Precision premium, a concept in astrometry that was firstly presented by Pascu in 1994, initially means that the relative positional measurement of the Galilean satellites of Jupiter would be more accurate when their separations are small. Correspondingly, many observations have been obtained of these Galilean satellites since then. However, the exact range of the separation in which precision premium takes effect is not clear yet, not to say the variation of the precision with the separation. In this paper, the observations of open cluster M35 are used to study precision premium and the newest star catalogue Gaia DR2 is used in the data reduction. Our results show that precision premium does work in about less than 100 arcsecs for two concerned objects, and the relative positional precision can be well fitted by a sigmoidal function. Observations of Uranian satellites are also reduced as an example of precision premium.

Characterization of the precision premium in astrometry

The 2014-2015 Brazilian mutual phenomena campaign for the Jovian satellites and improved results for the 2009 events

Decoupled and coupled moons’ ephemerides estimation strategies application to the JUICE mission

Astrometric results PHEMU-1985 and PHEMU-1991

Photometric observations of satellites during their mutual occultations and eclipses are a valuable source of astrometric data for studying the motion of natural planetary satellites. Worldwide photometric observation campaigns are organized in order to observe as many phenomena as possible. All the photometric results obtained during such an observation campaign are stored in a single database, and after some time, they undergo astrometric processing. After conducting the campaign and publishing the results, some observers find unused data, which appear valuable. We have collected these photometric observations of mutual occultations and eclipses of Jupiter’s Galilean satellites and processed them to utilize these valuable astrometric data. To obtain astrometric data from the photometric observations, we have applied our original method. The observations come from eight observatories worldwide. As a result, this work presents 32 new relative astrometric positions of Jupiter’s Galilean satellites in 2009 and 23 new positions in 2014–2015. The astrometric accuracy of the new data in comparison with the most developed theory (O–C) is approximately 0.05′′. The internal accuracy, based on estimates for random photometry errors, is 0.02′′.

Nicolai Emelyanov

Papers

Natural satellites mutual phenomena observations: Achievements and future