References of "Duffard, R"
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See detailThe Structure of Chariklo’s Rings from Stellar Occultations
Bérard, D.; Sicardy, B.; Camargo, J. I. B. et al

in Astronomical Journal (The) (2017), 154

Two narrow and dense rings (called C1R and C2R) were discovered around the Centaur object (10199) Chariklo during a stellar occultation observed on 2013 June 3. Following this discovery, we planned ... [more ▼]

Two narrow and dense rings (called C1R and 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 the physical properties of the ring and main body. Here, we use 12 successful occulations by Chariklo observed between 2014 and 2016. They provide ring profiles (physical width, opacity, edge structure) and constraints on the radii and pole position. Our new observations are currently consistent with the circular ring solution and pole position, to within the ±3.3 km formal uncertainty for the ring radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal significant width variations from ∼5 to 7.5 km. The width of the fainter ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and outer edges of C1R are consistent with infinitely sharp boundaries, with typical upper limits of one kilometer for the transition zone between the ring and empty space. No constraint on the sharpness of C2R’s edges is available. A 1σ upper limit of ∼20 m is derived for the equivalent width of narrow (physical width < 4 km) rings up to distances of 12,000 km, counted in the ring plane. [less ▲]

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See detailThe 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission
Snodgrass, C.; A'Hearn, M. F.; Aceituno, F. et al

in Philosophical Transactions : Mathematical, Physical & Engineering Sciences (2017), 375

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko ... [more ▼]

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies. This article is part of the themed issue 'Cometary science after Rosetta'. [less ▲]

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See detailStudy of the plutino object (208996) 2003 AZ84 from stellar occultations: size, shape and topographic features
Dias-Oliveira, A.; Sicardy, B.; Ortiz, J. L. et al

in The Astronomical Journal (2017), 154(1), 13

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 ... [more ▼]

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 solution with semi axes $(470 \pm 20) \times (383 \pm 10) \times (245 \pm 8)$~km % axis ratios $b/a= 0.82 \pm 0.05$ and $c/a= 0.52 \pm 0.02$, can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75~h) and the amplitude of its rotation light curve, we derive a density $\rho=0.87 \pm 0.01$~g~cm$^{-3}$ a geometric albedo $p_V= 0.097 \pm 0.009$. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003~AZ$_{84}$'s limb, that can be interpreted as an abrupt chasm of width $\sim 23$~km and depth $> 8$~km or a smooth depression of width $\sim 80$~km and depth $\sim 13$~km (or an intermediate feature between those two extremes). [less ▲]

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See detailDense and narrow rings discovered around the Centaur object (10199) Chariklo
Sicardy, B.; Braga-Ribas, F.; Benedetti-Rossi, G. et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

A stellar occultation observed on June 3, 2013 revealed the unexpected presence of two dense rings around (10199) Chariklo [1], the largest Centaur object known to date with a radius of 124±9 km [2]. The ... [more ▼]

A stellar occultation observed on June 3, 2013 revealed the unexpected presence of two dense rings around (10199) Chariklo [1], the largest Centaur object known to date with a radius of 124±9 km [2]. The two rings have respective orbital radii, widths, and normal optical depths of a_1= 391 km, W_1= 7 km, τ_1= 0.4 and a_2= 405 km, W_2= 3 km, τ_2= 0.06 [1]. They are separated by a gap of about 9 km with an optical depth less than 0.004 (1-sigma limit). The presence of those rings has been confirmed during another stellar occultation observed from ESO/NTT La Silla, ESO/VLT Paranal and San Pedro de Atacama on February 16, 2014. More results on the azimuthal variations of the rings and mass estimations of their putative shepherding satellites will be presented. This is the first ring system ever observed that does not pertain to a giant planet. The existence of such a system raises several questions as to the origin and evolution of rings around such a small object. This discovery also suggests that rings may be a more frequent feature than previously thought, in particular, around small bodies. Possible models for the ring formation will be proposed. They can be classified into collisional scenarios that disrupted an impactor or a pre-existing satellite, tidal disruption of an inward-migrating satellite, or material produced by a cometary activity of the central body. [less ▲]

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See detailA ring system detected around the Centaur (10199) Chariklo
Braga-Ribas; Sicardy; Ortiz et al

in Nature (2014)

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See detailThe Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations
Braga-Ribas, F.; Sicardy, B.; Ortiz, J. L. et al

in Astrophysical Journal (2013), 773

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation ... [more ▼]

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R [SUB]equiv[/SUB] = 555 ± 2.5 km and geometric visual albedo p[SUB]V[/SUB] = 0.109 ± 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of \epsilon = 0.087^{+0.0268}_{-0.0175}, an equatorial radius of 569^{+24}_{-17} km, and a density of 1.99 ± 0.46 g cm[SUP]–3[/SUP]. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere. [less ▲]

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See detailAlbedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation
Ortiz, J. L.; Sicardy, B.; Braga-Ribas, F. et al

in Nature (2012), 491

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris ... [more ▼]

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies. Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos. Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto, and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420+/-60km) and albedo are roughly known, there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere. Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430+/-9km (1σ) and 1,502+/-45km, implying a V-band geometric albedo p[SUB]V[/SUB] = 0.77+/-0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12nanobar (1σ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7+/-0.3gcm[SUP]-3[/SUP] is inferred from the data. [less ▲]

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See detailStellar Occultations by Large TNOs on 2012: The February 3rd by (208996) 2003 AZ84, and the February 17th by (50000) Quaoar
Braga Ribas, Felipe; Sicardy, B.; Ortiz, J. L. et al

in AAS/Division for Planetary Sciences Meeting Abstracts (2012, October 01)

On February 2012, two stellar occultation's by large Trans-neptunian Objects (TNO's) were observed by our group. On the 3rd, an event by (208996) 2003 AZ84 was recorded from Mont Abu Observatory and IUCAA ... [more ▼]

On February 2012, two stellar occultation's by large Trans-neptunian Objects (TNO's) were observed by our group. On the 3rd, an event by (208996) 2003 AZ84 was recorded from Mont Abu Observatory and IUCAA Girawali Observatory in India and from Weizmann Observatory in Israel. On the 17th, a stellar occultation by (50000) Quaoar was observed from south France and Switzerland. Both occultations are the second observed by our group for each object, and will be used to improve the results obtained on the previous events. The occultation by 2003 AZ84 is the first multi-chord event recorded for this object. From the single chord event on January 8th 2011, Braga-Ribas et al. 2011 obtained a lower limit of 573 +/- 21 km. From the 2012 occultation the longest chord has a size of 662 +/- 50 km. The other chords will permit to determine the size and shape of the TNO, and derive other physical parameters, such as the geometric albedo. The Quaoar occultation was observed from south of France (Observatoire de la Côte d'Azur, TAROT telescope and Valensole) and from Gnosca, Switzerland. Unfortunately, all three sites in France are almost at the same Quaoar's latitude, so in practice, we have two chords that can be used to fit Quaoar's limb. The resulting fit will be compared with the results obtained by Braga-Ribas et al. 2011. Braga-Ribas F., Sicardy B., et al. 2011, EPSC-DPS2011, 1060.Ribas F., Sicardy B., et al. 2011, EPSC-DPS2011, 1060. [less ▲]

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See detailA Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation
Sicardy, B.; Ortiz, J. L.; Assafin, M. et al

in Nature (2011), 478

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 ... [more ▼]

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163+/-6kilometres, density 2.52+/-0.05 grams per cm[SUP]3[/SUP] and a high visible geometric albedo, . No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun. [less ▲]

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See detailThe stellar occultation by Makemake on 2011 April 23
Ortiz, J. L.; Sicardy, B.; Assafin, M. et al

in EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. <A href="http://meetings.copernicus.org/epsc-dps2011">http://meetings.copernicus.org/epsc-dps2011</A>, p.704 (2011, October 01)

We have taken advantage of a stellar occultation by the dwarf planet Makemake on 2011 April 23, to determine several of its main physical properties. We present results from a multisite campaign with 8 ... [more ▼]

We have taken advantage of a stellar occultation by the dwarf planet Makemake on 2011 April 23, to determine several of its main physical properties. We present results from a multisite campaign with 8 positive occultation detections from 5 different sites, including data from the 8-m VLT and 3.5-m NTT telescopes in Chile, which have very high temporal resolution. Because the star was significantly fainter than Makemake (setting a record in the magnitude of a star whose occultation has been detected), the occultation resulted in a drop of just ~0.3 mag in the lightcurves. From the lightcurves we have been able to determine the size and shape of the body, its geometric albedo and constraints on its atmosphere. [less ▲]

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