Mutual Events Research Articles

Detecting companions to extrasolar planets using mutual events

We investigate a new approach to the detection of companions to extrasolar planets beyond the transit method. We discuss the possibility of the existence of binary planets. We develop a method based on the imaging of a planet-companion as an unresolved system (but resolved from its parent star). It makes use of planet-companion mutual phenomena, namely mutual transits and mutual shadows. We show that companions can be detected and their radius measured down to lunar sizes.

Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations

A long-term adaptive optics (AO) campaign of observing the double Asteroid (90) Antiope has been carried out in 2003–2005 using 8–10-m class telescopes, allowing prediction of the circumstances of mutual events occurring during the July 2005 opposition [Marchis, F., Descamps, P., Hestroffer, D., Berthier, J., de Pater, I., 2004. Bull. Am. Astron. Soc. 36, 1180]. This is the first opportunity to use complementary lightcurve and AO observations to extensively study the (90) Antiope system, an interesting visualized binary doublet system located in the main belt. The orbital parameters derived from the AO observations have served as input quantities for the derivation of a whole set of other physical parameters (namely shapes, surface scattering, bulk density, and internal properties) from analysis of collected lightcurves. To completely model the observed lightcurves, we employed Roche figures to construct an overall shape solution. The combination of these complementary observations has enabled us to derive a reliable physical and orbital solution for the system. Our model is consistent with a system of slightly non-spherical components, having a size ratio of 0.95 (with R avg = 42.9 ± 0.5 km , separation = 171 ± 1 km ), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves suggests that the real shapes of the components do not depart from Roche equilibrium figures by more than 10%. The J2000 ecliptic coordinates of the pole of the system are λ n = 200 ° ± 2 ° and α n = 38 ° ± 2 ° . The orbital period was refined to P = 16.5051 ± 0.0001 h , and the density is found to be slightly lower than previous determinations, with a value of 1.25 ± 0.05 g / cm 3 , leading to a significant macro-porosity of 30%. Possible scenarios for the origin of the system are also discussed.

Predictions of the mutual events of the Uranian satellites occurring in 2006–2009

Context. Every 42 years, the Earth and the Sun pass through the equatorial plane of Uranus allowing observations of mutual occultations and eclipses of the main satellites of Uranus. The next opportunity will occur in 2006-2009. Aims. Such events are uncommon and very rare, and they allow us to accurately determine the inclinations of the orbits of the satellites, which is usually difficult. However, in order to be able to observe, we need accurate predictions. Methods. To find these predictions, we developed a new dynamical model based on the most recent astrometric observations of the satellites. Results. This paper provides predictions of these events using two different models for the motion of the satellites, along with information useful for the observations. Data on the predictions of the events are available on the web server of the IMCCE at ftp.imcce.fr/pub/ephem/satel/pheura07. Conclusions. We therefore encourage professional and amateur astronomers to join the network of observers to get as many observations as possible.

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

Context. The photometry of mutual occultations and the eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by analyzing the light curves of the satellites observed during these mutual events. Aims. The final goal of observations is to refine the models of motion for the natural satellites, and to develop a very accurate photometric model of mutual occultations and eclipses of satellites. This paper is focusing on the differences of topocentric or heliocentric coordinates of satellites pairs by analyzing the photometry of mutual occultations and the eclipses of natural satellites. Methods. We propose the most accurate photometric model of mutual events to date based on all available data about the satellites, and have developed the corresponding method for extracting astrometric data. We analyze the errors of astrometric results obtained in terms of different scattering laws allowing for reflecting properties of the satellites surfaces. In addition we consider how to allow various previously neglected effects. Results. We describe the results obtained by applying our method to observations of mutual occultations and eclipses of the Galilean satellites of Jupiter made in 2002–2003. We show that the coordinate errors due to irreducible systematic errors of photometry are about the same as the errors introduced by neglecting the above effects. We find the available maps of satellites surfaces to be unsuitable for deriving photometric event models.

The PHEMU97 catalogue of observations of the mutual phenomena of the Galilean satellites of Jupiter

In 1997 the Sun and the Earth passed through the equatorial plane of Jupiter and therefore through the orbital planes of its main satellites. During this period, mutual eclipses and occultations occurred and were observed. We investigate the precision of the catalogue to produce improved data for the development of dynamical models. Light curves of mutual eclipses and occultations were recorded by the observers of the international campaign PHEMU97 organized by the Institut de Mecanique Celeste, Paris, France. We made 275 observations of 148 mutual events from 42 sites. For each observation, information is given about the telescope, the receiver, the site and the observational conditions. This paper gathers together the data and gives a first estimate of the precision. The catalogue of these rare events represents a collection of improved accurate astrometric data useful for the development of dynamical models.

A new data analysis technique in the study of mutual event lightcurves

The purpose of this paper is to develop a new methodology for analyzing astronomical data, in particular, one of the light curves obtained in the PHEMU campaign in 1997, where the mutual phenomena between Jupiter and its satellites were observed from the Earth due to the coincidence of the equatorial plane of Jupiter and the orbit plane of the Earth. The more specific aim of this study is to determine the times of the beginning and the end of the phenomena, and the moment when the recorded light flux was at a minimum. The techniques we applied were based on the wavelet theory, which allows us to study a signal from its approximations and details at different scales. Before applying the designed algorithm to our experimental data, we considered a synthetic light curve in order to check the reliability of our method. It should be mentioned that the results are not relevant from the astronomical point of view, since no corrections for albedo or illumination were applied to the recorded data.

Charon's radius and atmospheric constraints from observations of a stellar occultation

The physical characteristics of Pluto and its moon, Charon, provide insight into the evolution of the outer Solar System. Although previous measurements have constrained the masses of these bodies, their radii and densities have remained uncertain. The observation of a stellar occultation by Charon in 1980 established a lower limit on its radius of 600 km (ref. 3) (later refined to 601.5 km; ref. 4) and suggested a possible atmosphere. Subsequent, mutual event modelling yielded a range of 600-650 km (ref. 5), corresponding to a density of 1.56 +/- 0.22 g cm(-3) (refs 2, 5). Here we report multiple-station observations of a stellar occultation by Charon. From these data, we find a mean radius of 606 +/- 8 km, a bulk density of 1.72 +/- 0.15 g cm(-3), and rock-mass fraction 0.63 +/- 0.05. We do not detect a significant atmosphere and place 3sigma upper limits on atmospheric number densities for candidate gases. These results seem to be consistent with collisional formation for the Pluto-Charon system in which the precursor objects may have been differentiated, and they leave open the possibility of atmospheric retention by the largest objects in the outer Solar System.

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.

Mutual events of Jupiter's satellites observed in 1997 at the Bordeaux Observatory

We present photometric observations of mutual events of the Galilean satellites of Jupiter made in 1997 at the Bordeaux Observatory as part of the international PHEMU97 campaign. We observed 21 events which provided 14 high quality light curves with the CCD camera mounted on the 62 cm telescope. From these curves, we determined observed values and errors for the maximum intensity drop and the time of this light minimum. Phase correction was applied to this time for a proper comparison to theoretical values. Residuals between observed and computed values of both of these parameters have been derived from Arlot's G5 ephemerides. The discussion of errors and residuals shows that these observational parameters generally are so accurately determined that they lead to satellite positions with an angular precision of about ten milliarcseconds, never obtained with classical astrometry. In addition, some theoretical results have been derived from the analysis of our set of observations. The main result concerns the satellite J1 for which our observations of the time of maximum event suggest an advance in longitude of 269 km with respect to G5. Also, for the satellite J4, we similarly obtain a delay of about 170 km which appears to be a real effect.

Observation and reduction of mutual events in the solar system

Observation and reduction of mutual events in the solar system

Observation of 13 mutual events of Jovian satellites performed at Lille Observatory

We have observed the four Galilean satellites of Jupiter during their mutual occultations and eclipses from February to April 2003 using a CCD camera attached to the 32.5 cm refractor of the observatory of Lille. We have recorded 13 lightcurves of these events. We have performed a first astrometric reduction based on the method developed in Noyelles et al. (2003). This analysis of the results and comparison with theory show that the observations are good; the residuals are about 0.03 arcsec. The observations are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/343.

Astrometry from mutual events of Jovian satellites in 1997

Astrometric results of observations of the mutual events of the Galilean satellites of Jupiter of the PHEMU97 campaign by the Institut de Mecanique Celeste et de Calcul des Ephemerides are presented. These astrometric positions can be directly utilized in the construction of future ephemerides. We attempt here to compare the residuals of the relative astrometric positions of satellites with respect to the E3, G5, E5 and L1 ephemerides. The model to fit the observed light curves includes the intensity variations on the surface of satellites using the mosaics constructed by the teams at the US Geological Survey from Voyager and Galileo imagery.

Astrometric reduction of lightcurves observed during the PHESAT95 campaign of Saturnian satellites

In this paper, we present astrometric results derived from reduction of 65 lightcurves made in 1995-1996 during the PHESAT95 campaign of observation of Saturnian satellites mutual events. These results have an accuracy of about 20-30 mas and are compared to those obtained by Emelianov et al. (1997) for the 3 events observed in Crimea and Kazakhstan. We also discuss the reliability of the method used for reducing the lightcurves from the mutual events of 1980.

Unobservable mutual events of the Galilean satellites

Mutual eclipses and occultations of the Galilean satellites of Jupiter which will occur in 2002-2003 were predicted independently by J.-E. Arlot and by K. Aksnes, and information on the visibility of the events from any site on the Earth is provided on the IMCCE web site based on Arlot's predictions. However, many unobservable events, such as the eclipsed satellites are in the shadow of Jupiter, are included in Arlot's predictions and there is no way of eliminating of such unobservable events from his predictions. This paper lists all such events.

Astrometry from CCD photometry of mutual events of Jovian satellites from VBO during 1997

Astrometric results of CCD observations of the mutual events of the Galilean satellites of Jupiter from the Vainu Bappu Observatory are presented. The shifts in the photo-centers on the disks of Io and Europa due to albedo variations inferred from the available mosaics of Galileo imagery are determined. The estimated shifts from ≈ 90 km East to ≈ 50 km West on Io and from ≈ 50 km East to ≈ 30 km West for Europa during one orbital period are comparable to the accuracies provided by the present-day ephemerides. In a given mutual event series, the mutual events involving a given satellite pair dominate in number and occur nearly at the same orbital longitude within ± ; all the events are therefore delayed or all of them advanced depending on the direction of the shift of the photo-center. The implications of including these cumulative and sustained longitude residuals on the constructed ephemerides are discussed.

Predictions of the mutual events of the Galilean Satellites of Jupiter occurring in 2002–2003

Mutual occultations and eclipses of the Galilean satellites of Jupiter will occur in 2002-2003. This paper provides predictions of theses events as well as information useful for their observations. Such events are uncommon, since they occur only every 6 years when the Earth and the Sun pass through the common orbital plane of the Galilean satellites. Therefore, we encourage professional and amateur astronomers to join the networks of observers in order to get as many observations as possible. Data on the predictions of the events are available on the web server of the IMCCE (www.bdl.fr).

Secular Acceleration of Io Derived from Mutual Satellite Events

Timings and light curves of the mutual phenomena of the Galilean satellites in 1908, 1914, and 1973–1997 have been used first to improve the values of the most important parameters in Sampson's satellite theory (published in 1921) and second to reduce the considerable remaining discrepancies in the observations by solving for constant changes, Δni, and rates, i, in the mean motions of the four satellites. Earlier determinations of the values—primarily 1—have been based mainly on observations of ordinary eclipses that are much less precise than the mutual event observations and also suffer from uncertainty in the UT-ET correction prior to 1900. Because of strong correlations, it is not possible to obtain meaningful least-squares solutions for both Δni and i, except for Io for which we obtain Δn1 = (0.4 ± 1.1) × 10-6 deg day-1 and 1/n1 = 3.6 ± 1.0 in units of 10-10 yr-1. This Δn1 value is comparable to the values determined for Δn2, Δn3, and Δn4. Although the data can be satisfied nearly as well by correcting only the mean motions, this leads to a 10 times larger Δn1 value, which seems unacceptably large. Furthermore, 1 = 0 would require an unphysically large tidal torque from Jupiter to overcome Io's orbital decay because of the observed energy dissipation in Io. Our determination of 1/n1 is in reasonable agreement with the values 3.3 ± 0.5 (from de Sitter, published in 1928) and 4.54 ± 0.95 (from Goldstein & Jacobs, published in 1995), both of which were derived from analyses of eclipses of the satellites by Jupiter and some photographic observations. However, it conflicts with the value -0.074 ± 0.087 found by Lieske (published in 1987) from Jovian eclipse timings. Our results imply that Io is now spiraling slowly inward, losing more orbital energy from internal dissipation than it gains from Jupiter's tidal torque. These results suggest that Q, the specific dissipation function of Jupiter, is around 200,000 for an Io heat flux of 1.3 × 1014 W.

The PHESAT95 catalogue of observations of the mutual events of the Saturnian satellites

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 m ecanique c eleste, 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 rst estimate of the precision providing accurate astrometric data useful for the development of dynamical models.

Photometric observations of mutual events in Saturn’s system of regular satellites in 1995

We carried out observations of mutual events in Saturn’s system of satellites as part of the PHESAT95 International Program. Three light curves of these events were obtained. We developed a technique of allowance for the influence of the law of light reflection from the surfaces of Saturn’s satellites, photometric nonuniformity of their surfaces, the phase effect, and the illumination distribution in the satellite penumbra (given the brightness distribution over the solar disk) on the light curve of an occultation or eclipse of one satellite by another. This technique is used to interpret our observations of these events and to determine the minimum separations between satellites or between a satellite and the shadow center of another satellite and the corresponding timings.

ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] NICMOS Spectroscopy of Charon’s Leading and Trailing Hemispheres

We used the near-infrared camera and multiobject spectrometer NICMOS on the Hubble Space Telescope to obtain 1.1–2.4 μm, low-resolution (R ~ 200) slitless grism spectrophotometry of the individual members of the Pluto-Charon system. Water ice is present in its crystalline state on both the leading and trailing hemispheres of Charon. A 2.21 μm absorption band, possibly due to the presence of ammonia hydrate in surface, is detected in the reflectance spectrum of its leading side only. Geological activity on Charon or implantation of ions escaped from Pluto's atmosphere could account for the formation of species such as NH3 H2O locally on the satellite. We also measured a slightly higher geometric albedo for Charon than reported from the mid-1980s observations of the mutual events.