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THE PROJECT NAROO(NEW ASTROMETRIC REDUCTION OF OLD OBSERVATIONS)

JEAN-EUDES ARLOT1, MIREL BIRLAN1,2, VINCENT ROBERT1

1Institut de Mecanique Celeste et des Calculs des Ephemerides, CNRS UMR8028, Observatoire deParis

77 av Denfert-Rochereau75014 Paris Cedex, France

Email: [email protected]; [email protected]; [email protected] Institute, Romanian Academy

5-Cutitul de Argint040557 Bucharest, Romania

Abstract. The article presents concepts and milestones in the development of NewAstrometric Reduction of Old Observations (acronym NAROO).

Key words: astrometry – photographic plates – accuracy – measuring machine.

1. INTRODUCTION

We propose a project of setting up of a centre for sub micrometric digitizing ofphotographic plates and images analysis. This project will endorse:

• the making of a new reduction of old observations for observing in the past

• the creation of a centre for digitizing photographic plates and image analysis

• the data mining on CCD observations for a new astrometric reduction

• the use of new catalogues such as UCAC4 and Gaia reference star cataloguesfor the new reduction

Our goal is mainly to emphasizing the astrometry of solar system bodies in thescope of the arrival of a new astrometry thanks to the arrival of the Gaia referencecatalogue.

2. THE CONTEXT OF THE PROJECT

The studies of small effects in the motion of solar system objects increasedthe interest of old data useful for the dynamics of solar system objects and several

Romanian Astron. J. , Vol. 26, No. 1, p. 3–9, Bucharest, 2016

4 Jean-Eudes ARLOT, Mirel BIRLAN, Vincent ROBERT 2

Fig. 1 – Accuracy of astrometric measurements over the last two millennia.

projects for digitizing old plates arose. Even before the Gaia project, reference starcatalogues (UCAC, URAT) made progresses allowing to reduced old data. Besidesthe catalogue useful for the astrometric reduction, we had a progress of the technol-ogy of sub-micrometric scanners. Projects of scanning old photographic plates werestudied (Brussels, St. Petersburg, Shanghai, Harvard) and settled-up with severalobjectives.

The past progresses of astrometry are shown in Figure 1.The future progresses of astrometry are shown in the Figure 2 through the po-

sitional accuracy of the Gaia star catalogue for the period 1890–2090 giving the ac-curacy for several magnitudes of the reference stars. Star proper motions of the Gaiacatalogue will allow to go one century in the past.

3. THE SCIENTIFIC GOALS

There are many scientific goals which should be fulfilled thanks to our project.First, by providing a coherent reference system for all data, the extrapolation of theephemerides of solar system objects will become confident. More, for specific ob-jects such as TNO and NEO, we will be able to make pre-discoveries on astrographicplates such as Schmidt plate enlarging the sample of observational data.

By increasing the astrometric accuracy of one order of magnitude, we will beable to quantify small effects such as the dissipation of energy due to tides in thenatural satellites systems: internal structure and scenarios for the formation shouldbe validated. We would explain the thermal equilibrium of Io and the geysers on

3 The Project NAROO (New Astrometric Reduction of Old Observations) 5

Fig. 2 – Accuracy of astrometric measurements in the era of GAIA space mission.

Fig. 3 – Volcanoes on Io and geysers on Enceladus:an explanation through the explanation of their motion.

Enceladus by looking for an acceleration in the motion of the icy satellites (Figure3).

Concerning the Saturnian system, we look for old data helping to validate thescenarios of formation and evolution of the satellite system (Figure 4).

The astrometric observations of the natural planetary satellites may be cata-logued as follow:1) on photographic plates made from 1890;2) on CCD observations made from 1980;3) on astrometric observations from space probes.

More generally, an old observation worth to be re-reduced is an observationmade before the arrival of the Gaia catalogue (Figure 5).


Fig. 4 – The Saturnian satellites.

Fig. 5 – Example of old plates worth to be re-reduced and scanned as tests. Three exposures of theMartian system (left side) with a zoom of individual (positive) image on Phobos, Deimos near the

planet Mars. The accuracy of the reduction is the same as the accuracy of the observations byMariner made at the same time.

4. PRECURSORS AND COMPETITORS OF THE NAROO PROJECT

The scanning of photographic plates is performed by several observatories withdifferent purposes.

We will cite here, a non-exhaustive list:1) MAMA – the program was developped inside the Paris Observatoiry. The accu-racy of measurements was 1000 nm. The measuring machine is stopped for about 10years.2) Starscan – was a program of scanning developped at U.S. Naval Observatory fordigitizing with an accuracy of 500 nm.3) Harvard University Historic Sky Project was developped for scanning plates withan accuracy of 1000 nm4) Pulkovo Fantasy digitizer is a scanning system with an accuracy of 1000 nm.5) DAMIAN – Royal Observatory of Belgium is a program of scanning photograph-ica plates with an accuracy of 70 nm.


Table 1

Estimation of averaged Observed-Computed and accuracy in right ascension

and declination of Mars and its satellites

(O−C)α·cosδ σα·cosδ (O−C)δ σδNOE NOE

Mars -1.8 56.9 -5.3 50.7Phobos 6.0 58.3 61.7 48.6Deimos 4.3 41.9 -3.1 47.3

Table 2

Estimation of averaged Observed-Computed and accuracy in right ascension and declination of

Galilean satellites from the USNO plates obtained in 1974 and digitized using DAMIAN system

(in mas)

(O−C)α·cosδ σα·cosδ (O−C)δ σδINPOP06/L2 INPOP06/L2

JI -9 54 34 68J2 -10 56 14 70J3 1 63 39 72J4 -20 64 10 70

Inside NAROO we develop collaborations with laboratories owning sub-micro-metric scanners and photographic plates (USNO-Washington DC, ROB-Bruxelles,Bucharest Astronomical Institute, QMUL-London, OCA-Nice). We made an inven-tory of existing plates scientifically interesting and we found a large number of in-teresting available plates (until 200 000 plates) especially plates from refractors thefocal length of which being from 3 to 20 meters or from reflectors (Schmidt plates).We made tests by scanning Galilean, Saturnian and Martian plates with the ROB-DAMIAN digitizer. We got first encouraging results with the Martian satellites as-trometric positions (Table 1) the accuracy of which being the same than for Marinerdata made at the same date.

Tables 2 provides the O-C of the Galilean satellites in mas: they allow to val-idate Jupiter’s ephemerides and to show the biases in these ephemerides (Robert etal., 2011; Arlot et al., 2012; Robert et al., 2014).

Besides photographic plates, we analyzed CCD observations made in the 1990’ssuch as Flagstaff astrometric images. Small inner satellites may be referred to astro-metric stars which were not catalogued at the time of the first reduction but whichwill be included in the Gaia catalogue. We consider CCD observations of Dione,Tethys and the Lagrange L4 librators Helene and Telesto made with the Flagstaff61-inch telescope (Figure 6).


Fig. 6 – CCD image of Saturnian satellites obtained using Flagsatff 61-inch telescope.

5. IMAGES FROM SPACE PROBES

The observations made by space probes were also reduced with the availablereference star catalogues and may be re-reduced. Figure 7 shows an observation bythe space probe Cassini with the stars used for the reduction. With the UCAC2 or4 catalogue, the astrometric accuracy reaches 60 mas; the Gaia reference catalogueshould allow to reach an accuracy of 1 mas. In this case, many other problems shouldbe solved such as the figure of the satellite.

Fig. 7 – Astrometry of satellites Dione and Enceladus using ISS camera onboard Cassini. Thereferences for these measurements are the background stars.


6. CONCLUSION

Because of the large number of plates available and of the need of high astro-metric level of old data, we intend to continue our project of re-reducing old data. Ourtests made with the UCAC catalogues let us think that the use of the Gaia cataloguewill provide valuable data for the study of the dynamics of the solar system.

Acknowledgements. This paper was presented at the “Physics and Astrometry of Solar Sys-tem objects”, Hateg – Romania, in 28-30 May 2015. This conference was organized in theframework of PASSO “Capacities” project, Contract 769/24.04.2014. The NAROO project issupported by the ESPACE FP7 European project (grant agreement 263466), the Ile-de-FranceRegional grant program an the GRAM program of INSU/CNRS.

REFERENCES

Robert, V., de Cuyper, J.-P., Arlot, J.-E., de Decker, G., Guibert, J., Lainey, V., Pascu, D., Winter, L.,Zacharias, N.: 2011, P&SS 73, 66.

Arlot, J.-E., Desmars J., Lainey V., Robert V.: 2012 MNRAS 415, 701.Robert, V., Lainey V., Pascu D., Arlot J.-E., De Cuyper J.-P., Dehant V., Thuillot W.: 2014 A&A 572,

104.

Received on 17 November 2015

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