Abstract. This paper presents an analysis of astrometric reduction methods for the calibration of a CCD target. To compare these methods, we collected about 3000 recent CCD observations between 1990-1997. We discuss the comparison of the four main contemporary theories describing the eight major satellites of Saturn, used in recent CCD astrometric reduction. We show that these theories developed by Taylor & Shen (1988), Dourneau (1993), Harper & Taylor (1999) and Duriez & Vienne (1997), give a rather good representation of the orbits of the eight main satellites, especially for satellites III-VI. In the CCD astrometric reduction, we point out a bias of the theories on the derived satellite positions, which can reach about 0. 03. Duriez and Vienne's TASS theory (1997), built with significantly higher consistency than the other three, generally leads to the lowest residuals for the observations analysed here. Due to its high quality, we recommend use of this theory for CCD reduction. Systematic errors affecting satellites' derived positions should be small, due to the quality of the TASS theory. This procedure might be an alternative to the multi-theory reduction method previously proposed by Qiao et al. (1999). Observations of satellites obtained from CCD reduction using TASS are expected to be significantly more accurate (0. 015) than observations reduced from any other theory (about 0. 05).
Context. In 2009, the Sun and the Earth passed through the equatorial plane of Jupiter and therefore the orbital planes of its main satellites. It was the equinox on Jupiter. This occurrence made mutual occultations and eclipses between the satellites possible. Experience has shown that the observations of such events provide accurate astrometric data able to bring new information on the dynamics of the Galilean satellites. Observations are made under the form of photometric measurements, but need to be made through the organization of a worldwide observation campaign maximizing the number and the quality of the data obtained. Aims. This work focuses on processing the complete database of photometric observations of the mutual occultations and eclipses of the Galilean satellites of Jupiter made during the international campaign in 2009. The final goal is to derive new accurate astrometric data. Methods. We used an accurate photometric model of mutual events adequate with the accuracy of the observation. Our original method was applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites of Jupiter. Results. We processed the 457 lightcurves obtained during the international campaign of photometric observations of the Galilean satellites of Jupiter in 2009. Compared with the theory, for successful observations, the r.m.s. of O-C residuals are equal to 45.8 mas and 81.1 mas in right ascension and declination, respectively; the mean O-C residuals are equal to -2 mas and -9 mas in right ascension and declination, respectively, for mutual occultations; and -6 mas and +1 mas in right ascension and declination, respectively, for mutual eclipses.
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In 2003-2004, we obtained 115 new observations of Phoebe, the 9th Saturnian faint satellite (visual magnitude of about 16.5). We used a large CCD detector (2048 × 2048 pixels) mounted on the 1.56 m astrometric reflector at the Sheshan Station, near Shanghai. In our reduction, an up-to-date catalogue of stars, UCAC2 (Zacharias et al. 2004), was chosen to ensure a proper astrometric calibration. A comparison of our observations to three recently available, high quality ephemerides, including the JPL SAT185 by Jacobson (2004b), has shown that most of our observed positions of Phoebe present an accuracy of some tens of mas, which appears to be a very high level for such a faint satellite.
Abstract. In 1994-1996 the Sun and the Earth passed through the equatorial plane of Saturn and therefore through the orbital planes of its main satellites. During this period, phenomena involving seven of these satellites were observed. Light curves of eclipses by Saturn and of mutual eclipses and occultations were recorded by the observers of the international campaign PHESAT95 organized by the Institut de mécanique céleste, Paris, France. Herein, we report 66 observations of 43 mutual events from 16 sites. For each observation, information is given about the telescope, the receptor, the site and the observational conditions. This paper gathers together all these data and gives a first estimate of the precision providing accurate astrometric data useful for the development of dynamical models.
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