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New reduction of minor planets photographic plates obtained with Pulkovo Normal Astrograph

A.A. Berezhnoy Pulkovo Observatory of RAS, Saint-Petersburg, Russia


Minor Planet observations at Pulkovo

Periodical observations of 14 bright asteroids named Selected Minor Planets (SMP) were performed at Pulkovo since 1948 within the international framework started by works of B.V. Numerov and D. Brouwer. Long series of SMP observations have been used to calculate the mutual rotation parameters of dynamic reference frame of Solar system respect to fundamental catalogues reference systems (FK4, FK5, HCRF). First reductions had been performed in systems of various reference catalogues (Yale, SAO, AGK3 etc.) and additionally re-reduced in HCRF.


Advantages of new reductions

The new reductions of digitized plates images allows us to obtain the results directly in HCRF. Obtained coordinates of SMP can be used to increase of orientation parameters accuracy and to studying the dynamics of Solar system. In addition, the new reductions yield a great numbers of reference stars measurements for systematic errors analysis as well as background objects that were not previously measured.


Photographic material
Normal Astrograph D F 330 mm 3467 mm Photoplates Size Fieid of view Scale Image Format Size Resolution Scale Colour depth File size Tif ~20kx20k pix 3200 dpi 469 mas/pix 16 bit ~1 160x160 mm 22є 59.56 "/mm


Digitization and measurements
Flatbed scanner Microtek ScanMaker i900 calibrated for plate measurements is being used for digitization. About 2000 photographic plates with SMP obtained from 1948 to 1990 with Pulkovo Normal Astrograph were selected for this work. Regular measurements had started in the middle of 2010. More than 1500 plates already measured at present moment and successfully astrometric reductions of stellar fields have been done for more than 1250 of them. Proposed date of conclusion: October of 2011'.


Reductions overview
Number of measured plates Epochs Reference catalog Number of reference stars measurements Ephemerides Reduction model Number of measured SMP positions Number of measured LSPM positions 1262 1949,3-1985,11 UCAC3 ~280'000 & EPOS7 linear, 6 constant 1032 1055


Systematic effects
Atmosphere
Chromatic refraction Differential refraction ... Colour Index, height height, Temp, Pressure

Instrument
Distortion Coma Chromatic aberration ... ^3 , magn Color Index

Photoplate Scaner
Calibrated


Systematic errors
Magnitude equation: magn | (O-C)

Residuals vector fields: X, Y, X, Y

Avoided by instrumental passband + plate sensitivity

Color equation: Color Index | (O-C)


Systematic errors
Magnitude equation: magn | (O-C) Residuals vector fields: X, Y, X, Y
Common distortion + Magnitude equation

Magnitude: 8 ­ 10.5

Magnitude: 13 ­ 13.5


Systematic corrections
Before After
Reductions were remade and each measured position of reference star or target object was corrected by interpolation of whole set of vector fields and then each interpolation correction was fitted by polynomial of 3rd order.

Vector fields were constructed with averaged residuals of set of magnitude intervals

.

As a result:
Corrections allow us to decrease Unit Weight Error of reduction from 168 to 152 mas in RA and 172 to 156 mas in DEC


SMP results
Asteroids Ceres Pallas Juno Vesta Hebe Iris Parthenope Melpomene Phocaea Laetitia Harmonia Industria Herculina Interamnia Obs. Num. 108 133 113 74 124 67 97 88 14 84 64 5 20 19 Epochs (YYYY.MM)
1200

Mean values of total obs.
EPOS7, DE405
1000 800
mean, mas

1949.03 ­ 1981.05 1951.08 ­ 1983.10 1950.03 ­ 1983.10 1950.09 ­ 1984.03 1951.02 ­ 1982.04 1955.08 ­ 1980.12 1955.09 ­ 1984.03
M e a n e rro r, m a s

RA DEC

600 400 200 0 -200

Pallas Ves ta Iris Melpomene Lae titia Industria Interamnia Ceres Juno Heb e Parthenope Phocaea Harmonia Herculina

Mean error of a single observation
EPOS7, DE405
450 400 350 300 250 200 150 100 50 0 RA DEC

1955.02 ­ 1983.05 1976.05 ­ 1980.11 1949.04 ­ 1984.03 1958.02 ­ 1982.03 1976.09 ­ 1976.10 1976.10 ­ 1982.03 1975.10 ­ 1981.01

Pallas Ves ta Iris Melpomene Laetitia Industria Interamnia Ceres Juno Hebe Parthenope Phocaea Harmonia Herc ulina


SMP result comparison
Errors of single (O-C) of the series of coincident observations obtained in this work and re-reduced into HCRF from first reductions results (Chernetenko 2008, IAA) are compared.
Mean error of single observation, RA
700 600 500
error, mas

EPOS7, DE405

Asteroids
Ceres Pallas Juno Vesta Hebe Iris Parthenope Melpomene Phocaea Laetitia Harmonia Industria Herculina Interamnia

Coincident obs. Num.
81 101 77 50 98 49 50 65 2 37 34 0 0 0

Poulkovo IA A

400 300 200 100 Ceres P allas Juno Vesta Hebe Iri s Melpomene Harmoni a P arthenope Laeti ti a

Mean error of single observation, DEC
450 400 350 300 250 200 150 100 50 0 Ceres P allas Juno Vesta Hebe Iri s Melpomene Harmoni a P arthenope Laetitia

EPOS7, DE405
Pulkovo IA A


LSPM results
Number of LSPM objects Number of observations Mean of RA, mas Mean of DEC, mas Error of single obs: RA, mas DEC, mas 679.6 847.4 586 1055 2.3 ± 20.9 -15.4 ± 26


Conclusions
New reductions of 1262 digitized photographic plates with long series of SMP observations were performed. Systematic corrections based on averaged residuals of reference stars allow us to decrease systematic errors significantly (for both types of systematic errors: magnitude equation and common distortion). 1032 positions of SMP and 1055 LSPM stars positions were obtained in HCRF/UCAC3 reference system Comparison of (O-C) values of similar observations between new results and transformed previously on HCRF reference frame shows improvement of new ones.