RE-REDUCTION OF THE OLD PHOTOGRAPHIC OBSERVATIONS OF INTERAMNIA (704) BASED ON GAIA DR2 REFERENCE CATALOGUE

Анотація

A new astrometric reduction of old
photographic astroplates benefiting from integration of
modern technologies such as the high precision digitizing
machines and the high precision Gaia DR2 catalogue
could be useful to study the orbital motion of Solar system
minor bodies. Based on the newly released Gaia DR2 star
catalogue, the scans of the photographic plates containing
images of Interamnia (704) taken by the Zonal Astrograph
of Mykolaiv Astronomical Observatory (MAO) in 1974-
1985 were re-reduced. For our investigation we used 29
plates from the UkrVO archive digitized by commercial
EPSON scanner with 1600 dpi resolutions. Besides for 2
of them were digitized by the high precision digitizing
machine of Shanghai Astronomical Observatory of the
Chinese Academy of Sciences (ShAO) with 2540 dpi
resolution. Almost all the plates have 3 exposures with a
small shift. Each of 29 plates was scanned 6 times by
EPSON scanner in 0° direction. The ShAO digitizing
machine scanned 2 plates also 6 times but 3 times in 0°
direction and 3 times in 90° direction. Totally, 85 asteroid
positions taken from 29 plates were derived. Only 5
asteroid positions were calculated from ShAO scans.
The full identification was conducted and
coordinates of all objects were obtained with usage of
different options of astrometric reductions. The mean
inner accuracy of obtained asteroid positions is 0.03″ in
RA and 0.14″ in DEC for EPSON scanner and 0.014″ in
RA and 0.013″ in DEC for the ShAO digitizing machine
in 0° direction and 0.010″ in RA and 0.011″ in DEC in
90° direction. The comparison of the new topocentric
asteroid positions with Horizons ephemeris was made for
calculation (O-C) residuals and their RMS. The mean
residual differences between the scan obtained positions
and JPL calculated positions were (0.09 ± 0.16)″ in RA
and (-0.09 ± 0.25)″ in DEC for the MAO digitized plates;
the calculated differences for the ShAO scans are close to
zero. Comparison of the results obtained with previous
reductions of these observations with Tycho2 and UCAC4
reference catalogues showed that the use of the Gaia DR2
reference catalogue does not lead to a significant
improvement in the random and systematic component of
the residual differences (O-C) for scans with EPSON
scanner from the UkrVO archive. The results obtained by
processing images with the ShAO digitizing machine
suggest that in this case, the re-reduction of all
photographic observations based on the Gaia DR2 could
improve the accuracy of old photographic observations to
the level of modern ground-based CCD observations.