Occultations stellaires pour l’étude des objets trans-neptuniens et les Centaures : applications aux anneaux de Chariklo
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Date
2017
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Abstract
The present PhD thesis has been developed in the context of a cotutelle between the Pontificia Universidad Católica de Chile (PUC) and the Université Pierre et Marie Curie (UPMC). The first half of the PhD was done
in the Instituto de Astrofísica at PUC and the second half at the Labora-
toire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA) at
the Observatoire de Paris, in the context of the European Research Council
(ERC) project “Lucky Star", whose goal is to study the small objects of the
outer Solar System using stellar occultations.
Here, I address three important stages of the project: observations with
fast cameras, data analysis and physical interpretation of the results.
In the first part I describe tests performed on two occultation kits, each
consisting in a fast camera, a time registration system and an acquisition
software. I show that the EMCCD-based camera performs better than the
alternative CMOS camera, reaching stars one magnitude fainter in equivalent conditions. The time registration system (the TimeBox device) has an
accuracy below 20 ms with respect to the UTC reference time which is adequate for the timing of the observation of stellar occultations. Interactions
with the acquisition software manufacturer lead to the adaptation of such
software to the needs of the project.
In the second part I study the physical characterization of three ob-
ject with the analysis of stellar occultations. For the scattered disk object
2007 UK126 I derive the range and more probable density values analyzing the elliptical fits to a multi chord stellar occultation. For the plutino
2003 AZ84 I constrain the range of compatible density and orientation to
a narrow region around ∼870 kg m−3 and opening angle B ∼ 48◦ analyzing two multi-chord stellar occultations. The main subject of this section
is the adoption of a Bayesian-MCMC approach for analysis of five stellar
occultations by the Centaur object Chariklo. Chariklo appears to be consistent with an ellipsoid with semiaxes a = 148+6−4 km, b = 132+6−5 km, and c = 102+10−8 km presenting topographic features of the order of 6 km. From
this nominal model, I derive a body geometric albedo of 4.9±0.1% and a
ring reflectivity of 3.7±0.3%. The topographic features for this model are
∼ 6 km, comparable to those of Saturnian icy satellites with similar size
and density.
In the third part, I consider Lindblad resonances between the mean motions of ring particles and the rotation of an irregular body. Mass excess
departing from a spherical body exert strong torques on a collisional disk
that clear the material from the corotation radius up to the outermost resonance. Application to Chariklo indicates very short clearing timescales (
< 105 years) and explains the current location of the rings.
Description
Tesis (Docteur)--Université Pierre et Marie Curie, 2022
Tesis (Docteur en Astrophysique)--Pontificia Universidad Católica de Chile, 2022
Tesis (Docteur en Astrophysique)--Pontificia Universidad Católica de Chile, 2022