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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
CCD observations of planetary satellites and
occultations and close approachments of stars by
asteroids with 26­inch refractor of Pulkovo
observatory
T. P. Kiseleva, I. S. Izmailov, M. A. Mozhaev
Pulkovo Observatory, St. Petersburg, Russia
ST--6 CCD camera has been used with 26--inch Refractor at Pulkovo for ob­
servations of satellites of Saturn (1--8) and Jupiter (1--4), occultations and close
approachments of stars by asteroids and mutual events in satellites systems since
1995.
Observations have been made in series of CCD frames (10--100 and more
frames per series). It made possible to estimate errors of relative positions within
one series (internal errors). These estimates are \Sigma0:015 arcsec and \Sigma0:014 arcsec
for X and Y correspondingly.
Original method of determination of centers of star (planet) images on CCD
frame with high accuracy (ё 0:005 arcsec) had been worked out [3]. The ori­
entation of each CCD frame is determined with the help of daily trail of stars
or satellites. Mutual distances between objects are measured in CCD field. The
``scale--trail'' method is used for astrometric reduction of observations [1]. The cal­
ibration of CCD, necessary to obtain precise relative coordinates in ``scale­trail''
method, had been carried out.
Results of observations were compared with the ephemerides of Harper and
Taylor, calculated by N. V. Emelianov (SAI). Standard deviations, calculated on
the basis of (O--C), are equal to \Sigma0:146 arcsec and \Sigma0:069 arcsec for close pairs
of satellites (distance ! 50 arcsec) and \Sigma0:211 arcsec and \Sigma0:255 arcsec for wide
pairs. Mean (O--C) differences are close to zero proving the absence of systematic
errors in observations. The accuracy of the theory of motion of the saturnian
satellites was estimated to be 0.1 arcsec.
Photometric observations of mutual events in the Galilean satellites of Jupiter
have been made. Light curves, obtained from observations, make possible to de­
termine the mutual distances with very high accuracy [2].
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CCD observations of eight approachments and occultations of stars of Hip­
parcos, Tycho, GSC and ACT catalogues by asteroids had been carried out with
26--inch Refractor in 1998--2001 (see table below).
Mpl Star Date Ev. 1 Mpl Star Date Ev.
39 H28954 21.03.98 A 454 GSC4960196 15.04.98 A
535 H44806 24.03.98 A 11 ACT303945 14.03.99 A
97 H63455 15.03.99 A 111 H2559 10.09.00 O
40 H46751 20.04.94 A 64 T18931422 02.04.01 O
1 Kind of event (A --- approachment, O --- occultation)
Astrometric reduction of these observations had been performed using the
``scale--trail'' method. As a result of reduction the measured distances between
objects in a small CCD field (3 0 \Theta 2 0 ) are presented with high accuracy as func­
tions of time. The errors of these measurements are \Sigma0:01 arcsec for minimum
distances between objects (r 0
) and \Sigma(0:4 \Gamma 18) sec (depending on visual ve­
locities of asteroids) for moments of events (t 0 ). Finally, relative positions and
motions (V 0
) of asteroids, and (O--C) have been calculated with errors not more
than \Sigma0:025 arcsec. Also the variability of brightness of asteroid 454 has been
revealed (\Deltam ъ 0:15 m ; P ъ 4h).
Photographic observations of the saturnian satellites with 26--inch refractor at
Pulkovo are continued now as well. The accuracy of photographic observations is
also very high (\Sigma0:06 arcsec --- internal errors (for X and Y) and \Sigma0:12 arcsec ---
external errors), calculated with the help of (O--C). Totally over 100 relative
positions of saturnian satellites have been obtained from CCD observations and
over 500 relative positions --- from photo observations. Each CCD position is a
mean value in series of 10--100 frames.
References
1. Kiselev A. A. The theoretical foundation of photography astrometry. M.:
Nauka, 1989 (in Russian).
2. Emelianov N. V., Izmailov I. S., Kiselev A. A., Kiseleva T. P., et al. Mutual
positions of the Galilean satellites of Jupiter from photometric observations
during their mutual occultations and eclipses in 1997. A&AS, 2000, 141,
433--447.
3. Izmailov I. S., Kiselev A. A., Kiseleva T. P., Khrutskaya E. V. Using a
CCD camera in Pulkovo programs of observations of binary and multiple
stars and satellites of major planets with the 26­inch refractor. Astronomy
Letters, 1998, 24, 665--672.
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