2002/09/17 event : (345) Tercidina occults HIP 19388

Eric Frappa (updated : 2003 mar. 15)

2002/09/17 occultation by (345) Tercidina, crossing Europe from west to east,
is one of the best success
in the history of stellar occultations :

75 chords (66 in absolute timing,
9 in duration only) gather in
a well-defined asteroid profile.

The predictions

Among the Edwin Goffin's 2002 predictions (source : Edwin Goffin and Ludek Vasta), we find an event between (345) Tercidina and a 5.5 mag. Hipparcos star, in the night of september 16/17, for a 11.2s predicted max duration. The path has a west to east direction, from Saint-Brieuc (France) to Atyraou (Kazakhstan).

On september 3, Jan Manek gives an update on his website (source : Jan Manek), taking into account the latest astrometric observations (provided by Ron Stone, Bill Owen, Raoul Behrend, Stefano Sposetti and the Bordeaux-Floirac astrometric team). The new prediction shows a 200 km shift to the south of the occultation path (with a 77 km 2 sigma uncertainty for a 110 km path width), crossing France (Nantes to Mulhouse), Germany (Munich), Austria (Vienna), Slovakia (Bratislava), Hungary (north of Budapest), Romania, Moldavia, Ukraine to south Russia (south of Rostov).
On september 15, Steve Preston gives another update (source : Steve Preston), consistent with Manek's one. He announces a 27 km 1 sigma uncertainty for a 102 km path width.

The star

HIP 19388 = omega1 Tau = 43 Tau = BSC 1283 = SAO 93785 = PPM 119655
- Magnitude V : 5.51
- Type : K2 III (orange-coloured giant star)
- RA (2000) : 04 09 09.988
- Dec (2000) : 19 36 33.10
- Distance : 89 +/-7 parsecs (291 +/- 23 light years)

Very easy to spot, at half-way between Hyades and Pleiades.

Observing station 30 km
north of Dijon in France,
one hour before the event
(image courtesy of F. Colas).

The asteroid

(345) Tercidina

Discovered in 1892 november 23 by A. Charlois at Nice

- Magnitude : 12.8
- Orbital period : 3.55 years
- Type : C
- Rotation period : 12.371 h
- Estimated diameter : 100 +/-6 km

Situation at the moment of occultation
(source : Orbits - NASA)

Some positive recordings of the event

12.13s occultation -
42 km NNE of Dijon (FR)
camcorder MiniDV Sony TRV15 (25 fr/s)
+ 80mm
refractor (courtesy of C. Marlot)

11.8s occultation -
Tours (FR)
Hisis22 + 500mm Maksutov lens
(courtesy of P. Morel, SAF)

10.96s occultation - 12 km SW of Langres (FR)
PCV680K Vesta Pro webcam + 78mm refractor
(movie and sequence : E. Frappa)

7s movie (618 Ko) showing the 2 minima
courtesy of O. Kloes & S. Messer)
A probable grazing occultation was recorded by Oliver Kloes and Stefan Messer from the Black Forest (DE), close to the northern border of the path.

2 minima of different intensity are visible on the light curve (right). Recording with a 2006X BW Low Light video camera + 254mm reflector.

(courtesy of O. Kloes & S. Messer

Note that all the video recordings show gradual disappearance and reappearance, in agreement with the high angular diameter of the giant star omega1 Tau (around 1 mas).

Data reductions

Participation in this occultation was strong. Some people didn't hesitate to travel widely, crossing frontiers to join the occultation path.

105 known observers
of 17 different countries have been involved in this event.

75 observers are involved in a positive observation (without timing for some of them) and 75 chords have been produced (by multiple methods for some observers).

Employed instruments are going from simple 7x50 binoculars to 400mm reflector. Used methods are also of a large diversity : visual, video (low light video cameras, camcorders, webcam), CCD in drift scan mode, CCD trail, photographic trail.
Observers distribution

Look at the excellent reliability of the prediction
(figure : J. Lecacheux, Occult software map)
Reduction showing a wide field view
of the raw data
(with negative observations)

61 positive and 18 negative
observations are represented here.
Dotted lines are negative observations,
continuous segments are positive ones
(reduction and figure : J. Berthier - IMCCE)
Reduction of the raw observations
(with WinOccult, Dave Herald's software)

Each trail is one observation (star during time).
The two continuous trails are negative observations,
the others are interrupted by the star disappearance (red dots)
and go on with the star reappearance (green dots)

Only consistent raw observations (in absolute timing)
are represented here (figure : E. Frappa)
Improvement of the asteroid outline

Raw observations adjusted on a median occultation curve
(fitted through the mid-chord positions)

All known and usable chords are represented here
(reduction and figure : J. Lecacheux)

On the last figures, we see clearly the asteroid shape with the irregularities of its outline (particularly the prominence visible on the left side of the asteroid).

The size of Tercidina, seen under this particular angle, is 92x106 km.

(additional information is given by the light curve of the asteroid, visible on the Raoul Behrend page)

The data study made by J. Lecacheux shows that 35% of the observations reach an accuracy equal or better than 0.1s, concerning the mid-event time (± 0.1s is the wanted accuracy today for occultation observations). If a part of the observers failed in providing the needed precision in absolute timing, chord lengths are generally good, as seen on the data fit of the last figure.

Go back to the 2002 results page

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