New astrometric measurement and reduction of USNO photographic observations of the main Saturnian satellites: 1974−1998^⋆

¹ Institut Polytechnique des Sciences Avancées IPSA, 11−15 rue Maurice Grandcoing, 94200 Ivry-sur-Seine, France
e-mail: vincent.robert@obspm.fr
² Institut de Mécanique Céleste et de Calcul des Éphémérides IMCCE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Lille 1, 77 Av. Denfert-Rochereau, 75014 Paris, France
³ United States Naval Observatory USNO, 3458 Massachusetts Ave NW, Washington, DC 20392, USA
⁴ Royal Observatory of Belgium ROB, avenue Circulaire 3, 1180 Uccle, Belgique

Received: 28 September 2016
Accepted: 12 October 2016

Abstract

Context. Accurate positional measurements of planets and satellites are used to improve our knowledge of their orbits and dynamics, and to infer the accuracy of the planet and satellite ephemerides.

Aims. In the framework of the European FP7 ESPaCE program, we provide the positions of Saturn and its main satellites taken with the US Naval Observatory 26-inch refractor from 1974 to 1998.

Methods. We measured 526 astrophotographic plates with the digitizer of the Royal Observatory of Belgium and reduced them through an optimal process that includes image, instrumental, and spherical corrections using the UCAC4 catalog to provide the most accurate equatorial (RA, Dec) positions.

Results. We compared the observed positions of the satellites with the theoretical positions from INPOP13c and DE432 planetary ephemerides and from NOE-6-2015-SAT and SAT375 satellite ephemerides. The mean post-fit rms residuals in equatorial positions range from ±68 mas for the Titan observations or 400 km at Saturn, to ±100 mas for the Hyperion observations or 600 km at Saturn. The mean post-fit rms intersatellite residuals range from ±46 mas for the Rhea-Titan observations or 280 km at Saturn, to ±72 mas for the Hyperion-Titan observations or 430 km at Saturn.