Research Note

Mutual occultations between Galilean satellites observed at Yunnan Observatory in 2009^⋆

¹ National Astronomical Observatories/Yunnan Observatory, Joint Laboratory for Optical Astronomy, Chinese Academy of Sciences, Kunming, PR China
e-mail: zhangxiliang@ynao.ac.cn
² Graduate School of Chinese Academy of Sciences, Beijing 100039, PR China
³ Institut de mecanique celeste et de calcul des ephemerides, Observatoire de Paris, UMR 8028 du CNRS, 77 avenue Denfert-Rochereau, 75014 Paris, France

Received: 16 December 2010
Accepted: 13 June 2011

Abstract

Context. Photometry of mutual events between natural satellites has been shown to be a most effective and accurate ground-based method for obtaining accurate astrometric data by fitting the light curves observed during these events, and is invaluable for developing the orbital models of the natural satellites.

Aims. Mutual occultations of J2 Europa by J1 Io (Aug. 28, 2009), J1 Io by J2 Europa (Nov. 9 and Dec. 11, 2009), and J1 Io by J3 Ganymede (Nov. 28, 2009) were observed at Yunnan Observatory during the PHEMU09 international campaign. We calculate the astrometric data of satellites by analyzing and fitting the light curves that we derived.

Methods. The model proposed by Emelianov (2003, Sol. Syst. Res., 37, 314) was used to fit the light curves, while taking the Lommel-Seeliger scattering law into account.

Results. For each event, we derive dynamical quantities such as the deviation of the observed relative satellite motion from the theoretical motion provided by the relevant ephemeris denoted as D_x and D_y, and the impact parameter and its corresponding mid-time. These results have an accuracy of between about several mas and 90 mas for D_x and D_y, and 0.31–2.97 s for the mid-time. The residuals of the longitude shifts (δl₁ for J1 Io and δl₂ for J2 Europa) that represent the shifts of the mid-times of the events, are also calculated to be around 10 km with the most accurate available ephemerides.