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

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Highlights

  • Analysis of 47 mutual phenomena events between the Galilean satellites in 2014–2015.

  • Re-analysis of 25 mutual phenomena events between the Galilean satellites in 2009.

  • Analysis of 1 mutual eclipse between a Galilean satellite and Amalthea in 2014–2015.

  • The narrow band Methane filter was used to reduce Jupiter’s scattering light.

  • The Oren-Nayer reflectance model was used to simulate the illumination of the satellites.

Abstract

Progress in astrometry and orbital modelling of planetary moons in the last decade enabled better determinations of their orbits. These studies need accurate positions spread over extended periods. We present the results of the 2014–2015 Brazilian campaign for 40 mutual events from 47 observed light curves by the Galilean satellites plus one eclipse of Amalthea by Ganymede. We also reanalysed and updated results for 25 mutual events observed in the 2009 campaign.

All telescopes were equipped with narrow-band filters centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The albedos’ ratio was determined using images before and after each event. We simulated images of moons, umbra, and penumbra in the sky plane, and integrated their fluxes to compute albedos, simulate light curves and fit them to the observed ones using a chi-square fitting procedure. For that, we used the complete version of the Oren-Nayer reflectance model. The relative satellite positions mean uncertainty was 11.2 mas (~35 km) and 10.1 mas (~31 km) for the 2014–2015 and 2009 campaigns respectively. The simulated and observed ascii light curve files are freely available in electronic form at the Natural Satellites DataBase (NSDB).

The 40/25 mutual events from our 2014–2015/2009 campaigns represent a significant contribution of 17%/15% in comparison with the PHEMU campaigns lead by the IMCCE. Besides that, our result for the eclipse of Amalthea is only the 4th such measurement ever published after the three ones observed by the 2014–2015 international PHEMU campaign. Our results are suitable for new orbital/ephemeris determinations for the Galilean moons and Amalthea.

Introduction

Mutual phenomena between natural satellites – occultations and eclipses – have been successfully used to improve the orbital studies of these moons. For the Galilean satellites, they have been systematically observed since 1976 (Aksnes and Franklin, 1976). These phenomena occur as the Earth and the Sun cross the orbital plane of the satellites. For Jupiter, they happen every six years.

The photometry of these events offers a reliable source of very precise relative positions between two satellites. They often achieve uncertainties bellow 5 mas (~ 15 km) (Emelyanov, 2009; Dias-Oliveira et al., 2013; Arlot et al., 2014a; Saquet et al., 2018). These relative positions can constrain the orbital studies of these moons and give us hints about their structure and formation processes (Lainey et al., 2004b; a, 2009, 2017).

The uncertainty of the positions obtained from mutual phenomena is usually smaller than the ones obtained by other methods. For instance, classical CCD astrometry achieves uncertainties around 100 mas (~ 300 km) (Kiseleva et al., 2008). For satellite-pair distances, the uncertainties are at the 30 mas level (~ 90 km) (Peng et al., 2012). Mutual approximations, based in the same geometrical configuration of mutual occultations, achieve uncertainties at the 10 mas level (~ 30 km) (Morgado et al., 2016, 2019).

In this paper, we present results for 47 light curves, 31 occultations and 16 eclipses, representing 40 mutual events between the Galilean moons observed by three stations in Brazil, during the 2014–2015 mutual phenomena campaign. We also present one event, an eclipse involving the inner satellite Amalthea (J5). We also used our improved methods to re-analyse 25 light curves, 13 occultations and 12 eclipses, of 25 mutual phenomena observed by our group during the 2009 mutual phenomena campaign. We compared the new results with those by Dias-Oliveira et al. (2013), Arlot et al. (2014a) and Morgado et al. (2016).

In Section 2 we detail the observational campaigns. In Section 3 we present the photometry used to produce the observed light curves and describe the new, improved light-curve fitting procedures developed and used in this work. Section 4.1 contains new results from the re-analysis of 25 mutual events observed in 2009 and the comparison with the older results. In Section 4.2, we present the results for the 47 light curves involving 40 mutual events observed from Brazil during the 2014–2015 campaign. In Section 4.3, we present the result for the eclipse involving Amalthea. Our conclusions are set on Section 5.

Section snippets

Mutual phenomena campaign details

Every six years, during Jupiter equinox, we can observe mutual occultations and eclipses between Jupiter’s regular satellites. The results presented here come from the collaboration between five Brazilian institutes. The prediction of these events was provided by the Institut de Mécanique Céleste et de Calcul des Ephémérides (IMCCE)1 (Arlot et al., 2014a, b).

The 2009 mutual phenomena campaign was the first large attempt of the kind carried

Light curve analysis

In mutual phenomena, one can determine relative positions between the satellites through the analysis of the events’ light curves. In our procedure, we simulate theoretical light curves and use them to fit the observed ones.

The parameters of interest are: (i) the impact parameter (s0), the smallest apparent angular distance in the sky plane between both satellite’s centres in the case of occultations or between the eclipsed satellite centre and the centre of the eclipsing shadow in the sky

Re-analysis of the mutual phenomena between the Galilean moons - 2009

From April to October of 2009, 25 light curves for 25 mutual events between the Galilean moons, 13 occultations and 12 eclipses, were observed by our group with the 60 cm Zeiss telescope of the Observatório Pico dos Dias (OPD) using the methane filter. These events were analysed by Dias-Oliveira et al. (2013) and by Arlot et al. (2014a). However, the results obtained by both presented a significant difference (higher than 3σ).

More recently, Morgado et al. (2016) analysed 5 mutual approximations

Conclusions

We presented in this paper the results for 40 mutual events from the observation and analysis of 47 light curves, 31 occultations and 16 eclipses, obtained during the 2014–2015 mutual phenomena campaign between the Galilean satellites. The observations were made at three stations in the South and South-East of Brazil, using telescopes with diameters ranging between 28 and 60 cm. We also obtained updated results from the re-analysis of 25 mutual events, 13 occultations and 12 eclipses, observed

Acknowledgements

We thank our anonymous referee and N. Emelyanov for helpful comments. This study was financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. Part of this research is suported by INCT do e-Universo, Brazil (CNPQ grants 465376/2014-2). BM thanks the CAPES/Cofecub-394/2016-05 grant. RVM acknowledges the grants: CNPq-304544/2017-5, 401903/2016-8, Capes/Cofecub-2506/2015, FAPERJ: PAPDRJ-45/2013 and E-26/203.026/2015. MA thanks CNPq (Grants

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