Astrometric observations of major satellites of Saturn with a 26-inch refractor

The results of observations of Saturn and its satellites with the 26-inch refractor at Pulkovo are presented. Over the observing period from January 2008 until May 2009, results were found from more than 5000 CCD frames suitable for measurement. On the basis of these frames, 183 positions of major satellites of Saturn (with the exception of Mimas) were obtained. The astrometric reduction was based on the Turner method, with the use of the UCAC2 catalog as a reference. The obtained equatorial coordinates of satellites were compared with the TASS 1.7 theory, and results of comparison are presented. The accuracy of observed positions is 0.05″ on average. Positions of Saturn, calculated on the basis of positions of satellites and their theoretical saturnocentric coordinates according to the TASS 1.7, and the differential coordinates of satellites relative to each other, are also given.     

Estimates of the physical parameters of remote planetary satellites

Since 1998, 97 new remote satellites of Jupiter, Saturn, Uranus, and Neptune have been discovered. Since their brightness is rather weak, it is difficult to perform their photometry and determine their physical parameters. For 27 satellites from this group, different authors carried out special photometric investigations. For the other 70 satellites, the magnitudes accompanying the results of astrometric observations published in Minor Planet Circulars (MPC) are the only photometric data. In the present study, the photometric model parameters for all of the 97 remote satellites have been determined. From the hypothetic values of albedo and material density of the satellites, their sizes and gravitation parameters have been estimated. The whole volume of the obtained results is available in the database of the natural planetary satellites (NSDB) (Arlot and Emelyanov, 2009) published on the Internet ().     

Results of astrometric observations of Jupiter’s Galilean satellites at the Pulkovo Observatory from 1986 to 2005

The results of photographic observations of Jupiter’s Galilean satellites made with the 26-inch refractor at the Pulkovo Observatory from 1986 to 2005 are given. Satellite coordinates with respect to Jupiter and the mutual distances between the satellites have been determined. A scale-trale technique that does not require reference stars for the astrometric reduction of measurements has been used. The effect of the Jupiter phase has been taken into account in the jovicentric coordinates. The observation results have been compared with a modern theory of the Galilean satellites’ motions. Systematic observation errors depending on the observation technique have been studied. The intrinsic observation accuracy in the random quotient is characterized by the values 0.041″ over X and Y. The external accuracy of the relative Galilean satellite coordinates determined by comparing the observations with modern ephemerides turned out to be equal to 0.165″, 0.213″ for the Jovicentric coordinates and 0.134″, 0.170″ for the “satellite-satellite” coordinates. The highest accuracy of the relative satellite coordinates is reached at small distances between the satellites which are less than 100″: the corresponding mean-square errors of one observation are equal in to the external convergence to 0.050″, 0.070″. The results of photographic observations have been compared with the first CCD observations of the Jupiter satellites made in 2004 with the 26-inch refractor.     

Astrometric studies of the series of photographic and CCD observations of the Saturnian system with the 26-inch Pulkovo refractor in 1995-2007

The results of the reduction, investigation, and comparison of the photographic observations of the major Saturnian satellites and CCD observations with an ST6 CCD camera obtained at the 264nch Pulkovo refractor in 1995–2007 are presented. A comparison of the observational results with the TASS 1.7 theory of motion of the Saturnian satellites has served as the basis for investigating and comparing the series of observations. The period-averaged (O-C) residuals and observational errors have been calculated. A comparison of the series of CCD and photographic observations has shown the same external accuracy of the observations at a higher internal accuracy of the CCD observations than that of the photographic ones. A comparison of the Pulkovo results with those of other authors has shown them to be close in accuracy. The accuracy of the theory has been estimated by comparing simultaneous (on the same night) CCD and photographic observations. The errors of the observations and the theory have been found from this comparison to be the following: 0.081“ and 0.067” for the observations and 0.077“ and 0.115” for the theory (inxandy, respectively). An analysis of the dependence of (O-C)x,y for three satellites (the sixth, seventh, and eighth) on the satellite positions in Saturn-centered orbits has revealed systemat ic deviations for the seventh satellite in both coordinates. The positions of Saturn have been determined from satellite observations without measuring its images on photographic plates with accuracies of 0.121“ and 0.105” in right ascension and declination, respectively.     

A comparison of some observations of the Galilean satellites with Sampson's tables

An analysis is made of two series of photographic observations of the Galilean satellites of Jupiter. In the comparison of theory with observation, the aim of this work is to solve for systematic errors in the observations as well as those in the theory. The observations are those made by D. Pascu with the McCormick refractor during the apparition of 1967–1968 and with the 26" refractor of the U.S. Naval Observatory in 1973. Neutral density filters were used for magnitude compensation between the planet and the satellites as well as between the satellites themselves. Preliminary positions were derived by the trail/scale method using a scale value derived from scale plates taken during the observational program. The mean error of these observations is expected to be about ±0".10. The computed positions are those supplied by the Bureau des Longitudes and are based on Sampson's theory. Both intersatellary and planet-satellite positions were used in the comparison of theory with observation. The least squares adjustment included as unknowns, corrections to the longitudes, inclinations and scale for both observation types, and an additional periodic term to account for residual phase defect for the planet-satellite coordinates. The validity of the results is discussed in terms of the unknowns introduced, the correlations between them and the reduction of the residuals.     

Determination of the orbits of inner Jupiter satellites

Some problems in determining the orbits of inner satellites associated with the complex behavior of the target function, which is strongly ravine and which possesses multiple minima in the case of the satellite orbit is determined based on fragmentary observations distributed over a rather long time interval, are studied. These peculiarities of the inverse problems are considered by the example of the dynamics of the inner Jupiter satellites: Amalthea, Thebe, Adrastea, and Metis. Numerical models of the satellite motions whose parameters were determined based on ground-based observations available at the moment to date have been constructed. A composite approach has been proposed for the effective search for minima of the target function. The approach allows one to obtain the respective evaluations of the orbital parameters only for several tens of iterations even in the case of very rough initial approximations. If two groups of observations are available (Adrastea), a formal minimization of the target function is shown to give a solution set, which is the best solution from the point of view of representation of the orbital motion, which is impossible to choose. Other estimates are given characterizing the specific nature of the inverse problems.     

Unstable kinetic Alfvén wave in partially ionized plasma

The stability of kinetic Alfven waves is discussed for a partially ionized plasma with a flux of ionizing electrons which balance the plasma particle losses. Accidental electromagnetic perturbations are shown to be unstable due to the energy change of ionizing electrons.     

Perihelion motion of small irregular dust particles due to radiation forces

Perihelion motion, i.e. a secular change of longitude of perihelion, of interplanetary dust particles is investigated under the action of solar gravity and solar electromagnetic radiation. As for spherical particle [Kla?ka, J., 2004. Electromagnetic radiation and motion of a particle. Cel. Mech. Dynam. Astron. 89, 1-61]: (i) perihelion motion is of the order ( is heliocentric velocity of the meteoroid and c is the speed of light in vacuum), if a component of electromagnetic radiation acceleration is considered as a part of central acceleration; (ii) perihelion motion is of the first order in if the total electromagnetic radiation force is considered as a disturbing force. The new facts presented in this paper concern irregular dust particles. Detailed numerical calculations were performed for the grains ejected at aphelion of comet Encke. Perihelion motion for irregular interplanetary dust particles exists already in the first order in for both cases of central accelerations. Moreover, perihelion motion of irregular particles exhibits both positive and negative directions during the particle orbital motion. Irregularity of the grains causes not only perihelion motion, but also dispersion of the dust in various directions, also normal to the orbital plane of the parent body.     

CCD and photon-counting photometric observations of asteroids carried out at Padova and Catania observatories

We present the results of observational campaigns of asteroids performed at Asiago Station of Padova Astronomical Observatory and at M.G. Fracastoro Station of Catania Astrophysical Observatory, as part of the large research programme on Solar System minor bodies undertaken since 1979 at the Physics and Astronomy Department of Catania University. Photometric observations of six Main-Belt asteroids (27 Euterpe, 173 Ino, 182 Elsa, 539 Pamina, 849 Ara, and 984 Gretia), one Hungaria (1727 Mette), and two Near-Earth Objects (3199 Nefertiti and 2004 UE) are reported. The first determination of the synodic rotational period of 2004 UE was obtained. For 182 Elsa and 1727 Mette the derived synodic period of 80.23±0.08 and , respectively, represents a significant improvement on the previously published values. For 182 Elsa the first determination of the H-G magnitude relation is also presented.     

Models for planetary eclipses of the uranian satellites

A model for computing the brightness of a satellite in the shadow of a planet is described, which takes into account the Sun–planet–satellite–sensor geometry, the satellite bi-directional reflectance function, and the refraction of sunlight in the planetary atmosphere. Synthetic light curves for eclipse ingress or egress of the five large satellites of Uranus are generated. The model luminosities can be fitted to photometric observations in order to calculate a precise distance between the centers of the satellite and the planet. Alternately, when the satellite ephemeris is accurately known the atmospheric state of the planet can be studied.     

New evidence of precision premium for Galilean satellites from CCD imaging

After a CCD image of the four Galilean satellites of Jupiter is obtained by a long focal length telescope, we can compare the theoretical positions of these satellites with their pixel positions so as to obtain the calibration parameters of the CCD field of view. In theory, when two of the four satellites have small enough separation, their relative positional measurement will have a good accuracy since the error existing in the solved calibration parameters has a direct proportional effect on the separation of the two satellites. The 347 CCD images taken by 1-m long focal length telescope at Yunnan Observatory in 2002-2005 are used to perform the experimental test. After we improve the centroid algorithm for the satellites and our former halo-removal technique, the results show that the positional measurement of two small-separation satellites has an external precision as good as 0.01-0.03 arcsec. This precision has comparability as that from rarely occurring mutual events of the Galilean satellites. This experiment confirms the finding of the “precision premium” firstly presented by Pascu [1994. An appraisal of the USNO program of photographic astrometry of bright planetary satellites. In: Morrison, L.V., Gilmore, G.F., (Eds.), Galatic and Solar System Optical Astrometry, pp. 304-311] using photographic observations. We believe that this type of observations, besides mutual event observations, might also be used to improve our knowledge of the orbital motions of the Galilean satellites because of its much more opportunities.     

Photometric study of the major satellites of Uranus

In this paper, we analyze the results of ground-based and space-born photometric observations of the major satellites of Uranus—Miranda, Ariel, Umbriel, Titania, and Oberon. All sets of photometric observations of the satellites available in the literature were examined for uniformity and systematic differences and summarized to a unified set by wavelength ranging from 0.25 to 2.4 μm. This set covers the interval of phase angles from 0.034° to 35°. The compound phase curves of brightness of the satellites in the spectral bands at 0.25, 0.41, 0.48, 0.56, 0.75, 0.91, 1.4, and 1.8 μm, which include a pronounced opposition surge and linear part, were constructed. For each satellite, the geometric albedo was found in different spectral bands taking into account the brightness opposition effect, and its spectral dependence was studied. It has been shown that the reflectance of the satellites linearly depends on the wavelength at different phase angles, but has different spectral gradients. The parameters of the phase functions of brightness, including the amplitude and the angular width of the brightness opposition surge, the phase coefficient, and the phase angle at which the nonlinear increase in brightness starts, were determined and their dependences on wavelength and geometric albedo were analyzed. Our investigations show that, in their optical properties, the satellites Miranda and Ariel, Titania and Oberon, and Umbriel present three types of surfaces. The observed parameters of the brightness opposition effect for the Uranian satellites, some ice satellites of Jupiter and Saturn, and the E-and S-type asteroids are analyzed and compared within the framework of the coherent backscattering and mutual shadowing mechanisms.     

Mutual events of the uranian satellites 2006-2010

The upcoming crossing of the Sun and the Earth through the equatorial plane of the planet Uranus presents an opportunity to observe mutual eclipses and occultations of the uranian satellites. We present predictions for 321 such events from 2006 to 2010. 230 of these events are “nominal” i.e. they are predicted to occur based on the currently available ephemeris while a further 91 “grazing” events are allowable given the positional uncertainties of the satellites. Taking into account the statistical frequency of events that occur too close to the planet, during solar conjunction or are too “shallow” to observe, we conclude that about 150 events should be detectable from different longitudes around the world. We argue that a worldwide campaign of photometric observations of these events will yield, as in the case of the jovian and saturnian systems, high-precision astrometric information on the satellites toward improving their ephemerides as well as the system constants (satellite masses, uranian zonal harmonics, etc.). In addition, mathematical inversion of the lightcurves should permit, subject to the photometric quality and number of observed events, mapping of albedo variegations over the satellite hemispheres that were in darkness during the Voyager 2 encounter with the uranian system in 1985/1986.     

Problems on the Galilean satellites of Jupiter

The purpose of this paper is to present a critical review of some problems concerning the dynamics of Jupiter's Galilean system of satellites. Theory, ephemeris and observation are considered.Two theories were proposed by Ferraz-Mello and by Sagnier. The main characteristics of these theories are that the frequencies are allowed to be kept fixed for all times from the earlier stages, and so to have a purely trigonometric solution.For a completely satisfactory work we need many more observations than actually exist. Two kinds of observations seem to be the best suitable: long-focus photographic plates and photometric records of mutual events.The most recent photographic observations are discussed in order to state guidelines for future work. The problem of the precision of Sampson's tables is discussed on the grounds of the recent observations.Paper presented at IAU Colloquium, No. 28, Ithaca, N.Y., August, 1974.     

Ultraviolet observations of Mars and Saturn by the TDIA and OAO-2 satellites

Ultraviolet photometric and spectrophotometric observations of Mars and Saturn obtained by two Earth-orbiting satellites are combined in this report. High-resolution data from the S59 experiment aboard TD1A reveal no definite absorption features in the spectra of either planet. The absence of a prominent absorption in the Mars data near 2150 Å can be reconciled with the preliminary Viking measurement of NO only if that gas is preferentially concentrated at high Martian altitudes. Broadband photometry from OAO-2 shows that atmospheric dust on Mars during the great dust storm of 1971–1972 reduced the ultraviolet geometric albedo by a factor of ?3 at the height of the storm. This atmospheric energy deposition is probably an important mechanism in the storm dynamics. Diurnal variation in the ultraviolet brightness of Mars appears to be marginally detectable during the dust storm. A real brightness variation during a clear season is observed. The combined Saturn data from the two satellites strongly suggest that NH₃ does not influence the ultraviolet spectrum of Saturn, but that some other absorber does. A candidate for such an absorber, H₂S, is investigated. OAO-2 broadband photometry of Jupiter and of Saturn demonstrate that these planets have very similar albedos from 2100 to 2500 Å. This implies a common ultraviolet absorber on both planets, other than NH₃.     

New confirmation of image-processing techniques for astrometry of Saturn and its satellites

The image-processing techniques used by Peng et al. are further improved to measure precisely the positions of Saturn and its satellites. 495 CCD images taken with the 1-m telescope at the Yunnan Observatory during the years 2002–2004 are processed with these techniques. These measured pixel positions are compared to their theoretical positions computed with the ephemerides of TASS1.7 for the satellites and JPL DE405 for Saturn itself. Analysis of the data for the intersatellite positions among four bright Saturnian satellites (S3–S6) and for Saturn–satellite (i.e. Saturn–Titan) positions shows that these measured positions have the same dispersions, i.e. about 0.05 and 0.06 arcsec in right ascension and declination, respectively. However, for the fainter satellites, Enceladus and Mimas, poorer residuals up to 0.1 and 0.2 arcsec, respectively, in both directions are found mainly due to their small separations from the primary planet and short exposure time in order to obtain useful images of Saturn.     

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002–2003: final astrometric results

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events.
This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data.
We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites.
We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms 'O-C' residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17.     

Astrometric results of observations of mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002-2003

We suggest a new approach and develop an original method for deriving astrometric data from the photometry of mutual occultations and eclipses of planetary satellites. We decide to model not the relative apparent motion of one satellite with respect to another satellite but the deflection of the observed relative motion with respect to the theoretical motion implied by appropriate ephemerides.We have attempted to reduce the results of photometric observations of the Gallilean satellites during their mutual occultations and eclipses in 2002-2003. The data of observation for 319 light curves of 106 mutual events were received from the observers. The reliable 245 light curves were processed with our method. Eighty six apparent relative positions have been obtained.Systematic errors arise inevitably while deriving astrometric data. Most of them are due to factors that are unrelated to the methods for deriving astrometric data. The systematic errors are more likely due to incorrect excluding the effect of background on photometric counts. In the case of mutual occultations, the flux drop is determined to a considerable degree by the ratio of the mean albedos of the two satellites. Some mutual event observations revealed wrong adopted values of the mean albedos.     

Deciphering the origin of the regular satellites of gaseous giants - Iapetus: The Rosetta ice-moon

Ever since their discovery the regular satellites of Jupiter and Saturn have held out the promise of providing an independent set of observations with which to test theories of planet formation. Yet elucidating their origins has proven elusive. Here we show that Iapetus can serve to discriminate between satellite formation models. Its accretion history can be understood in terms of a two-component gaseous subnebula, with a relatively dense inner region, and an extended tail out to the location of the irregular satellites, as in the SEMM model of Mosqueira and Estrada (2003a,b) (Mosqueira, I., Estrada, P.R. [2003a]. Icarus 163, 198-231; Mosqueira, I., Estrada, P.R. [2003b]. Icarus 163, 232-255). Following giant planet formation, planetesimals in the feeding zone of Jupiter and Saturn become dynamically excited, and undergo a collisional cascade. Ablation and capture of planetesimal fragments crossing the gaseous circumplanetary disks delivers enough collisional rubble to account for the mass budgets of the regular satellites of Jupiter and Saturn. This process can result in rock/ice fractionation as long as the make up of the population of disk crossers is non-homogeneous, thus offering a natural explanation for the marked compositional differences between outer solar nebula objects and those that accreted in the subnebulae of the giant planets. For a given size, icy objects are easier to capture and to ablate, likely resulting in an overall enrichment of ice in the subnebula. Furthermore, capture and ablation of rocky fragments become inefficient far from the planet for two reasons: the gas surface density of the subnebula is taken to drop outside the centrifugal radius, and the velocity of interlopers decreases with distance from the planet. Thus, rocky objects crossing the outer disks of Jupiter and Saturn never reach a temperature high enough to ablate either due to melting or vaporization, and capture is also greatly diminished there. In contrast, icy objects crossing the outer disks of each planet ablate due to the melting and vaporization of water-ice. Consequently, our model leads to an enhancement of the ice content of Iapetus, and to a lesser degree those of Titan, Callisto and Ganymede, and accounts for the (non-stochastic) compositions of these large, low-porosity outer regular satellites of Jupiter and Saturn. For this to work, the primordial population of planetesimals in the Jupiter-Saturn region must be partially differentiated, so that the ensuing collisional cascade produces an icy population of ?1 m size fragments to be ablated during subnebula crossing. We argue this is likely because the first generation of solar nebula ∼10 km planetesimals in the Jupiter-Saturn region incorporated significant quantities of ²⁶Al. This is the first study successfully to provide a direct connection between nebula planetesimals and subnebulae mixtures with quantifiable and observable consequences for the bulk properties of the regular satellites of Jupiter and Saturn, and the only explanation presently available for Iapetus’ low density and ice-rich composition.