Astrometry of the main satellites of Uranus: 18 years of observations

TL;DR

This study presents 18 years of precise astrometric measurements of Uranus's main satellites, improving orbital data and refining Uranus's positional accuracy using advanced reduction techniques and multiple ephemerides comparisons.

Contribution

It provides a comprehensive long-term astrometric dataset of Uranus's satellites and introduces a novel reduction method to minimize scattered light effects, enhancing positional accuracy.

Findings

Overall satellite offsets are approximately -29 mas in RA and -27 mas in Dec.

Offsets of Oberon relative to other satellites are minimal, around +3 mas in RA and -2 mas in Dec.

Largest positional discrepancies stem from planetary ephemeris uncertainties.

Abstract

We determine accurate positions of the main satellites of Uranus: Miranda, Ariel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those of these satellites, are also determined. The observational period spans from 1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil. We used the software called Platform for Reduction of Astronomical Images Automatically (PRAIA) to minimise (digital coronography) the influence of the scattered light of Uranus on the astrometric measurements and to determine accurate positions of the main satellites. The positions of Uranus were then indirectly determined by computing the mean differences between the observed and ephemeris positions of these satellites. A series of numerical filters was applied to filter out spurious data. These filters are mostly based on the comparison between the positions of Oberon with those of the other satellites and on the offsets as given by the differences between the observed and ephemeris positions of all satellites. We have, for the overall offsets of the five satellites, -29 (+/-63) mas in right ascension and -27 (+/-46) mas in declination. For the overall difference between the offsets of Oberon and those of the other satellites, we have +3 (+/-30) mas in right ascension and -2 (+/-28) mas in declination. Ephemeris positions for the satellites were determined from DE432+ura111. Comparisons using other modern ephemerides for the solar system -INPOP13c- and for the motion of the satellites -NOE-7-2013- were also made. They confirm that the largest contribution to the offsets we find comes from the motion of the barycenter of the Uranus system around the barycenter of the solar system, as given by the planetary ephemerides. Catalogues with the observed positions are provided.