Spectral properties of nine M-type asteroids

Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at http://www.aanda.org.International audienceAims. We present spectroscopic results for nine M-type asteroids (325 Heidelberga, 497 Iva, 558 Carmen, 687 Tinette, 766 Moguntia, 860 Ursina, 909 Ulla, 1280 Baillauda, and 1564 Srbija) in the 0.8−2.5 μm spectral region. One visible spectrum is also presented for the asteroid 497 Iva. These asteroids were observed during several runs between 2003 and 2007, and the main goal was to investigate the NIR spectral region of M-type asteroids. Methods. The data was obtained with SpeX/IRTF in Prism mode and Dolores/TNG in LR-B mode. Spectral analysis was performed by comparing the M-type spectra and the meteorite ones (χ2 approach) and the Modified Gaussian Model. Results. With one exception, the asteroids present positive slopes of the spectra, with no absorption features, in good agreement with the spectra of metallic meteorites. The analysis of the asteroid 766 Moguntia was done by means of χ2, MGM techniques, and the Shkuratov scattering law. We conclude that the mineralogy is dominated by olivine. Its NIR spectrum is similar to those of CO/CV meteorites

E-type asteroid (2867) Steins: flyby target for Rosetta

Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at http://www.aanda.org.International audienceAims. The mineralogy of the asteroid (2867) Steins was investigated in the framework of a ground-based science campaign dedicated to the future encounter with Rosetta spacecraft. Methods. Near-infrared (NIR) spectra of the asteroid in the 0.8−2.5 μm spectral range have been obtained with SpeX/IRTF in remoteobserving mode from Meudon, France, and Cambridge, MA, in December 2006 and in January and March 2007. A spectrum with a combined wavelength coverage from 0.4 to 2.5 μm was constructed using previously obtained visible data. To constrain the possible composition of the surface, we constructed a simple mixing model using a linear (areal) mix of three components obtained from the RELAB database. A space-weathering model was applied to the aubrite ALH-78113 spectrum. Results. The four new NIR spectra reveal no major absorption features. The best-fit model for the constructed visible-plus-NIR spectrum is represented by a mixture of 57% enstatite, 42% oldhamite, and 1% orthopyroxene. These results place Steins in a subdivision of the E-type class with objects like Angelina, Eger, and Nereus. This group is not sampled by the current collection of aubrite meteorites. Interestingly, the reddened aubrite spectrum also provides a good match to the Steins VNIR spectrum

Apparent close approaches between near-Earth asteroids and quasars. Precise astrometry and frame linking

Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at www.aanda.org.International audienceAims. We investigate the link between the International Celestial Reference Frame (ICRF) and the dynamical reference frame realized by the ephemerides of the Solar System bodies. Methods. We propose a procedure that implies a selection of events for asteroids with accurately determined orbits crossing the CCD field containing selected quasars. Using a Bulirsch-Stoer numerical integrator, we constructed 8-years (2010-2018) ephemerides for a set of 836 numbered near-Earth asteroids (NEAs). We searched for close encounters (within a typical field of view of groundbased telescopes) between our selected set of asteroids and quasars with high-accuracy astrometric positions extracted from the Large Quasars Astrometric Catalog (LQAC). Results. In the designated period (2010-2018), we found a number of 2924, 14 257, and 6972 close approaches (within 10') between asteroids with a minimum solar elongation value of 60◦and quasars from the ICRF-Ext2, the Very Large Baseline Array Calibrator Survey (VLBA-CS), and the Very Large Array (VLA), respectively. This large number of close encounters provides the observational basis needed to investigate the link between the dynamical reference frame and the ICRF

Near infra-red spectroscopy of the asteroid 21 Lutetia. II. Rotationally resolved spectroscopy of the surface

Reproduced with permission. Copyright ESO. Article published by EDP Sciences and available at http://www.aanda.orgInternational audienceAims. In the framework of the ground-based science campaign dedicated to the encounter with the Rosetta spacecraft, the mineralogy of the asteroid (21) Lutetia was investigated. Methods. Near-infrared (NIR) spectra of the asteroid in the 0.8−2.5 μm spectral range were obtained with SpeX/IRTF in remote observing mode from Meudon, France in March and April 2006. We analysed these data together with previously acquired spectra - March 2003, August 2004. I-band relative photometric data obtained on 20 January 2006 using the 105 cm telescope from Pic du Midi, France has been used to build the ephemeris for physical observations. A χ2 test using meteorite spectra from the RELAB database was performed in order to find the best fit of complete visible + infrared (VNIR) spectra of Lutetia. Results. The new spectra reveal no absorption features. We find a clear spectral variation (slope), and a good correspondence between spectral variations and rotational phase. Two of the most different spectra correspond to two opposite sides of the asteroid (sub-Earth longitude difference around 180◦). For the neutral spectra a carbonaceous chondrite spectrum yields the best fit, while for those with a slightly positive slope the enstatitic chondrite spectra are the best analog. Based on the chosen subset of the meteorite samples, our analysis suggests a primitive, chondritic nature for (21) Lutetia. Differences in spectra are interpreted in terms of the coexistence of several lithologies on the surface where the aqueous alteration played an important role

Transient hepatic attenuation difference (THAD) or fat sparing? Aberrant right gastric vein (ARGV) determining a pseudolesion at the border of the IInd/IIIrd liver segments. Review of developmental concepts

The aberrant right gastric vein (ARGV) is a rare anatomical variation. It can be responsible for unexplained hyperdensities in the hepatic parenchyma on CT scans, also known as third inflow effects. We present two cases sharing similar vascular pattern and slightly different imagistic findings on ultrasound and computer-tomography performed studies. Both ultrasonographies showed a nodular-geographic hypoechoic area within a hyperechogenic fatty liver. Further CT evaluation showed in both cases a hyperattenuating homogenous area clearly visible on all four phases at the border of the IInd/IIIrd hepatic segment, that enhance especially on the portal venous phase, with no slow-fill, wash-out, central scar or rim-like features. The areas were considered to be focal fat sparing areas in diffuse fatty liver or a perfusion disorder due to the presence of an aberrant right gastric vein. The aim of this paper is to discuss the embryological aspects which are the groundwork for this vascular anomaly and to correlate the findings with imagistic aspects. These two ARGV produced pseudolesions, understood as focal fat sparing areas within diffuse fatty livers. These pseudolesions mimic liver tumours, therefore it is important to look for such an aberrant vessel in order to rule out other diagnoses

Analyse spectrale et photométrique de l'astéroïde 21 Lutetia, cible de Rosetta

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Analyse spectrale et photométrique de l'astéroïde 21 Lutetia, cible de Rosetta

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Ground based science of ESA's Rosetta mission targets: (21) Lutetia and (2867) Steins

International audienceIn the framework of ground-based science campaign dedicated to the encounter with Rosetta spacecraft, the mineralogies of the asteroids (21) Lutetia and (2867) Steins were investigated. Near-infrared (NIR) spectra of the asteroid in the 0.8-2.5 mum spectral range have been obtained with SpeX/IRTF in remote-observing mode from Meudon, France, and Cambridge, MA, in March, April and December 2006 and in January and March 2007. A chi2 test using meteorite spectra from the RELAB database was performed in order to find the best fit of complete visible infrared (VNIR) spectra of Lutetia. To constrain the possible composition of Steins' surface, we constructed a simple mixing model using a linear (areal) mix of three components obtained from the RELAB database. A space-weathering model was applied to the aubrite ALH-78113 spectrum. In the case of (21) Lutetia we find a clear spectral variation (slope), and a good correspondence between spectral variations and rotational phase. The surface mixing model places Steins in a subdivision of the E-type class with objects like Angelina, Eger, and Nereus, a group not sampled by the current collection of aubrite meteorites

Collisions history in the main-belt by spectroscopic methods /ESLAB-40

International audienc