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Speckle observations of the binary asteroid (22) Kalliope with C2PU/PISCO
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Abstract
We present new speckle measurements of the position of Linus, the satellite of the asteroid (22) Kalliope, obtained at the 1m C2PU-Epsilon telescope on the Plateau de Calern, France. Observations were made in the visible domain with the speckle camera PISCO. We obtained 122 measurements in February-March 2022 and April 2023, with a mean uncertainty close to 10 milli-arcseconds on the angular separation.
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Context. The sample of Solar system objects has dramatically increased over the last decade. The number of measured properties (e.g., diameter, taxonomy, rotation period, thermal inertia, etc.) has expanded even more quickly. However, this wealth of information is spread over a myriad of studies, with different designations reported per object.
Aims. We provide a solution to the identification of Solar system objects based on any of their multiple names or designations. We also compile and rationalize their properties to provide an easy access to them. We aim to continuously update the database as new measurements become available.
Methods. We built a Web Service, SsODNet , which offers four access points, each corresponding to an identified necessity in the community: name resolution ( quaero ), compilation of a large corpus of properties ( dataCloud ), determination of the best estimate among compiled values ( ssoCard ), and a statistical description of the population ( ssoBFT ).
Results. The SsODNet interfaces are fully operational and freely accessible to everyone. The name resolver quaero translates any of the ~5.3 million designations of objects into their current and official designation. The dataCloud includes about 105 million parameters (osculating and proper elements, pair and family membership, diameter, albedo, mass, density, rotation period, spin coordinates, phase function parameters, colors, taxonomy, thermal inertia, and Yarkovsky drift) from over 3000 articles (updated continuously). For each of the known asteroids and dwarf planets (~1.2 million), a ssoCard that provides a single best-estimate for each parameter is available. The SsODNet service provides these resources in a fraction of second upon query. Finally, the extensive ssoBFT table compiles all the best estimates in a single table for population-wide studies.
Context. The classification of the minor bodies of the Solar System based on observables has been continuously developed and iterated over the past 40 yr. While prior iterations followed either the availability of large observational campaigns or new instrumental capabilities opening new observational dimensions, we see the opportunity to improve primarily upon the established methodology.
Aims. We developed an iteration of the asteroid taxonomy which allows the classification of partial and complete observations (i.e. visible, near-infrared, and visible-near-infrared spectrometry) and which reintroduces the visual albedo into the classification observables. The resulting class assignments are given probabilistically, enabling the uncertainty of a classification to be quantified.
Methods. We built the taxonomy based on 2983 observations of 2125 individual asteroids, representing an almost tenfold increase of sample size compared with the previous taxonomy. The asteroid classes are identified in a lower-dimensional representation of the observations using a mixture of common factor analysers model.
Results. We identify 17 classes split into the three complexes C, M, and S, including the new Z-class for extremely-red objects in the main belt. The visual albedo information resolves the spectral degeneracy of the X-complex and establishes the P-class as part of the C-complex. We present a classification tool which computes probabilistic class assignments within this taxonomic scheme from asteroid observations, intrinsically accounting for degeneracies between classes based on the observed wavelength region. The taxonomic classifications of 6038 observations of 4526 individual asteroids are published.
Conclusions. The ability to classify partial observations and the reintroduction of the visual albedo into the classification provide a taxonomy which is well suited for the current and future datasets of asteroid observations, in particular provided by the Gaia, MITHNEOS, NEO Surveyor, and SPHEREx surveys.
Context. Asteroid (22) Kalliope is the second largest M-type asteroid in the main belt and is orbited by a satellite, Linus. Whereas the mass of Kalliope is already well constrained thanks to the presence of a moon, its volume is still poorly known, leading to uncertainties on its bulk density and internal structure.
Aims. We aim to refine the shape of (22) Kalliope and thus its diameter and bulk density, as well as the orbit of its moon to better constrain its mass, hence density and internal structure.
Methods. We acquired disk-resolved observations of (22) Kalliope using the VLT/SPHERE/ZIMPOL instrument to reconstruct its three-dimensional (3D) shape using three different modeling techniques. These images were also used together with new speckle observations at the C2PU/PISCO instrument as well as archival images from other large ground-based telescopes to refine the orbit of Linus.
Results. The volume of (22) Kalliope given by the shape models, corresponding to D = 150 ± 5 km, and the mass constrained by its satellite’s orbit yield a density of ρ = 4.40 ± 0.46 g cm ⁻³ . This high density potentially makes (22) Kalliope the densest known small body in the Solar System. A macroporosity in the 10–25% range (as expected for this mass and size), implies a grain density in the 4.8–5.9 g cm ⁻³ range. Kalliope’s high bulk density, along with its silicate-rich surface implied by its low radar albedo, implies a differentiated interior with metal contributing to most of the mass of the body.
Conclusions. Kalliope’s high metal content (40–60%) along with its metal-poor mantle makes it the smallest known Mercury-like body. A large impact at the origin of the formation of the moon Linus is likely the cause of its high metal content and density.
Aims. To interpret adaptive-optics observations of (216) Kleopatra, we need to describe an evolution of multiple moons orbiting an extremely irregular body and include their mutual interactions. Such orbits are generally non-Keplerian and orbital elements are not constants.
Methods. Consequently, we used a modified N -body integrator, which was significantly extended to include the multipole expansion of the gravitational field up to the order ℓ = 10. Its convergence was verified against the ‘brute-force’ algorithm. We computed the coefficients C ℓm , S ℓm for Kleopatra’s shape, assuming a constant bulk density. For Solar System applications, it was also necessary to implement a variable distance and geometry of observations. Our χ ² metric then accounts for the absolute astrometry, the relative astrometry (second moon with respect to the first), angular velocities, and silhouettes, constraining the pole orientation. This allowed us to derive the orbital elements of Kleopatra’s two moons.
Results. Using both archival astrometric data and new VLT/SPHERE observations (ESO LP 199.C-0074), we were able to identify the true periods of the moons, P 1 = (1.822359 ± 0.004156) d, P 2 = (2.745820 ± 0.004820) d. They orbit very close to the 3:2 mean-motion resonance, but their osculating eccentricities are too small compared to other perturbations (multipole, mutual), meaning that regular librations of the critical argument are not present. The resulting mass of Kleopatra, m 1 = (1.49 ± 0.16) × 10 ⁻¹² M ⊙ or 2.97 × 10 ¹⁸ kg, is significantly lower than previously thought. An implication explained in the accompanying paper is that (216) Kleopatra is a critically rotating body.
The possibility is shown that the phase of an object transform can be
determined from the autocorrelation of the image transform. The two
together should give a diffraction-limited image of the object. A
thereon based technique for the recovery of images from atmospherically
degraded short-exposure photographs is proposed. Results from a
one-dimensional computer simulation are used for a preliminary
demonstration of the technique.
We present in this paper a technique for imaging binary stars from speckle data. This technique is based upon the computation of the cross-correlation between the speckle frames and their square. This may be considered as a simple, easy to implement, complementary computation to the autocorrelation function of Labeyrie's technique for a rapid determination of the position angle of binary systems. Angular separation, absolute position angle and relative photometry of binary stars can be derived from this technique. We show an application to the bright double star Sge observed at the 2 m Telescope Bernard Lyot.
The fork algorithm for accurately estimating the intensity ratio of binary stars from speckle interferometry data is presented. For brighter stars simulation results suggest that the fork algorithm can attain a signal-to-noise ratio roughly 10 times greater than that of other algorithms, such as triple correlation and shift-and-add. The results of the application of the algorithm to Capella (Alpha Aurigae) data are described.
We present relative astrometric measurements of visual binaries made during the first semester of 2005, with the Pupil Interferometry
Speckle Camera and Coronagraph (PISCO) at the 102-cm Zeiss telescope of the Brera Astronomical Observatory, in Merate. We
performed 214 new observations of 192 objects, with angular separations in the range 0.2–4.3 arcsec, and with an average accuracy
of 0.01 arcsec. Most of the position angles could be determined without the usual 180° ambiguity, and their mean error is
. Our sample contains orbital couples as well as binaries whose motion is still uncertain. The purpose of this long-term programme
is to improve the accuracy of the orbits and constrain the masses of the components.
For the first time with PISCO, the astrometric calibration was made with a grating mask mounted at the entrance of the telescope.
The advantage of this procedure is to provide a reliable and fully independent scale determination.
We have found two possible new triple systems: ADS 7871 and KUI 15. We propose a preliminary orbit for ADS 4208.
In 2003, we initiated a long-term Adaptive Optics campaign to study the orbit of various main-belt asteroidal systems. Here we present a consistent solution for the mutual orbits of four binary systems: 22 Kalliope, 45 Eugenia, 107 Camilla and 762 Pulcova. With the exception of 45 Eugenia, we did not detect any additional satellites around these systems although we have the capability of detecting a loosely-bound fragment (located at 1/4×RHill) that is ∼40 times smaller in diameter than the primary. The common characteristic of these mutual orbits is that they are roughly circular. Three of these binary systems belong to a C-“group” taxonomic class. Our estimates of their bulk densities are consistently lower (∼1 g/cm3) than their associated meteorite analogs, suggesting an interior porosity of 30–50% (taking CI-CO meteorites as analogs). 22 Kalliope, a W-type asteroid, has a significantly higher bulk density of ∼3 g/cm3, derived based on IRAS radiometric size measurement. We compare the characteristics of these orbits in the light of tidal-effect evolution.
In 2007, the M-type binary Asteroid 22 Kalliope reached one of its annual equinoxes. As a consequence, the orbit plane of its small moon, Linus, was aligned closely to the Sun's line of sight, giving rise to a mutual eclipse season. A dedicated international campaign of photometric observations, based on amateur–professional collaboration, was organized and coordinated by the IMCCE in order to catch several of these events. The set of the compiled observations is released in this work. We developed a relevant model of these events, including a topographic shape model of Kalliope refined in the present work, the orbit solution of Linus as well as the photometric effect of the shadow of one component falling on the other. By fitting this model to the only two full recorded events, we derived a new estimation of the equivalent diameter of Kalliope of 166.2±2.8 km, 8% smaller than its IRAS diameter. As to the diameter of Linus, considered as purely spherical, it is estimated to 28±2 km. This substantial “shortening” of Kalliope, gives a bulk density of 3.35±0.33 g/cm3, significantly higher than past determinations but more consistent with its taxonomic type. Some constraints can be inferred on the composition.
- A Labeyrie
Labeyrie A., 1970, A&A, 6, 85
- J L Margot
- M E Brown
Margot J. L., Brown M. E., 2001, IAU Circ., 7703, 3
- W J Merline
- F Menard
- L Close
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2