172 research outputs found
Simulated families: A test for different methods of family identification
No full textA set of families generated in fictitious impact events (leading to a wide range of 'structure' in the orbital element space have been superimposed to various backgrounds of different densities in order to investigate the efficiency and the limitations of the methods used by Zappala et al. (1990) and by Bendjoya et al. (1990) for identifying asteroid families. In addition, an evaluation of the expected interlopers at different significance levels and the possibility of improving the definition of the level of maximum significant of a given family were analyzed
A new calibration of the albedo-polarization relation for the asteroids
No full textWe present a new calibration of the geometric albedo versus linear polarization relation for the asteroids. We use the classical relation logpv=C1logh+C2, where p V is the geometric albedo and h is the slope of the phase-polarization curve. We have obtained new values for the C 1 and C 2 coefficients and their nominal uncertainties, by means of dedicated polarimetric observations of a number of asteroids for which the albedo is supposed to be known with good accuracy [Shevchenko and Tedesco. Icarus 2006;184:211-220]. The new calibration proposed in this paper represents the state of the art based on currently available data. However, the uncertainties on the derived calibration coefficients are still not negligible, and we suggest that alternative forms of the albedo-polarization relation should be explored in the future, possibly based on a bigger data set of polarimetric measurements.Fil: Cellino, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Gil Hutton, Ricardo Alfredo. 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"; ArgentinaFil: Dell'Oro, A.. Istituto Nazionale di Astrofisica; ItaliaFil: Bendjoya, Ph.. Observatoire de la Cote D'Azur; FranciaFil: Cañada Assandri, Marcela Inés. Universidad Nacional de San Juan; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Di Martino, M.. Istituto Nazionale di Astrofisica; Itali
Catastrophic Collisions in the Asteroid Belt - The Identification of Dynamical Families
No full textImpacts on Earth, The Spring School of Astronomy and Astrophysics of Goutelas, Lecture Notes in Physics 505, pp. 3-30 (2003)International audienc
Polarimetric evidence of close similarity between members of the Karin and Koronis dynamical families
No full textInternational audienc
The close-in companion of the fast rotating Be star Achernar
No full textAccepted for publication as an A&A LetterContext: Be stars are massive dwarf or subgiant stars that present temporary emission lines in their spectrum, and particularly in the Halpha line. The mechanism triggering these Be episodes is currently unknown, but binarity could play an important role. Aims: Previous observations with the VLT/VISIR instrument (Kervella & Domiciano de Souza 2007) revealed a faint companion to Achernar, the brightest Be star in the sky. The present observations are intended to characterize the physical nature of this object. Methods: We obtained near-IR images and an H-band spectrum of Achernar B using the VLT/NACO adaptive optics systems. Results: Our images clearly show the displacement of Achernar B over a portion of its orbit around Achernar A. Although these data are insuficient to derive the orbital parameters, they indicate a period of the order of 15 yr. The projected angular separation of the two objects in December 2007 was smaller than 0.15 arcsec, or 6.7 AU at the distance of Achernar. Conclusions: From its flux distribution in the near- and thermal-IR, Achernar B is most likely an A1V-A3V star. Its orbital period appears similar to the observed pseudo-periodicity of the Be phenomenon of Achernar. This indicates that an interaction between A and B at periastron could be the trigger of the Be episodes
Détection de familles d'astéroides : un problème de segmentation non superviée
No full textGRETSI 2005, n/a, pp. 257-260 (2005)International audienc
Unsupervised clustering with MST : Application to asteroid data
No full textPSIP 2005, Paper 01-03, (2005)International audienc
Fast ray-tracing algorithm for circumstellar structures (FRACS) I. Algorithm description and parameter-space study for mid-IR interferometry of B[e] stars
No full textInternational audienc
High-resolution thermal infrared imaging of MWC300
No full textContext.B[e] stars are expected to possess dusty circumstellar
environments, which are responsible for a strong infrared (IR)
excess.
Aims.Using single-dish diffraction-limited imaging in the thermal
infrared domain, we aim at measuring the angular extension of the
dusty environment of the galactic B[e] MWC 300.
Methods.We obtained diffraction-limited images of MWC 300 at
11.25 μm using the BURST mode of the VLT/VISIR instrument.
Results.MWC 300 is partially, but statistically significantly, resolved by
VISIR so that we could measure the size of its dusty envelope for
the first time. By assuming a 2D circular Gaussian intensity
distribution and using different image analysis methods we
measured a FWHM angular size of 69 ± 10 mas. For a distance of
1.8 kpc, we obtain a linear size of
125±18 AU = (1.87±0.26) 1013 m for the
circumstellar dust emitting in the mid-IR. This measured size is
shown to agree with a model that was calculated with our
radiative radiative transfer code and constrained by previously
reported SED data. Additionally, the flux of MWC 300 at
11.25 μm is estimated as 84.5±1.4 Jy = (20.0±0.3) 10-13 W/m2/μm.
Conclusions.The VLT/VISIR now offers the possibility of obtaining mid-IR diffraction-limited images with a high signal-to-noise ratio. The MWC 300's size as directly measured in this work is compatible with the theoretical size of a nearly edge-on dusty disc estimated in previous works. Interferometric data at milliarcsec angular resolution are required to reveal details on this dusty envelope
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