20 research outputs found
Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020-2021 apparition data
Context. The close approach of the near-Earth asteroid (99942) Apophis to
Earth in 2029 will provide a unique opportunity to examine how the physical
properties of the asteroid could be changed due to the Earth's gravitational
perturbation. As a result, the Republic of Korea is planning a rendezvous
mission to Apophis. Aims. Our aim was to use photometric data from the
apparitions in 2020-2021 to refine the shape model and spin state of Apophis.
Methods. Using thirty-six 1 to 2-m class ground-based telescopes and the
Transiting Exoplanet Survey Satellite, we performed a photometric observation
campaign throughout the 2020-2021 apparition. The convex shape model and spin
state were refined using the light-curve inversion method. Results. According
to our best-fit model, Apophis is rotating in a short axis mode with rotation
and precession periods of 264.178 hours and 27.38547 hours, respectively. The
angular momentum vector orientation of Apophis was found as (275,
-85) in the ecliptic coordinate system. The ratio of the dynamic
moments of inertia of this asteroid was fitted to ,
which corresponds to an elongated prolate ellipsoid. These findings regarding
the spin state and shape model could be used to not only design the space
mission scenario but also investigate the impact of the Earth's tidal force
during close encounters.Comment: 14 pages, 5 figures; Accepted for publication on Astronomy &
Astrophysic
The changing material around (2060) Chiron from an occultation on 2022 December 15
We could accurately predict the shadow path and successfully observe an
occultation of a bright star by Chiron on 2022 December 15. The Kottamia
Astronomical Observatory in Egypt did not detect the occultation by the solid
body, but we detected three extinction features in the light curve that had
symmetrical counterparts with respect to the central time of the occultation.
One of the features is broad and shallow, whereas the other two features are
sharper with a maximum extinction of 25 at the achieved spatial
resolution of 19 km per data point. From the Wise observatory in Israel, we
detected the occultation caused by the main body and several extinction
features surrounding the body. When all the secondary features are plotted in
the sky plane we find that they can be caused by a broad 580 km disk with
concentrations at radii of 325 \pm 16 km and 423 \pm 11 km surrounding Chiron.
At least one of these structures appears to be outside the Roche limit. The
ecliptic coordinates of the pole of the disk are = 151
8 and = 18 11, in agreement with previous
results. We also show our long-term photometry indicating that Chiron had
suffered a brightness outburst of at least 0.6 mag between March and September
2021 and that Chiron was still somewhat brighter at the occultation date than
at its nominal pre-outburst phase. The outermost extinction features might be
consistent with a bound or temporarily bound structure associated with the
brightness increase. However, the nature of the brightness outburst is unclear,
and it is also unclear whether the dust or ice released in the outburst could
be feeding a putative ring structure or if it emanated from it.Comment: 6 pages, 4, figure
Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020-2021 apparition data
Context. The close approach of the near-Earth asteroid (99942) Apophis to Earth in 2029 will provide a unique opportunity to examine how the physical properties of the asteroid could be changed due to the Eartha's gravitational perturbation. As a result, the Republic of Korea is planning a rendezvous mission to Apophis. Aims. Our aim was to use photometric data from the apparitions in 2020 2021 to refine the shape model and spin state of Apophis. Methods. Using thirty-six 1-to 2-meter-class ground-based telescopes and the Transiting Exoplanet Survey Satellite, we carried out a photometric observation campaign throughout the 2020 2021 apparition. The convex shape model and spin state were refined using the light-curve inversion method. Results. According to our best-fit model, Apophis is rotating in a short-axis mode with rotation and precession periods of 264.178 h and 27.38547 h, respectively. The angular momentum vector orientation of Apophis was found to be (275, 85) in the ecliptic coordinate system. The ratio of the dynamic moments of inertia of this asteroid was fitted to Iaa:a Iba:a Ica =a 0.64a:a 0.97a:a 1, which corresponds to an elongated prolate ellipsoid. These findings regarding the spin state and shape model can be used to both design the space mission scenario and investigate the impact of the Eartha's tidal force during close encounters
A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS measured from stellar occultations
This work aims at constraining the size, shape, and geometric albedo of the
dwarf planet candidate 2002 MS4 through the analysis of nine stellar
occultation events. Using multichord detection, we also studied the object's
topography by analyzing the obtained limb and the residuals between observed
chords and the best-fitted ellipse. 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 three to up to sixty-one positive chords. Using 13
selected chords from the 8 August 2020 event, we determined the global
elliptical limb of 2002 MS4. The best-fitted ellipse, combined with the
object's rotational information from the literature, constrains the object's
size, shape, and albedo. Additionally, we developed a new method to
characterize topography features on the object's limb. The global limb has a
semi-major axis of 412 10 km, a semi-minor axis of 385 17 km, and
the position angle of the minor axis is 121 16. From
this instantaneous limb, we obtained 2002 MS4's geometric albedo and the
projected area-equivalent diameter. Significant deviations from the fitted
ellipse in the northernmost limb are detected from multiple sites highlighting
three distinct topographic features: one 11 km depth depression followed by a
25 km height elevation next to a crater-like depression with an
extension of 322 39 km and 45.1 1.5 km deep. Our results present an
object that is 138 km smaller in diameter than derived from thermal
data, possibly indicating the presence of a so-far unknown satellite. However,
within the error bars, the geometric albedo in the V-band agrees with the
results published in the literature, even with the radiometric-derived albedo
The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
Haumeaâone of the four known trans-Neptunian dwarf planetsâis a very elongated and rapidly rotating body1, 2, 3. In contrast to other dwarf planets4, 5, 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 system7, and the Centaur Chiron was later found to possess something similar to Charikloâs rings8, 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 Haumeaâs equator and the orbit of its satellite Hiâiaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumeaâs spin periodâthat 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. Haumeaâs 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 estimates1, 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.J.L.O. acknowledges funding from Spanish and Andalusian grants MINECO AYA-2014-56637-C2-1-P and J. A. 2012-FQM1776 as well as FEDER funds. Part of the research leading to these results received funding from the European Unionâs Horizon 2020 Research and Innovation Programme, under grant agreement no. 687378. B.S. acknowledges support from the French grants âBeyond Neptuneâ ANR-08-BLAN-0177 and âBeyond Neptune IIâ ANR-11-IS56-0002. Part of the research leading to these results has received funding from the European Research Council under the European Communityâs H2020 (2014-2020/ERC grant agreement no. 669416 âLucky Starâ). A.P. and R.S. have been supported by the grant LP2012-31 of the Hungarian Academy of Sciences. All of the Hungarian contributors acknowledge the partial support from K-125015 grant of the National Research, Development and Innovation Office (NKFIH). G.B.-R., F.B.-R., F.L.R., R.V.-M., J.I.B.C., M.A., A.R.G.-J. and B.E.M. acknowledge support from CAPES, CNPq and FAPERJ. J.C.G. acknowledges funding from AYA2015-63939-C2-2-P and from the Generalitat Valenciana PROMETEOII/2014/057. K.H. and P.P. were supported by the project RVO:67985815. The Astronomical Observatory of the Autonomous Region of the Aosta Valley acknowledges a Shoemaker NEO Grant 2013 from The Planetary Society. We acknowledge funds from a 2016 âResearch and Educationâ grant from Fondazione CRT. We also acknowledge the Slovakian project ITMS no. 26220120029
Occultation Portal: a web-based platform for data collection and analysis of stellar occultations
International audienceRecording a stellar occultation is one powerful method that gives direct information about the physical properties of the occulting Solar system object. In order to obtain reliable and accurate results, simultaneous observations from different locations across-track of the projected path are of great importance. However, organising all the observing stations, aggregating, and analysing the data is time-consuming and not that easy. We have developed a web portal named Occultation Portal (OP) to manage all those occultation observation campaigns from a central server. With this portal, the instrumental and observational information of all observers participating in a stellar occultation campaign and the concerned data are archived systematically in a standard format. The researchers can then visualise the archived data on an event basis. The investigators can also extract the light curve for each data-set with the added reduction pipeline to the portal base. This paper describes in detail the portal structure and the developed features
Shape model and spin state of non-principal axis rotator (5247) Krylov
Context. The study of non-principal axis (NPA) rotators can provide important clues to the evolution of the spin state of asteroids. However, very few studies to date have focused on NPA-rotating main belt asteroids (MBAs). One MBA known to be in an excited rotation state is asteroid (5247) Krylov.
Aims. By using disk-integrated photometric data, we construct a physical model of (5247) Krylov including shape and spin state.
Methods. We applied the light curve convex inversion method employing optical light curves obtained by using ground-based telescopes in three apparitions during 2006, 2016, and 2017, along with infrared light curves obtained by the Wide-field Infrared Survey Explorer satellite in 2010.
Results. Asteroid (5247) Krylov is spinning in a short axis mode characterized by rotation and precession periods of 368.7 and 67.27 h, respectively. The angular momentum vector orientation of Krylov is found to be λL = 298° and ÎČL = â58°. The ratio of the rotational kinetic energy to the basic spin-state energy EâE0 â 1.02 shows that the (5247) Krylov is about 2% excited state compared to the principal axis rotation state. The shape of (5247) Krylov can be approximated by an elongated prolate ellipsoid with a ratio of moments of inertia of Ia : Ib : Ic = 0.36 : 0.96 : 1. This is the first physical model of an NPA rotator among MBAs. The physical processes that led to the current NPA rotation cannot be unambiguously reconstructed
Observation campaign of (99942) Apophis in the 2021 apparition
We report the physical properties of 99942 Apophis obtained from our extensive observation campaign during its 2021 apparition. We refined its convex shape model and spin state and detected its different taxonomic signatures in the different phases
Changing material around (2060) Chiron revealed by an occultation on December 15, 2022
International audienceWe were able to accurately predict the shadow path and successfully observe an occultation of a bright star by Chiron on December 15, 2022. The Kottamia Astronomical Observatory in Egypt did not detect the occultation by the solid body, but we found three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. One of the features is broad and shallow, whereas the other two features are sharper, with a maximum extinction of âŒ25% at the achieved spatial resolution of 19 km per data point. From the Wise Observatory in Israel, we detected the occultation caused by the main body and several extinction features surrounding the body. When all the secondary features are plotted in the sky plane, we find that they can be caused by a broad âŒ580 km disk with concentrations at radii of 325 ± 16 km and 423 ± 11 km surrounding Chiron. At least one of these structures appears to be outside the Roche limit. The ecliptic coordinates of the pole of the disk are λâ=â151°â
±8° and ÎČâ=â18°â
±11°, in agreement with previous results. We also reveal our long-term photometry results, indicating that Chiron had suffered a brightness outburst of at least 0.6 mag between March and September 2021 and that Chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. The outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. However, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or whether it is emanating from it