10
   + 11 00 00   + 39 25 56    5 31 33   20   -11
   +  9 00 00   + 40 36 10    5 31 41   22   -13
   +  7 00 00   + 41 45 43    5 31 51   24   -15
   +  5 00 00   + 42 54 27    5 32 00   25   -17
   +  3 00 00   + 44 02 13    5 32 10   27   -18
   +  1 00 00   + 45 08 53    5 32 21   29   -20
   -  1 00 00   + 46 14 18    5 32 32   30   -22
   -  3 00 00   + 47 18 24    5 32 43   32   -23
   -  5 00 00   + 48 21 02    5 32 54   33   -25
   -  7 00 00   + 49 22 08    5 33 06   35   -26
   -  9 00 00   + 50 21 36    5 33 17   36   -27
   - 11 00 00   + 51 19 24    5 33 29   37   -29
   - 13 00 00   + 52 15 26    5 33 40   38   -30
   - 15 00 00   + 53 09 41    5 33 52   39   -31
   - 17 00 00   + 54 02 07    5 34 04   41   -32
   - 19 00 00   + 54 52 42    5 34 16   42   -33
   - 21 00 00   + 55 41 25    5 34 27   42   -34
   - 23 00 00   + 56 28 17    5 34 39   43   -35
   - 25 00 00   + 57 13 16    5 34 50   44   -36
   ........ 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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