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Saint-Étienne, France

Carry B.,University of Paris Descartes | Carry B.,University Paris Diderot | Kaasalainen M.,Tampere University of Technology | Leyrat C.,University of Paris Descartes | And 24 more authors.
Astronomy and Astrophysics | Year: 2010

Aims: We determine the physical properties (spin state and shape) of asteroid (21) Lutetia, target of the International Rosetta Mission of the European Space Agency, to help in preparing for observations during the flyby on 2010 July 10 by predicting the orientation of Lutetia as seen from Rosetta. Methods: We use our novel KOALA inversion algorithm to determine the physical properties of asteroids from a combination of optical lightcurves, disk-resolved images, and stellar occultations, although the last are not available for (21) Lutetia. Results: We find the spin axis of (21) Lutetia to lie within 5° of (λ = 52°, β = -6°) in the Ecliptic J2000 reference frame (equatorial α = 52°, δ = +12°), and determine an improved sidereal period of 8.168 270±0.000 001 h. This pole solution implies that the southern hemisphere of Lutetia will be in "seasonal" shadow at the time of the flyby. The apparent cross-section of Lutetia is triangular when seen "pole-on" and more rectangular "equator-on". The best-fit model suggests there are several concavities. The largest of these is close to the north pole and may be associated with strong impacts. © ESO 2010. Source

Marciniak A.,Adam Mickiewicz University | Michalowski T.,Adam Mickiewicz University | Polinska M.,Adam Mickiewicz University | Bartczak P.,Adam Mickiewicz University | And 20 more authors.
Astronomy and Astrophysics | Year: 2011

Context. The set of more than 100 asteroids, for which spin parameters have been modelled using an amplitude, magnitude or epoch methods, showed a pronounced gap in the distribution of the asteroid spin axes. These spin axes are rarely aligned with the ecliptic plane. Aims. The number of asteroids with known spin parameters should be increased to allow for statistical investigations. Methods. We gathered extensive photometric datasets on four selected main-belt asteroids to model their spin and shape parameters using the lightcurve inversion method. Our only criterion of selection was their observability for small telescopes. Results. All four of the modelled asteroids happened to have rotational poles that lie close to the ecliptic plane (periods and J2000 north pole coordinates): (94) Aurora -P = 7.226191 h, λp1 = 58°, βp1 = + 16°; λp2 = 242°, βp2 = + 4°; (174) Phaedra - P = 5.750249 h, λp = 265°, βp = + 5°; (679) Pax - P = 8.456016 h, λp1 = 42°, βp1 = -5°; λp2 = 220°, βp2 = + 32° (pole 2 preferred after comparison with AO-resolved observations); (714) Ulula - P = 6.998376 h, λp1 = 42°, βp1 = -9°; λp2 = 227°, βp2 = -14°. Conclusions. This work suggests that asteroid spin axes do not avoid the ecliptic plane, contrary to what the classical modelling suggested. © 2011 ESO. Source

Hanus J.,Charles University | Durech J.,Charles University | Broz M.,Charles University | Marciniak A.,Adam Mickiewicz University | And 70 more authors.
Astronomy and Astrophysics | Year: 2013

Context. The larger number of models of asteroid shapes and their rotational states derived by the lightcurve inversion give us better insight into both the nature of individual objects and the whole asteroid population. With a larger statistical sample we can study the physical properties of asteroid populations, such as main-belt asteroids or individual asteroid families, in more detail. Shape models can also be used in combination with other types of observational data (IR, adaptive optics images, stellar occultations), e.g., to determine sizes and thermal properties. Aims. We use all available photometric data of asteroids to derive their physical models by the lightcurve inversion method and compare the observed pole latitude distributions of all asteroids with known convex shape models with the simulated pole latitude distributions. Methods. We used classical dense photometric lightcurves from several sources (Uppsala Asteroid Photometric Catalogue, Palomar Transient Factory survey, and from individual observers) and sparse-in-time photometry from the U.S. Naval Observatory in Flagstaff, Catalina Sky Survey, and La Palma surveys (IAU codes 689, 703, 950) in the lightcurve inversion method to determine asteroid convex models and their rotational states. We also extended a simple dynamical model for the spin evolution of asteroids used in our previous paper. Results. We present 119 new asteroid models derived from combined dense and sparse-in-time photometry. We discuss the reliability of asteroid shape models derived only from Catalina Sky Survey data (IAU code 703) and present 20 such models. By using different values for a scaling parameter cYORP (corresponds to the magnitude of the YORP momentum) in the dynamical model for the spin evolution and by comparing synthetic and observed pole-latitude distributions, we were able to constrain the typical values of the c YORP parameter as between 0.05 and 0.6. © 2013 ESO. Source

Marciniak A.,Adam Mickiewicz University | Bartczak P.,Adam Mickiewicz University | Santana-Ros T.,Adam Mickiewicz University | Michalowski T.,Adam Mickiewicz University | And 31 more authors.
Astronomy and Astrophysics | Year: 2012

Context. The shapes and spin states of asteroids observed with photometric techniques can be reconstructed using the lightcurve inversion method. The resultant models can then be confirmed or exploited further by other techniques, such as adaptive optics, radar, thermal infrared, stellar occultations, or space probe imaging. Aims. During our ongoing work to increase the set of asteroids with known spin and shape parameters, there appeared a need for displaying the model plane-of-sky orientations for specific epochs to compare models from different techniques. It would also be instructive to be able to track how the complex lightcurves are produced by various asteroid shapes. Methods. Basing our analysis on an extensive photometric observational dataset, we obtained eight asteroid models with the convex lightcurve inversion method. To enable comparison of the photometric models with those from other observing/modelling techniques, we created an on-line service where we allow the inversion models to be orientated interactively. Results. Our sample of objects is quite representative, containing both relatively fast and slow rotators with highly and lowly inclined spin axes. With this work, we increase the sample of asteroid spin and shape models based on disk-integrated photometry to over 200. Three of the shape models obtained here are confirmed by the stellar occultation data; this also allowed independent determinations of their sizes to be made. Conclusions. The ISAM service can be widely exploited for past and future asteroid observations with various, complementary techniques and for asteroid dimension determination. © 2012 ESO. Source

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