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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
Using positional observations of minor planets for
improving the orientation of star catalogue
Yu. A. Chernetenko
Institute of Applied Astronomy, St. Petersburg, Russia
Discovery of new groups of minor planets (NEAs, Koiper belt, binary as­
teroids) attracts attention of observers mainly to these objects. Bright minor
planets of the main belt have long observational history and therefore we know
their orbital parameters rather precisely. That is why these minor planets are not
considered now as very interesting objects for positional observations. But expe­
rience shows that this kind of observations can be used succesfully for improving
orientation parameters of star catalogues with respect to dynamical reference
system. However, for their advantageous use these observations should be homo­
geneous, cover sufficiently long time interval and be reduced to one reference star
catalogue. One can note the following two groups of observations: 1) photographic
observations of 15 selected minor planets made during 1950--2000 [1] with accura­
cy on the order of 0.25 00
\Gamma 0:30 00 and 2) Hipparcos observations of 48 bright minor
planets made during 3.3 years, referred to ICRF and having accuracy of about
0.015 00 . Combined processing of these two groups of observations made it possible
to obtain orientation of ICRF with respect to DE200 [2]. The accuracy of this
result was proved to be comparable with those of LLR and VLBI measurements.
Since 1997 Stone [3] realizes a new program of observations of the first 2000
numbered minor planets. The CCD observations were taken with Flagstaff As­
trometric Scanning Transit Telescope (FASTT) and were reduced differentially
to ICRF equatorial positions using reference stars taken from the ACT star cat­
alogue.
In present paper all these series of observations have been used for improving
the orientation of Hipparcos star catalogue. For this purpose about 500 minor
planets having sufficiently large number of observations (? 70) were selected
from those observed by Stone. For the observations of these planets the best
accuracy value is equal to 0.050 00 , the mean accuracy is equal to 0.09 00 \Gamma0:10 00 . Such
an accuracy is several times better than the mean accuracy of usual positional
observations of minor planets.
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Then, preliminary simulation of solution was done with the aim to reveal the
most suitable minor planets for solving our task. This simulation confirms the
known result, i.e. all other things being equal the nearer object is to the Earth
the better results can be obtained using its observations for determination of
orientation parameters. Then, it was shown that for the best determination of
velocity changes of orientation parameters the semi­major axes within the limits
2.0 -- 2.5 a.u. should be chosen.
The following model of motion and processing observations was used. Posi­
tions of minor planets were determined with accounting for the perturbations
from nine major planets in correspondence with DE403. Besides, the perturba­
tions from 300 minor planets were taken into account. Masses of these 300 minor
planets were taken in conformity with DE403, their coordinates were obtained by
numerical integration starting from the osculating elements published in EMP.
The relativistic terms due to the Sun were included in the equations of motion.
The observations were corrected for gravitational deflection of light and for phase
effect. For accounting for the phase effect Lommel--Zeeliger, Akimov [4] and Hap­
ke [5] laws of light scattering were used in different solutions.
Observations of 90 selected minor planets were used in general solution for
their orbital elements, orientation parameters and some parameters of phase re­
duction. The results obtained are discussed in the paper.
References
1. Chernetenko Yu. A. International program of observations of selected minor
planets: first results. Cel. Mech. & Dyn. Astron. 2001, 80, 185--194.
2. Batrakov Yu. V., Chernetenko Yu. A., Gorel G. K., Gudkova L. A. Hipparcos
catalogue orientation as obtained from observations of minor planets. Astron.
Astrophys. 1999, 352, 703--711.
3. Ronald C. Stone. Accurate FASTT positions and magnitudes of asteroids:
1997--1999 observations. Astron. J., 2001, 120, 2708--2720.
4. Akimov L. A. Light scattering by the Moon. Kinematika i phizika nebesnyh
tel. 1988, 4, 3--10 (in Russian).
5. Bowell E., Hapke B. et al. Application of photometric models to asteroids.
Asteroids II. Eds. Binzel R. P., Gehrels T., Matthews M. S. Tucson: Univ.
Arizona Press, 1989, 524--556.
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