References of "Klotz, A"
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See detailA modern study of HD 166734: a massive supergiant system
Mahy, Laurent ULiege; Damerdji, Yassine ULiege; Gosset, Eric ULiege et al

in Astronomy and Astrophysics (2017), 607

Aims: HD 166734 is an eccentric eclipsing binary system composed of two supergiant O-type stars, orbiting with a 34.5-day period. In this rare configuration for such stars, the two objects mainly evolve ... [more ▼]

Aims: HD 166734 is an eccentric eclipsing binary system composed of two supergiant O-type stars, orbiting with a 34.5-day period. In this rare configuration for such stars, the two objects mainly evolve independently, following single-star evolution so far. This system provides a chance to study the individual parameters of two supergiant massive stars and to derive their real masses. Methods: An intensive monitoring was dedicated to HD 166734. We analyzed mid- and high-resolution optical spectra to constrain the orbital parameters of this system. We also studied its light curve for the first time, obtained in the VRI filters. Finally, we disentangled the spectra of the two stars and modeled them with the CMFGEN atmosphere code in order to determine the individual physical parameters. Results: HD 166734 is a O7.5If+O9I(f) binary. We confirm its orbital period but we revise the other orbital parameters. In comparison to what we found in the literature, the system is more eccentric and, now, the hottest and the most luminous component is also the most massive one. The light curve exhibits only one eclipse and its analysis indicates an inclination of 63.0° ± 2.7°. The photometric analysis provides us with a good estimation of the luminosities of the stars, and therefore their exact positions in the Hertzsprung-Russell diagram. The evolutionary and the spectroscopic masses show good agreement with the dynamical masses of 39.5 M[SUB]⊙[/SUB] for the primary and 33.5 M[SUB]⊙[/SUB] for the secondary, within the uncertainties. The two components are both enriched in helium and in nitrogen and depleted in carbon. In addition, the primary also shows a depletion in oxygen. Their surface abundances are however not different from those derived from single supergiant stars, yielding, for both components, an evolution similar to that of single stars. Based on observations collected at the European Southern Observatory (La Silla, Chile) with FEROS and TAROT and on data collected at the San Pedro Mártir observatory (Mexico).The reduced spectra and the light curves are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A96">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A96</A> [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 detailNew and updated convex shape models of asteroids based on optical data from a large collaboration network
Hanuš, J.; Ďurech, J.; Oszkiewicz, D. A. et al

in Astronomy and Astrophysics (2016), 586

Asteroid modeling efforts in the last decade resulted in a comprehensive dataset of almost 400 convex shape models and their rotation states. This amount already provided a deep insight into physical ... [more ▼]

Asteroid modeling efforts in the last decade resulted in a comprehensive dataset of almost 400 convex shape models and their rotation states. This amount already provided a deep insight into physical properties of main-belt asteroids or large collisional families. We aim to increase the number of asteroid shape models and rotation states. Such results are an important input for various further studies such as analysis of asteroid physical properties in different populations, including smaller collisional families, thermophysical modeling, and scaling shape models by disk-resolved images, or stellar occultation data. This provides, in combination with known masses, bulk density estimates, but constrains also theoretical collisional and evolutional models of the Solar System. We use all available disk-integrated optical data (i.e., classical dense-in-time photometry obtained from public databases and through a large collaboration network as well as sparse-in-time individual measurements from a few sky surveys) as an input for the convex inversion method, and derive 3D shape models of asteroids, together with their rotation periods and orientations of rotation axes. The key ingredient is the support of more that one hundred observers who submit their optical data to publicly available databases. We present updated shape models for 36 asteroids, for which mass estimates are currently available in the literature or their masses will be most likely determined from their gravitational influence on smaller bodies, which orbital deflection will be observed by the ESA Gaia astrometric mission. This was achieved by using additional optical data from recent apparitions for the shape optimization. Moreover, we also present new shape model determinations for 250 asteroids, including 13 Hungarias and 3 near-Earth asteroids. [less ▲]

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See detailThe non-convex shape of (234) Barbara, the first Barbarian
Tanga, Paolo; Carry, B.; Colas, F. et al

in Monthly Notices of the Royal Astronomical Society (2015)

Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits ... [more ▼]

Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits several peculiar features, most notably its polarimetric behavior. In recent years other objects sharing the same property (collectively known as ”Barbarians”) have been discovered. Interferometric observations in the mid-infrared with the ESO VLTI suggested that (234) Barbara might have a bi-lobated shape or even a large companion satellite. We use a large set of 57 optical lightcurves acquired between 1979 and 2014, together with the timings of two stellar occultations in 2009, to determine the rotation period, spin-vector coordinates, and 3-D shape of (234) Barbara, using two different shape reconstruction algorithms. By using the lightcurves combined to the results obtained from stellar occultations, we are able to show that the shape of (234) Barbara exhibits large concave areas. Possible links of the shape to the polarimetric properties and the object evolution are discussed. We also show that VLTI data can be modeled without the presence of a satellite [less ▲]

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See detailInstrumental methods for professional and amateur collaborations in planetary astronomy
Mousis, O.; Hueso, R.; Beaulieu, J.-P. et al

in Experimental Astronomy (2014), 38

Amateur contributions to professional publications have increased exponentially over the last decades in the field of planetary astronomy. Here we review the different domains of the field in which ... [more ▼]

Amateur contributions to professional publications have increased exponentially over the last decades in the field of planetary astronomy. Here we review the different domains of the field in which collaborations between professional and amateur astronomers are effective and regularly lead to scientific publications.We discuss the instruments, detectors, software and methodologies typically used by amateur astronomers to collect the scientific data in the different domains of interest. Amateur contributions to the monitoring of planets and interplanetary matter, characterization of asteroids and comets, as well as the determination of the physical properties of Kuiper Belt Objects and exoplanets are discussed. [less ▲]

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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 detailDetection of a Stellar Occultation by (87) Sylvia I (Romulus)
Berthier, J.; Frappa, E.; Klotz, A. et al

in Central Bureau Electronic Telegrams (2013)

Report of the successful stellar occultations by the triple minor-planet system (87) Sylvia on Jan. 6.06742 UT of the star HD 244394 (mag 10.8). twelve positive chords of the occultation by the primary ... [more ▼]

Report of the successful stellar occultations by the triple minor-planet system (87) Sylvia on Jan. 6.06742 UT of the star HD 244394 (mag 10.8). twelve positive chords of the occultation by the primary, lasting between 4 s and 26 s, were successfully reported. Observations recorded by 4 teams permitted the detection of a brief (0.5-2 s) stellar occultation at the expected position of the large satellite Romulus. Preliminary analysis of the Romulus chords suggest that the shape of the satellite is extremely elongated or irregular (a/b > 2), with a major axis oriented toward the primary, and an equivalent diameter between 18 and 28 km. [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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