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The Central Astronomical Observatory of RAS at Pulkovo The Paris Astronomical Observatory and IMCCE

Royal Observatory of Belgium

THE RESULTS OF NEW REDUCTION OF PULKOVO PHOTOGRAPHIC PLATES WITH SELECTED ASTEROIDS AND PLUTO USING THE DAMIAN DIGITIZER.
E.V.Khrutskaya1, J-P. De Cuyper2, S.I.Kalinin1, A.A. Berezhnoy1, J.de Decker2. 1 The Central Astronomical Observatory of the Russian Academy of Sciences at Pulkovo, Russia, orion@gao.spb.ru 2 Royal Observatory of Belgium, Belgium

This work was supported by grant from the Department of Science at the French Embassy in Russian Federation.


The library of photographic plates of Pulkovo Observatory.
The glass plate archive of the Pulkovo observatory contains more than 50000 photographic plates with observations of astronomical objects. Among them more than 5400 plates with images of planets, planetary satellites and asteroids.

The number of photographic plates with images of the Solar system bodies and observation periods.

Saturn and its satellites ­ 800 plates (1972 - 2007). Jupiter and Galilean satellites ­ 500 plates (1976 ­ 2005). Mars ­ 763 plates (1960 - 1988). Uranus and its satellites ­ 250 plates (1910-2004). Neptune ­ 237 plates (1899 - 1955). Pluto ­ 250 plates (1930 ­ 1994) 18 selected asteroids ­ 2655 plates (1949-2004


Microtek flatbed scanner.
Technical characteristics of the scanner: optical resolution: 3200 dpi number of bits per pixel (grayscale mode): 16 maximum size of scanned plates: 200x250 mm time needed to scan one 160x160 mm plate:~ 5 min. sensor: one-dimensional CCD sensor. interface: USB 2.0

To measure the available photographic plates and them a new reduction in the Pulkovo Observatory were developed two software packages: SCANSOFT (S.I.Kalinin, E.V.Khrutskaya)
for calibration and getting measured coordinates X, Y

RULER3PL (A.A.Berezhnoy)
for astrometric reduction from X,Y to RA, DECL

What came out of it you will learn from the report of A.A. Berezhnoy


DAMIAN (Digital Access to Metric Images Archive Network) digitizer at ROB.

Manufacturer: AEROTECH (USA) Positioning system: AEROTECH ABL3600 on granit plate 1.5 m x 1.2 m x 0.2 m Optical block: Schneider Xenoplan telecentric objective 1:1, 12 bit CMOS camera (BCi4), size of field 1280x1024 px, Size of pixel: 7x7 micron

The system of "climate control" Standard: Temperature +20oC+-0.05o Relative humidity 50%+-1%


Construction of overall mosaic FITS image of the whole photographic plate.
Significant systematic errors (about 2-3 microns) due to optical distortion of the lens were found on the edges of the field (1280x1024). The stepping of 704 pixels was chosen in order to restrain the optical distortion effects in the non-overlapping parts of the sub-images.

An overall mosaic FITS image of the whole photographic plate is also generated from the inner non overlapping (704 x 704 pixels) part of the individual images.


CALIBRATION
For calibration Damian digitizer we used photographic plates with a large of quantity of stars (Pleiades). Each plate was measured at four positions with the rotation of that at 90 degrees. It was assumed that values of systematic errors and their structure are identical in all individual fields (704x704 px)

The each sub-image (704x704 px) of overall mosaic image was divided into 8 parts in X and Y directions. Size such of small fields is 88x88px

The aim of the calibration ­ determination of systematic errors of the DAMIAN digitizer for each small field of size 88x88 px


Let (, ) - true coordinates of some star, and (x, y) - measured coordinates. ex(x,y) and ey(x,y) - unknown corrections which represent systematic errors in different small fields of sub-images = x + FW(m) = y + GW(m) (1)

F is the vector of ex(x,y) corrections, G is the vector of ey(x,y) corrections, m is the number of the square which contains that star: m = [x/w] + [y/w]*M + 1 W is the vector representing position of that star in the field of size 704x704 px, components of vector W are: W(i) = 1, if i=m, W(i) = 0, if i m.

Vectors F and G are common for all stars and all plates. Their components are calculated during calibration and are invariable till the next calibration.

For each pair of scans (A, B) were constituted the conditional equation of the form (2).

FW (m ) cos + GW (m A ) sin - FW (m ) = x - x A cos - y A sin - S
GW ( m ) cos - FW ( m ) sin - GW ( m ) = y B - y cos + x sin - S

x
y

(2)

Estimates of the parameters of connection ( - rotation angle, Sx - shift along X axis, Sy shift along Y axis) were obtained for each pair of the scans (6 pairs). Error in the determination of these parameters lie in the ranges: for Sx, Sy - ± 0.006-0.008 micron, for - ± 0."08 - 0."1 Systematic corrections (components of F, G) were determined using the parameters of connection between pairs of scans from the common system of conditional equations of form (2) which formed for all the stars of all pairs of scans by the method of least squares.


Vector diagram showing systematic error values of DAMON in field of size 704x704 px. The largest vectors are about 0.5 microns long .


(X0-X180) micron

X mm

Residual errors of measurement which obtained by comparison of two scans of one and the same plate with rotated by 180o after exclusion of systematic errors (plate C844, 1820 stars). The mean value of the standard deviation is 0.30 microns (~20 mas)


The method of "moving dot" to DAMIAN calibrate was used at ROB. A special the plate with "fictitious stars" was used for calibration at ROB. The plate was digitized in step mode with step corresponding to exactly 70,4 pixels in the X and Y directions

An example of a field calibration plate.

Model of link of true and measured coordinates of "fictitious stars" was constructed. The parameters of model were determined. These parameters were used to correct the measured coordinates of the stars on real plates.
Such technique has been used during reduction USNO plates with satellites of Jupiter.
(V.Robert, J-P,De Cuyper, J-E.Arlot et al. "A new astrometric reduction of photographic plates using the DAMIAN digitizer:improving the dynamics of Jovian system", MNRAS, 2011).


Further work with digitized plates included:
·exclusion of non- stellar objects ·separation of exposures relevant to each object averaging coordinates for these exposures ·introduction of systematic corrections in the measured coordinates (X,Y).

Exclusion of non- stellar objects:

A Lorentz profile was used to fit the stellar images.

For example, plate N 5766 with the asteroid, obtained with three expositions before and after exclusion of non-stellar objects.

Before exclusion non-stellar objects many objects on the plate were higher than the background level

After exclusion of non-stellar objects


Separation of exposures relevant to each object averaging coordinates for these exposures. For example, the apparent speed motion of asteroids Ceres and Hebe (relative to the stars) as a function of elongation.

Ceres

Hebe


The results of test measurements of the Pulkovo plates and their reduction.
59 Pulkovo photographic plates with selected asteroids were measured using DAMIAN digitizer at Royal Observatory of Belgium (ROB) in September 2009 and January 2010. All plates were obtained on Normal astrograph Pulkovo Observatory in period 1954-1983. The size of the plates 160x160mm Numbers of Asteroids: 1,2,3,4.6,7,11,18,39,40,532 Magnitudes: 9 - 12 The six-constant method, with the UCAC3 catalogue as reference, was used for the astrometric reduction. There were from 20 to 200 reference stars per plate depending on the galactic latitude. The average value of the standard error of the measured coordinates on one plate lies within 15-20 mas. Mean precision of reduction (error unit of weight) is 85-105 mas for RA and DECL. The accuracy of a single asteroid observations lies within 60-90 mas for both coordinates. To comparing, the accuracy of a single observation of the same asteroids taken with ASCOREKORD (observation period 1994-1997, reference catalog PPM) was 180-200 mas


PLUTO OBSERVATIONS Besides the asteroids with using the Damian digitizer was measured 50 plates with Pluto (observations 1931-1960, mag=15.9-14.5) Observations of Pluto at Pulkovo were begun in March 1930 on the Normal astrograph S.G. Kostinsky.
Normal astrograph was installed at the Pulkovo Observatory at 1893. The instrument has two lenses mounted in a tube. First of them is photographic lens (D = 330 mm, F = 3467 mm), the second lens is visual, intended for guiding (D = 250 mm, F = 3650 mm). Image scale of the plate is M = 59. "56 mm, field of view is 2x2 degrees. Normal Astrograph had been equiped by CCD at 2004. CCD-observations of the Solar system bodies and observations of stars with large proper motions are performed now.

Normal Astrograph

S.G.Kostinsky

Photographic observations of Pluto were conducted at Pulkovo up to 1994 when it crossed celestial equator. During the period from 1930 to 1994 was obtained 250 photographic plates.


The results of a new reduction of Pluto. During the period 1930-1960 period with the Normal astrograph was obtained 66 plates with Pluto. 50 plates have been digitized by Damian digitizer. The six-constant method, with the UCAC3 catalogue as reference, was used for the astrometric reduction Mean precision of a single Pluto observations is: RAcos=170 mas; DECL= 137 mas.

To comparing, the accuracy of a single observation of Pluto taken with REPSOLD meter (observation period 1930-1965) was: RAcos=260 mas, DECL= 200 mas. ("Precise Positions of Pluto During 1930-1965 from Photographic Observations at Pulkovo", V.V.Lavdovsky, 1968)


Comparison of the Pluto observations with INPOP10, INPOP8, DE405, EPM2008.
To calculate the ephemeris service of IMCCE was used (http://www.imcce.fr/fr/ephemerides/generateur/.htm)
Ephemeredes Mean (O-C)RA 0".0701 1".1056 -0".3150 -0".1625 Mean (O-C)DECL -0".0366 -0".1958 -0".1229 -0".1904 External RA 0".5805 1".1932 0".4303 0".3275 External DECL 0".1974 0".3040 0".2128 0".2643

INPOP10 INPOP8 DE405 EPM2008

Mean (O-C)RA and External RA are not multiplied by cos

DE200

-0".1278

-0"4108

0".2519

0".4377

Only observations 1950-1960 were used when compared with DE200(31 pl.)


Comparison with EPM2008 and INPOP10, period of observations 1931-1960

Comparison with JPL DE202, period of observations 1930-1994, V.P.Ryl'kov, Izv GAO, 210,1996


CONCLUSION 1. Test measurements of Pulkovo plates and their further reduction have shown that DAMIAN digitizer can well be used for high-precision astrometric measurements. Digitization of old photographic plates and their new astrometric reduction in the modern reference system together with recent CCD observations forms a basis for the construction, improvement and testing of theories of the Solar system bodies dynamic. These researches are actual for the ephemeris support of space missions and for investigation of structure and evolution of the Solar system, and also for determining relation between the dynamic and reference systems. 2. The plates which were obtained with single exposure should be measured twice with rotation of the plate by 180 degrees. 3. Since there is no reliable theory of Pluto's motion nowadays, it is extremely desirable to perform digitization and new reduction of all the plates with Pluto in all the observatories worldwide. 4. It is desirable start regular photographic plate measurements with DAMIAN digitizer as soon as possible. Since the mass character of digitization and reduction of old plates will be to needs financial support, it is necessary to impart international status to this project.


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