Observational detection of eclipses of J5 Amalthea by the Galilean satellites

Abstract

Aims. We carried out observations of the small jovian satellite Amalthea (J5) as it was being eclipsed by the Galilean satellites near the 2009 equinox of Jupiter in order to apply the technique of mutual event photometry to the astrometric determination of this satellite's position. Methods. The observations were carried out during the period 06/2009−09/2009 from the island of Maui, Hawaii and Siding Spring, Australia with the 2m Faulkes Telescopes North and South respectively. We observed in the near-infrared part of the spectrum using a PanStarrs-Z filter with Jupiter near the edge of the field in order to mitigate against the glare from the planet. Frames were acquired at rates >1/min during eclipse times predicted using recent JPL ephemerides for the satellites. Following subtraction of the sky background from these frames, differential aperture photometry was carried out on Amalthea and a nearby field star. Results. We have obtained three lightcurves which show a clear drop in the flux from Amalthea, indicating that an eclipse took place as predicted. These were model-fitted to yield best estimates of the time of maximum flux drop and the impact parameter. These are consistent with Amalthea's ephemeris but indicate that Amalthea is slightly ahead of, and closer to Jupiter than, its predicted position by approximately half the ephemeris uncertainty in these directions. We argue that a ground-based campaign of higher-cadence photometry accurate at the 5% level or better during the next season of eclipses in 2014-15 should yield positions to within 0. 05 and affect a corresponding improvement in Amalthea's ephemeris.

Eclipses of the inner satellites of Jupiter observed in 2015

“…Mutual events have been observed since the 1970s for the Galilean moons and have contributed to improving considerably their dynamical models. The inner moons were observed during the previous mutual event season (Christou et al 2010).…”

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

“…The result of this event is displayed in the last line of Table 5. The positions obtained by Christou et al (2010) had mean uncertainty of 82 mas (∼ 246 km) and the ones obtained by Saquet et al (2016) had a mean uncertainty of 45 mas (∼ 135 km).…”

“…The observation of mutual eclipses involving Galilean moons and inner satellite was strongly advocated by Vachier et al (2002). The first registration of this kind of event was given by Christou et al (2010) After correcting by Bias and Flat-Field using the same procedure described above, we applied a digital coronagraphy technique to reduce the influence of Jupiter brightness in the images, this coronagraphy was done using the PRAIA package (Assafin et al, 2008(Assafin et al, , 2009. Briefly, the procedure is as follows.…”

CCD astrometric observations of Amalthea and Thebe in the Gaia era

“…It is obvious that new observations will help in improving our knowledge of both the satellite dynamics and the ring system. However, the last available astrometric data were published by Kulyk (2008), and the last photometric data by Christou et al (2010).…”