Yazar "Sicardy, B." seçeneğine göre listele

Listeleniyor 1 - 3 / 3
  • [ X ]
    Öğe
    A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS4 measured from stellar occultations
    (Edp Sciences S A, 2023) Rommel, F. L.; Braga-Ribas, F.; Ortiz, J. L.; Sicardy, B.; Santos-Sanz, P.; Desmars, J.; Camargo, J. I. B.
    Context. The physical characterization of trans-Neptunian objects is essential for improving our understanding of the formation and evolution of our Solar System. Stellar occultation is a ground-based technique that can be successfully used to determine some of the TNOs' fundamental physical properties with high precision, such as size and shape. Aims. This work is aimed at constraining the size, shape, and geometric albedo of the dwarf planet candidate (307261) 2002 MS4 through the analysis of nine stellar occultation events. Using multichord detection, we also study the object's topography by analyzing the obtained limb and residuals between the observed chords and the best-fit ellipse. Metods. We predicted and organized the observational campaigns of nine stellar occultations by 2002 MS4 between 2019 and 2022, resulting in two single-chord events, four double-chord detections, and three events with between 3 and 61 positive chords. We derived the occultation light curves using differential aperture photometry, from which the star ingress and egress instants were calculated. Using 13 selected chords from the 8 August 2020 event, we determined the global elliptical limb of 2002 MS4. The best-fit ellipse, combined with the object's rotational information from the literature, sets constraints on the object's size, shape, and albedo. Additionally, we developed a new method to characterize the topography features on the object's limb. Results. The global limb has a semi-major axis of a' = 412 +/- 10 km, a semi-minor axis of b'= 385 +/- 17 km, and the position angle of the minor axis is 121 degrees +/- 16 degrees. From this instantaneous limb, we obtained 2002 MS4's geometric albedo of p(V) = 0.1 +/- 0.025, using HV = 3.63 +/- 0.05 mag and a projected area-equivalent diameter of 796 +/- 24 km. Significant deviations from the fitted ellipse in the northernmost limb were detected from multiple sites, highlighting three distinct topographic features: one 11 km depth depression, followed by a 25(-5)(+4) km height elevation next to a crater-like depression, with an extension of 322 +/- 39 km and 45.1 +/- 1.5 km deep. Conclusions. Our results indicate the presence of an object that is approximate to 138 km smaller in diameter than that derived from thermal data, possibly indicating the presence of a thus-far unknown satellite. However, within the error bars, the geometric albedo in the V-band is in agreement with the results published in the literature, even with the radiometric-derived albedo. This stellar occultation has allowed for the first multichord measurement of a large topography in a TNO.
  • [ X ]
    Öğe
    Physical properties of the trans-Neptunian object (38628) Huya from a multi-chord stellar occultation
    (Edp Sciences S A, 2022) Santos-Sanz, P.; Ortiz, J. L.; Sicardy, B.; Popescu, M.; Benedetti-Rossi, G.; Morales, N.; Vara-Lubiano, M.
    Context. As part of our international program aimed at obtaining accurate physical properties of trans-Neptunian objects (TNOs), we predicted a stellar occultation by the TNO (38628) Huya of the star Gaia DR2 4352760586390566400 (m(G) = 11.5 mag) on March 18, 2019. After an extensive observational campaign geared at obtaining the astrometric data, we updated the prediction and found it favorable to central Europe. Therefore, we mobilized half a hundred of professional and amateur astronomers in this region and the occultation was finally detected by 21 telescopes located at 18 sites in Europe and Asia. This places the Huya event among the best ever observed stellar occultation by a TNO in terms of the number of chords. Aims. The aim of our work is to determine an accurate size, shape, and geometric albedo for the TNO (38628) Huya by using the observations obtained from a multi-chord stellar occultation. We also aim to provide constraints on the density and other internal properties of this TNO. Methods. The 21 positive detections of the occultation by Huya allowed us to obtain well-separated chords which permitted us to fit an ellipse for the limb of the body at the moment of the occultation (i.e., the instantaneous limb) with kilometric accuracy. Results. The projected semi-major and minor axes of the best ellipse fit obtained using the occultation data are (a ', b ') = (217.6 +/- 3.5 km, 194.1 +/- 6.1 km) with a position angle for the minor axis of P ' = 55.2 degrees +/- 9.1. From this fit, the projected area-equivalent diameter is 411.0 +/- 7.3 km. This diameter is compatible with the equivalent diameter for Huya obtained from radiometric techniques (D = 406 +/- 16 km). From this instantaneous limb, we obtained the geometric albedo for Huya (p(V) = 0.079 +/- 0.004) and we explored possible three-dimensional shapes and constraints to the mass density for this TNO. We did not detect the satellite of Huya through this occultation, but the presence of rings or debris around Huya was constrained using the occultation data. We also derived an upper limit for a putative Pluto-like global atmosphere of about p(surf) = 10 nbar.
  • [ X ]
    Öğe
    The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
    (Nature Portfolio, 2017) Ortiz, J. L.; Santos-Sanz, P.; Sicardy, B.; Benedetti-Rossi, G.; Berard, D.; Morales, N.; Duffard, R.
    Haumea-one of the four known trans-Neptunian dwarf planets is a very elongated and rapidly rotating body(1-3). In contrast to other dwarf planets(4-6), its size, shape, albedo and density are not well constrained. The Centaur Chariklo was the first body other than a giant planet known to have a ring system(7), and the Centaur Chiron was later found to possess something similar to Chariklo's rings(8,9). Here we report observations from multiple Earth-based observatories of Haumea passing in front of a distant star (a multi chord stellar occultation). Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea's equator and the orbit of its satellite Hi'iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea's spin period-that is, Haumea rotates three times on its axis in the time that a ring particle completes one revolution. The occultation by the main body provides an instantaneous elliptical projected shape with axes of about 1,704 kilometres and 1,138 kilometres. Combined with rotational light curves, the occultation constrains the three-dimensional orientation of Haumea and its triaxial shape, which is inconsistent with a homogeneous body in hydrostatic equilibrium. Haumea's largest axis is at least 2,322 kilometres, larger than previously thought, implying an upper limit for its density of 1,885 kilograms per cubic metre and a geometric albedo of 0.51, both smaller than previous estimates(1,10,11). In addition, this estimate of the density of Haumea is closer to that of Pluto than are previous estimates, in line with expectations. No global nitrogen- or methane-dominated atmosphere was detected.