Update for (287) Nephthys - September 6, 2004

  • Update computed by Jan Manek;   issued 24 Aug 2004 00:30 +0200 (CEST)

  • Jan Manek's update

                         IOTA/IOTA-ES occultation update for
             (287) Nephthys / eta Oph = HIP 84012 on September 6, 2004
          visible from S France, NE Spain, S Sardinia, NE Africa in daylight,
           Arabic Peninsula, Sri Lanka and Malaysia/Thailand border in night

    In the day/night of September 6, 2004 a bright 2.4 mag star eta Oph = HIP 84012 will be occulted by a 70 km asteroid (287) Nephthys. This update is based on USNO/Flagstaff and TMO astrometry for the asteroid and Hipparcos star position.

    The updated path shows no sognificant path shift with time ~0.5 minutes earlier compared to Edwin Goffin's nominal prediction.

    Updated path runs over S France ~15:23.7 UT, NE Spain ~15:23.7 UT, S Sardinia ~15:24.1 UT, NE Africa ~15:26 UT all in broad daylight, Arabic Peninsula ~15:28 UT, Sri Lanka ~15:31.3 UT and Malaysia/Thailand border ~15:32.7 UT in night. Please check the path chart for details.

    For Europe the occultation takes place in broad daylight, locating the target star should be trained well before the event. Also possible satellite search can be conducted. Target star is brighter component of close (~0.6") pair, so the full drop will not be visible for those not able to separate components. In this case ~1.0 mag drop will occur.

    Clear sky and good luck !!!

    The event at one glimpse:
     * date and approx. UT time of event: September 6, 2004 @ 15:24 UT (Europe)
     * magnitude of target star: 2.4
     * magnitude drop [mag]: 1.0
     * estimated maximum duration [s]: 4.1
     * approx. V mag of minor planet at event [mag]: 12.8
     * geocentric parallax of minor planet ["]: 4.386
     * apparent motion of minor planet ["/h]: 42.65
     * angular distance to moon, phase of moon [deg,%]: 169, 50%
     * Goffin's original chart reference: A04_0918
    The occultation path with path maps:
     * approximate ground width [km]: 85
     * uncertainty [path widths]: 0.6
     * uncertainty in time [s]: 4
     * map: Overview
            European part
            SE Asian part
     * remarks: Path uncertainties [2 sigmas] are given according to nominal star
                position errors and expected asteroid positional accuracy.
    Elements for WinOccult - use 'Save as ...' to download and save these elements.
    Finding charts (prepared in GUIDE8):
     * occulted star is in center - labeled with cross
     * labeled stars have indicated SAO numbers
     * (smaller) square box shows 30' field in all wider field charts
     * (larger) square box shows 3° field in wide field charts
     * remarks:
       !!! IMPORTANT !!!
       Purple stars in identification chart are so called 'non-star' objects in GSC; in dense fields
       the 'non-stars' are often real stars or blends of close pairs. Be careful about this.
       40-degree chart
       3-degree chart
       0.5-degree chart
    Data for the target star:
     * name: eta Oph = HIP 84012 = SAO 160332 = PPM 232699 = BU 1118 A
     * constellation: Ophiuchus
     * J2000 position [h,m,s; o,',"]: 17h 10m 22.6963s; -15o 43' 29.212"
     * position source: Hipparcos including parallax
     * estimated accuracy ["]: 0.03" (0.03", 0.02")
     * V mag [mag]: 2.43
     * B-V [mag]: +0.06
     * remarks: Target star is binary (2.4+3.0, sep ~0.6" currently) showing orbital motion.
        For the star A position were applied corrections to original HIP position found by Jean Lecacheux :
     	"A pure linear extrapolation at occultation date of the Hipparcos measurements made around 1991.25 yields
    	PA= 245 and Rho= 0".65 (as computed by myself from the derived catalog "Hipparcos, Double and Multiple
    	Components Solution" (ESA, 1997)). From the older (?) Hipparcos main Catalog, I obtained PA= 243 and Rho
    	~0".62 (i.e. the values used by Goffin and Preston).
    	No doubt that now the A component lies at W or WNW from that point, due to the path curvature inward.
    	Is the Rho ephemeris proposed by the USNO very reliable ?
    	I have just made a refined measurement of my Eta OPH images of 2003.7, as previously I considered only 18
    	selected exposures, and now 45. Now my best value becomes 0".56, no longer 0".58. It should correspond
    	to 0".565 at the occultation date, in possible optimal agreement with the sabikd.gif graph.
    	Note that from the "Hipparcos, Double and Multiple Components Solution" we can derive
    	     AP / AB = 0.365  0.015.
    	Finally, from the bulk of data, and using Steve's error box, my own prediction is the following (with 2 sigmas uncertainties) :
    		 B relative to A :  PA= 238.5  1  Rho= 0".56   0".02
    		 A relative to P :  PA=  58.5  1  Rho= 0".205  0".015
    	A relative to its official Hipparcos position :
             0".027  0".036 West   0".004  0".023 North"
    Data for the minor planet:
     * general information:
         number, name: (287) Nephthys
         approx. diameter [km]: 70
     * orbital information
         orbit source: calculation Manek
         source of used astrometry: USNO/Flagstaff (Ron Stone), TMO (Bill Owen)
         number of used observations: 169 USNO, 53 TMO
         number of rejected observations: 0
         time covered by the observations: 1997 05 22 - 2004 08 04
         rms residuals ["] (RA,DE): 0.08", 0.08"
         estimated positional accuracy at epoch of event ["]: 0.03", 0.02"
     * orbital elements
    	Semimajor axis     =   2.35275128300304
    	Eccentricity       =   0.023375925109504
    	Inclination        =  10.0233443939142 deg
    	Long. of node      = 142.4931728470867 deg
    	Arg. of pericenter = 120.0227764345686 deg
    	Mean anomaly       =  20.1582997877734 deg
    	Epoch of elements  : MJD   53254.64000000 TDT (Sep  6, 2004, 15.360000 h)
    Path coordinates: click here
    Calculator(s): Jan Manek
    Jan Manek
    Werichova 950
    152 00  Praha 5 - Barrandov                                         |_|_|
    Czech Republic                                                      /   \
    Internet : jan.manek AT worldonline.cz                             |-O-O-|

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