J/A+A/645/A76 Saturnian satellites in the Gaia ref. frame (Khovritchev+, 2021)
Astrometric measurement and reduction of Pulkovo photographic observations of
the main Saturnian satellites from 1972 to 2007 in the Gaia reference frame.
Khovritchev M.Yu., Robert V., Narizhnaya N.V., Vasilyeva T.A.,
Apetyan A.A., Bikulova D.A.
<Astron. Astrophys. 645, A76 (2021)>
=2021A&A...645A..76K 2021A&A...645A..76K (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Planets ; Positional data ; Plate data ;
Ephemerides
Keywords: astrometry - ephemerides -
planets and satellites: individual: Saturn -
techniques: image processing
Abstract:
We present a remeasurement of old photographic plates, providing
important raw data for dynamical studies of the Saturnian satellite
system. The unprecedentedly accurate realization of the Gaia reference
frame allows us to make a precise calibration of digitized
astronegatives of the Saturnian satellite images. We reprocessed 357
astronegatives taken with the 26-inch refractor and the normal
astrograph of the Pulkovo Observatory between 1972 and 2007 to obtain
the positions of the main Saturnian moons in the second Gaia data
release (Gaia DR2) system. Photographic plates were digitized with the
Pulkovo Mobile Digitizing Device (MDD) scanner. The New Astrometric
Reduction of Old Observations (NAROO) digitizer at the Paris
Observatory was used to calibrate the scanned images. Satellite image
centering and astrometric reduction were performed. In total, 6487
positions (equatorial coordinates) have been determined with an
accuracy of 50mas. This is confirmed by a comparison of our data with
modern ephemerides. The verification of the results was performed
using data from past close approaches by Saturnian satellites to Gaia
reference stars, showing the adequacy of the current residual
analysis. A joint review of the Pulkovo and the United States Naval
Observatory (USNO) intersatellite positions allows us to conclude
about the existence of faint systematic effects in the satellite
theories of motions at the 10mas level.
Description:
Photographic observations of the main Saturnian satellites were
performed at Pulkovo Observatory with the 26-inch refractor (hereafter
P26; D=0.65m, F=10.413m) and the normal astrograph (hereafter PNA;
D=0.33m, F=3.463m). The effective field of view (FOV) is 30x30arcmins
for the P26 and 2x2degrees for the PNA. The corresponding angular
scales of the astronegatives are 19.8078arcsec/mm and 59.56arcsec/mm.
The results obtained with a small set of 14 of those plates are
included in this paper. These plates were obtained with the Zeiss
Double Astrograph (ZDA; D=0.4m, F=3.024m, FOV=3.5x4.5degrees,
angular scale is 68arcsec/mm) of the Abastumani Astrophysical
Observatory in Georgia 1984. The Pulkovo Mobile Digitizing Device
(MDD) was used to scan 357 photographic plates. The field distortion
pattern of the MDD lens was investigated by comparing scans of the
same plate taken with the MDD and the New Astrometric Reduction of Old
Observations digitizer located at the Paris Observatory (NAROO
https://omekas.obspm.fr/s/naroo-project/page/home). Further
astrometric calibration was performed with the linear model using the
Gaia DR2 catalog as a reference. As a result, the described approach
of digitization and calibration allows us to reach a 1mkm-1.5mkm
accuracy level for the positional measurements of the satellite images
on the photographic plates. In total, 6487 positions (equatorial
coordinates) have been determined with an accuracy of 50mas. This is
confirmed by a comparison of our data with modern ephemerides. The
verification of the results was performed using data from past close
approaches by Saturnian satellites to Gaia reference stars, showing
the adequacy of the current residual analysis. The electronic tables
that contain the equatorial coordinates of the main Saturnian
satellites and the parameters of the close approaches of the
satellites to the Gaia DR2 stars are available online.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
satpos.dat 53 6487 Positions of the Saturnian satellites
appulses.dat 123 51 Close approaches of the satellites to Gaia stars
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: satpos.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.5 d MJD Modified Julian date of observation (UTC)
14- 16 A3 --- Inst Instrument designation (1)
18- 27 A10 --- Sat Saturnian satellite name
29- 40 F12.7 h RAhour Right Ascension (J2000), Gaia DR2 system
42- 53 F12.6 deg DEdeg Declination (J2000), Gaia DR2 system
--------------------------------------------------------------------------------
Note (1): P26 is the 26-inch refractor, PNA is the normal astrograph,
ZDA is the Abastumani Zeiss Double Astrograph.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: appulses.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.5 d MJD Modified Julian date of observation (UTC)
14- 23 A10 --- Sat Saturnian satellite name
25- 27 A3 --- Inst Instrument designation (1)
29- 48 I20 --- GAIADR2 Gaia DR2 source_id
50- 61 F12.8 deg RAdeg Right ascension (J2000) form Gaia DR2 at MJD
63- 74 F12.8 deg DEdeg Declination from (J2000) Gaia DR2 at MJD
76- 81 F6.3 mag Gmag G magnitude from Gaia DR2
83- 90 F8.3 arcsec DRA Difference in RA
92- 99 F8.3 arcsec DDE Difference in Dec
101-103 I3 mas e_RAdeg ? Standard error in RA
105-107 I3 mas e_DEdeg ? Standard error in DEC
109-111 I3 --- Nobs Number of observations (2)
113-117 I5 mas (O-C)RA (O-C) in right ascension (3)
119-123 I5 mas (O-C)DE (O-C) in declination (3)
--------------------------------------------------------------------------------
Note (1): P26 is the 26-inch refractor, PNA is the normal astrograph,
ZDA is the Abastumani Zeiss Double Astrograph.
Note (2): Number of separate measurements of the coordinate differences.
Note (3): The MULTI-SAT service (2008A&A...487..759E 2008A&A...487..759E,
http://nsdb.imcce.fr/multisat) was used to calculate the (O-C) values.
--------------------------------------------------------------------------------
Acknowledgements:
Maxim Khovritchev
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(End) M. Khovritchev [Pulkovo obs., Russia], P. Vannier [CDS] 12-Dec-2020