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
Summary
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"
remarks:
* 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
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Jan Manek
Werichova 950
152 00 Praha 5 - Barrandov |_|_|
Czech Republic / \
Internet : jan.manek AT worldonline.cz |-O-O-|
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