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Register a new userThe 2014-2015 Brazilian Mutual Phenomena campaign for the Jovian satellites and improved results for the 2009 events
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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 ($sim$35 km) and 10.1 mas ($sim$31 km) for the 2014-2015 and 2009 campaigns respectively. The simulated and observed textsc{ascii} light curve files are freely available in electronic form at the textit{Natural Satellites DataBase} (NSDB). The 40/25 mutual events from our 2014-2015/2009 campaigns represent a significant contribution of 17%/15% in comparison with the PHEMU campaigns lead by the IMCCE. Besides that, our result for the eclipse of Amalthea is only the 4$^{th}$ 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.
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We present the results of photometric observations of the mutual phenomena in the system of Galilean satellites obtained during 2014-2015. The observations were performed using the 26-inch refractor, Normal Astrograph, ZA-320 telescope of the Pulkovo Observatory (084) and MTM-500 telescope at Pulkovo mountain station at Kislovodsk (C20). We made observations a total of 72 phenomena. We had derived 51 light curves of good and medium quality for 34 events. The RMS of determining the brightness is within a range from 0.02 to 0.19 mag, the average RMS is 0.06 mag. This work was supported by RFBR grant (project 15-02-03025).
The one-meter telescope-reflector `Saturn (D=1 m, F = 4 m) was partially renovated at the Pulkovo observatory at the end of 2014. The telescope was equipped by CCD camera S2C with 14x14 arcmin field of view and 824 mas per pix scale. The observations of outer Jovian satellites have been performed in a test mode since January 2015. The exposure time of 30 seconds allows us to obtain images of stars up to magnitude 19.5 with the present state of the mirror and the equipment. The observations of outer Jovian satellites have been performed during testing period. These objects are interesting targets because their astrometric observations required to improve ephemeris and dynamic studies. Satellites positions have been determined on the basis of CCD images obtained within 6 nights. Astrometric reduction is performed by linear method using HCRF/UCAC4 and HCRF/URAT1. Internal accuracy of satellites positions has been estimated as 20 - 100 mas. The absolute values of residuals O-C do not exceed 100 mas in most cases. The independent tests have been carried out by the direct comparison with the results of observations of the Jovian satellite Himalia performed simultaneously by the Normal astrograph (the largest difference was 113 mas). This work has been partially supported by RFBR (12-02-00675-a) and the 22 Program of RAS Praesidium.
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s) dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
Mid-infrared 7-20 $mu$m imaging of Jupiter demonstrates that the increased albedo of Jupiters South Equatorial Belt (SEB) during the `fade (whitening) event of 2009-2010 was correlated with changes to atmospheric temperature and aerosol opacity. The opacity of the tropospheric condensation cloud deck at pressures less than 800 mbar increased by 80% between May 2008 and July 2010, making the SEB ($7-17^circ$ S) as opaque in the thermal infrared as the adjacent equatorial zone. After the cessation of discrete convective activity within the SEB in May 2009, a cool quiescent band of high aerosol opacity (the SEB zone at $11-15^circ$ S) was observed separating the cloud-free northern and southern SEB components. The cooling of the SEBZ (with peak-to-peak contrasts of $1.0pm0.5$ K), as well as the increased aerosol opacity at 4.8 and 8.6 $mu$m, preceded the visible whitening of the belt by several months. A chain of five warm, cloud-free `brown barges (subsiding airmasses) were observed regularly in the SEB between June 2009 and June 2010, by which time they too had been obscured by the enhanced aerosol opacity of the SEB, although the underlying warm circulation was still present in July 2010. The cool temperatures and enhanced aerosol opacity of the SEBZ after July 2009 are consistent with an upward flux of volatiles from deeper levels (e.g., ammonia-laden air) and enhanced condensation, obscuring the blue-absorbing chromophore and whitening the SEB by April 2010. Revival of the dark SEB coloration in the coming months will ultimately require sublimation of these ices by subsidence and warming of volatile-depleted air. [Abridged]
The technique of mutual approximations accurately gives the central instant at the maximum apparent approximation of two moving natural satellites in the sky plane. This can be used in ephemeris fitting to infer the relative positions between satellites with high precision. Only the mutual phenomena -- occultations and eclipses -- may achieve better results. However, mutual phenomena only occur every six years in the case of Jupiter. Mutual approximations do not have this restriction and can be observed at any time along the year as long as the satellites are visible. In this work, we present 104 central instants determined from the observations of 66 mutual approximations between the Galilean moons carried out at different sites in Brazil and France during the period 2016--2018. For 28 events we have at least two independent observations. All telescopes were equipped with a narrow-band filter centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The telescope apertures ranged between 25--120 cm. For comparison, the precision of the positions obtained with classical CCD astrometry is about 100 mas, for mutual phenomena it can achieve 10 mas or less and the average internal precision obtained with mutual approximations was 11.3 mas. This new kind of simple, yet accurate observations can significantly improve the orbits and ephemeris of Galilean satellites and thus be very useful for the planning of future space missions aiming at the Jovian system.
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