New precise astrometric positions of Himalia in 2016-2018 based on Gaia DR2

Abstract

Himalia is the largest irregular satellite of Jupiter. A total of 267 new observed positions of Himalia in the period 2016-2018 were collected by the 1.0 m telescopes at Yunnan Astronomical Observatory during 10 nights. Thanks to the high-quality reference catalogue Gaia DR2 and suitable processing methods for images (ie. image enhancement technique), the precision of our new observations of Himalia is higher than those of the previous observations. We compared our observations to the best ephemerides of Himalia available now. This comparison has shown that our observations provide standard deviations of residuals better than 25 mas and mean residuals lower than 5 mas. The precision of our new observations reached the best level of ground-based astrometric observations of Himalia.