Update for (68) Leto - May 23, 1999

Jan Manek's update

                      IOTA/IOTA-ES occultation update for
             (68) Leto / TYC 1951 00705 1 event on 1999, May 23
                   visible from Portugal and western Spain


Summary 

On the night May 23, 1999 will be occulted faint 10.5 mag star by a 127 km asteroid (68) Leto. This update is based on USNO/Flagstaff and TMO astrometry for asteroid and ACT star position.

This update gives ~1 path width western shift and time ~0.3 minutes later compared to the Goffin's nominal prediction.

Path runs over south Portugal, Gibraltar and Morocco. Within expected errors is whole Portugal and NW + SW Spain. Madrid is probably too east, but observations from here may be valuable.

The event at one glimpse:
 * date and approx. UT time of event: May 23, 1999 @ 22:40.5 UT
 * magnitude of target star: 10.5
 * magnitude drop [mag]: 2.7
 * estimated maximum duration [s]: 5.4
 * path description: Path runs over south Portugal, Gibraltar and Morocco.
     Within expected errors is whole Portugal and NW + SW Spain. Madrid is
     probably too east, but observations from here may be valuable.

The occultation path:
 * approximate width [km]: 180
 * uncertainty [path widths]: 1.5
 * uncertainty in time [s]: 10
 * 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: TYC 1951 00705 1
 * constellation: Cancer
 * J2000 position [h,m,s; o,',"]: 09h 17m 31.759s; +23o 21' 12.19"
 * position source: ACT
 * estimated accuracy ["]: 0.04"  (0.03", 0.02")
 * Johnson V mag [mag]: 10.50
 * B-V [mag]: +0.65
 * remarks: TRC1.0 gives very slightly different position having end figures
     31.760s and 12.20" with nominal accuracy (0.04", 0.03"). TYCHO gives
     quality flag 4 (high) with 'no investigation for duplicity' flag.

     Target star is in eastern Cancer, not far from border with Leo.
     Is is 3.2 degrees west of 4.3 mag star lambda Leo or 2.3 NE of 5.2 mag
     star ksi Cnc. The star itself is 19' west of 7.6 mag star SAO 80731 or
     17' north of 7.0 mag star SAO 80744. There is also 10.8 mag star
     GSC 1951.1364 only 1.8' exactly south of target.

     Be sure to have enough time for finding the correct star.

Data for the minor planet:
 * general information:
     mumber, name: (68) Leto
     approx. diameter [km]: 127
 * orbital information
     orbit source: calculation Manek
     source of used astrometry: USNO/Flagstaff (Ron Stone), TMO (Bill Owen)
     number of used observations: 14 USNO, 2 TMO
     number of rejected observations: 0
     time covered by the observations: 1998 12 02 - 1999 05 09
     rms residuals ["] (RA,DE): 0.05", 0.04"
     estimated positional accuracy at epoch of event ["]: 0.06"
     remarks:

Data for the event:
 * UT date and time of least geocentric approach: 22:38:14 UT
 * approx. V mag of minor planet at event [mag]: 13.1
 * geocentric parallax of minor planet ["]: 2.564
 * magnitude drop [mag]: 2.7
 * estimated maximum duration [s]: 5.4
 * apparent motion of minor planet ["/h]: 33.98
 * angular distance to moon, phase of moon [deg,%]: 37, 66%
 * remarks:

Calculator(s): Jan Manek





Path coordinates:
                                       Altitude
  E. Longitude    Latitude     U.T.    star  sun
   ......... shortened .........................
   - 22 00 00   + 49 44 08   22 39 21   37   -11
   - 20 00 00   + 47 51 35   22 39 31   36   -13
   - 18 00 00   + 45 59 54   22 39 41   35   -15
   - 16 00 00   + 44 09 33   22 39 50   33   -18
   - 14 00 00   + 42 21 01   22 40 00   32   -20
   - 12 00 00   + 40 34 38   22 40 08   30   -22
   - 10 00 00   + 38 50 46   22 40 17   28   -25
   -  8 00 00   + 37 09 41   22 40 24   26   -27
   -  6 00 00   + 35 31 39   22 40 31   24   -29
   -  4 00 00   + 33 56 51   22 40 38   22   -31
   -  2 00 00   + 32 25 27   22 40 44   20   -33
   +  0 00 00   + 30 57 35   22 40 50   18   -35
   +  2 00 00   + 29 33 22   22 40 54   16   -37
   +  4 00 00   + 28 12 53   22 40 59   14   -39
   +  6 00 00   + 26 56 10   22 41 02   12   -41
   +  8 00 00   + 25 43 15   22 41 05   10   -43
   + 10 00 00   + 24 34 12   22 41 08    8   -44
   ......... 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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