M. Assafin
A5087170240- Astro and Planetary Science
- Stellar, planetary, and galactic studies
- Astronomical Observations and Instrumentation
- Planetary Science and Exploration
- Astronomy and Astrophysical Research
- Solar and Space Plasma Dynamics
- Atmospheric Ozone and Climate
- Isotope Analysis in Ecology
- Geophysics and Gravity Measurements
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Space Exploration and Technology
- Adaptive optics and wavefront sensing
- Inertial Sensor and Navigation
- Geomagnetism and Paleomagnetism Studies
- GNSS positioning and interference
- Geology and Paleoclimatology Research
- Geological and Geochemical Analysis
- Scientific Research and Discoveries
- History and Developments in Astronomy
- Historical Astronomy and Related Studies
- Space Satellite Systems and Control
- Ionosphere and magnetosphere dynamics
- Calibration and Measurement Techniques
- Galaxies: Formation, Evolution, Phenomena
Universidade Federal do Rio de Janeiro
2015-2025
Laboratório Interinstitucional de e-Astronomia
2017-2025
Valongo Observatory
2015-2024
Institut de Mécanique Céleste et de Calcul des Éphémérides
2004-2022
Observatoire de Paris
2009-2022
National Observatory
1992-2019
Roche (France)
2013-2015
Centre National de la Recherche Scientifique
2015
Laboratoire de Tribologie et Dynamique des Systèmes
2004-2011
Hospital Universitário Antônio Pedro
2009
Abstract The physical and orbital parameters of trans-Neptunian objects provide valuable information about the solar system’s formation evolution. In particular, characterization binaries provides insights into mechanisms that may be playing a role at such large distances from Sun. Studies show two distinct populations, (38628) Huya occupies an intermediate position between unequal-sized those with components roughly equal sizes. this work, we predicted observed three stellar occultation...
Jupiter Trojans preserve primitive formation characteristics owing to their collisionless, stable orbits. Determination of shapes and size-frequency distribution helps constrain the collisional evolution parent population, which also originated Kuiper Belt. We started a programme find precise sizes/shapes for Trojans, combining stellar occultations Database Asteroid Models from Inversion Techniques (DAMIT) three-dimensional shape models. report results Diomedes, by fitting its unit...
We present a catalog of mean proper motions and membership probabilities individual stars for optically visible open clusters, which have been determined using data from the UCAC4 in homogeneous way. The motion cluster region each were by applying statistical method modified fashion. In this study, we applied global optimization procedure to fit observed distribution with two overlapping normal bivariate frequency functions, also take errors into account. For 724 is first determination...
ABSTRACT We present results from a multi-chord Pluto stellar occultation observed on 2015 June 29 New Zealand and Australia. This occurred only two weeks before the NASA Horizons flyby of system serves as useful comparison between ground-based space results. find that Pluto's atmosphere is still expanding, with significant pressure increase 5 ± 2% since 2013 factor almost three 1988. trend rules out, today, an atmospheric collapse associated recession Sun. A central flash, rare occurrence,...
Quaoar is a classical Trans-Neptunian Object (TNO) with an area equivalent diameter of 1,100 km and orbital semi-major axis 43.3 astronomical units. Based on stellar occultations observed between 2018 2021, inhomogeneous ring (Q1R, Quaoar's first ring) was detected around this body. Aims. A new occultation by August 9th, 2022 aiming to improve shape models the physical parameters Q1R while searching for additional material Methods. The provided nine effective chords across Quaoar, pinning...
Comets offer valuable insights into the early Solar System's conditions and processes. Stellar occultations enable detailed study of cometary nuclei typically hidden by their coma. Observing star's light passing through coma helps infer dust's optical depth near nucleus determine dust opacity detection limits. 29P/Schwassmann-Wachmann 1, a Centaur with diameter approximately 60 km, lies in region transitioning from Centaurs to Jupiter-family comets. Our presents first-ever observed...
We present results derived from the first multi-chord stellar occultations by transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, a single-chord occultation October 15. If timing of five chords obtained in were correct, then Quaoar would possess topographic features (crater or mountain) that be too large for body this mass. An alternative model consists applying time shifts to some account possible errors. Satisfactory elliptical fits are possible, yielding an...
We 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 solid body, but we found three extinction features light curve that had symmetrical counterparts with respect central time occultation. One is broad shallow, whereas other two are sharper, maximum ∼25% at achieved spatial resolution 19 km per data point. From Wise Israel, detected caused main...
We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, monitored respectively from five six sites. They provide a total of fifteen light-curves, twelve them being used for simultaneous fit that uses unique temperature profile, assuming clear (no-haze) pure N_2 atmosphere, but allowing possible pressure variation between the dates. find solution fits satisfactorily (i.e. within noise level) all providing atmospheric constraints ~1,190 km...
Two narrow and dense rings (called C1R C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned observations of several occultations by Chariklo's system in order to better characterize physical properties ring main body. Here, use 12 successful occulations between 2014 2016. They provide profiles (physical width, opacity, edge structure) constraints radii pole position. Our new are currently...
Combining stellar occultation observations probing Pluto's atmosphere from 1988 to 2013, and models of energy balance between surface atmosphere, we find the preferred are consistent with Pluto retaining a collisional throughout its 248-year orbit. The results show an increasing atmospheric pressure time in current epoch, trend present only high thermal inertia permanent N2 ice cap at north rotational pole.
We present the kinematics of hundreds open clusters, based on UCAC2 Catalogue positions and proper motions. Membership probabilities were obtained for stars in cluster fields by applying a statistical method uses stellar All clusters with known distance investigated, 75 this is first determination mean motion. The results, including DSS images cluster's kinematic members marked, are incorporated Open Clusters supported line our group.
Context. The prediction of stellar occultations by trans-Neptunian objects (TNOs) and Centaurs is a difficult challenge that requires accuracy both in the occulted star position object ephemeris. Until now, most used method prediction, involving dozens TNOs/Centaurs, has been to consider constant offset for right ascension declination with respect reference ephemeris, usually latest public version. This determined as difference between recent observations TNO/Centaur can be successfully...
We use data from five stellar occultations observed between 2013 and 2016 to constrain Chariklo's size shape, the ring reflectivity. consider four possible models for Chariklo (sphere, Maclaurin spheroid, tri-axial ellipsoid Jacobi ellipsoid) we a Bayesian approach estimate corresponding parameters. The spherical model has radius $R=129\pm3$ km. equatorial polar radii $a=b=143^{+3}_{-6}$ km $c=96^{+14}_{-4}$ km, respectively, with density $970^{+300}_{-180}$ kg m$^{-3}$. ellipsoidal semiaxes...
We present results derived from four stellar occultations by the plutino object (208996) 2003~AZ$_{84}$, detected at January 8, 2011 (single-chord event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid solution for 2003~AZ$_{84}$'s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial with semi axes $(470 \pm 20) \times (383 10) (245 8)$~km % axis ratios $b/a= 0.82...
Context. Pluto's tenuous nitrogen (N2) atmosphere undergoes strong seasonal effects due to high obliquity and orbital eccentricity, has been recently (July 2015) observed by the New Horizons spacecraft. Goals are (i) construct a well calibrated record of evolution surface pressure on Pluto (ii) constrain structure lower using central flash in 2015. Method: eleven stellar occultations between 2002 2016 used retrieve atmospheric profiles (density, pressure, temperature) $\sim$5 km $\sim$380...