42 research outputs found
Physical properties of Centaur (60558) 174P/Echeclus from stellar occultations
The Centaur (60558) Echeclus was discovered on March 03, 2000, orbiting
between the orbits of Jupiter and Uranus. After exhibiting frequent outbursts,
it also received a comet designation, 174P. If the ejected material can be a
source of debris to form additional structures, studying the surroundings of an
active body like Echeclus can provide clues about the formation scenarios of
rings, jets, or dusty shells around small bodies. Stellar occultation is a
handy technique for this kind of investigation, as it can, from Earth-based
observations, detect small structures with low opacity around these objects.
Stellar occultation by Echeclus was predicted and observed in 2019, 2020, and
2021. We obtain upper detection limits of rings with widths larger than 0.5 km
and optical depth of = 0.02. These values are smaller than those of
Chariklo's main ring; in other words, a Chariklo-like ring would have been
detected. The occultation observed in 2020 provided two positive chords used to
derive the triaxial dimensions of Echeclus based on a 3D model and pole
orientation available in the literature. We obtained km, km, and km, resulting in an area-equivalent
radius of km. Using the projected limb at the occultation epoch
and the available absolute magnitude (), we
calculate an albedo of . Constraints on the
object's density and internal friction are also proposed.Comment: Corrected and typeset versio
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
Constraints on (2060) Chiron's size, shape, and surrounding material from the November 2018 and September 2019 stellar occultations
After the discovery of rings around the largest known Centaur object, (10199)
Chariklo, we carried out observation campaigns of stellar occultations produced
by the second-largest known Centaur object, (2060) Chiron, to better
characterize its physical properties and presence of material on its
surroundings. We predicted and successfully observed two stellar occultations
by Chiron. These observations were used to constrain its size and shape by
fitting elliptical limbs with equivalent surface radii in agreement with
radiometric measurements. Constraints on the (2060) Chiron shape are reported
for the first time. Assuming an equivalent radius of R =
105 km, we obtained a semi-major axis of a = 126 22 km.
Considering Chiron's true rotational light curve amplitude and assuming it has
a Jacobi equilibrium shape, we were able to derive a 3D shape with a semi-axis
of a = 126 22 km, b = 109 19 km, and c = 68 13 km, implying
in a volume-equivalent radius of R = 98 17 km, implying a density
of 1119 4 kg m. We determined the physical properties of the 2011
secondary events around Chiron, which may then be directly compared with those
of Chariklo rings, as the same method was used. Data obtained from SAAO in 2018
do not show unambiguous evidence of the proposed rings, mainly due to the large
sampling time. Meanwhile, we discarded the possible presence of a permanent
ring similar to (10199) Chariklo's C1R in optical depth and extension. Using
the first multi-chord stellar occultation by (2060) Chiron and considering it
to have a Jacobi equilibrium shape, we derived its 3D shape. New observations
of a stellar occultation by (2060) Chiron are needed to further investigate the
material's properties around Chiron, such as the occultation predicted for
September 10, 2023
The Trans-Neptunian Object (84922) 2003 VS2 through Stellar Occultations
We present results from three world-wide campaigns that resulted in the detections of two single-chord and one multi-chord stellar occultations by the plutino object (84922) 2003 VS2. From the single-chord occultations in 2013 and 2014 we obtained accurate astrometric positions for the object, while from the multi-chord occultation on 2014 November 7, we obtained the parameters of the best-fitting ellipse to the limb of the body at the time of occultation. We also obtained short-term photometry data for the body in order to derive its rotational phase during the occultation. The rotational light curve present a peak-to-peak amplitude of 0.141 ± 0.009 mag. This allows us to reconstruct the 3D shape of the body, with principal semi-axes of a = 313.8 ± 7.1 km, = - + b 265.5 9.8 8.8 km, and = - + c 247.3 43.6 26.6 km, which is not consistent with a Jacobi triaxial equilibrium figure. The derived spherical volume equivalent diameter of - + 548.3 44.6 29.5 km is about 5% larger than the radiometric diameter of 2003 VS2 derived from Herschel data of 523 ± 35 km, but still compatible with it within error bars. From those results we can also derive the geometric albedo ( - + 0.123 0.014 0.015) and, under the assumption that the object is a Maclaurin spheroid, the density r = - + 1400 300 1000 for the plutino. The disappearances and reappearances of the star during the occultations do not show any compelling evidence for a global atmosphere considering a pressure upper limit of about 1 microbar for a pure nitrogen atmosphere, nor secondary features (e.g., rings or satellite) around the main body.Fil: Benedetti Rossi, Gustavo. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Laboratório Interinstitucional de e-Astronomia; BrasilFil: Santos Sanz, P.. Instituto de Astrofísica de Andalucía; EspañaFil: Ortiz, J. L.. Instituto de Astrofísica de Andalucía; EspañaFil: Assafin, M.. Observatório do Valongo; BrasilFil: Sicardy, B.. Sorbonne University; Francia. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Morales, N.. Instituto de Astrofísica de Andalucía; EspañaFil: Vieira Martins, R.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Laboratório Interinstitucional de e-Astronomia; Brasil. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Duffard, R.. Instituto de Astrofísica de Andalucía; EspañaFil: Braga Ribas, F.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Laboratório Interinstitucional de e-Astronomia; Brasil. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia. Universidade Tecnologia Federal do Parana; BrasilFil: Rommel, F. L.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Laboratório Interinstitucional de e-Astronomia; BrasilFil: Camargo, J. I. B.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; Brasil. Laboratório Interinstitucional de e-Astronomia; BrasilFil: Desmars, J.. Instituto de Astrofísica de Andalucía; EspañaFil: Colas, A. F.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Vachier, F.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Alvarez Candal, A.. Ministério de Ciencia, Tecnologia e Innovacao. Observatorio Nacional; BrasilFil: Fernández Valenzuela, E.. University of Central Florida; Estados UnidosFil: Almenares, L.. Universidad de la Republica; UruguayFil: Artola, R.. Estación Astrofísica de Bosque Alegre; ArgentinaFil: Baum, T. P.. Observatoire Astronomique des Makes; FranciaFil: Behrend, R.. Observatoire de Genève; ItaliaFil: Bérard, D.. Centre National de la Recherche Scientifique. Observatoire de Paris; FranciaFil: Bianco, F. B.. University of Delaware; Estados Unidos. University of New York; Estados UnidosFil: Brosch, N.. Universitat Tel Aviv; IsraelFil: Ceretta, A.. Observatorio Astronómico Los Molinos; UruguayFil: Colazo, C. A.. Estación Astrofísica de Bosque Alegre; ArgentinaFil: Gomes Junior, A. R.. Laboratório Interinstitucional de e-Astronomia; Brasil. Universidade Estadual Paulista Julio de Mesquita Filho. Faculdade de Engenharia; BrasilFil: Ivanov, V. D.. Observatorio Europeo del Sur; AlemaniaFil: Jehin, E.. Université de Liège; BélgicaFil: Kaspi, S.. Universitat Tel Aviv; IsraelFil: Gil Hutton, Ricardo Alfredo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Geofísica y Astronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; Argentin
Stellar occultations enable milliarcsecond astrometry for Trans-Neptunian objects and Centaurs
Trans-Neptunian objects (TNOs) and Centaurs are remnants of our planetary
system formation, and their physical properties have invaluable information for
evolutionary theories. Stellar occultation is a ground-based method for
studying these small bodies and has presented exciting results. These
observations can provide precise profiles of the involved body, allowing an
accurate determination of its size and shape. The goal is to show that even
single-chord detections of TNOs allow us to measure their milliarcsecond
astrometric positions in the reference frame of the Gaia second data release
(DR2). Accurated ephemerides can then be generated, allowing predictions of
stellar occultations with much higher reliability. We analyzed data from
stellar occultations to obtain astrometric positions of the involved bodies.
The events published before the Gaia era were updated so that the Gaia DR2
catalog is the reference. Previously determined sizes were used to calculate
the position of the object center and its corresponding error with respect to
the detected chord and the International Celestial Reference System (ICRS)
propagated Gaia DR2 star position. We derive 37 precise astrometric positions
for 19 TNOs and 4 Centaurs. Twenty-one of these events are presented here for
the first time. Although about 68\% of our results are based on single-chord
detection, most have intrinsic precision at the submilliarcsecond level. Lower
limits on the diameter and shape constraints for a few bodies are also
presented as valuable byproducts. Using the Gaia DR2 catalog, we show that even
a single detection of a stellar occultation allows improving the object
ephemeris significantly, which in turn enables predicting a future stellar
occultation with high accuracy. Observational campaigns can be efficiently
organized with this help, and may provide a full physical characterization of
the involved object.Comment: 16 pages, 28 figures. The manuscript was accepted and is to be
publishe
Physical properties of Centaur (60558) 174P/Echeclus from stellar occultations
peer reviewedThe Centaur (60558) Echeclus was discovered on 2000 March 03, orbiting between the orbits of Jupiter and Uranus. After exhibiting frequent outbursts, it also received a comet designation, 174P. If the ejected material can be a source of debris to form additional structures, studying the surroundings of an active body like Echeclus can provide clues about the formation scenarios of rings, jets, or dusty shells around small bodies. Stellar occultation is a handy technique for this kind of investigation, as it can, from Earth-based observations, detect small structures with low opacity around these objects. Stellar occultation by Echeclus was predicted and observed in 2019, 2020, and 2021. We obtain upper detection limits of rings with widths larger than 0.5 km and optical depth of τ = 0.02. These values are smaller than those of Chariklo's main ring; in other words, a Chariklo-like ring would have been detected. The occultation observed in 2020 provided two positive chords used to derive the triaxial dimensions of Echeclus based on a 3D model and pole orientation available in the literature. We obtained a = 37.0 ± 0.6 km, b = 28.4 ± 0.5 km, and c = 24.9 ± 0.4 km, resulting in an area-equivalent radius of 30.0 ± 0.5 km. Using the projected limb at the occultation epoch and the available absolute magnitude (Hv= 9.971 +- 0.031), we calculate an albedo of pv = 0.050 ± 0.003. Constraints on the object's density and internal friction are also proposed
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
Results on stellar occultations by (307261) 2002 MS4
Transneptunian Objects (TNOs) are the remnants of our planetary system and can retain information about the early stages of the Solar System formation. Stellar occultation is a groundbased method used to study these distant bodies which have been presenting exciting results mainly about their physical properties. The big TNO called 2002 MS4 was discovered by Trujillo, C. A., & Brown, M. E., in 2002 using observations made at the Palomar Observatory (EUA). It is classified as a hot classical TNO, with orbital parameters a = 42 AU, e = 0.139, and i = 17.7º. Using thermal measurements with PACS (Herschel) and MIPS (Spitzer Space Telescope) instruments, Vilenius et al. 2012 obtained a radius of 467 +/- 23.5 km and an albedo of 0.051.Predictions of stellar occultations by this body in 2019 were obtained using the Gaia DR2 catalogue and NIMA ephemeris (Desmars et al. 2015) and made available in the Lucky Star web page (https://lesia.obspm.fr/lucky-star/). Four events were observed in South America and Canada. The first stellar occultation was detected on 09 July 2019, resulting in two positives and four negatives chords, including a close one which proven to be helpful to constrain the body’s size. This detection also allowed us to obtain a precise astrometric position that was used to update its ephemeris and improve the predictions of the following events. Two of them were detected on 26 July 2019, separated by eight hours. The first event was observed from South America and resulted in three positive detections, while the second, observed from Canada, resulted in a single chord. Another double chord event was observed on 19 August 2019 also from Canada.Facultad de Ciencias Astronómicas y Geofísica